Epidermoid cyst (cholesteatoma) and cholesterol granuloma of the temporal bone and epidermoid cysts affecting the brain.

Five cases of petrous apex epidermoid cysts, six cases of petrous apex cholesterol granuloma cysts, and seven cases of intradural cerebellopontine angle (CPA) or intracranial epidermoid cysts are reviewed. Petrous epidermoid cysts (cholesteatomas) and cholesterol granuloma cysts cannot be differentiated definitely from each other on CT scans. On MR imaging, epidermoid cysts exhibit long T1 and long T2 characteristics and can be differentiated from cholesterol granuloma cysts, which exhibit short T1 and long T2 characteristics. Intradural epidermoid cysts involving the CPA or other portions of the brain, also demonstrate long T1 and long T2 characteristics on MR scans. Intradural epidermoid cysts exhibit curvilinear areas of higher intensity on T1-weighted images, which were best evaluated on T1-weighted MR images obtained with more averages (6 to 8).