Endoscopic Third Ventriculostomy in the Pediatric Patient

Abstract

Endoscopic third ventriculostomy (ETV) is one of the two surgical procedures for the treatment of hydrocephalus, its main indication being obstructive hydrocephalus. Its efficacy is related to the age of the patient and the etiology of the hydrocephalus; however, more studies appear where ETV has gained ground beyond obstructive hydrocephalus, and despite the fact that there is still a lack of evidence to issue a grade of recommendation. ETV has shown to be useful even in communicating hydrocephalus and in patients younger than 6 months. This chapter shows a summary of the most important points to take into account in this procedure. Likewise, the third endoscopic ventriculostomy gives us the opportunity to continue studying the intraventricular dynamics of the cerebrospinal fluid, the ventricular anatomy, the pathology around or within the ventricular system and other details that can open doors for us to understand the concept of hydrocephalus, improve its treatment and improve known surgical techniques.

1. Introduction

It was the German urologist Maximilian Carl-Friedrich Nitze who introduced the modern endoscope (Figure 1) [1, 2]. Viktor Lespinasse was the first neuroendoscopist in 1910. He treated two children with hydrocephalus by using a urethroscope to access the lateral ventricles, [1, 2, 3, 4]. In 1922, Dandy described ventriculoscopy [5, 6], as well as a technique for performing the third ventriculostomy as a treatment for hydrocephalus via frontal and subtemporal. In another hand, William Mixter was the first surgeon to combine diagnostic ventriculoscopy with ventriculostomy. In 1923, he used a urethroscope to perform an ETV to treat noncommunicating hydrocephalus in a 9-year-old girl [7, 8].

Figure 1.

CSF circulation.

By 1932, Dandy was again attempting an endoscopic choroid plexectomy [2].

In 1934, Tracy Putnam, following the work of Dandy and Mixter, developed instruments for intracranial procedures for the ventriculoscope. In 1935, John Scarff made modifications to Putnam’s ventriculoscope, adding an irrigation system [8, 9]. In 1947, H. F. McNickle reported two cases of communicating hydrocephalus that responded to ventriculostomy [10].

There were two reasons why neuroendoscopy had a recess at this time: one was Dandy’s results, perhaps they were not the most encouraging with the first designs, and the second was in 1949 Frank Nulsen and Eugene Spitz introduced the concept of the shunt. In 1955, John Holter added a one-way valve to the device; Holter’s invention was inspired by the death of his son, Casey, from the complications of myelomeningocele and hydrocephalus (Table 1) [2, 3].

Substance	CSF	Serum
Water content (%wt)	99	93
Protein (mg/dL)	35	7000
Glucose (mg/dL)	60	90
Osmolarity (mOsm/L	295	295
Sodium (mEq/L)	138	138
Potassium (mEq/L)	2.8	4.5
Calcium (mEq/L)	2.1	4.8
Magnesium (mEq/L)	2.0–2.5	1.7
Chloride (mEq/L)	119	102
pH	7.33	7.41

Table 1.

Comparison of serum and cerebrospinal fluid.

2. Endoscopic anatomy

When performing a third endoscopic ventriculostomy, we must consider three spaces or cavities, in a descending direction:

1. Cavity of lateral ventricles (Figures 2 and 3) in this space, we must identify:

   1. Foramen of Monro.

   2. Anterior septal vein.

   3. Choroid plexus.

   4. Striated thalamic vein.

   5. Fornix.

   In the ventricular cavity, it is advisable to initially identify the choroid plexus, which is the most reliable landmark for finding Monroe’s foramen, since in some cases said foramen is not evident, due to some anatomical variant (Table 2).

2. Cavity of the third ventricle in this space, we must identify:

   1. Mammillary bodies.

   2. Premammillary membrane.

   3. Infundibular recess.

   This space presents many anomalies or variants, as can be seen in the following figure, where a band was found that traversed the premammillary membrane transversely. The ostomy of the floor of the third ventricle is recommended to be performed at an intermediate point between the mammillary bodies and the infundibular recess, where in this case it is marked by this transverse band (Figures 4–6).

3. Cisternal space in this space, we must recognize:

   1. Basilar artery and its terminal branches.

   2. Liliequist’s membrane (sometimes trabeculated or some portion not present).

   3. Clivus (Figures 7–10).

Figure 2.

Lateral ventricles, supraforaminal view.

Figure 3.

View through Monroe’s foramen.

Figure 4.

Cavity and floor of the 3rd ventricle.

Figure 5.

3rd ventricle floor.

Figure 6.

Third ventricular floor.

Figure 7.

Cisternal space (prepontine).

Figure 8.

Prepontine cisternal space.

Figure 9.

Prepontine space. Lilliequist’s membrane (mesencephalic portion) open spontaneously, but present forming a tent in the cisternal space.

Figure 10.

Floor of the 3rd ventricle. Variant in a patient with hydrocephalus and myelomeningocele. Indistinguishable mammillary bodies, transparent premammillary membrane revealing the vascular anatomy: Basilar artery and its terminal branch.

Anatomical site of the lesion	Clinical alteration
Fornix	Anterograde amnesia
Mammillary bodies	Episodic or recollective amnesia [11]
Infundibular recess	Primarily constitutes nerve fibers traveling from the hypothalamus to the pituitary gland. Rather than providing signaling to the gland, many of these fibers actually function as the source of the substances released by the posterior lobe of this gland [12]

Table 2.

Anatomical lesions and their clinical correlation.

Liliequist’s membrane (mesencephalic portion) opens spontaneously but presents forming a tent in the cisternal space.

Liliequist’s membrane.

Originally described by Key and Retzius in 1875, and after described by Liliequist in 1956 [13, 14] is an arachnoid membrane separating the chiasmatic cistern, interpeduncular cistern and prepontine cistern. It arises anteriorly from the diaphragma sellae and extends posteriorly separating into two sheets, The membrane of Liliequist is a partially trabecular, partially dense folded inner arachnoid membrane, and a very important anatomic landmark in the anatomy of the interpeduncular fossa and sellar and parasellar regions [15]. The membrane of Liliequist consists of two leaves: a superior diencephalic and an inferior mesencephalic one [16], these leaves are highly variable in their shape, distribution, and density, most commonly trabeculate (Table 3).

Score	Age	Etiology	Previous shunt
0	<1 month	Postinfectious	Previous shunt
10	1 month to <6 months		No previous shunt
20		Myelomeningocele, IVH, Nontectal brain tumor
30	6 months to <1 year	Aqueductal stenosis, tecctal tumor, other
40	<10 years
50	> Or = 10 yrs

Table 3.

ETVSS.

3. Anatomical injuries

With endoscopic access, there is a risk of injuring anatomical structures that are in the surgical corridor or adjacent structures that can be directly injured or by vascular lesions.

4. Indications

Obstructive hydrocephalus.

1. Aqueductal stenosis.

2. Posterior fossa tumors.

3. Sellar region tumors.

4. Multitabulated hydrocephalus.

5. Dandy-Walker malformation.

6. Galen vein malformation.

7. Chiari malformation.

8. Myelomeningocele.

9. Encephalocele.

10. Craniosynostosis.

11. Post-infectious hydrocephalus.

12. Shunt malfunction.

13. Posthemorrhagic.

14. Tumor etiology (supratentorial).

15. Cerebral or cerebellar infarcts.

16. Intraventricular tumors.

4.1 Communicating hydrocephalus

Even though this indication may be controversial, various studies have published its usefulness in normal pressure hydrocephalus. Sufficient evidence is lacking to establish a grade of recommendation [12, 17, 18, 19].

5. ETVSS

Kulkarni et al. created a scale considering the etiology of the hydrocephalus, the patient’s age, and the presence of a previous shunt to calculate the success of the ETV with which the ETVSS was created [20].

This scale predicts the 6-month success rate of ETV for children with hydrocephalus, based on some characteristics Scores range from 0 (extremely poor chance of ETV success) to 90 (extremely high chance of ETV success), and it is calculated as the sum of the age score (max 50), etiology score (max 30), and previous shunt score (max 10).

The high-ETVSS group [21] is associated with a lower risk of failure right from the early postoperative phase. The moderate-ETVSS group [22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42] has a higher initial failure rate, but, after about 3 months, the risk of ETV failure becomes slightly lower than shunt failure. Finally, in the low-ETVSS group [43], the early risk of ETV failure is much higher than the risk of shunt failure, but the risk becomes lower than the risk of shunt failure at about 6 months following the procedure [20, 44, 45].

6. Preoperative imaging

1. The main requirement to be able to perform an ETV is ventricular dilatation, although in some cases depending on the clinical condition of the patient, etiology, and prognosis, among other factors, it is possible to perform an ETV with a moderate dilation guided by neuronavigation. If that ventricular dilation is evident at the time of diagnosis and, it is recommended:

2. Evaluate prepontine space in CT or MRI, there must be an evident space between the clivus and the protuberance, ideally greater than the diameter of the endoscope to be used (3.7–4.2 mm).

3. Evaluate the presence and shape of the mesencephalic and diencephalic portion of the liliequist membrane, using MRI.

4. Evaluate vascular anatomy through 3D sequence and multiplanar reformat images, these images can also help in the identification of liliequist’s membrane.

5. Evaluate the distance of the frontal horn of the right lateral ventricle to the cerebral cortex.

6. Evaluate the cisterns with special emphasis on the prepontine cistern. In cases of cisternal neurocysticercosis, the vesicular ones are abundant at the base around the brain stem, which means that the TVE does not work.

7. Cine phase-contrast magnetic resonance imaging (CISS o FIESTA) can be utilized as a method of distinguishing between communicating and noncommunicating hydrocephalus and any abnormality in basal cisterns [46, 47].

7. Post surgical evaluation

Remember: Since the size of the ventricles, seen on CT or MRI after ETV, decreases more slowly than after shunt placement, in fact, ventriculomegaly after ETV can take weeks to reduce or persist [44].

G.Cinalli et al., established radiological criteria for the success of ETV: [45, 47, 48, 49, 50].

1. Reduction in ventricular size ranging from 10 to 50% must be observed from the first week.

2. Periventricular lucency, if present before the operation, must disappear.

3. CSF flow artifact must be visible on sagittal median T2-weighted fast spin-echo MRI sequences and a flow void must be detectable on the stoma on 3D-CISS MRI.

4. The floor of the third ventricle, if bulging downward in the preoperative images must be straight on postoperative images.

5. Atrial diverticula and pseudocystic dilatation of the suprapineal recess, if present preoperatively, must disappear or decrease significantly.

6. Pericerebral sulci, if not visible before operation, must reappear or increase in size.

7.1 Remember

• The third ventricle is the quickest to decrease and remains stationary in size 3 months later.

• The downward deviation and flattening of the brainstem reverts within 1 year, whereas the width and height of the lateral ventricles continue to decrease steadily for 2 years [45, 51].

Mortality: 0.5–1.0% [44, 45, 52, 53, 54].

8. Complications

All complication rate of 8.5%, [43, 55, 56, 57, 58, 59].

1. Injury to the basilar artery 0.3%.

2. Minor bleeding 16.5%.

3. CSF leak 1.6%.

4. Abandonment of the procedure 4.16%.

5. Thalamic lesion 0.12%.

6. Forniceal injury 0.04%.

7. Hypothalamic lesion 0.04%.

8. Postoperative fever 65.1–84.4%.

9. Meningitis o ventriculitis 1.6–6.1%.

10. Bradycardia at the time of fenestration 26.8–43%.

11. Diabetes insipidus 0.64%.

12. Gaze paralysis 0.60%.

13. Endocrine and electrolyte disturbances 0.94%. [22, 55, 56, 57, 58, 60, 61, 62, 63]

14. Other complications with very low frequencies: subdural, epidural, intracerebral, and intraventricular hematomas [57]. The author had a patient in the first 24 hours after performing the procedure, developed slit ventricles.

9. Avoiding complications

IR: infundibular recess.

MB: mammillary bodies.

1. Adequate surgical indication.

2. Carefully evaluate preoperative neuroimaging studies, assess prepontine space and look for anatomical alterations that may interfere with the passage of the endoscope, evaluate premammillary membrane density, vascular anatomy, and presence or absence of Liliequist’s membrane [22].

3. Ventricular entry point: assess the trajectory and distance from the cerebral cortex to the ventricle. In some cases, such as intraventricular tumors with purely endoscopic access in which ETV is considered at the same time, it is advisable to modify the shape of the burr hole and the trajectory by modifying the entry point, (Figure 11), a burr hole can be used oval in case the endoscope inside the ventricular cavity has to be mobilized anteriorly or posteriorly [64].

4. In the event of intraventricular bleeding, apply constant irrigation, with increased pressure in the irrigation at the site of the hemorrhage and close one of the ports [23, 26], open the port intermittently to drain the amount of fluid inserted and avoid increases in intracranial pressure, a lot of patience with the irrigation. In these cases, closely monitor changes in blood pressure and heart rate.

5. Move the tip of the fiber optic away, when inserting an instrument through the working port, and move the instrument closer to the target site only when you have visual control of the tip of said instrument. Remember that the visual range of the endoscope is less than 180° [56].

6. In the floor of the third ventricle, increasing the intensity of the light source, bring the optical fiber closer and visualize the position of the basilar artery, in most cases, it is possible to observe through the premammillary membrane, observe the blood vessels visible in this membrane as well as the distance from the mammillary bodies to the infundibular recess and make the stoma in the avascular area, (Figure 12), very gently irrigate and verify that there is no bleeding. When the ostomy was performed with a blunt object and without applying heat, expand the ostomy only when there is no bleeding. In case of bleeding at the ostomy site, insert the Fogarty balloon and apply pressure with it for 2 or 3 minutes.

7. Upon reaching the Liliquist (LM) membrane, evaluate its characteristics and increase the intensity of the light source when approaching to visualize the density of this membrane, remember that at this point the cranial nerve that can be injured is the third nerve. To avoid this, the diencephalic and mesencephalic portion of the LM must be carefully visualized and the opening performed delicately, patiently, and verify that a valvular effect occurs after opening it, the same that must be observed in the premammillary membrane already open (Figure 13).

8. Irrigate with Ringer’s solution at a temperature of 36°C, making sure that the irrigation solution is not cold, which produces sudden and dangerous changes in heart rate, especially when irrigating the prepontine space.

9. Remember the vascular landmarks around Monroe’s foramen and the 3D layout of the ventricular anatomy (Figure 14).

10. All efforts must be made to close the wound, layer-by-layer, using dura mater grafts, if necessary, perform the Valsalva maneuver by the anesthesiologist upon completion of the closure and verify that there is no leakage of CSF, it is convenient to place gelfoam and surgicel in the burr hole area. After placing the bone flap, close the epicranial fascia, if possible, subcutaneous tissue and skin (Figure 14).

Figure 11.

IR: Infundibular recess; MB: Mammillary bodies.

Figure 12.

Schematic representation of the Lilliequist membrane (LM) and its distribution, sagittal view.

Figure 13.

Path through Kocher's point to access the floor of the 3rd ventricle in obstructive hydrocephalus.

Figure 14.

Premamillary membrane and its relationship with the diencephalic portion of the membrane of Liliequist membrane (LM).

10. Surgical technique

The Kocher point is the most common access site for ETV [31], it is located 2 cm lateral to the midline and 2 cm anterior to the coronal suture [33]. Other access points can be used, depending on the associated pathology [32]. In infants with a patent fontanelle, this corridor can be used by making the incision at the lateral end of the fontanelle rhombus (Figure 15) [33].

Figure 15.

Ventricular system and relationship with the endoscopic access points to the floor of the 3rd ventricle.

10.1 Other access points

1. Keen.

   

2. Frazier.

   

3. Dandy.

   

4. Kaufman.

   

5. Tubbs.

   

6. Kocher.

   

10.2 Before starting

1. Review the images.

2. Verify proper positioning of the head and neck.

3. Adjust the position of the monitors for an adequate vision.

4. Fluid for irrigation at 36°C (lactate ringer’s).

5. Remember the distance from the cortex to the ventricle.

The insertion of the endoscope must be done gently, without exerting pressure on the endoscope, bearing in mind the distance measured in the neuroimaging, when reaching the ventricle and even though the brain parenchyma does not offer resistance to the insertion of the endoscope, a sensation can be felt. Change in resistance to the advancement of the endoscope.

Upon reaching Monroe’s foramen, we must observe the landmarks of this point: choroid plexus, anterior septal and thalamus striate vein, and fornix. It is convenient at this point to observe all possible anatomical details of the third ventricle.

When descending to the third ventricle, the landmarks must be recognized: mammillary bodies, infundibular recess, and premammillary membrane. At this point, it is convenient to transilluminate the premammillary membrane to try to observe the anatomy of the basilar artery.

Perforation of the floor of the third ventricle must be done with a blunt object, it can be the coagulator (without activating heat), it has been mentioned that heat can generate an inflammatory response that leads to closure of the fenestration [31], or the clamp forceps, others have mentioned the use of laser as an option to perform fenestration [34]. The initial ostomy should be the size of the perforating object, it is also convenient to maintain irrigation at this time and observe if there is bleeding, gently remove the perforating object and if there is no bleeding, expand the ostomy with a Fogarty 3 or 4 catheter. If you do not have a Fogarty catheter, this amplification can be done with forceps, always gently and patiently, or with the coagulator moving on the edge of the ostomy from right to left from front to back, very gently and making sure not to contact neural structures with the highest part of the endoscope.

The opening of the Liliequist’s membrane (LM) is of vital importance for the success of the ETV, for which special attention should be paid to the prepontine space and to visualize as much as possible the characteristics of this membrane for its opening [31, 35, 37, 42], after this opening, the interpeduncular cistern and the prepontine cistern should be visualized, to inspect that there is no other arachnoid membrane that interferes with the passage of CSF.

11. TVE/VP shunt comparison

ETV was associated with a statistically significant lower risk of procedure-related infection compared to shunt [21]. It is generally accepted that true differences exist regarding complication rates among centers or among individual neurosurgeons, according to their personal experience [59, 65, 66].

Despite the fact that the calculation of the Costs to compare TVE vs. VP shunt may vary from country to country, ETV represents less economic costs if it is taken into account that no device is left, and the number of surgeries per patient may be less in the patient who receives TVE; however, there are not enough relative studies to establish a significant difference, since various studies that have been carried out were carried out in countries with different economic incomes and did not show statistical significance in terms of costs [67] others compared and the VP shunt, endoscopic third ventriculostomy (ETV) was proven to be better in terms of infection, length of hospital stay, cost-effectiveness, and complication rate [68].

Much more evidence and comparative studies are needed.

12. ETV & choroid plexus coagulation (CPC)

It may become an efficient treatment for obstructive HCP in infants [69]. However, the etiology of the hydrocephalus, the age of the patient, and the extent of coagulation of the choroid plexuses must be considered [70, 71, 72]. These factors can influence the results.

13. Conclusion

ETV is a safe, effective procedure, for many years included as one of the two surgical alternatives for hydrocephalus. In the pediatric patient with great value. In low-income countries, ETV represents an excellent alternative, where a wide variety of newer and more sophisticated shunting systems, self-regulating systems, or antibiotic-impregnated systems are not available. On the other hand, it has shown a lower frequency of complications and it is not necessary to leave any foreign body in the patient. Infections in shunt systems are common infections that require several days of stay, with high hospitalization and drug costs, and with functional complications derived from neuroinfection, especially in children under 1 year of age. ETV infections have been shown to be very rare and respond well to antibiotic treatment. For all these reasons, ETV should be considered the first treatment option for obstructive hydrocephalus in pediatric patients.

Thanks

To my father William.