Pre- and Suprasellar Meningiomas

Abstract

The meningioma is the most common intracranial tumor in adults, with 20 % occurring at the skull base. This benign tumor arises from arachnoidal cells of the meninges. The common sites of origin are the planum sphenoidale, the tuberculum sellae, the clinoid processes, the sellar diaphragm, and the cavernous sinus. Pre- and suprasellar meningiomas can be revealed by anosmia, frontal syndrome, and visual disturbance when the optic chiasm or optic nerves are compressed. Meningioma appears iso to hyperintense on T2WI and is hypo- to isointense on T1WI. Postcontrast scan shows marked homogeneous enhancement of the mass on both CT and MRI (Fig. 23.1). The presence of a ring of CSF delineating the tumor contours is frequent. Hyperostosis is commonly associated with meningiomas of the planum sphenoidale, tuberculum sellae, and clinoid processes (Fig. 23.2). Upward convexity of the jugum sphenoidale in front of the insertion of the meningioma, termed blistering, is a fundamental but not pathognomonic sign of meningioma. It may result in the extension of the underlying sinus, a phenomenon named pneumosinus dilatans. Extensive edema can be observed around the large presellar meningioma: the vasogenic edema associated with meningioma is thought to be related to tumor secretion of vascular endothelial growth factor (Fig. 23.3). Heterogeneous enhancement can be related to intratumoral calcifications or cysts. In the largest hypervascularized tumors, tortuous and enlarged peritumoral vessels and intratumoral vasculature can be visualized (Fig. 23.4). Extension of the presellar meningioma along the dural sheath of the optic nerve may occur (Fig. 23.5). Posterior extension of the large meningioma arising from the planum sphenoidale or tuberculum sellae can completely recover the sellar diaphragm, making difficult the identification of the site of tumoral insertion. Meningiomas of the sellar diaphragm are the most tricky. The normal pituitary gland is usually easily identifiable below the tumor on high-resolution T1 and T2 WI (Fig. 23.6). Dynamic MR sequencing shows the more intense and earlier enhancement of the meningioma when compared with the normal pituitary gland (Fig. 23.7). Moreover, dynamic imaging can be helpful in the rare cases of association of meningioma and pituitary adenoma (Fig. 21.7). It is important to remember that meningiomas are often multiple; complete MR examination of the brain is needed in all cases. On DWI, the ADC is often low in meningioma (Fig. 23.8). However, this sequence does not have a major role in the differential diagnosis. On perfusion imaging, sellar meningiomas show high values of rCBV and signal intensity curves with little or no return to the baseline levels, similarly to adenomas. Bladowska has proposed the use of fixed cutoff values to differentiate meningioma from pituitary adenoma: maximum rCBV exceeding 7.14 and mean rCBV above 5.74 with a time–intensity curve not returning to the baseline level are suggestive of the diagnosis of meningioma. Perfusion imaging is not a reliable technique to differentiate the different histological types of meningioma; however, the CBV is markedly increased in angiomatous meningioma. MR spectroscopy, which demonstrates increased choline peak, no N-acetylaspartate, and alanine peak at 1.46 ppm (inconstant), is not particularly useful in the differential diagnosis. Moreover, the bony structures of the skull base and pneumatization of the sphenoid sinus are frequently the source of artifacts degrading the spectrum.