Epidermoid brain cyst

Epidermoid brain cysts (also called intracranial epidermoid cysts or tumors) usually form in the very early stages of the development of a baby (embryo). The cysts develop when cells that are meant to become skin, hair, and nails (epithelial cells) are trapped among the cells that form the brain.^[1][2][3] Less commonly, the cysts may develop later in life (acquired) when an injury or surgery causes epithelial cells to be trapped in brain tissue.^[3] An epidermoid brain cyst has a thin outer layer of epithelial cells surrounding fluid, keratin, and cholesterol.^[1][2][3]

Although epidermoid brain cysts are usually benign (not cancerous) and slow growing, the cysts may grow around and encase cranial nerves and arteries. Thus, epidermoid brain cysts are most often diagnosed in middle-aged adults when the cysts have grown large enough to cause symptoms.^[1][2][3] Symptoms may include hearing loss, ringing in the ears (tinnitus), headaches, involuntary twitching of the face, or chronic, severe face pain (trigeminal neuralgia).^[2][3] Rarely, an epidermoid cyst may leak into surrounding tissue and cause the lining of the brain (meninges) to become inflamed (aseptic meningitis, meaning the meningitis is not caused by a virus or bacteria).^[2]

Epidermoid brain cysts may be diagnosed by MRI and CT scans. Treatment usually involves surgery. Complete removal may be difficult if the cysts have surrounded or are very close to cranial nerves, arteries, or brain tissue.^[1][2][3] Regrowth of the cysts may occur, but in most cases, due to slow growth, symptoms may not return for years. If aseptic meningitis develops due to leakage of the cyst, steroids may be used to control the inflammation. There have been some reports of existing cysts or remnants of cysts left behind after surgery developing into cancer (since the cyst is made of skin cells, the cancer is usually a form of skin cancer, most commonly squamous cell carcinoma).^[1][2]

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