Epidermoid Cyst

What Is It?

An epidermoid cyst is typically a benign brain tumor that arises from abnormal cells being left in the nervous system during development. Ectodermal cells that normally form skin are trapped in the developing nervous system, creating a cyst which is lined inside with ectodermal cells. In other words, there are skin-like cells lining the inside of the cyst. This lining grows and sloughs much like skin does, but because it is towards the inside of the cyst, the sloughed cells stay inside the cyst and expand the cyst. Therefore, these cysts glow slowly and are filled with a flaky material.

Epidermoid cyst can occur in many parts of the body, but in the central nervous system, they most frequently occur in the space between the brain stem and cerebellum (called the cerebellopontine angle or CP angle), above the pituitary gland or near the temporal lobe of the brain. The CP angle is the most common site in the nervous system.

Although these tumors are congenital (present at birth), they typically do not present until older age (20 - 40 years old on average) because they take a long time to expand to a size that causes symptoms.

Epidermoids are related to, but different from, dermoid cysts. In the later, the abnormal ectodermal cells differentiate more into skin forming tissues which include both epidermal and dermal elements, so that these tumors typically have sweat glands, hair follicles and other dermal appendages.

What Types of Symptoms Are Typical?

The presentation and clinical symptoms of these tumors vary depending on size and location. In the CP angle, they tend to cause headache, double vision (diplopia), gait disturbances, and/or facial pain or numbness. These symptoms and others will vary from patient to patient.

How Is The Diagnosis Typically Made?

As with most tumors, after a neurological examination, a CT scan or MRI scan is needed to detect the tumor. Typically, tumors require a sample of tumor tissue to make the definitive diagnosis by pathological examination.

In the case of epidermoid cyst, the appearance on MRI is fairly characteristic. However, they can appear very similar to another type of mass called an arachnoid cyst. Some special MRI sequences (a diffusion weighted image or DWI) can help to distinguish these two diagnoses. Definitive diagnosis generally does require tumor tissue however.

What Are Some Common Treatments?

As with all tumors of the central nervous system, treatment decisions vary greatly depending on the patient and the specifics of each case. However, generally, epidermoid cysts that are causing symptoms are generally recommended to be treated. Treatment usually consists of a surgical resection of the tumor. The goal is total removal of the tumor but due to their cystic nature, they can be difficult to remove in their entirety, particularly if parts of the cyst wall are adherent to important structures such as nerves or the brainstem. While these are generally benign tumors, they can continue to enlarge slowly and recur after surgery if any of the cyst wall was not removed.

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Important Note: This site is not intended to offer medical advice. Every patient is different, and only your personal physician can help to counsel you about what is best for your situation. What we offer is general reference information about various disorders and treatments for your education.

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