Sections show predominantly keratinous debris together with a fibrous cyst wall containing foci of dystrophic calcification and patchy chronic inflammation. No intact cyst wall lining is evident. Hemosiderin laden macrophages and cholesterol clefts are present, consistent with previous hemorrhage. No skin adnexal structures are seen. There is no evidence of malignancy.
This case remains a little unresolved. Clearly the majority of the mass is an epidermoid cyst, which is the favored imaging feature. The clearly fatty components are unusual, and most likely this represents a variation of a white epidermoid cyst; a rare variant where abundant lipids result in lower CT values and T1 shortening. I am unable to find a reference for whether or not white epidermoids suppress on fat saturated sequences.