Trigeminal schwannoma

There is a large mass arising from the left middle cranial fossa displacing brain superiorly and demonstrating a CSF cleft within the limits of CT. Small calcifications are demonstrated at the peripheries of this mass lesion, which is internally heterogeneous, with a suggestion of a thin slightly hyperdense capsule. No surrounding edema. There is no associated hyperostosis, with the left middle cranial fossa remodeled around the inferior aspect of the lesion lesion. There is marked thinning of the left lateral wall of sphenoid sinus and anterior wall of the left carotid canal, as well as deficient left clinoid processes and dorsum sellae. The floor of the left middle cranial fossa is depressed and thinned, with deficient medial wall of the left foramen ovale. The left optic canal is remodeled medially and narrowed. The left orbital apex is also remodeled/narrowed. No bony destruction. The sella is not depressed. The left lateral ventricle is distorted by the mass and there is dilatation of the right lateral ventricle. Mild periventricular hypodensity is noted. There is crowding of cerebral sulci.

Large extraaxial mass in the left middle cranial fossa is again demonstrated with well defined margins including a thin T2 hypointense rim, and slight lobulation. Scalloping and remodeling of the left squamous temporal bone, thinning of the wall of left carotid canal, and erosion of both anterior and posterior clinoid processes and dorsum sella on the left are better appreciated on recent CT. 

The mass demonstrates heterogeneous signal: predominantly T2 hyperintense with patchy areas of low signal, mixed FLAIR signal, patchy areas of intrinsic high T1 (not fat density on CT), and blooming. There is heterogeneous enhancement following contrast administration. Mild abutting tentorial thickening. No definite dural tail. There appears to be some extension through the left foramen ovale. 

The mass compresses anterior left temporal lobe posterolaterally, elevates the inferior frontal lobe, left insula, and left basal nuclei. There is mass effect on the left cerebral peduncle and left anterior pons. A component of the tumor extends into the sella and suprasellar cistern and abuts the stalk. It is not clearly separable from pituitary gland and left cavernous sinus and Meckel's cave. No extension into the orbit but there is narrowing of the bony orbital apex and left optic canal with tumor in close proximity to the intracranial segment of the left optic nerve. It displaces the cavernous left internal carotid medially, and terminal left internal carotid anteriorly. Left MCA again drapes over the anterosuperior surface of the tumor. There is diffuse sulcal effacement in the left hemisphere and 4mm midline shift to the right.

Conclusion: 

Extra-axial mass centered in the left middle cranial fossa with mass effect but minimal surrounding edema. The amount of bony remodeling suggests this is long standing. The signal heterogeneity, bright T2 hyperintensity with suggestion of a capsule and bony remodeling and no hyperostosis most favors a large schwannoma (i.e. trigeminal). Unusual appearing meningioma with past hemorrhage and cystic change less likely. Although a pituitary macroadenoma can have this signal appearance, the epicenter does not favor a pituitary origin.