R. NICKBRYANMDS. JAMESZINREICHMD
The differential diagnosis of petrous apex lesions is broad. Cholesterol granuloma is recognized as the most common lesion of the petrous apex. This collection of cholesterol crystals, lipids, foreign body giant cells, fibrous tissue, and hemosiderin-laden macrophages appears as a smoothly marginated mass on CT scans. Cholesterol granulomas are markedly hyperintense on both T1- and T2-weighted MRI scans and do not demonstrate a change with gadolinium contrast.
Congenital cholesteotomas are less commonly found in the petrous apex. Like cholesterol granulomas, they are smooth, expansile lesions that are hyperintense on T2 images and do not enhance with gadolinium. Their hypointense signal on T1 images differentiates them radiologically from cholesterol granulomas. Congenital cholesteotomas are generally indistinguishable from cholesterol granulomas on CT scans. Unlike congenital cholesteotomas, acquired cholesteotomas are identified by chronic inflammatory changes in the mastoid and in the destructive pathway connecting the middle ear disease to the petrous apex.
Radiology Quiz Case 1—Diagnosis. Arch Otolaryngol Head Neck Surg. 2003;129(1):131-132. doi:10.1001/archotol.129.1.129