Epidermoid Cyst
An epidermoid cyst is a slow-growing, benign cystic lesion that develops from skin-like cells trapped during early fetal development. Inside the skull, these cysts most commonly occur within the spaces surrounding the brain rather than within the brain tissue itself. Epidermoid cysts typically enlarge gradually over many years and may cause symptoms only when they become large enough to compress nearby nerves or brain structures. Many are discovered incidentally during imaging performed for unrelated reasons.
What is it?
Epidermoid cysts arise from embryonic cells that were intended to form skin but became trapped within the developing nervous system during fetal development. Over time, these cells continue to shed keratin and cellular debris, causing the cyst to enlarge slowly.
The cyst wall is thin and lined with skin-like tissue, while the interior contains soft layers of keratin and debris. Intracranial epidermoid cysts most commonly occur near the base of the brain, particularly in regions such as the cerebellopontine angle, suprasellar cistern, and around the brainstem.
Unlike many tumors, epidermoid cysts tend to grow slowly and spread along natural fluid spaces rather than aggressively displacing nearby tissue. As a result, they may become relatively large before producing noticeable symptoms. When symptoms occur, they are usually related to compression of cranial nerves or nearby brain structures.
MRI is the preferred imaging test for evaluating epidermoid cysts because it provides detailed visualization of the lesion and surrounding anatomy. Specialized MRI techniques—especially diffusion-weighted imaging (DWI)—are particularly helpful for distinguishing epidermoid cysts from arachnoid cysts and other cystic lesions. CT imaging may also detect these cysts but is generally less specific than MRI.
Important to Know
Most epidermoid cysts are benign and grow very slowly. Small cysts without symptoms are often monitored with periodic imaging rather than treated immediately.
When symptoms develop or imaging demonstrates significant growth or compression of surrounding structures, surgical removal may be considered. Complete removal can sometimes be difficult because these cysts may wrap around important nerves and blood vessels. If portions of the cyst lining remain, recurrence is possible over time.
A rare but important complication is rupture of the cyst, which can release cyst contents into surrounding cerebrospinal fluid spaces and trigger inflammation known as chemical meningitis. Symptoms may include severe headache, neck stiffness, fever-like symptoms, or worsening neurological complaints.
Red flag symptoms include sudden severe headache, worsening neurological symptoms, vision changes, facial weakness or numbness, hearing loss, balance problems, seizures, or loss of consciousness. These symptoms require prompt medical evaluation.