H/O progressive loss of vision bilaterally, left more than right.
There is evidence of a lobulated extra-axial mass lesion in the suprasellar cistern. The lesion is predominantly hypointense on the T1W and FLAIR images and hyperintense on the T2W and STIR images. The optic chiasm is compressed upon and the optic nerves are splayed. The pituitary stalk is stretched. However, the pituitary gland is well identified. The supraclinoid segments of both internal carotid arteries appear to be encased by the lesion. The patient had refused contrast administration.
Cranial epidermoids can occur within the subcutaneous soft tissues, calvarium, brain, petrous apex and subarachnoid spaces. The cerebello-pontine angle cistern (CPA) is the most common location for these tumors. Although congenital in nature, they usually present in the third or fourth decades. The lesions may be extradural or intradural in location.
Pathology:
Epidermoids are congenital lesions of ectodermal origin. Histologically they are composed of an internal layer of stratified squamous epithelium covered by an external fibrous capsule. They grow by progressive desquamation of epithelial cells with their conversion to keratin and cholesterol crystals. It grows slowly and is very pliable, conforming to the shape of the adjacent brain and CSF spaces in which it is growing. They are also known as "pearly tumors". Focal calcifications may be seen in their walls.
MRI:
The intradural lesions are frequently located in the CPA, supra and parasellar regions, middle cranial fossa and the cisterna magna. Tumors may also develop in the tela choroidea, usually in the temporal horn of the lateral ventricle but occasionally in the third and fourth ventricles. On CT the lesions are hypodense and usually do not enhance with contrast material.
On T1W images, they are mildly hypointense, usually between that of the CSF and brain parenchyma. There is usually mild inhomogeneity of low intensity, with some patchy regions of isointensity within the lesion. On T2W images the tumors show marked hyperintensity similar to or greater than that of CSF, with significant heterogeneity of the signal intensity. They have various imaging appearances depending on their chemical content. If they are primarily water, the signal intensity parallels CSF, except that they do not have cisternal pulsatile flow patterns. Therefore sequences sensitive to motion demonstrate differences in signal intensity from the adjacent CSF cisternal spaces. They have a frond like surface and can insinuate within the cisternal spaces and around surrounding vessels and nerves. Some contain nontriglyceride fats and have fatty density on CT scans but do not have high signal on the T1W images. Some contain triglyceride fat and have high signal intensity on T1W images or fluid-fluid levels. They may have solid components as well. The low-intensity signals within the tumor hyperintense pattern are probably the result of cellular debris and solid cholesterol crystals. A high-intensity rim may surround the lesion on the T2W images and probably represents a CSF cleft. Hydrocephalus may be induced due to a chemical meningitis. Usually, there is no brain edema, and there is rarely hydrocephalus despite the presence of a large mass. One of the most characteristic patterns of epidermoids is apparent expansion of the adjacent CSF spaces, including the CPA, Meckel's cave and suprasellar or prepontine cisterns. The tumors may be dumbbell-shaped in configuration and extend from the middle cranial fossa into the posterior fossa.
Differential Diagnosis:
For sellar and suprasellar lesions:
Craniopharyngioma
Rathke Cleft Cyst
Meningioma
Germinoma and Teratoma
Arachnoid Cyst
Large Pituitary Adenoma (cystic changes)
Glioma - Chiasmatic and Hypothalamic
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