New Progress in Imaging of Pituitary Diseases

Abstract

In the last 20 years, there have been advances in imaging techniques for pituitary diseases. Magnetic resonance imaging (MRI) particularly presents high-quality structural images and the essential information needed to authorize surgery, radiation therapy, and/or drug therapy. These images can assist in monitoring long-term outcomes. Recent technological advances, such as the advent of 7-Tesla MRI, have been used for measuring tumor consistency in pituitary adenomas. Microadenomas and other pituitary incidentaloma have been more recognized in the presence of golden-angle radial sparse parallel imaging and conventional dynamic contrast-enhanced techniques. However, standard structural (anatomical) imaging, mainly in the form of MRI, acts inadequately to identify all tumors, especially microadenomas (< 1 cm diameter), recurrent adenomas, and several incidentalomas. In this respect, nuclear isotope (radionuclide) imaging promotes tumor detection beneficially. All these imaging improvements may play a central role in clinical practice, especially when considering diagnosis, differential diagnosis, or definitive intervention. They further form accurate diagnosis, advise surgery, and decrease the risk of disrupting normal pituitary function.

1. Introduction

The pituitary is a small endocrine gland seated in the sella turcica of the central skull base and is surrounded by the neurovascular structures of the parasellar region. The pituitary gland demonstrates many pathologies with multiple components and cell types, including neoplastic, vascular, and inflammatory processes. These conditions can affect the pituitary gland and produce endocrinologic and neurologic abnormalities. Pituitary lesions are always benign, but hypersecreted hormones or masses can seriously affect the quality of life. Therefore, early, accurate diagnosis and treatment are important. The most common lesions of the pituitary gland are adenomas. Magnetic resonance imaging (MRI) is the standard approach for evaluating the pituitary gland. Recent advances in MRI and positron emission tomography (PET) have facilitated the successful detection of tumors that may be only a few millimeters in diameter. Here, studies have indicated a prevalence rate of 3.5 to 5 times higher than previously suspected [1].

Many imaging methods focus on the diagnosis and demonstration of pituitary lesions and have already made huge progress. However, an optimal assessment has not been clarified for some occult lesions. This comprehensive review aims to discuss various updated imaging technologies regarding pituitary lesions.

2. Anatomy of the pituitary gland

Understanding the underlying anatomy depends on interpreting imaging studies of the sellar and parasellar regions. A complex neuroendocrine organ is located within the sella turcica (a cup-shaped depression in the sphenoid bone, which is also bordered anteriorly and inferiorly by the sphenoid sinus). This organ is the pituitary gland. The suprasellar cistern, which consists of the optic chiasm, is above the pituitary gland. The cavernous sinus forms the lateral walls of the pituitary fossa. It contains the sixth cranial nerve and the internal carotid arteries. It more laterally contains the third and fourth nerves. Additionally, the first and second divisions of the fifth cranial nerve sit in its walls. Anatomically, the pituitary gland is connected to the hypothalamus, which typically is via the infundibulum. Regarding embryology, the anterior and posterior pituitary lobes are distinct [2]. The adenohypophysis, the pituitary’s anterior lobe, and the neurohypophysis, the pituitary’s posterior lobe, emerge from embryological structures. The adenohypophysis is derived from the oral ectoderm and synthesizes multiple hormones, such as prolactin, adrenocorticotropic, thyroid-stimulating and follicle-stimulating hormones, and growth and luteinizing hormones. Arising from neural ectoderm, the neurohypophysis contains axons from the hypothalamus. It is responsible for secreting oxytocin and vasopressin. A vestigial intermediate lobe lies between the anterior and posterior lobes. The lobe is a potential site for Rathke cleft cysts [3].

Generally, the average pituitary gland is larger in women than in men. Its height is between 3 and 8 mm [4]. At birth, the size of the gland varies, when it is typically globular in shape (more so during adolescence) due to its physiological hypertrophy [5]. Yet, during pregnancy, the gland progressively develops to a large degree, where it can reach a height of up to 10 mm instantly after delivery [6]. Its size may increase in women during their 50s [6].

3. Imaging technology in pituitary and pituitary adenomas

3.1 Standard pituitary magnetic resonance imaging

Magnetic resonance imaging has brought the most advances regarding sellar and parasellar structures’ radiological assessment. Magnetic resonance imaging powerfully demonstrates both normal and abnormal anatomy. It even permits detecting subtle abnormalities within an overall normally dimensioned gland. Subtle abnormalities include 1–2 mm microadenomas and infiltration/inflammation [7, 8]. The high-quality imaging of sellar and parasellar structures is critical to decision-making when radiotherapy and/or surgery are not recommended.

The pituitary gland and hypothalamus imaging have multiple potentially beneficial MRI sequences. The pituitary MRI protocol may comprise pre-contrast T1- and T2-weighted (T1W/T2W) coronal and sagittal sections with thin slices. It also should include gadolinium (Gd)-enhanced coronal and sagittal T1W images [9, 10]. Nevertheless, T1W sequences are typically used in clinical practice. They present clear contrasts between the pituitary gland and adjacent cerebrospinal fluid, blood vessel flow voids, paranasal sinus air, and bone marrow fat. T2W sequences are further utilized because their sensitivity to changes in water content can be advantageous in detecting and evaluating pituitary lesions and assessing adjacent neurological structures, such as the hypothalamus and optic chiasm. The normal anterior pituitary gland is shown to be isointense to gray matter in non-contrast T1W and T2W standard spin echo (SE) sequences. On the other hand, neurohypophysis depicts an intrinsic high T1 signal; however, it is hypointense on T2 [3, 11].

The high signal on non-contrast T1W imaging is attributed to phospholipid vesicles containing neurosecretory granules [12, 13, 14]. The absence of bright spots in the posterior pituitary may alert the clinician to the likelihood of underlying pituitary pathology; some normal subjects do not exhibit this high signal. The extent to which the posterior lobe bright spot is faint or apparent in each patient varies from scan to scan [8, 15]. Occasionally, the posterior pituitary bright spot is abnormally placed, residing in the proximal infundibulum or hypothalamus, for a commonly named ectopic posterior pituitary bright spot. This is associated with some forms of congenital hypopituitarism, specifically concerning growth hormones (GHs). There are possibly other structural abnormalities, for instance, septal hypoplasia and agenesis of the corpus callosum [16]. The position of the bright spot can also be removed with pituitary stalk interference, which is shown to follow trauma or surgical transection after damaged neurosecretory granule migration [17, 18, 19].

Intravenous injection of a paramagnetic contrast agent is a common practice and enhances the pituitary gland and stalk on T1W images. The cavernous sinuses are hypointense in relation to the pituitary gland. They are adjacent to the brain and display enhancement after contrast. The cavernous sinus’s medial dural border is generally poorly visualized as a distinct structure compared with the lateral dural wall, which is more easily defined. During pituitary imaging, the naturally occurring lanthanide, Gd, is the most frequently utilized contrast agent. It changes the magnetic properties of tissues, in which it accumulates. As a result, it enhances the structure seen in MRI. Gadolinium uptake by pituitary adenomas is slower in most cases. Consequently, it triggers delayed improvement and washout characteristics. It assists in revealing a different image, especially poorly visualized microadenoma.

Gadolinium is toxic, even in its free form, and must be chelated to a carrier ligand to be permitted in clinical settings. Recently, attention has been brought to the safety of Gd-based contrast agents (GBCAs) owing to the potential for long-term central nervous system retention, typically in patients with normal renal function. As mentioned, many pituitary patients require long-term imaging surveillance with GBCAs resulting in retention of Gd in the tissues [20, 21]. Macrocyclic GBCAs show greater chemical stability compared with that of their linear counterpart. This is due to their connection with a lower risk of nephrogenic systemic fibrosis and decreased Gd tissue deposition; nevertheless, they seem to transmit a higher, albeit comparatively rare, risk of allergic reactions. Thus, while GBCAs are crucial in sellar and parasellar regions’ imaging, to decrease exposure, it is essential to acknowledge when contrast agents may not be needed [22, 23, 24].

3.2 Dynamic contrast-enhanced magnetic resonance imaging

Dynamic contrast-enhanced (DCE) MRI takes a series of images over time after an intravenous contrast media. As a type of permeability imaging, it measures T1W signal-intensity changes in the process of allocating an intravenous bolus of GCBA. According to initial studies, DCE-MRI was particularly effective in detecting and precisely delineating microadenomas without contour abnormalities [25, 26, 27, 28].

Given its intricate vascular anatomy characteristics, the pituitary gland is assured to benefit from dynamic imaging evaluation. The adenohypophysis receives most of the blood from the hypophyseal portal system supplies. The superior hypophyseal artery starts with small branches that enter the hypothalamus. It forms a primary capillary plexus. Subsequently, it transmits portal veins via the infundibulum to a secondary plexus and supplies blood to the adenohypophysis. Conversely, the neurohypophysis is supplied directly by the inferior hypophyseal artery. The inferior hypophyseal artery is an artery that branches from the internal carotid artery. Capillaries in the pituitary gland have unique fenestrations outside the blood–brain barrier, which cause the gland to strengthen with intravenous contrast administration [29].

Recent studies have proven the importance of this technique via the detection of microadenomas in patients, particularly those with Cushing’s disease, with a sensitivity of 67–95% compared with that of 50–60% under conventional contrast-enhanced MRI [30, 31, 32]. Microadenomas show delayed enhancement and regression, making them more visible on DCE-MRI than conventional sequences, and a few may only appear on dynamic sequences [33]. Dynamic contrast-enhanced magnetic resonance imaging has become routine for initial imaging studies in central endocrine disorders, namely, prolactinomas, due to its negative predictive value and high sensitivity in detecting microadenomas [33]. Additionally, DCE-MRI advances surgical planning by distinguishing between normal tissue and lesions [8, 34].

Nonetheless, conventional pituitary DCE-MRI has several limitations. A trade-off happens between spatial and temporal resolutions, and the optimal parameters for collection and reconstruction are unfamiliar. Variations in slice thickness, slice interval, and imaging duration due to the absence of standardized protocols may hinder comparisons between studies and institutions. In most instances, the lack of temporal resolution hinders quantitative pharmacokinetic analysis. In the postoperative setting, conventional techniques are insufficient in fat saturation, which typically is advantageous in contrasts of hemorrhage, fat, and surgical packing material [33].

3.3 Golden-angle radial sparse parallel imaging

Golden-angle radial sparse parallel (GRASP) imaging focuses on maneuvering the restrictions posed by conventional DCE-MRI. Golden-angle radial sparse parallel imaging uses a three-dimensional gradient-echo sequence with golden-angle ordering and radial “stack-of-stars” k-space sampling [35, 36]. Conventional DCE-MRI techniques implement the acquisition of numerous images. Golden-angle radial sparse parallel imaging develops all the dynamic data by completion in a single persistent scan. First, the data is separated into sequential time frames and then recreated via an iterative method, which connects compressed sensing and parallel imaging [33, 36, 37].

This method allows the recreation of extremely under-sampled data to submillimeter isotropic resolution using a total-variation time constraint. The isotropic resolution permits multiplanar reconstruction in all time points. Golden-angle radial sparse parallel imaging may be able to distinctively permit retrospective modification of temporal resolution as high as approximately 2.5 s per frame due to the uniform distribution of the profiles in k-space. Golden-angle radial sparse parallel imaging delivers higher planar resolution, increased sensitivity to motion and flow, and improved fat suppression compared to conventional two-dimensional turbo SE examinations [33, 37]. Research on the application of GRASP imaging for pituitary imaging is in its infancy, and there are many potential avenues of research. A few published studies validate the potential of this technology to assist in managing, characterizing, and diagnosing pituitary pathology [38, 39, 40, 41].

Golden-angle radial sparse parallel imaging has been utilized to describe the permeability features in the normal pituitary gland [40]. The posterior lobe and median eminence in normal pituitary glands show faster washin and time to the maximum enhancement than that of the anterior lobe. The median eminence and anterior lobe show faster washout than that of the posterior lobe. These results are coherent with previous DCE-MRI studies and note the gland’s complex vascular anatomy [33]. Direct arterial supply to the posterior lobe allows premature improvement. The pituitary portal system, which provides the anterior lobe, is relatively slow yet proceeds in greater maximal improvement due to a stronger vascular plexus.

Golden-angle radial sparse parallel imaging illustrates in patients of subtle differences with central endocrine disturbances except morphologically normal pituitary glands. Typically, patients with GH disturbances do not have focal pituitary lesions. Golden-angle radial sparse parallel imaging has shown that in these patients, the permeability parameters of the pituitary contradict those in healthy controls [30, 40]. Particularly, the pituitary glands of hypopituitarism show fundamentally lower washin and washout in the anterior and posterior lobes. According to a prior DCE-MRI study, patients with idiopathic GH deficiency and morphologically normal pituitary glands have shown comparable permeability differences [17, 35]. For the pituitary gland, GRASP imaging permeability parameters are necessary to determine reference ranges in prospective studies with larger samples.

Golden-angle radial sparse parallel imaging aids contrasting and detecting microadenomas and cysts. Compared with the normal parenchyma of the anterior lobe, microadenomas were enhanced, albeit at a significantly lower level. Utilizing acquisitions with 20 s temporal resolution, this contrast in improvement was exposed at all time points from 60 to 140 s after contrast injection [33]. Microadenomas showed maximal enhancement at 90 ± 10 s after contrast administration, compared with that at 80 ± 10 s in the anterior lobe. In differentiating, cysts failed to enhance.

Regarding preoperative planning, GRASP imaging improves macroadenoma assessment by distinguishing normal pituitary tissue from macroadenomas [41]. Damage to the normal pituitary gland possibly impacts hypopituitarism for approximately 5% of patients during transsphenoidal resection [42]. This risk may be reduced by using preoperative imaging to localize the pituitary gland. In one study, three independent readers, a radiology resident, a medical student, and an attending neuroradiologist, localized the normal pituitary gland in patients with macroadenomas on GRASP images with an almost-perfect agreement [41]. This technique’s reliability makes it an attractive option to enhance surgical planning, especially toward experience levels.

3.4 Nuclear isotope (radionuclide) imaging

3.4.1 Positron emission tomography (computed tomography/magnetic resonance imaging)

In the pituitary evaluation, the radionuclide technique has a comparatively limited role. However, some radiologists have experienced various modalities, including somatostatin receptor scintigraphy or PET, ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG)-PET, and ¹¹C-methionine (¹¹C-Met)-PET. For instance, the ¹¹¹indium labeled octreotide is utilized for investigating nonfunctioning adenomas [12, 43, 44]. Yet its practicality is insufficient, as other parasellar tumors, namely, meningiomas, may express somatostatin receptors and take up octreotide [3, 45]. For assessing the biological activity of pituitary tumors, there are limited uses for PET using ¹⁸F-FDG, in which most pituitary lesions are slow in growth and thus metabolically inactive. Even though the short half-life and obvious high cost of production of such pharmaceutical procedures nowadays restrict their usage for research purposes, tracers such as ¹¹C-Met have demonstrated some promise [45].

3.4.2 Somatostatin receptor scintigraphy and positron emission tomography

Within the normal human pituitary tissue, somatostatin receptors (SSTRs) are expressed in different subtypes of pituitary adenoma in varying degrees. For example, in most somatotroph adenomas, SSTR subtype 2 (SSTR2) is detectable, whereas SSTR5 expression is more changeable [46]. In managing and examining pituitary adenomas, the benefit of somatostatin receptor scintigraphy (e.g., ¹¹¹indiumpentetreotide) is thus complicated by certain factors: the tumor’s dependence on SSTR subtype expression, the normal pituitary tissue’s background uptake, and the minimal spatial resolution and sensitivity of scintigraphy when joined with single-photon emission computerized tomography [47].

3.4.3 ¹⁸F-fluorodeoxyglucose positron emission tomography

There have been numerous case reports of incidental ¹⁸F-FDG uptake by pituitary adenomas in the literature [48, 49, 50]. As the normal pituitary gland fails to display FDG uptake above the background activity, any significant FDG uptake generally implies pathology [51]. The usage of ¹⁸F-FDG PET has been considered in various subtypes of pituitary adenoma [49, 50]. However, the findings have been greatly discouraging. For localizing corticotroph adenomas, ¹⁸F-FDG PET is similar to MRI. In their retrospective study, Alzahrani et al. reported a detection rate of 58% in 12 patients who underwent conventional ¹⁸F-FDG PET/computed tomography (CT) [52]. Correspondingly, ¹⁸F-FDG PET still has a role in the routine management of pituitary adenomas. However, the outcome of ¹⁸F-FDG PET in the identification of de novo and residual/recurrent pituitary adenomas is satisfactory [53, 54]. In addition, ¹⁸F-FDG PET can help differentiate residual or recurrent adenoma from the remaining normal pituitary tissue because of transsphenoidal surgery once merged with ⁶⁸Ga-DOTATATE PET [55, 56].

3.4.4 11C-methionine PET

¹¹C-methionine PET (Met-PET) has been established to be beneficial in localizing the entire range of pituitary adenoma subtypes in terms of recurrent and newly diagnosed tumors [53, 55, 57, 58, 59], especially microadenomas [7, 55, 60]. ¹¹C-methionine PET makes the most from a substantially lower brain uptake. It not only enhances sensitivity compared with ¹⁸F-FDG PE but also generates a more conductive target-to-background ratio [53, 55, 61]. Nonetheless, when Met-PET/CT is contrasted with MRI, an important limitation is the relative insufficiency of anatomical detail from CT. Thus, its capability to instruct precision surgery or radiotherapy is insufficient. To mitigate such limitations, some groups have evaluated the importance of co-registering PET/CT and MRI images to enhance the anatomical delineation at these sites of Met-PET uptake, instruct certain treatment decisions, and assist in clinical outcomes [59, 62, 63]. Thus, the ¹¹C-Met uptake site(s) may be accurately delineated.

Gillett et al. detected that Met-PET scans ought to be normalized to the cerebellum to decrease the effects in the pituitary gland of physiological variations of the uptake of ¹¹C-Met, namely, in comparison to serial imaging. This new technique permits enhanced localization of adenomas in comparison with conventional imaging modalities, specifically because the cerebellum is utilized as the reference region. It is used between baseline Met-PET images and registered suppressed Met-PET by highlighting the regions of change. In clinical practice, implementing this technique is valuable due to definitive intervention. For example, transsphenoidal pituitary surgery or stereotactic radiosurgery is deliberated to assist targeted intervention and mitigate the liability of breaking the normal pituitary gland function. This PET/MRI generation process will eventually have minimal difficulty and be more accessible, which has been proven with various tracers [47].

3.5 7-Tesla magnetic resonance imaging in predicting the tumor consistency of pituitary adenomas

Tumor consistency is an important factor in surgical planning, as it affects resection relief and exposure to surgical operation morbidity [64, 65, 66]. Typically speaking, through the process of suction and curettage, tumors, usually with a soft consistency, are easily removed. Consistency in predicting tumors with the use of MRI is well-documented. According to T2W imaging, the hypointense tends to be associated with firmer tumors, possibly due to their increased collagen content [65, 67]. On T2W imaging, softer tumors are likely to be hyperintense, possibly in relation to much higher cystic components and/or water content [68].

Yao et al. proved that 7-Tesla (7 T) MRI could predict pituitary adenoma consistency and histopathological characteristics [66]. In the 7 T voxel-based analysis of tumor imaging, the authors demonstrated that it enabled previously inaccessible recognition of tumor heterogeneity. With permission from the ultrahigh field MRI, such techniques are facilitated by the high in-plane resolution. Moreover, the authors detected a positive correlation between tumor consistency and vascularity. With 7 T MRI, soft tumors were inclined to have a higher density of blood vessels [66].

Voxel-based particle analysis combined with 7 T MRI may be beneficial. It potentially maximizes the spatial resolution and possibly provides a more sensitive application from such use of this new imaging technique. Advanced post-processing image analysis techniques combined with 7 T ultrahigh-field MRI, for instance, the voxel-based analysis, may offer radiological tumor characterization. In such cases, they may aid in surgical decisions for the resection of pituitary adenomas.

4. Imaging technology in pituitary incidentalomas

Within the pituitary gland, pituitary incidentalomas are lesions detected incidentally in imaging for unrelated causes, such as headache, trauma, or symptoms involving the neck or central nervous system. With the wide application of imaging techniques, more and more imaging studies have found incidental pituitary tumors. The estimated prevalence of incidental pituitary adenomas is approximately 0.7/1000 (0.07%) [69]. The etiology of pituitary incidentalomas comprises many pathologies, most of which are benign adenomas. Pituitary adenomas account for approximately 90%, with most of them being Rathke’s cysts, craniopharyngiomas, and meningiomas [70, 71, 72].

Magnetic resonance imaging acts as a central position in the initial evaluation. Pituitary adenomas are defined by the displacement of the pituitary stalk and perhaps deformation of the sellar diaphragm. They most commonly measure less than 1 cm and are located within the adenohypophysis. They appear to have hypointensity on the T1W series and hyperintensity on the T2W series. Nevertheless, many GH-secreting adenomas may be isointense or hypointense on T2W sequences. Many microadenomas show delayed enhancement and washout, making them more pronounced on DCE-MRI than on conventional sequences.

A few may be apparent only in dynamic sequences [9, 73]. However, compared with the normal parenchyma of the anterior lobe, microadenomas were enhanced at significantly lower levels. Golden-angle radial sparse parallel magnetic resonance imaging has excellent spatial and temporal resolutions. The potential of this technique shown in the current study was exploited in assessing the pituitary gland with an in-plane resolution of 0.7 mm, serial slice thickness of 0.8 mm, and a temporal resolution of 20 s [33]. An acquisition time of 120 s after contrast agent administration is sufficient for adequate dynamic assessment of the pituitary gland, optimizing scan time using the magnet.

In contrast to conventional dynamic MRI techniques that accomplish multiple separate exams, GRASP technology acquires all dynamic information in a single sequential scan where contrast agent injection occurs. Image reconstruction is later achieved by merging the data into consecutive time frames and reconstructing the frames using an iterative method combining parallel imaging and compressed sensing [36, 40]. Therefore, GRASP provides higher planar resolution, increased sensitivity to motion and flow, and improved fat suppression compared to conventional two-dimensional turbo-SE examinations [74]. Rathke’s cysts are the most generally known cystic pituitary incidentalomas, and MRI findings depend on the cyst’s contents. Rathke’s cysts are commonly hyperintense on T1W imaging with characteristic T2 hypointense intra-cystic nodules. In most cases, the cyst wall fails to enhance following contrast administration [75, 76]. The appearance of craniopharyngiomas on MRI also depends on the content of the cyst, the proportion of solid components, and the probable presence of calcifications. Their solid portion is commonly iso- or hypointense on T1 and hyperintense on T2, whereas the cystic portion is hyperintense on T1W sequences. Calcified tumors are characteristic. Rim and nodular calcifications are greatly identified on CT [77].

5. Imaging technology in primary hypophysitis and immunotherapy-related hypophysitis

The classification of primary hypophysitis includes plasmacytic, granulomatous, lymphocytic, xanthomatous, or mixed [78]. Generally, they are nearly identical to immunotherapy-associated hypophysitis (IH) and share the same radiographic features. Immunotherapy-associated hypophysitis is a generally known immune-related adverse event that happens most frequently with regimens comprising cytotoxic T-lymphocyte antigen 4 suppression, especially ipilimumab. The MRI plays a crucial role in diagnosing hypophysitis. And 2-[¹⁸F]-fluoro-2-deoxy-D-glucose PET/CT gives complementary diagnostic information.

For primary hypophysitis and IH, the key feature of MRI is the diffuse and transient enlargement of the pituitary gland, which is always modest [79, 80]. The absolute peak size shown in the study of the pituitary gland was 2 cm in 59 patients with IH. In primary hypophysitis and IH, the posterior pituitary bright spot with connected infundibular/suprasellar abnormality appears absent in the MRI. Lesions are, for the most part, T1 isointense. Usually, they improve markedly on contrast T1W imaging [81]. Homogeneous pituitary enhancement is often accompanied by hypophysitis, and other pituitary lesions often accompany heterogeneous enhancement. Pituitary stalk thickening is seen in IH in 59% of the cases [80]. Immunotherapy-associated hypophysitis causes a transient increase in pituitary size, which generally resolves within several months. In terms of monitoring IH, FDG-PET/CT holds value [79]. The normal pituitary gland fails to exhibit FDG uptake above background activity, so any significant FDG uptake usually demonstrates pathology. However, the pituitary should be monitored exclusively during the FDG-PET/CT studies routinely performed after initiating an immune checkpoint inhibitor (ICI) to determine the pathological uptake. In the case of longitudinal imaging, PET can individualize hypophysitis from neoplastic lesions, such as metastases or macroadenomas [82]. After ICI initiation, transient pituitary FDG hypermetabolism is a common sign of IH [79]. The insufficiency of FDG uptake in sellar lesions also aids in characterization, advising non-neoplastic pathology, such as Rathke’s cleft cyst or a microadenoma (approximately half do not demonstrate FDG uptake) [83].

6. Conclusion

Imaging examination is indispensable in diagnosing and managing pituitary lesions, especially MRI. With the understanding of such lesions, there is a higher demand for the development of imaging technology. New evaluation methods have been adopted for diagnosing pituitary microadenoma, pituitary incidentaloma, hypophysitis, and recurrent pituitary tumors, such as 7 T MRI, DCE imaging, and nuclear isotope imaging. With the progress of technology, more new technologies will be available to assess diagnosis and treatment options.

Conflict of interest

The author declares no conflict of interest.