Medically reviewed by Edward Tavel, MD, Medical Director · Last reviewed 22 August 2026
An epidermoid cyst is a slow-growing, benign lesion that forms when a small nest of skin-forming cells becomes trapped in the wrong place very early in development, during the weeks when the neural tube is closing. Those cells continue doing what skin cells do, shedding keratin layer by layer, and over many years the accumulated material forms a cyst. Inside the skull, the most common location is the cerebellopontine angle, the space between the cerebellum and the brainstem, where it ranks as the third most frequent lesion after vestibular schwannoma and meningioma. Epidermoids also occur in the parasellar region and within the bones of the skull.
Because they grow at roughly the pace of normal skin turnover, epidermoid cysts expand extremely slowly and often cause no symptoms for decades. Many are discovered incidentally during imaging performed for an unrelated reason. When symptoms do develop, they come from gentle pressure on nearby structures rather than from invasion, and headache is the most frequently reported complaint. Dizziness, hearing changes, facial weakness, and balance difficulty can occur when the cyst sits close to the cranial nerves in the cerebellopontine angle.
MRI is what makes this diagnosis possible. On standard sequences, an epidermoid cyst mimics cerebrospinal fluid almost exactly, appearing dark on T1-weighted images and bright on T2-weighted images, which is why it can be mistaken for a simple arachnoid cyst. Two findings separate them. On diffusion-weighted imaging, an epidermoid restricts diffusion and lights up brightly, while an arachnoid cyst does not. On FLAIR sequences, an epidermoid suppresses incompletely and retains a slightly dirty signal, while an arachnoid cyst suppresses fully. This is one of the clearest illustrations of why diffusion-weighted imaging is included in a thorough brain protocol.
Management depends entirely on symptoms. An incidental, asymptomatic epidermoid cyst is typically monitored with periodic imaging rather than treated. When a cyst causes symptoms, surgical removal is the mainstay, since there is no medication that shrinks it. Surgeons aim for complete removal where it is safe, because remnants of the cyst capsule are associated with recurrence, and they will deliberately leave capsule behind when it is adherent to critical nerves or vessels. A separate and far more common entity shares the name: a cutaneous epidermoid cyst, the small keratin-filled lump under the skin often informally called a sebaceous cyst. That version is unrelated to the intracranial lesion and is generally harmless.
If an epidermoid cyst appears on your imaging report, the appropriate next step is a conversation with your physician or a neurosurgeon about whether monitoring or treatment makes sense. To learn more about comprehensive imaging and what it covers, explore what we scan for.
Frequently asked questions
Is an epidermoid cyst cancerous?
No. An epidermoid cyst is benign. It grows slowly by accumulating keratin rather than by dividing abnormally, and malignant transformation is extremely rare.
How is it different from an arachnoid cyst?
They look nearly identical on standard MRI sequences. An epidermoid restricts diffusion on DWI and suppresses incompletely on FLAIR; an arachnoid cyst does neither. Those two sequences settle the question.
Does an epidermoid cyst always need surgery?
No. Asymptomatic cysts found incidentally are usually monitored. Surgery is considered when the cyst causes symptoms through pressure on nearby nerves or brain structures.
How fast do they grow?
Very slowly, at approximately the rate of normal skin cell turnover. Many people carry one for decades without ever knowing it is there.
Is a skin epidermoid cyst the same thing?
No. A cutaneous epidermoid cyst is a common, benign lump under the skin. It shares the name and the keratin-filled structure but is an entirely separate condition from the intracranial lesion.
Sources
A whole-body MRI at MRI Wellness looks at the brain, spine, chest, abdomen and pelvis in a single session, without radiation or contrast dye. No referral is needed.
