Dermoid and Epidermoid
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Spinal dermoid and epidermoid cysts are benign growths in the spine. They are not cancerous and they will not spread. However, they may compress important structures like the spinal cord or spinal nerves, and they may eventually rupture. When they are found in the spine, therefore, these cysts are surgically removed.
In medicine, a cyst is a hollow sac that contains something. Both dermoid and epidermoid cysts contain skin material. Both are lined with a layer of skin that naturally sheds dead cells. But instead of shedding to the outside of the body, the shed skin cells accumulate inside the cyst. In this way, the cysts gradually expand.
Dermoid and epidermoid cysts differ in their other contents. Epidermoid cysts are lined with simple skin cells, and they contain only the products of skin cells (like the protein keratin) and an accumulation of shed skin cells. Dermoid cysts contain skin cells, their products, many other skin components (hair follicles, hair, or sweat glands, for example) and may also contain other material (tooth material, oil, or blood, for example).
Symptoms
In the spine, these cysts usually cause symptoms as they grow and compress nearby structures. Symptoms may include weakness, clumsiness, and pins-and-needles in the arms and legs, trouble walking, and incontinence. Exact symptoms depend on the cyst’s size and location.
Diagnosis
Spinal dermoid and epidermoid cysts can be seen on imaging studies:
- Magnetic Resonance (MR) imaging: MR scans use a combination of large magnets, radio waves, and a computer to produce detailed images of organs and structures inside the body. They are sometimes performed with intravenous contrast enhancement. In an MR with intravenous contrast enhancement, a special tracer–a substance like a dye that is visible to the MR scan–is injected into the blood vessels. Contrast enhancement can help provide more information about abnormal structures like cysts.
- Computed Tomography (CT) scan: CT scans use a computer to put together information from X-rays. A CT scan is more detailed than a general X-ray. Like MR scans, CT scans can also be performed with contrast enhancement.
Spinal dermoid cysts may be associated with spinal abnormalities like spinal dysraphism, dermal sinus tract, spina bifida, spina bifida occulta, or myelomeningocele. Dermoid cysts may be discovered incidentally while diagnosing or treating those conditions.
Risk Factors
Dermoid and epidermoid cysts are rare overall, but are much more commonly diagnosed in children than in adults. They can be either congenital (present at birth) or iatrogenic (arising later in life as the result of a medical procedure).
- Congenital: Congenital cysts form early during embryonic development. They may be associated with dysraphism, a condition that affects the developing spinal cord. This is the most common cause of dermoid cysts.
- Iatrogenic: Iatrogenic cysts are the result of the introduction of skin cells into the space around the spinal cord. This may occur during the closure of a dysraphism or during a lumbar puncture. These are the most common cause of epidermoid cysts.
Treatments
Microsurgical removal is the treatment of choice for most spinal cysts. In microsurgical removal, a surgeon uses a surgical microscope and very fine instruments to expose and remove the cyst.
Microsurgery to remove a dermoid or epidermoid spinal cyst is performed under general anesthesia (the patient is unconscious) with the patient positioned face-down. If the surgery will involve the spinal cord itself, spinal cord function is carefully monitored using precise electrophysiological techniques such as SSEP (somatosensory evoked potentials) and MEP (motor evoked potentials).
A laminectomy, or removal of a portion of the back of the spine, is performed to gain access to the spinal canal. If necessary, the thin covering of the spinal canal known as the spinal dura is opened to expose the spinal cord, and a narrow opening in the back portion of the spinal cord may be made to expose the cyst.
The goal of the procedure is complete removal of the cyst. However, if the wall of the cyst adheres strongly to the spinal cord or spinal nerves, complete removal may not be safely possible. In such cases, the surgeon removes as much as safely possible.