Epidermoid Cyst (Cerebellopontine Angle)

Diagnosis Definition

• Epidermoid cysts arise from ectopic inclusion of ectodermal cells during embryonic development
• They represent 5% of all cerebellopontine angle (CPA) tumors
• Presentation (most commonly between the 2nd and 5th decades of life) is often a result of mass effect on adjacent cranial nerves
• A long history of tinnitus and hearing loss is the most common presentation
• The primary differential diagnosis is arachnoid cyst, which is usually managed conservatively, whereas epidermoid cyst is often surgically removed to alleviate symptoms and prevent growth

Imaging Findings

• Epidermoid cysts usually follow the intensity of cerebrospinal fluid (CSF) on T1 and T2 sequences, although the T1 signal varies with the amount of protein content (e.g., “white” epidermoids are bright on T1 due to high protein content)
• Epidermoid cysts are markedly hyperintense on diffusion weighted imaging (DWI), which distinguishes them from arachnoid cysts
• T2 FLAIR sequences show a dirty, heterogeneous appearance with intermediate signal, another feature that may help distinguish epidermoid cysts from arachnoid cysts
• Epidermoid cysts generally do not enhance with contrast
• They typically have undulating margins, insinuating around and encasing cranial nerves and vessels, and model their shape to conform to the CPA without extending into the internal acoustic meatus

KEY IMAGES

Pearls

• When evaluating epidermoid cysts, it is important to evaluate their relationship to adjacent cranial nerves and major vessels

References

1. Bonneville F, Sarrazin JL, Dupuch KM, Iffenecker C, Cordoliani YS, Doyon D, Bonneville JF. Unusual Lesions of the Cerebellopontine Angle: A Segmental Approach. RadioGraphics 2001; 21:419-438