Radiologia Brasileira - Publicação Científica Oficial do Colégio Brasileiro de Radiologia

INTRODUCTION

The sellar region, albeit small, encompasses a number of important structures, including the bone component of the sella turcica, as well as the pituitary gland, cavernous sinus, and suprasellar cistern. Abnormalities in this region can be attributed to the underproduction or overproduction of hormones or to the neurological signs and symptoms resulting from the compression of adjacent structures. Virtually any of those factors can lead to disease, ranging from the innocuous to the severe^(1,2). Magnetic resonance imaging (MRI) is currently the method of choice, having supplanted computed tomography (CT), for evaluation of the sellar/juxtasellar region⁽³⁾.

Although pituitary adenomas are the most common lesions in the sellar/juxtasellar region, lesions originating in other structures can also affect the region, complicating the diagnosis. We retrospectively evaluated 70 cases of sellar/juxtasellar abnormalities, confirmed by histopathology or on the basis of clinical and biochemical findings, in order to describe the common and unusual aspects of these alterations that aid in the differential diagnosis.


ADENOMA

Pituitary adenomas represent the most common sellar lesions. They are classified, by size, as macroadenomas (≥ 10 mm) or microadenomas (< 10 mm) and, by hormone production, as secreting or nonfunctioning^(4–6).

On MRI, adenomas typically present hypointense signals in T1-weighted sequences and signals of variable intensity in T2-weighted sequences. One important aspect is that, due to those hypointense signals, the majority of adenomas can be detected in T1-weighted sequences, which makes such sequences the most important of the MRI protocol for the evaluation of this alteration, given that it allows the diagnosis even without contrast administration. Another important aspect is that most adenomas present post-contrast enhancement slower than does the normal parenchyma (Figure 1), making it important to use dynamic contrast-enhanced MRI sequences for the detection of microadenomas^(7–9).




Among secreting adenomas, the most common are prolactin producers (prolactinomas). In most cases, prolactinomas can be treated exclusively with dopaminergic agonists, although such treatment can result in alterations to the imaging aspects (Figure 2), which must be recognized by the radiologist⁽⁶⁾.



Macroadenomas sometimes extend beyond the boundaries of the sellar region, invading the cavernous sinus, sphenoid sinus, or clivus, as well as compressing the optic chiasm and enveloping the internal carotid artery (Figure 3). On MRI, invasion of the cavernous sinus is defined as a situation in which at least two-thirds of the circumference of the cavernous segment of the internal carotid artery is encompassed by the lesion. Therefore, it is occasionally necessary to make the differential diagnosis with other lesions that can occur in this region, such as meningiomas and even aneurysms^(4,5). Large adenomas are usually heterogeneous, containing cystic areas resulting from cystic degeneration or necrosis, and can occasionally develop infarction or hemorrhage, due to poor vascular supply^(3,8).




CRANIOPHARYNGIOMA

Craniopharyngiomas are slow-growing epithelial neoplasms that originate from the remnant of the craniopharyngeal duct and account for 3–5% of intracranial neoplasms. Their incidence shows two peaks, the first occurring between 10 and 14 years of age and the second between the fourth and sixth decade of life. Although craniopharyngiomas are suprasellar in origin, approximately 50% extend into the sellar region. The typical appearance includes solid-cystic components and calcifications^(3,5,9).

The classic, adamantinomatous, type of craniopharyngioma has a cystic appearance and contains heterogeneous nodules. The least common, squamous papillary, type has a predominant solid component. In T2-weighted MRI sequences, the cystic component shows a hyperintense signal, whereas the solid components show heterogeneous signals. After contrast administration, the solid portions show intense heterogeneous enhancement and there is enhancement of the cystic walls (Figure 4)^(3,8).



Although macroadenomas with pituitary apoplexy (Figure 5) and Rathke’s cleft cysts can have aspects quite similar to those of craniopharyngiomas, an important distinguishing aspect of craniopharyngiomas is the presence of calcifications. Therefore, when the MRI findings are inconclusive for calcifications, non-contrast-enhanced CT should be performed in order to confirm their presence and corroborate the diagnosis (Figure 6).







RATHKE’S CLEFT CYSTS

Rathke’s cleft cysts are benign, often asymptomatic, lesions of the sellar region, most often being intrasellar. On MRI, they usually show a hyperintense signal in T2-weighted sequences, whereas they can show hyperintense or hypointense signals on T1-weighted sequences, depending on their protein content (Figure 7). The differential diagnosis of Rathke’s cleft cysts always includes craniopharyngioma. The absence of calcifications favors the diagnosis of a Rathke’s cleft cyst⁽⁶⁾.




MENINGIOMA

Sellar meningiomas account for 20–30% of all intracranial meningiomas. On MRI, sellar meningiomas show an isointense signal in T1-weighted sequences and an isointense or hyperintense in T2-weighted sequences, as well as early enhancement, usually accompanied by the dural tail sign (Figure 8). When they invade the cavernous sinus, they tend constrict the carotid artery (Figure 9), which rarely occurs in cases of adenoma. The presentation of a sellar meningiomas can also include calcifications and hyperostosis^(5–8).







ANEURYSM

Aneurysms of the sellar region typically originate from the cavernous or supraclinoid portion of the internal carotid artery, accounting for up to 10% of all cerebral aneurysms. Their diagnosis is made more easily with MRI than with CT, because the former can reveal a flow void, due to the rapid luminal flow, and heterogeneous signal intensity in areas with slow, turbulent flow (Figure 10). However, thrombosed aneurysms can occasionally cause diagnostic difficulties, as described in Figure 11^(3,5).







HYPOTHALAMIC HAMARTOMA

Hypothalamic hamartomas consist of ectopic foci of neural tissue (gray matter), typically located in the tuber cinereum and mammillary bodies. They typically manifest as an increase in the size of the tuber cinereum. On MRI, hypothalamic hamartomas present signals that are, in comparison with that of the gray matter, isointense in T1-weighted MRI sequences (Figure 12) and isointense or hyperintense, without contrast enhancement or calcifications, in T2-weighted sequences. They can be parahypothalamic or intrahypothalamic (Figure 13), the latter more often being associated (clinically) with epilepsy, including gelastic seizures, whereas the former are more often associated with precocious puberty. The stability of hypothalamic hamartomas over time facilitates the differential diagnosis with other lesions occurring in the same region, such as gliomas^(3,5,6,9).







HEMANGIOMA

Hemangiomas constitute vascular malformations found in various organ systems, including the central nervous system. When extracerebral, they can originate from the cavernous sinus or from the adjacent tissues. Like hepatic hemangiomas, hemangiomas in the sellar region manifest on MRI as well-defined masses with hypointense or isointense signals in T1-weighted sequences and markedly hyperintense signals in T2-weighted sequences (Figure 14), initially with peripheral contrast enhancement, centripetal filling leading to late homogeneous enhancement. Therefore, dynamic contrast-enhanced MRI (Figure 15) is essential for the accurate characterization of the lesion⁽¹⁰⁾.






HYPOPHYSITIS

Inflammation of the pituitary gland, or hypophysitis, comprises a complex group of diseases, with two main histological forms: lymphocytic (the most common, autoimmune, form); and granulomatous (secondary to infection, sarcoidosis, or Langerhans cell histiocytosis). Because it is practically impossible to distinguish between the two forms on the basis of the radiological findings, the clinical history has great value in the differential diagnosis. On MRI, hypophysitis presents as thickening of the pituitary gland in combination with intense contrast enhancement, as shown in Figure 16^(1,5,11,12).




ECTOPIC NEUROHYPOPHYSIS

Normally, the neurohypophysis is located within the sella turcica, posterior to the adenohypophysis. It consists of the terminal axons of neurons projected from the hypothalamus, differentiated to store oxytocin and the antidiuretic hormone. Ectopic neurohypophysis occurs in three situations: when there is compression of the pituitary stalk by an expansile lesion (Figure 17); when a trauma has injured the pituitary stalk; and when there is a congenital anomaly (Figure 18). The last situation is associated with idiopathic growth hormone deficiency^(11,13,14).







CONCLUSION

The great number of lesions that can affect the sellar/juxtasellar region requires that radiologists not only possess knowledge of the anatomy and the contents of this region but also familiarize themselves with the various possible aspects of such lesions. In most cases, the application of such knowledge can lead to an accurate etiological diagnosis.


REFERENCES

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1. MD, Radiologist, São Carlos Imagem, Fortaleza, CE, Brazil
2. MD, Resident in Radiology and Diagnostic Imaging, Universidade Federal do Ceará (UFC), Fortaleza, CE, Brazil
3. PhD, MD, Neuroradiologist, Associate Professor of Radiology in the Department of Clinical Medicine, Universidade Federal do Ceará (UFC), Fortaleza, CE, Brazil

Mailing address:
Dra. Denislene da Silva Eduardo
Avenida Beira Mar, 3960, ap. 1508, Mucuripe
Fortaleza, CE, Brazil, 60165-121
E-mail: denislene.se@gmail.com

Study conducted at the Hospital Universitário Walter Cantídio da Universidade Federal do Ceará (UFC), Fortaleza, CE, Brazil.

Received February 29, 2016. Accepted after revision July 24, 2016.