Epidermoid Tumor Cyst

Epidermoid cysts account for fewer than 1% of all intracranial tumors. Presumed to be products of disordered embryogenesis, epidermoid cysts arise from the aberrant inclusion of epithelial tissue or "rests" at the time of neural tube closure or cerebral vesicle formation. Their predilection for basal brain areas and their ability to permeate along cisternal pathways accounts for approx one third of all intracranial epidermoids involving the suprasellar and parasellar regions. Despite their embryonic origins, few epidermoids are symptomatic before middle age.

Grossly, epidermoid cysts appear as glistening "pearly" white encapsulated lesions having a waxy texture and a friable flaky consistency. Their growth is slow—a process involving progressive desquamation of capsular elements and the accumulation of keratin and cholesterol debris. Displacing rather than invading anatomic structures, parasellar epidermoid cysts are frequently seen to encase chiasmatic, cranial nerve, and basal arterial structures and are often tenaciously adherent to the same. Although pure intrasellar epidermoid cysts have been reported (131), most epidermoids have a sellar component as the result of secondary extension from a contiguous suprasellar or parasellar lesion (Fig. 5A,B).

When symptomatic, headaches and visual dysfunction are their most common symptoms; endocrine abnormalities occur much less frequently, and hydrocephalus is rare. Because parasellar epidermoids embed themselves in the mesial temporal lobe, partial complex seizures are an occasional accompaniment. The major complications of epidermoid cysts are chemical meningitis as the result of leakage of irritative cyst contents into the CSF and the rare phenomenon of malignant transformation into squamous cell carcinoma (132).

The treatment of symptomatic parasellar epidermoid cysts is operative. The surgical objective is to decompress the optic apparatus and other compromised structures, removing as much tumor as is safely possible. Although a substantial portion of these cysts is easily removed, fragments densely adherent to neural and vascular structures should be left. Regrowth of residual fragments is so slow that symptomatic recurrence is infrequent. Although pure intrasellar epidermoid cysts, including those having a suprasellar component, can be approached transsphenoidally, the majority of epidermoids in this location, because of their frequent and often extensive lateral extensions, are approached transcranially.

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