Perineural cysts (also called Tarlov cysts) are abnormal fluid-filled sacs located in the sacrum, the base of the spine.
Description
Perineural cysts appear to be dilated or ballooned areas of the sheaths that cover nerve roots exiting from the sacral area of the spine. The spaces or cysts created by the dilated sheaths are directly connected to the subarachnoid area of the spinal column, the area through which cerebrospinal fluid flows. Many people have perineural cysts but no symptoms at all; in fact, the majority of people with these cysts are completely unaware of their existence. However, when conditions cause these perineural cysts to fill with cerebrospinal fluid and expand in size, they can begin to compress important neighboring nerve fibers, resulting in a variety of symptoms, including pain, weakness, and abnormal sensation.
Demographics
More women than men develop perineural cysts.
Causes and symptoms
A variety of conditions that can increase the flow of cerebrospinal fluid may cause perineural cysts to expand in size, creating symptoms. Such conditions include traumatic injury, shock, or certain forms of exertion (such as heavy lifting) or exercise. Prolonged sitting or standing may cause cysts to fill and retain fluid. Other research suggests that herpes simplex virus can cause the body chemistry to become more alkaline, which predisposes the cerebrospinal fluid to fill the perineural cysts, thus prompting the advent of symptoms.
The symptoms of expanding perineural cysts occur due to compression of nerve roots that exit from the sacral area. Symptoms may include back pain and sciatica, a syndrome of symptoms that occur due to compression or inflammation of the sciatic nerve. Sciatica results in burning, tingling, numbness, stinging, or electric shock sensations in the lower back, buttocks, thigh, and down the leg to below the knee. Severe sciatica may also result in weakness of the leg or foot. Other more severe symptoms of perineural cysts include loss of bladder control and problems with sexual functioning.
Diagnosis
Because most perineural cysts don't cause symptoms, most perineural cysts are never diagnosed. When symptoms do develop that are suggestive of perineural cysts, MRI will usually demonstrate their presence, and CT myelography (a test in which dye is injected into the spine) may demonstrate the cerebrospinal fluid flow between the spinal subarachnoid area and the cyst.
Treatment team
Neurologists and neurosurgeons usually treat individuals with perineural cysts. A urologist may be called in to consult with individuals whose cysts are interfering with bladder or sexual functioning.
Treatment
Although using a needle to drain fluid from perineural cysts can temporarily relieve their accompanying symptoms, eventually the cysts will refill with cerebrospinal fluid and the symptoms will recur. Similarly, steroid injections can provide short-term pain relief. Pain may also be temporarily controlled by injecting the cysts with fibrin glue (a substance produced from blood chemicals involved in the clotting mechanism). Using diet or dietary supplements to decrease the body's alkalinity may prevent perineural cysts from filling with more fluid. Medications used to treat chronic nerve-related pain (such as anticonvulsants and antidepressants) may be helpful.
When pain is intractable despite a variety of interventions, or when weakness or other neurological symptoms become severe, surgery to remove the cysts may be necessary. This is the only permanent treatment for perineural cysts; once removed, they very rarely recur.
Prognosis
Most individuals with perineural cysts have no symptoms whatsoever. Those who do have symptoms run a risk of neurological damage if the cysts continue to compress nerve structures over time. Individuals who undergo neurosurgery to remove the cysts usually have an excellent outcome, with no cyst recurrence.
BOOKS
Braunwald, Eugene, et al., eds. Harrison's Principles of Internal Medicine. NY: McGraw-Hill Professional, 2001.
Goetz, Christopher G., ed. Textbook of Clinical Neurology. Philadelphia: W. B. Saunders Company, 2003.
Goldman, Lee, et al., eds. Cecil Textbook of Internal Medicine. Philadelphia: W. B. Saunders Company, 2000.
