BRAIN

SPINE

Perineurial (Tarlov) cysts are meningeal dilations of the posterior spinal nerve root sheath that most often affect sacral roots and can cause a progressive painful radiculopathy. These lesions have been estimated to affect between 4.6 and 9% of the adult population and are commonly found during the third and fourth decades. Although originally believed by Tarlov to be asymptomatic lesions, these cysts, when present in the sacral neural canal and foramina, can cause a variety of symptoms, including radicular pain, paresthesias, and urinary or bowel dysfunction. Although the term Tarlov cyst has often been erroneously applied to other cystic spinal lesions, the distinctive feature of the Tarlov perineurial cyst is the presence of spinal nerve root fibers within the cyst wall, or the cyst cavity itself.

Another type of cyst has bveen decribed by Schreiber. In this case the arachnoid membrane was found to expand through a congenital defect or weakness in the radicular dura mater towards the epidural space. This membrane had a stalk that got inserted into the nerve root sheath more proximal than the Tarlov type cysts. Though they had a predilection for the sacral region, they could also be seen in the cervical or thoracic regions. The ball-valve like mechanism in the neck of this diverticulum allows the development of high intracystic pressures. The wall of these cysts are made of arachnoid membrane and did not contain ganglion or nerve fibers. Tarlov cysts are most commonly diagnosed by lumbosacral magnetic resonance imaging and can often be demonstrated by computerized tomography myelography to communicate with the spinal subarachnoid space. The cyst can enlarge via a net inflow of cerebrospinal fluid, eventually causing symptoms by distorting, compressing, or stretching adjacent nerve roots.

Surgical management

It is generally agreed that asymptomatic Tarlov cysts do not require treatment. When symptomatic, the potential surgery-related benefit can have a long duration. Surgery consists mainly in partial excision and plication of the cyst wall in order to reduce the size of the cyst and to decompress the surrounding nerve roots. It is still possible for the membrane to regrow or the arachnoid to proliferate to resume the valve-like action, but, however, it is very unlike the symptoms recur in a near future. Although no consensus exists on the definitive treatment of symptomatic Tarlov cysts, to date surgical methods have yielded the best long-term results.

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