First AD

Second AD

A 41-year-old female with no significant history presents with a several month history of headache.


Axial MR images through the posterior fossa demonstrate a large, extra-axial mass in the cerebellopontine angle and prepontine cistern that has irregular, frond-like margins, isointense signal to CSF on T1-weighted and T2-weighted sequences, incomplete attenuation on FLAIR, restricted diffusion on DWI/ADC, and no enhancement on postcontrast sequences. Findings are most consistent with an epidermoid cyst.


Lesions of the cerebellopontine angle (CPA) are frequent, representing up to 10% of all intracranial tumors. Vestibular schwannomas and meningiomas account for 85%-90% of CPA masses. The third most common CPA mass is an epidermoid cyst.

Epidermoid cyst, also known as a primary cholesteatoma, is a congenital inclusion of ectodermal epithelial elements during neural tube closure. Lesion growth is due to accumulation of keratin and cholesterol produced from desquamation of its squamous epithelium lining. On CT (not depicted), epidermoid cysts are hypoattenuating, similar to that of CSF, with irregular, lobulated margins. On MR, epidermoid cysts are heterogeneous with a similar to slightly higher signal intensity than CSF on T1-weighted and T2-weighted sequences. When lesion signal intensity is very similar to CSF, FLAIR sequences are valuable as lesion conspicuity is increased due to incomplete attenuation. Occasionally, signal intensity may exceed that of brain parenchyma on T1-weighted sequences, the so-called “white epidermoid,” which is due to high triglyceride and fatty acid content. Minimal marginal enhancement can be seen after administration of gadolinium. High signal on DWI and low signal on ADC is characteristic. Diffusion weighted imaging is essential in postsurgical evaluation of recurrence.

Epidermoid cysts are benign masses with a broad range of ages at presentation (eg, 20-60 years). Most common signs and symptoms at presentation are sensorineuronal hearing loss, trigeminal neuralgia, facial neuralgia, and headache, all of which are typically present for several years before diagnosis. Complete surgical resection is curative. However, larger lesions have more significant surgical complications as they may be adherent to cranial nerves, arteries, and brainstem at time of operation.

Bonneville F, et al. Unusual lesions of the cerebellopontine angle: a segmental approach. 

41-year-old female presents with chronic headache.

Image IQ: 41-year-old Female with Chronic Headache

Erini Makariou MD

Alex E. Heaton, MD