Surgical Principles for Spinal Meningiomas

Abstract

Spinal meningiomas, which are usually benign character, rarely show an invasive course. Since they grow slowly in the intradural extramedullary space, clinical symptoms also progress slowly. It is usually diagnosed in the later periods, when the tumor reaches to large size. They most commonly show location in the thoracic region. Although it does not have a real capsule, they can be removed completely or close to total by microsurgical methods, since they are well-demarcated solitary tumors. The most important factor in the complete and safe removal of spinal meningioma is the selection of the surgical approach suitable for the size, localization, and topography of the tumor. In the postoperative period, improvement in neurological functions is observed generally and their prognosis is good. In this study, the natural history of the tumor is explained in detail, by examining the pathogenesis and predisposing factors and clinical symptomatology in the spinal meningiomas. Moreover, it has been also focused on describing the surgical approaches and operative techniques to be used in the complete and safe removal of the spinal meningioma, according to the localization and topography of the tumor.

1. Introduction

The spinal meningiomas (SMs), which originate from the cap cells of the arachnoid membrane, are generally benign character and tumors of which prognosis is positive [1]. While SMs constitute 25–46% of all intradural spinal tumors, and they constitute 12% of all meningiomas [2, 3]. Its incidence is 0.5–2/100,000 per year [4]. It progresses to the subarachnoid space by growing slowly in the intradural extramedullary distance. When they reach to large sizes, they first cause stretching of the surrounding arachnoid and then they press on the spinal cord and nerve roots. In these cases, the diagnosis is usually made late due to the slowly progressive character of clinical symptoms. Different clinical symptoms can be observed in patients with the SMs, depending on the localization, topographic structure, and size of the tumor. The tumors can mostly dissect from the spinal cord and nerve roots, because of their solitary structure and the presence of arachnoid and good surgical cleavage between the spinal cord and them. It is possible to remove total or near-total with microsurgical methods. They rarely exhibit invasive character [5]. In the postoperative period, a rapid improvement is observed in the neurological functions of the patients [6, 7].

2. Spinal meningioma

2.1 Epidemiology and predisposing factors

The SMs are more common in women than men and the female, male ratio was 4:1. It is frequently observed in middle-aged women and the mean age was 57.6 years [2, 6]. It has been thought that the reason why it is more common seen in women may be due to the response of the tissues to sex hormones [8]. However, the effects of hormones on SM development are still controversial [9]. Although no definite predisposing factor has been identified, it has been stated that steroid, aminergic, and growth factor receptors will be able to play a role in SM development pathogenesis [10]. However, neurofibromatosis type 2 accompanies 12% of the SM cases under 50 years of age. It has been also stated that the 22^nd chromosome deletion and inactivation were frequently observed in the sporadic meningiomas accompanying neurofibromatosis type 2 in the genetic studies conducted [11]. It has been stated that SM was observed in the patients who received radiotherapy to the spinal region and also in the patients with a history of intraventricular ependymoma and breast adenocarcinoma in the literature [12].

2.2 Rare tumor forms

The intramedullary-located SMs, which are seen as rare, are frequently observed in the cervical region, especially in the C2–C4 localization. In fewer cases, the thoracic region localization has also been stated. There are varying degrees of neurological deficits in the clinic of these cases, which are frequently observed in the fifth decade. No specific tumor subtype has been stated for the intramedullary SMs [13, 14, 15]. Other rare extradurally located SMs show location in the thoracic region with a rate of 53% and in the cervical region with a rate of 42%. They are observed in women and before the third decade. It has also been stated in the literature that they could be removed totally; therefore, the recurrence rate was higher in these cases, due to their invasion of neighboring important anatomical structures in some cases of the extradural SM [16]. Rare cases of SM have also been stated in the literature, as a result of an intracranial meningioma reaching the spinal region via cerebrospinal fluid (CSF). Similarly, it has been stated in rare cases that SM was observed in another spinal region in the patient with a diagnosis of SM during the follow-up [17, 18, 19].

2.3 Localization and topography

In a systematic review conducted by Pereira et al. regarding the SMs, it was most commonly localized in the thoracic region with a rate of 64.6%, and this was followed by the cervical region with 22.7% and other region localizations with 12.7%, respectively [20]. In the literature, the thoracic region localization rates have been stated as 83% by Solero et al., as 79% by Voldrich et al., as 76% by Gottfried et al. and as 72% by Gezen et al. [7, 21, 22, 23]. On the other hand, in the analysis conducted by Ozkan et al. in the patients with the ventral and ventrolateral SM, the localization was observed in the thoracic region (between T1 and T9 levels) in the rate of 52.7%, in the cervical region in the rate of 27.3% (between C0 and C7 levels), and the thoraco-lumbar region (between T10 and L2 levels) in the rate of 20% [24].

In the literature, although there is no specific topographic classification for the SMs, it has been stated that the tumors were frequently located on the dorsal and dorsolateral of the spinal cord [2]. The ventral and ventrolateral localization rates have been stated as 39% by Roux et al., 33.5% by Ozkan et al., 13% by Yoon et al., and 15% by Solero et al. [7, 24, 25, 26]. On the other hand, in the topographic examination of the SMs, it has been stated lateral localization in 45–71%, dorsal localization in 10–31%, and ventral localization in 15–27% [7, 23, 27]. Generally, while the tumors localized in the thoracic region are observed in the dorsal spine of the spinal cord, the tumors localized in the cervical region are observed in the ventral part of the spinal cord [2, 7, 28]. Ozkan et al. have stated that only ventral-located cases were seen in 21.8% of the ventral and ventrolateral SMs and ventrolateral-located cases were seen in 78.2% of them [24].

Although they mostly show intradural extramedullary localization, approximately 10% of SMs are located extradurally or extra-intradurally. It is found as 5.4% by King et al., 14% by Gezen et al., and 17% by Cohen-Gadol et al. [5, 21, 23, 29].

2.4 Histopathological analysis and tumor subtypes

The World Health Organization (WHO) has classified SMs into three grades, according to the degree of malignancy. The WHO grade-I SMs constitute more than 90% of the tumors [30]. In a recent systematic review of the SMs, the histopathology of 1415 tumors has been analyzed and it has been stated that the WHO grade-I meningiomas were the most common with a rate of 94.8%. On the other hand, when the subtypes of the WHO grade-I meningiomas were examined, it has been stated that the psammomatous meningioma, which was found at a rate of 27.8%, and meningothelial meningioma, which was found at a rate of 25.2%, were the most common tumor subtypes. This was followed by the WHO grade-II meningiomas (clear cell, choroidal, and atypical) with a rate of 4.4% and the WHO grade-III meningiomas (anaplastic and papillary) with a rate of 0.8%, respectively [20]. There are spinal invasion, aggressive course, and high recurrence rates in the WHO grade-II and WHO grade-III SMs with high mitotic activity [31, 32, 33, 34]. Similarly, in other studies stated in the literature; the transitional, fibrous, chordoid, and metaplastic meningioma subtypes have been observed to be less common. Moreover, it has also been stated that there was no correlation between the age of the patients and the histopathological subtypes of the tumor [12].

2.5 Clinical presentations

Different clinical symptoms are observed, depending on the location and topography of the tumor, its growth pattern, and size. The SMs cause misdiagnosis and/or late diagnosis because of their different symptoms and slow growth potential. It is observed that the average diagnosis time is usually around 1 year [12, 29]. The most common symptom is pain. While localized pains are observed more, the pains in the radicular nature are less common [21]. Although it varies according to the growth pattern of the tumor in the extramedullary region, the spinal cord compression findings come to the fore, especially in large-dimensioned tumors. In these cases, various degrees of muscle weakness (spastic paresis or plegia), sensory deficit (hypoesthesia, anesthesia, or paresthesia), and corticospinal tract findings, such as sphincter dysfunctions and Brown-sequard syndrome, can develop [2, 6, 7, 23, 25, 35, 36]. In the study conducted by Voldrich et al., movement disorders depending on muscle weakness have been stated in 79%, sensory disorders in 70%, and sphincter dysfunction in 10%. In this study, the rate of asymptomatic cases was 11% [21]. On the other hand, Ozkan et al. have stated that the nonspecific symptoms, such as sensory impairment, were observed more frequently at a rate of 94.5%;therefore, the diagnosis was made later in these cases, especially in the ventral and ventral localized SMs [24]. While the most common symptom was radiculopathic pain in the study in which Han et al. analyzed the patients with high-grade SM, this was followed by motor weakness, sensory deficit, and sphincter disorders, respectively. In this study by Han et al.; it has been emphasized that the asymptomatic period observed in the patients with high-grade SMs was much shorter than in the WHO grade-I SMs [37].

2.6 Neurodiagnostic techniques

Spinal magnetic resonance imaging (MRI) is currently the best diagnostic tool for SMs. In earlier periods, when the spinal MRI technique was not used, these cases were often misdiagnosed [2, 23]. Klekamp and Samii have stated that early diagnosis can be made in these cases by means of the spinal MRI and they also affected the neurological outcome after surgery [27]. Ozkan et al. have stated that the time between the symptom duration and diagnosis was around 6 months by means of the spinal MRI [24]. In the spinal MRI T1- and T2-sequences, the tumors are usually observed isointense with the spinal cord. On the other hand, in the MRI images made after the intravenous injection of Gadolinium-DTPA, the SMs show intense homogeneous contrast enhancement. By means of the spinal MRI, the localization of the tumor, its size, the invasive behavior, and its relationship with neighboring tissues can also be examined in detail [25, 38]. The intratumoral calcifications can be shown by computed tomography (CT) [39]. Ono et al. have stated that the tumor stiffness developed due to calcifications would be able to be defined by the Spinal MRI T1-sequences and CT [40]. On the other hand, the tumors with ossification and infiltration of the adjacent structures with a broad tumor base have been radiologically defined as the “en plaque meningiomas” [35, 41, 42].

3. Surgical treatment

3.1 General surgical principles

The majority of SMs are benign, and the first choice in their treatment is surgery. The first successful surgical treatment of SM was performed by Sir Victor Horsley in 1887 [6]. The surgical timing is performed under emergency or elective conditions, by taking into account the patient’s neurological picture. The gold standard in surgical treatment is total resection of the tumor by the microsurgical method [43, 44]. In the preoperative period, the tumor localization and size should be examined in detail with the contrast-enhanced spinal MRI, and the tumor level should be determined with the intraoperative C-arm scopy. The most important issue in surgical planning is to determine the appropriate surgical approach, according to the location and spread of the tumor in the spinal axis. Especially, in surgical approaches requiring a laminectomy, the laminectomies should be performed from the cranial to the caudal and the spinal cord should be rotated with appropriate techniques [43, 45, 46]. The aim of the surgery is to completely remove the SM without damaging the neural elements, such as the adjacent spinal cord and nerve roots, which are exposed to tumor compression. After the microsurgical tumor resection, the resection and/or coagulation of the tumor-infiltrated dural base should also be planned. It is very useful to use intraoperative neuromonitoring techniques (with somatosensory-evoked potential (SSEP) and motor-evoked potential (MEP) recordings) to increase surgical safety. On the other hand, intraoperative ultrasonography (USG) can be used in the internal debulking phase to reduce the volume of the tumor in large tumors [47].

3.2 Surgical approaches, principles, and operative techniques

3.2.1 Upper cervical spinal meningioma

Almost 27% of all cervical meningiomas have been stated in the upper cervical spine and only 3% in the foramen magnum area [48, 49]. Topographically, in approximately 50% of patients, the tumor is located ventral or ventrolateral to the spinal cord [50]. The gold standard in the surgery of upper cervical SMs is complete removal. The dorsal and dorsolaterally located upper cervical SMs can be safely and effectively removed with the standard posterior midline approach [51, 52].

3.2.1.1 Lateral and far-lateral approaches

The posterior midline approach is insufficient for surgical access to the ventral and ventrolateral of the upper cervical region. Because of this difficulty in surgical exposure, the tumors are often incompletely removed. Similarly, because of the posterior midline approach, which requires significant spinal cord and brainstem retraction, the tumors in this region have a high risk of postsurgical morbidity [51, 52].

The lateral and far-lateral approaches have been developed to avoid the disadvantages of the posterior midline approach and to access the foramen magnum and the upper cervical region ventral [53, 54, 55, 56, 57, 58, 59, 60]. With the lateral transcondylar approach, which provides a more comprehensive surgical perspective from the lateral to the foramen magnum, the tumors located ventrally in the foramen magnum can now be successfully removed in many clinics [61, 62, 63]. George et al. expressed the borders of the foramen magnum as the region between the lower 1/3 of the clivus and the upper corner of the C2 vertebra corpus in the anterior, between the occipital squamous anterior edge and the C2 spinous process in the posterior, and between the jugular tubercles and the upper edges of the C2 laminae laterally [64]. The far-lateral approach was first described by George et al. in 1988 to reach the lesions in front of the foramen magnum. The lesions located in the ventral/ventrolateral of the foramen magnum and upper cervical region can be safely removed by means of the far-lateral approach and its modified subtypes developed in the following years.

The critical issue in the far-lateral approach is the manipulation of the vertebral artery [51]. The extreme-lateral craniocervical approach has been developed by modifying the far-lateral approach by Salas et al. in 1999. In later years, the extreme-lateral craniocervical approach has been modified and new approaches, such as transfacet and retrofacet approaches, have been developed for the removal of the intradural lesions located ventral to the upper cervical region. After all, the tumors located in the foramen magnum and upper cervical region ventrals are removed and are now used as a standard approach by many surgeons, by means of the far-lateral approach and its modified subtypes [54].

3.2.2 Subaxial cervical spinal meningioma

The SMs below the C2 level can be removed with both anterior and posterior approaches. On the other hand, in the removal of dorsal and dorsolateral subaxial SMs, the standard posterior approaches performed with the laminectomy or laminotomy are usually sufficient [43, 46]. The cervical SMs located ventrolaterally are operated with the modified posterior approaches by using laterally extended laminectomy techniques [2, 7, 23, 25, 27]. On the other hand, the standard anterior cervical approach is preferred for the removal of ventrally located subaxial cervical tumors [46].

3.2.2.1 Modified posterior approach with lateral extension

There are difficulties in the surgical removal of the SMs that are completely ventral and located with their dural base [2, 7, 23, 25]. Levy et al. stated that the prognosis was worse in ventrally located cervical SMs they operated [2]. To overcome these surgical difficulties, laterally extended modified posterior approaches have been developed. Klekamp et al. have operated on 130 patients with the SMs (27% ventrally located) for the laminectomy, by using the modified posterior approach with facetectomy added as needed [27]. On the other hand, Roux et al. have operated on 54 patients with SM (39% ventral and ventrolateral localization), by using a modified posterior midline approach with articular process resection added as needed [25]. After all, the lateral extension laminectomy techniques have been the most commonly used approach for the removal of the ventral cervical SMs. However, a modified posterior approach using the bilateral extended laminectomy has also been described to be able to minimize spinal cord manipulation. As an advantage of this technique, it has been emphasized that the tumor in front of the spinal cord could be approached bilaterally [7, 23, 28].

Solero et al. stated that all ventrally located cervical SMs were successfully removed with the modified posterior approach in which bilaterally extended laminectomy was used. In this study, they have stated that the dura was opened in a T-shaped and the dentate ligaments were also cut, in addition to bilaterally extended laminectomy to minimize spinal cord manipulation and to provide a better surgical perspective [7]. Similarly, Gezen et al. have stated that the postoperative results were good with bilaterally extended laminectomies in operated ventrally located SMs, as a result of the compilation that they perform an analysis for 36 patients [23]. After all, it has been stated that the prognosis was good in the patients operated with the modified posterior approaches by using a laterally extended laminectomy in the patient series stated in the literature all with ventrally located tumors [7, 23, 25].

3.2.2.2 Anterior cervical approach with corpectomy

Payer et al. stated that the most important advantages of the anterior cervical approach were the opening of a large bone window with corpectomy and reaching a direct ventral cervical SM without the need for spinal cord manipulation, as a result of the systematic review they made and other studies stated in the literature. In ventrally located SMs, extradural coagulation of pathological vascular structures, which are the tumor feeder observed in the anterior dura, can also be easily performed before the dura is opened [65, 66, 67, 68, 69].

In the literature, it has been stated the anterior cervical approach was used successfully in the removal of ventrally located cervical SMs. Giroux et al. have stated that the complete tumor resection was performed, without making spinal cord manipulation, after the C5 corpectomy and opening dura with a midline vertical incision with the anterior cervical approach. Better control of bleeding has also been stated [66]. Lenelle et al. have stated that the tumor was completely removed along with the tumor-infiltrated dural base, after opening the dura in an ellipsoid shaped in the cranial and caudal vertical axis with the tumor centered with the corpectomy involving the C4 corpus inferior, C5 corpus, and C6 corpus superior. Duraplasty has been performed by using fascia taken from the iliac region. Moreover, they have emphasized that the surgery was more comfortable by means of the coagulation of pathological dural vascular structures, which are tumor feeders, with this approach [67]. Sava et al. have stated that the tumor was completely removed with the dural base in the cranio-caudal direction, by making multiple corpectomy from C3 to T1 of intradural SM extending between foramen magnum and T2 vertebra levels with this approach. The lumbar CSF drainage has been also applied to prevent CSF leakage in the patient who underwent duraplasty by using fascia [68]. Payer et al. have stated that the intradural ventrally located broad-based SM extending between C5 and C7 levels were completely removed by performing C5, C6, and C7 corpectomy with the anterior cervical approach. The dura has been opened with a midline vertical incision, and the tumor has been dissected from the spinal cord nerve roots and dural base. It has been also emphasized that the tumor-infiltrated dural base was coagulated intradurally and the inner layer of the dura was extensively coagulated by separating it with a microdissector, after the tumor removal [65].

3.2.3 Thoracic and lumbar spinal meningioma

The standard posterior midline approach with laminectomy or laminotomy is usually sufficient in the removal of dorsal, lateral, and ventrolateral thoracic SMs. Nowadays, laminectomies can be extended laterally with the techniques of adding articular process resection to the hemilaminectomy or adding unilateral facetectomy to the laminectomy. On the other hand, in tumors that are completely or mostly ventrally located, the laminectomies can be also extended laterally bilaterally to provide bilateral exposure. In these cases, laminoplasty techniques with miniplates are also used in the same session to avoid spinal instability. While the hemilaminectomy or laminoplasty techniques are preferred more in the cervical localized cases, the laminectomy techniques are generally preferred in the thoracic and thoracolumbar localized cases. In tumors in which the ventrolateral component is larger, hemilaminectomy or laminoplasty techniques are preferred [24].

Moreover, the modified posterior approaches with the lateral extension improved by adding techniques, such as unilateral total facetectomy, pedicle resection, costotransversectomy, and partial vertebrectomy to laminectomy or laminotomy have also been developed to reach ventrally located thoracic tumors [43, 46, 70]. The anterior transthoracic approach is no longer used today since serious vascular injuries have been stated with severe lung retraction in ventrally located thoracic tumor resections [46, 71]. The posterior and modified posterior approaches are sufficient in most cases in the removal of dorsal, lateral, ventrolateral and ventral lumbar SMs. On the other hand, another advantage of using the posterior approaches used in tumor resections at the lumbar level is that the spinal cord and nerve root retraction, which is necessary for revealing the tumor, can be performed more safely by the surgeon. Despite these approaches, the anterior transabdominal approach and the lateral retroperitoneal approach, which are rarely used nowadays, can be preferred in very few cases where the tumor cannot be removed [46, 72].

3.2.3.1 Posterior midline approach and operative technique

The posterior approaches with the laminectomy or laminotomy are usually sufficient in the surgical resection of dorsal and dorsolateral SMs [43]. Considering the extent of tumoral dural involvement, compression, and displacement levels in the spinal cord that is proportional to the size of the tumor, and findings, such as CSF blockage and laminectomy or laminotomy, should be planned. Generally, the laminectomy or laminotomy is performed at a lower and an upper level together with the tumor level in a way it will cover the cranial and caudal poles of the tumor, which is revealed under the guidance of fluoroscopy [45, 46, 61]. In order to prevent spinal instability that will be able to develop in the long-term postoperatively in the posterior approaches, the laminoplasty techniques are now preferred by using laminotomies or microplates performed with pneumatic cutters instead of the laminectomy [24]. The laminectomy and/or laminotomy are performed starting from the cranial in order to prevent postoperative neurological losses that will be able to develop due to spinal cord herniation. If possible, it would also be helpful at this stage to check the localization and extent of the tumor by intraoperative ultrasonographic examination. The dura is opened by making a linear incision in the dorsal small SMs [45, 46]. The dura is ellipsoid-shaped and opened in the cases of large dorsal SM with a wide base and severe adhesion to the dura in order to perform a total resection of the dural base, where the tumor is attached, together with the tumor [46]. The dural leaves are suspended with the sutures. In the arachnoid dissection stage, the patient is placed in the slight trandelenburg position and cotonoids are placed in the cranial and caudal regions of the surgical field in order to reduce CSF leakage and blood flow to the subarachnoid space [45]. Although they do not have a true capsule, the SMs can be separated from the normal tissue by a good surgical cleavage through the arachnoid [47]. The microsurgical tumor resection should be performed with intraoperative neuromonitoring techniques in order not to damage the spinal cord and nerve roots. With these surgical procedures, the tumor volume is reduced by the internal debulking first, and then a total resection of the tumor is performed with the tumor-infiltrated dural base (according to Simpson grade-I resection). The cavitron ultrasonic aspirators (CUSA) can be used for the internal debulking of large tumors with a wide dural base. However, during the use of CUSA, utmost care should be taken not to damage the spinal cord [45, 61, 73, 74]. In the surgeries, where only the tumor is removed and the tumor-infiltrated dural base is coagulated (according to Simpson’s grade-II resection), the dura is closed by primary suturing in a water-tight manner. However, in the surgeries in which the tumor is completely removed with the tumor-infiltrated dural base (according to Simpson’s grade-I resection), the dural opening is usually closed by duraplasty (using autografts and allografts) and fibrin tissue adhesives are placed on it [45]. The total resection (according to Simpson’s grade-I resection) and gross-total resection (according to Simpson’s grade-II resection) can be successfully performed in most dorsal SM cases with the posterior midline approach following the above surgical procedures.

3.2.3.2 Modified posterior approach and operative technique

The modified posterior approaches have been developed in the removal of ventrally located thoracic SMs since more lateral exposure is required in surgery. In this approach, the laminectomy or laminotomy can be extended more laterally, depending on the location and topography of the tumor, by means of the techniques described above. For ventrally located tumors, the dura can be opened with a straight, curve-linear, or T-shaped incision and arachnoid dissection is performed. The dentate ligament is tractioned with a silk suture placed on one side. The spinal cord is then rotated slightly to provide a better surgical perspective of the ventral spinal cord. A much wider surgical exposure can be achieved by cutting the dentate ligaments after the dura is opened [24]. With the increase in the size of the ventrally located tumor, the spinal cord compression increases, and the spinal cord is displaced. For this reason, in order to minimize spinal cord injury in ventrally located large tumors, an incision is made on the side of the dural attachment and away from the spinal cord. Then, the tumor volume is reduced by internal debulking accompanied by intraoperative neuromonitoring. Thus, the spinal cord is decompressed and tumor borders can be observed better. While internal debulking is performed in large tumors, and can be used in the CUSA. However, extreme care should be taken to avoid serious spinal cord injuries due to the size of the CUSA probes [50]. During the complete removal of the SMs, the sensory nerves attached to the tumor can be cut [24]. Thus, the completely free tumor is mobilized by placing a traction suture, and the SM is completely removed (according to Simpson’s grade-II resection) [61, 73, 74].

However, in large-sized thoracic tumors that are completely ventrally located, the total resection of the tumor cannot always be performed with the modified posterior approach described above. In this situation, there is a need for the modified posterior approaches (with the classical laminectomy or laminotomy with unilateral total facetectomy, pedicle resection, costotrasversectomy, and/or partial vertebrectomy added) that provide more lateral surgical exposure. The dural resection is almost impossible in ventrally located tumors with a wide base and severe adhesion to the dura; therefore, the tumor-infiltrated dural base is coagulated, by leaving it in place (according to Simpson’s grade-II resection) [46, 61]. In addition, in the microsurgery of the SMs located in the thoracic and thoracolumbar regions, maximum care should be taken not to injury the Adamkiewicks artery (arteria radicularis magna; 90% observed between T7 and L1 levels and on the left side), which is a serious feeder of the spinal cord [45].

3.2.3.3 Illustrative case

A 68-year-old female patient having localized back pain for the last 3 months applied to our outpatient clinic. Her neurological examination was normal. In the contrast-enhanced spinal MRI of the patient, at T12 vertebral level, a mass lesion, which as intradural extramedullary located, smooth-contoured, in 18x14 mm size, showed a location in the spinal cord ventral, and was compatible with spinal meningioma, was detected. Moreover, it was also observed that the tumor located in the ventral of the spinal cord displaced the conus medullaris posteriorly (Figure 1). The patient was operated with a modified posterior midline approach with the bilateral extended laminectomy. First, T11 and then T12 bilateral extended laminectomy was made from the cranial to the caudal, and then right unilateral median facetectomy was performed. The dura was opened with a slight curve-linear vertical incision. The tumor was completely removed, by leaving the tumor-infiltrated dural base in place with the neuromonitoring and microsurgical technique. The tumor-infiltrated dural base was coagulated with the bipolar. Thus, the tumor was completely removed according to Simpson’s grade-II tumor resection. The neurological examination of the patient in the postoperative period revealed that the left leg muscle strength was grade 4+/5. After a 10-day physical therapy and rehabilitation program, the patient’s left leg muscle strength improved to grade 5/5. The pathology result came as psammomatous meningiomas (WHO grade-I). In the contrast-enhanced spinal MRI performed on the 7^th postoperative day, the contrast enhancement was not detected in favor of the residual tumor (Figure 2).

Figure 1.

In the preoperative period spinal magnetic resonance imaging; at T12 vertebral level, a mass lesion, which was intradural-extramedullary localized, displaced the conus medullaris posteriorly in the ventral of the spinal cord, was 18 x 14 mm in size, and was a hypointense and well-contoured in the unenhanced sagittal T2- (A) and axial T2- (B) sequences, was observed. In the contrast-enhanced sagittal T1- sequence (C), homogeneous contrast enhancement is observed in the lesion. In the spinal MRI-myelography (D), the CSF blockade is observed at the level of the relevant spinal cord.

Figure 2.

In the contrast-enhanced spinal magnetic resonance imaging performed on the 7^th postoperative day, in the unenhanced sagittal T2- (A) and axial T2- (B) sequences, the mass lesion observed in the preoperative period was removed, and contrast enhancement in favor of residual tumor was not detected in the contrast-enhanced sagittal T1- sequence (C). The spinal MRI-myelography (D) shows that CSF flow is normal.

3.3 Types of surgical tumor removal

The grading system defined by Simpson for intracranial meningiomas is used to evaluate the scope of surgical resection in SMs [75]. The tumor-infiltrated dural base can be resected more radically in the microsurgery of the intracranial meningiomas compared to the SMs. Therefore, the use of Simpson’s grading system in SM surgery is limited. While the term complete is used for Simpson’s grade-I and grade-II resections in some clinics, in some clinics, gross-total resection terms are used for Simpson’s grade-I and grade-II resections, and subtotal resection terms are used for grade-III and higher resections. The complete tumor removal rates of the SMs observed in all localizations range from 82 to 98% [2, 7, 8, 22, 23, 27, 50]. In a systematic review conducted by Pereira et al., it has been stated that 94.5% of the SMs were extracted according to Simpson grade-I and grade-II resection, and 5.5% of them, the extraction was performed according to Simpson grade-III or higher resection [20].

Abou-Madawi et al. have stated the results of 23 patients (Foramen magnum in 10 patients, C1–C2 levels in 7 patients, C2–C3 levels in 4 patients, and C3–C4 levels in 2 patients) with the ventral (7 patients) and ventrolateral (16 patients) foramen magnum and upper cervical meningiomas operated with the retrofacet approach, which was a subtype of the far-lateral approach. In this study, it has been stated that the tumor was removed completely in 91.3% of the patients, and subtotal removal was performed in 8.7% of the patients because the tumor has adhered to the intradural vertebral artery. As a result of this study, it has been emphasized that the far-lateral approach was a safe surgical corridor [76]. On the other hand, it has been stated by Slin’ko et al. that the total tumor resection was performed in only 74% of the ventral/ventrolaterally located patients operated with the standard posterior midline approach and its modified forms [77].

The subaxial cervical SMs located intradurally ventrally are excised with the anterior cervical approach performed with the uni- or multi-segmental corpectomies. Giroux et al. and Banczerowski et al. stated that the intradural ventral SMs at the C5 level were completely removed with the anterior cervical approach [66, 69]. A ventrally located SM at the level of the C5 vertebra has been removed by Lenelle et al. with the anterior approach, along with the tumor-infiltrating dural base, and the tumor was completely excised [67]. Payer et al. have completely removed an intradural broad-based ventrally located SM extending between C5 and C7 levels with an anterior approach accompanied by the multi-segmental corpectomy [65]. On the other hand, the tumor has been completely removed by Sawa et al. with the tumor-infiltrating dural base with the multi-segmental corpectomy anterior cervical approach of the intradural SM extending between the foramen magnum and T2 vertebrae from C3 to T1.

Ozkan et al. have stated the surgical results of the patients (29 patients (52.7%) with the SMs with only ventral and ventrolateral localization between T1–T9 and surgical results in 11 patients (20%) they operated with a modified posterior approach by using the technique of lengthening laminectomies to the laterals. It has been stated that 53 (96.4%) of a total of 55 SMs were successfully removed with this approach (according to Simpsons grade-II resection) [24].

3.3.1 Surgical difficulty in tumor removal: en plaque, calcified, and recurrent tumors

Although complete tumor resection is the gold standard in SM surgery, the complete removal of en plaque and recurrent tumors with arachnoid infiltration is very difficult [34, 43, 44]. The ossified SMs are observed from0.7% to 5.5% of all SMs. The complete removal of the ossified SMs is difficult due to their hard consistency and strong adhesion to the spinal cord [44, 78, 79]. Therefore, the surgical approaches that offer a narrower surgical perspective make the removal of ossified tumors more difficult and increase the postoperative morbidity in these cases. Therefore, the microsurgical dissection of the tumor and pia-mater is recommended in the ossified SMs. It has been stated that the tumor could be removed as a block with this method [78]. The ventral location of the tumor is another factor that complicates the complete resection. In the study conducted by Ozkan et al. on 55 patients with the SM located ventrally and ventrolaterally have stated the total removal of the SM, according to Simpson’s grade-II resection in 53 patients (96.4%), and the subtotal removal of the SM because of intratumoral calcification in 2 patients (3.6%) [24]. Similarly, Levy et al. have emphasized that the total excision of the tumors should not be performed in the calcified meningiomas located close to the spinal cord due to the high risk of postoperative morbidity [2]. It has been stated that the complete removal of the tumor together with the tumor-infiltrated dural base, if possible, in the SM surgery, and coagulation of the dura in cases where removal was not possible, reduced the tumor recurrence. Moreover, the surgical technique in which the inner and outer dura layers of the dura are separated and the inner dura layer is removed with the tumor, and the intact outer dura layer is sutured has been described in the literature. By means of this technique, there will be no need for the duraplasty using the fascia or synthetic dura grafts [24, 47, 80]. The arachnoid scar formation also complicates the total removal of recurrent tumors [20].

4. Surgical outcomes

4.1 Improvement in neurological functions

A specific classification developed for the SMs has not been stated in the evaluation of the neurological functions of patients in the preoperative and postoperative period. However, it has been observed that the McCormick classification was used in the spinal ependiomas in some clinics, and other functional neurological classifications, such as modified McCormick (MMC), Frankel, and Japanese Orthopedic Association (JOA) classifications, were used in some clinics [24, 37, 70, 76]. In the patients having whole SMs, functional and neurologic recovery rates after surgery range from 61 to 98% [2, 7, 23, 25, 27, 48, 81]. In the patients with the SMs, recovery of neurological functions is observed with rapid recovery in the postoperative period [73, 74]. Klekamp and Samii have stated that 80% of the patients with the SMs were able to walk 1 year after surgery [27]. Riad et al. have stated some improvement in sphincter dysfunction in 67% of the cases [82]. Specifically, in the study involving the ventral and ventrolateral SMs, while the rate of independent walking in the preoperative period was 72.7% in the preoperative period, it increased to 90.9% with a significant improvement in the postoperative period [24]. After all, it is understood that the postoperative functional and neurologic recovery rates in the ventral and ventrolateral SMs are compatible with all SMs. In the studies published in recent years, the postoperative permanent neurological deterioration rates have been stated in the range from 0 to 10% [2, 22, 26, 29, 50, 83, 84]. Many potential risk factors that will be able to cause permanent postoperative neurological deterioration have been stated in the literature [7, 24, 25, 48, 85].

4.2 Incomplete removal of calcified tumor and surgical outcome

It is observed that the neurologic deterioration rates are higher in the postoperative period in patients with especially SM with massive calcification, in which the complete removal of the tumor by microsurgery is difficult [2, 24, 44, 86, 87]. Levy et al. have stated poor postoperative clinical outcomes in three (75%) of four patients with the calcified SMs. As a result of this study, it has been emphasized that the total resection of tumors should not be performed in calcified meningiomas located close to the spinal cord [2]. Ozkan et al. have stated a total of seven patients (12.7%) with the calcified SMs in their series of 55 patients with ventrally located SMs. In this study, they have stated total the removal of SM (according to Simpson’s grade-II resection) in five patients with ventrally located calcified tumors and the subtotal removal of meningioma in two patients. In this study, it has been stated that postoperative neurological deterioration was detected in five patients (9.1%), and four of these patients recovered in the early postoperative period [24]. When this study and other studies in the literature are evaluated together, it is understood that the calcified SMs should be evaluated separately as a specific issue.

4.3 Histopathological subtypes of the tumor and surgical outcome

Schaller et al. stated in their series that the neurological deficits of 33 patients (8 dorsal, 6 ventral, and 19 ventrolateral tumors) improved in 79% of the patients in the postoperative period, and neurological functions worsened in 21% [48]. In this study, the histopathology of the tumor has been observed to be psammomatous meningioma in all cases whose neurological functions worsened in the postoperative period [48]. On the other hand, Ozkan et al. stated in their study on the ventral SMs that they did not find any relationship between the psammomatous meningioma subtype and the negative clinical outcomes of the patients [24]. Han et al. analyzed the results of 20 operated patients with high-grade SMs. In this study, the SMs have been removed according to Simpson’s grade-II resection in 80% of the patients and resection has been performed in 20% of the patients according to Simpson’s grad-III. As a result of this study in which the surgical results were evaluated with the MMC grading, it has been stated that 73.7% of the patients improved in their neurological functions and no change occurred in the neurological functions of 15.7%.

4.4 Tumor localization and surgical outcome

4.4.1 Upper cervical spinal meningioma and surgical outcome

4.4.1.1 Lateral and far-lateral approaches

Abou-Madawi et al. evaluated the postoperative results of the patients with ventrally located foramen magnum and upper cervical region meningioma, which they operated with the far-lateral retrofacet approach, according to the JOA score, and they have stated that 70% of the patients had completed recovery and 30% of the patients had a reduction in preoperative symptoms. It has been also stated that there was no worsening of the neurological functions in the postoperative period in any of the patients [76]. On the other hand, Slin’ko et al. have analyzed the results of a total of 140 patients with the SMs, which were topographically located at 24% ventrally and 76% ventrolaterally, they operated with different approaches, such as posterior approach, laterally extended modified posterior approach, and anterolateral approach. In the postoperative period, it has been stated that 50% of the patients recovered completely, 38% improved, 7% did not change their neurological functions compared to the preoperative period, and 5% worsened [77]. After all, in many studies stated in the literature, it has been stated that the postoperative results in the ventral/ventrolateral SMs operated with the lateral approach were better than those operated with the posterior midline approach and its modified forms [44, 49, 77, 88, 89].

4.4.2 Subaxial cervical spinal meningioma and surgical outcome

4.4.2.1 Modified posterior midline approach with lateral extension

Slin’ko et al. have stated that the postoperative clinical outcomes were worse in the patients with ventral tumor, who were operated with different approaches, such as posterior approach, laterally extended modified posterior approach, and anterolateral approach, according to tumor topography, compared to the patients with ventrolateral tumor [77]. Joachim et al. have recommended cutting the dentate ligaments to prevent postoperative neurological deterioration in the tumors located ventrally. It has been stated with this technique that the stretch of the spinal cord released from the dentate ligaments was reduced and it could be mobilized more easily [88]. On the other hand, Ozkan et al. have stated the surgical results of 55 patients (27.3% localized between C0–C7 levels) with ventral and ventrolateral SMs localized in all spinal regions they operated with a modified posterior approach by using the technique of lengthening laminectomies to the laterals. They have stated successful complete removal of the SM (according to Simpsons grade-II resection) in 53 patients (96.4%) with this approach. They have stated that they were removed incompletely due to calcification of the tumor in two cases located close to the spinal cord. With this approach, the rate of independent walking, which was observed at a rate of 72.7% in the preoperative period for all patients according to Frankel grading, improved significantly in the postoperative period and increased to 90.9% [24].

4.4.2.2 Anterior cervical approach with corpectomy

In most of the studies reported in the literature, it has been stated that the neurologic functions mostly improved in the postoperative period in cases where the intradural ventrally located subaxial SMs were completely removed by the operation with an anterior cervical approach with uni- or multi-segmental corpectomy [65, 66, 67, 69]. In a case with the intradural SM extending between the foramen magnum and T2 vertebra level, the tumor has been completely removed by Sawa et al. with the tumor-infiltrated dural base by the anterior approach. Multi-segmental corpectomy has been performed from C3 to T1. It has been observed that the quadriparesis observed in this patient first deteriorated in the postoperative period, but improved significantly within months [68].

4.4.3 Thoracic and Lumbar spinal meningioma and surgical outcome

4.4.3.1 Modified posterior approach with lateral extension

Goel et al. have stated that the postoperative clinical results of 17 patients with the SM located ventral and ventrolateral and operated with the posterior midline approach (82.3% gross-total resection) were bad [90]. On the other hand, Ozkan et al. have stated the surgical results of 55 patients (52.7% localized between T1–T9 levels and 20% between T10–L2 levels) with the ventral and ventrolateral SMs localized in all spinal regions they operated with the modified posterior approach by using the technique of lengthening laminectomies to the laterals. They have stated successful complete removal of the SM (according to Simpsons grade-II resection) in 53 patients (96.4%) with this approach. They have stated that they removed the tumor incompletely due to calcification located close to the spinal cord in two cases. With this approach, the rate of independent walking, which was observed at a rate of 72.7% in the preoperative period for all patients according to Frankel grading, improved significantly in the postoperative period and increased to 90.9%. As a result of this study, it has been stated that the technique of extending laminectomies to the laterals (modified posterior approach) could be applied bilaterally when necessary by providing a wider and more reliable surgical perspective bilaterally for the ventral-located tumor. In addition, it has been emphasized that spinal cord manipulation could be performed more reliably without excessive traction by means of the technique of bilateral lengthening of the laminectomy [24].

4.4.3.2 Anterior approach

D’Aliberti et al. have evaluated the results of 145 patients with lesions located in the thoracic and lumbar spinal regions that were operated with the anterior approach and suggested that the ventral approach should be used for the removal of extradural lesions [91].

5. Management of the postoperative complications

5.1 Overview of postoperative complications

The postoperative complication rates vary depending on the localization and topographic structure of the tumor and the surgical approach in SMs. Sandalcioglu et al. have stated that postoperative complications developed in 3.3% of the patients in their series of 131 patients with the SMs, who were operated with the standard posterior midline approach [50]. On the other hand, Ozkan et al. have stated the postoperative complication rate was 13.5% in a series of 55 patients with the ventral and ventrolateral SMs. They operated with the modified posterior approach extended laterally [24]. When the postoperative complications are examined, the CSF leakage draws attention, especially. In addition, the complications, such as venous thrombosis, epidural hematoma, and myocardial infarction, delayed wound healing and bifrontal intracranial air trapping have been reported in the literature [21, 24, 50, 66, 67, 68, 69, 76, 92].

5.2 Cerebrospinal fluid leakage and management

The rate of CSF leakages observed in the postoperative period in the SMs has been stated between 0 and 4% [4, 22]. It is most commonly observed after the surgery for the SMs located in the upper thoracic region due to the stretch in the interscapular region [45]. Sandalcioglu et al. have stated the postoperative CSF leakage rate of 0.8% in a series of 131 patients with the SMs that they operated with the standard posterior midline approach [50]. On the other hand, Ozkan et al. have stated the postoperative CSF leakage rate as 5.5% in a series of 55 patients with the ventral and ventrolateral SMs that they operated with the modified posterior approach extended laterally [24]. The CSF leakage observed in the postoperative period in the lateral and far-lateral approaches used for the removal of ventrally located cervical SMs is particularly noteworthy. The postoperative CSF leakage was detected in 4 (17.3%) of 23 patients with the ventral/ventrolateral SM in the upper cervical region who were operated with the far-lateral retrofacet approach, and all of these patients recovered with CSF drainage [76]. Sen et al. have stated that CSF leakage was detected in the postoperative period in 2 (33.3%) of 6 patients with the foramen magnum and cervical intradural lesions, who were operated with the extreme-lateral approach. It has been emphasized that the CSF leakage developed due to excessive dural coagulation [92]. Similarly, CSF leakage has also been stated in the postoperative period in the anterior cervical approach used for the removal of ventrally located cervical SMs [66, 67, 68, 69]. Therefore, in the majority of the studies reported in the literature, it has been recommended that excessive coagulation of dura should be avoided in order to prevent CSF leakage [66, 67, 68, 69, 76, 92].

In the majority of cases, the CSF leakages developed from the small dural openings. To prevent CSF leakage, the dura leaves should be closed with primary suturing, especially in a water-tight manner. However, if the dural opening is too large to be closed with the primary suturing, the duraplasty should be performed by using autografts (with fascia) or allografts (with dural synthetic grafts). Then, the fibrin tissue adhesives are placed on the sutured dura area in the necessary cases. In the cases with CSF leakage that cannot be prevented by these surgical strategies, the autogenous blood injection into the epidural space and the lumbar CSF drainage can be performed, respectively. If there is no improvement in the CSF leakage within 3 days in the postoperative period, the surgical field should be reopened and dura repair should be performed [45].

5.3 Spinal instability and fusion requirement

In the posterior midline approaches used for the removal of SMs observed in the cervical and cervico-thoracic junction, the kyphotic deformity will be able to develop in the long-term postoperatively when the multilevel laminectomy is performed. Therefore, arthrodesis is recommended in cases with more than three levels of laminectomy. In these cases, laminoplasty techniques can be used as an alternative [93]. Moreover, spinal instability also develops in the modified posterior approaches, where the total facetectomy is performed with the laminectomy in the cervical and lumbar regions [45]. To prevent spinal instability, posterior stabilization with instrumentation should be performed with lateral mass screwing for the cervical region and transpedicular screwing for the lumbar region, in the same session [45, 46, 94]. In the thoracic region, spinal instability due to the laminectomy is observed very rarely, even in patients who have undergone facetectomy [24]. Menku et al. have recommended that the lamina provided a safe mechanical barrier; therefore, the laminoplasty should be performed in posterior approaches, where laminectomy is used [95]. Therefore, the laminoplasty techniques performed by placing the mini-plates on the laminotomy sites with the pneumatic cutters are preferred in patients who need multi-segmental laminectomy [45, 95]. Even if the laminotomy is performed to reduce the risk of postoperative spinal instability, in all cases, where posterior approaches are used in surgery, all anatomical structures in the surgical area, especially interspinous ligaments should be closed by suturing regularly and tightly. In the anterior transabdominal approaches, where the extensive vertebrectomy is performed, which is now very rarely preferred, the instrumented fusion with the corpectomy cage should be performed in the same session to prevent postoperative instability [46, 94].

One of the most important disadvantages of the anterior cervical approach with the corpectomy used for the removal of ventrally located cervical SMs is spinal instability. It has been stated that placing an autogenous bone graft or cage in the corpectomy area and fusion with the anterior cervical plate-screw system was sufficient in patients who have undergone one- or two-level corpectomies. On the other hand, in cases with three or more corpectomies, the risk of pseudoarthrosis increases after the anterior cervical fusion described above. Therefore, posterior cervical stabilization is recommended to prevent spinal instability that will be able to develop in these cases [96, 97]. Ozkan et al. have stated that 53 of 55 ventrally located SMs were completely removed with the modified posterior approach, in which the laminectomies were extended laterally, and that the secondary stabilization was not performed in any of these cases due to the potential instability due to laminectomy [24].

5.4 Postoperative pain

The somatic pain observed in the preoperative period in the SMs mostly resolves in the postoperative period. On the other hand, analgesic drugs are used together with psychotherapy in the postoperative period, especially in the sub-observed prolonged central pain. The dorsal colon stimulation and morphine pumps can also be used in resistant cases [45].

6. Recurrence

6.1 Extent of surgical tumor removal

The surgical resection coverage is very important in terms of the postoperative tumor recurrence and thus prognosis in the SMs [21]. In the systematic review conducted by Pereira et al., it has been stated that Simpson grade-I and grade-II resection was performed in 94.5% of the SMs, and Simpson grade III or higher resection was performed in 5.5% of them. In this study, the tumor recurrence rate was reported as 4.3% in the SM cases [20]. As a result of another study, it has been stated that the tumor recurrence rate range from 1.3 to 6.4%, and tumor recurrences developed within 1 to 17 years [6].

When other series in the literature were examined, the rates of complete tumor removal in SMs have been reported between 82% and 98% [2, 7, 8, 22, 23, 27]. Similarly, the tumor recurrence rates reported in retrospective studies range from 1 to 15% [5, 22, 23, 27]. While the local tumor recurrence was observed in the majority of SM cases, the tumor recurrence has also been reported in a spinal region other than the region where the tumor was first removed [2].

Voldrich et al. have emphasized that the patient follow-up periods after surgery were also important in determining the frequency of tumor recurrence in Simpson’s grade-II resection cases [21, 98]. In the retrospective study conducted by Mirimanoff et al., the tumor recurrence rates were reported as 7%, 10%, and 12% in 5, 10, and 15-year follow-up periods of all meningiomas (intracranial and spinal meningioma) who underwent total resection. However, it has been also stated that 8% of the cases included in this study had SM [85]. On the other hand, Naito et al. have performed a retrospective analysis of 35 patients with the WHO grade-I SMs and stated that no local recurrence was observed in 31 patients (88.6%), who underwent Simpson’s grade-I and grade-II resections during 2 years of follow-up [99].

In the study conducted by Klekamp and Samii, they stated that tumor recurrence was observed at a rate of 29.5% in the cases with complete resection, and at a rate of 100% in the cases with partial resection [27]. As a result of many studies reported in the literature, it has been stated that there was no relationship between the treatment modalities (dural resection or dural coagulation) applied to the tumor-infiltrated dural base and tumor recurrence in SMs, unlike intracranial meningiomas [5, 7, 23, 27]. In the systematic study conducted by Pereira et al., although it has been emphasized that partial tumor resection was a risk factor for tumor recurrence [100], it has not been shown that the subtotal tumor resection could definitely lead to the recurrence [5].

6.2 Histopathological tumor subtype and recurrence

In addition to the scope of surgical resection in the SMs, the histological WHO grade of the tumor plays a very important role in tumor recurrence [101]. Most of the SMs are WHO grade-I meningiomas with psammomatous, meningothelial, and other subtypes. The WHO grade-II atypical meningiomas with clear-cell and chordoid subtypes and the WHO grade-III malignant meningiomas are observed less frequently. In particular, the risk of local recurrence is higher in the WHO grade-III malignant meningiomas [102]. The tumor recurrences can be observed rarely in the WHO grade-II atypical meningiomas and very rarely in the WHO grade-I meningiomas [12]. In conclusion, it has been observed in the literature that the risk of tumor recurrence was higher in the WHO grade-II and WHO grade-III SMs and their subtypes, in proportion to the increase in the degree of malignancy [13, 18, 23]. Setzer et al. have stated that the tumor recurrence rates observed in the WHO grade-I, WHO grade-II, and WHO grade-III SMs were 1.4%, 50%, and 100%, respectively. Zorludemir et al. stated that the recurrence rate in the clear cell SMs was 61%. Han et al. analyzed 20 patients with high-grade SMs who were operated on. In this study, it has been stated that the SM was removed according to Simpson’s grade-II resection in 16 (80%) patients and it has been removed according to Simpson’s grade-III resection in 4 patients (20%), and the tumor recurrence has been observed in a total of 3 patients (15%) [37]. Mauri et al. have stated that the arachnoid invasion in the SMs and the high Ki-67 proliferative index of the tumor were risk factors for tumor recurrence. On the other hand, it has been stated in the same study that the microsurgical dural resection grade, tumor size, and progesterone receptor expression were not risk factors for tumor recurrence [103].

6.3 Reoperation during relapse

Nakamura et al. stated that the WHO grade-I SMs were completely removed with the tumor-infiltrated dural base (according to Simpson’s grade-I resection) and reported that the tumor recurrence was lower than in the cases in which the tumor-infiltrated dural base was coagulated and left in place and only the tumor was completely removed (according to Simpson’s grade-II resection). However, Sandalcioglu and King have stated that the tumor recurrence was low in the WHO grade-I SMs, even if the tumor-infiltrated dural base was not removed [5, 50, 104]. The total removal of recurrent tumors is difficult due to the arachnoid scar formation. For this reason, the tumor recurrence will be able to be seen in the reoperated cases. Therefore, the aim of surgery should be the total removal of the SM in the first operation [20]. The total removal of recurrent high-grade SMs is difficult because they adhere tightly to the surrounding tissues, spinal cord, and nerve roots. Han et al. stated the results of four patients with recurrent high-grade SM. In this study, they have stated that the SM was incompletely removed (according to Simpson’s grade-III resection) in three cases with the ventral location and tightly adhered to the spinal cord, and complete removal of the SM in one case with the challenging surgery (according to Simpson’s grade-II resection) [37].

7. Adjuvant therapies

7.1 Adjuvant radiotherapy and stereotactic radiosurgery

Adjuvant radiotherapy is still a controversial issue because of radiation-induced spinal cord damage (radiation myelopathy) [23]. The radiation myelopathy develops, especially as a result of the radiotherapy applications to a 10 cm part of the spinal cord at a dose of more than 1400 cGy [45]. Therefore, the opinion that adjuvant radiotherapy should be used in multiple recurrent tumors or SMs with atypical (WHO grade-II) or malignant (WHO grade-III) histopathology has gained weight [50, 105]. In addition, it has been stated that the adjuvant stereotactic radiosurgery was beneficial in cases with a radiological increase in tumor size [106, 107]. Flores et al. stated in their review that successful local tumor control was achieved with the fractionated stereotactic radiosurgery in one patient with ventrally located foramen magnum meningioma who was operated with the far-lateral approach [52].

7.2 Medical and physical therapy

The physical therapy applied in the postoperative period has a great role in improving the neurological functions of patients. Therefore, physical therapy and rehabilitation programs should be started as soon as possible in patients with SM, who have neurological dysfunction in the postoperative period [61]. Moreover, it will be beneficial to use the peroperative methyl-prednisolone treatment in patients with SM pressing on the spinal cord [108].

8. Prognosis

The prognosis is good in most of the patients with the SMs, and significant improvement in neurological functions is observed in the postoperative period. The rates of improvement in neurological functions in the postoperative period have been stated in the range from 61 to 98%. The permanent postoperative worsening rates have been observed in the literature between 0% and 10% [24, 82]. In a systematic review, the mortality rate has been stated to be 3%. In the literature, it has been stated that aspiration pneumonia, stroke, and myocardial infarction caused more postoperative mortality, especially in pulmonary embolism [5, 27]. It has been observed that the prognosis was better in the SMs localized below the C4 level and topographically located dorsally and dorsolaterally. Moreover, it has been observed that the prognosis was better in patients under 60 years of age and in patients with short duration of clinical symptoms [48]. On the other hand, it has been stated that the prognosis was worse in the SM cases with intratumoral calcifications due to the difficulties experienced in the surgery [2].

Moreover, by means of the developments in the imaging techniques, such as spinal MRI and digital subtraction angiography, the SMs could be diagnosed early and endovascular embolization could be performed in the preoperative period of vascular structures that were tumor feeders. Performing the microsurgical procedures with intraoperative neuromonitoring, ultrasonography, and cavitron ultrasonic aspirator facilitate safe complete removal of the tumor. The use of these preoperative techniques contributes to the significant reduction in the postoperative morbidity and mortality rates in patients with the SMs, and ultimately to a better prognosis [5, 7, 22, 109].

9. Conclusions

The SMs, which are usually benign and grow slowly, are usually diagnosed late. However, the presence of a good surgical cleavage between the spinal cord and the tumor enables the total or near-total removal of SMs by microsurgical methods. The most important factor in the complete and safe removal of the SM is the selection of the surgical approach suitable for the localization and topography of the tumor. In surgical approaches with a high risk of spinal instability, the instrumented fusion should also be performed in the same session. In the postoperative period, rapid improvement in neurological functions is observed in most of the patients. In order to prevent CSF leakage, which is the most common postoperative complication, the excessive coagulation of dura should be avoided. Adjuvant radiotherapy or stereotactic radiosurgery can be used in recurrent SMs with malignant histopathology.

Conflict of interest

The authors declare no conflict of interest.

Acronyms and abbreviations

CSF	cerebrospinal fluid
CT	computerized tomography
CUSA	cavitron ultrasonic surgical aspirator
JOA	Japanese orthopedic society
MEP	motor-evoked potentials
MMC	modified McCormick
MRI	magnetic resonance imaging
SSEP	somatosensory-evoked potentials
SM	spinal meningioma
USG	ultrasonography
WHO	World Health Organization