Tarlov Cysts

Epidemiology

Tarlov, or perineurial, cysts are one of the most common forms of meningeal cyst. There are no good epidemiological studies of Tarlov cysts. Estimates vary as to prevalence of meningeal cysts, including Tarlov cysts. A large study of 3535 MRIs revealed a 1.5% incidence of Tarlov cysts ; an incidence of 1% to 2% is accepted in the general population. However, a study of 500 consecutive patients with back pain undergoing lumbosacral MRI demonstrated a 5% incidence of meningeal cysts, one-fifth of which were thought to be symptomatic.

Tarlov cysts, particularly those that are symptomatic, are more common among women. The reason for this is unclear. In Long’s series, there was a male to female ratio of 1:4.5, with ages ranging from 27 to 68 years. This epidemiological disparity may be potentially genetically related, or the result of the hormonal influence of estrogen upon collagenous and other connective tissue constituents of dura mater and perineurial tissue around the spinal nerve roots.

Histopathology

Tarlov distinguished perineurial cysts from other meningeal cysts based on several histological criteria. ^{, ,} He defined them as perineurial dilations between the endoneurium and perineurium, typically of the S2 or S3 nerve roots, just distal to the dorsal root ganglion ( Fig. 26.1 ). Individual sensory nerve fibers of the root, located along the inner lining of the cyst cavity, distinguishes the Tarlov cyst from other meningeal cyst subtypes, such as meningeal diverticula and arachnoid cysts, wherein the walls are typically devoid of nerve root fibers. Cyst enlargement results in bone erosion, and, presumably through pressure upon adjacent spinal nerve roots, produces radiculopathy.

Clinical Findings

Sacral, perineal, and leg pain aggravated by sitting should prompt consideration of Tarlov cyst syndrome. In order of decreasing frequency, patients presented with local sacral pain (98.5%), generalized back pain (89%), perineal or pelvic pain (78.9%), sciatica (70.5%), complaints of bladder and or bowel function (72%), and decreased sensation with sexual intercourse (42.6%). Occasionally patients reported isolated dyspareunia, coccydynia (1.5%), or paralysis of plantar or dorsiflexion (each 1%). Importantly, 28% of patients have bowel, bladder, and sexual problems without sciatic pain. Neurogenic bladder may be manifest by urgency, frequency, nocturia, and hesitancy, with the need to perform a Valsalva or Credé maneuver to initiate voiding. Also common are neurogenic bowel symptoms, such as constipation requiring the use of laxatives, or rectal incontinence. Dyspareunia and erectile dysfunction are common.

Sacral Tarlov cysts are characterized by sacral pain, numbness radiating down the backs of the legs in the S1 or S2 dermatomes, perineal pain, rectal pain, and numbness in the S2‒S5 dermatomes. The pain may be “crippling,” and patients report inability to sit, the feeling of “sitting on a rock,” and constantly shifting from hip to hip when seated, with difficulty driving, sitting at a desk, or even engaging in nonwork activities such as dining, going to movies, and sitting through religious services. Many carry cushions or pillows to ameliorate their seated discomfort.

Many patients are told by their medical professionals that Tarlov cysts are asymptomatic, with the obvious inference that there is no reason for the pain which they are reporting. However, the limitations and lower quality of life experienced by these patients may result in loss of employment, depression, marital dysfunction, and divorce.

The more common neurological findings include hypoesthesia in the sacral dermatomes, absent ankle reflex (64%), weakness of plantar flexion (42%), rectal sphincter weakness (29%), and positive straight-leg raising sign (18%).

A Tarlov cyst in the sacral spinal canal arising from the S3 nerve root can cause symptomatic impingement of the ipsilateral S2 nerve root beside it, or of the S4 or S5 nerve root below ( Fig. 26.2 ). A Tarlov cyst can also produce contralateral symptoms if it is large enough to extend across the midline and compress contralateral nerve roots. Nerve root fibers running inside a Tarlov cyst are often splayed out over the inner wall of the cyst, causing in neural fiber alteration and stretching, resulting in pain and sensory deficits.