Giant cholesterol cysts of the petrous apex: radiologic features.

Four cysts are described that expanded and destroyed the bone of the petrous apex. All patients with these cysts had a sensorineural hearing loss. Mild symptoms referable to cranial nerves VI, VII, IX, X, XI, and XII were seen also. The cysts range in size from 1.5 X 1.5 X 3 cm to 5 X 5 X 6 cm. Grossly and histologically, they were distinct from any lesions seen previously. The lesions were large and contained glistening brown, watery fluid filled with cholesterol crystals. The cyst wall was predominantly fibrous tissue without an epithelium. Minimal chronic inflammatory change and granuloma formation were present within and just outside the cyst wall. These cysts have been described as mastoid cysts, epidermoids, mucoceles, and cholesterol granulomas; until now, they have not been recognized as a single distinct entity. A name emphasizing the pathologic characteristic of the lesion, giant cholesterol cyst, has been suggested. Distinguishing them from other petrous apex lesions preoperatively is difficult, but if the cystic nature of the lesion can be recognized or at least anticipated, more conservative surgery, such as simple drainage versus a more radical procedure, may be possible.