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Figure. Sagittal MRI shows 25.0-mm defect in the lower spine.
A 37-year-old man presents with a month-long history of lower back pain that radiates to the right buttock. He believes the pain started after he reached for something on the floor and felt and strain in his lower back. He denies any changes in bowel or bladder function. On physical examination, he has a mild positive straight leg raise test on the right side with motor and sensation completely intact in the lower extremities. He has mild paraspinous muscle spasm and tenderness to palpation on the lower back. Radiography of the lumbar spine shows mild degenerative changes in the lumbar spine without fracture. Magnetic resonance imaging (MRI) shows a small disc herniation at L5-S1 causing impingement on the right-sided sacral nerve roots. The MRI shows a right-sided Tarlov cyst at S3 measuring 2.5 by 1.8 cm (Figure).
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Tarlov cysts, or perineural cysts, are found within the spinal canal generally at the sacral level.1 The cysts grow within the nerve roots and the cyst walls are made of neural tissue. The cysts communicate with the subarachnoid space and are filled with cerebral spinal fluid (CSF). The general theory is that the cyst has a one-way valve that allows CSF to enter but not leave.1,2
Most of these cysts will remain small and asymptomatic (they occur in up to 9% of the population) but some can grow large enough to cause local nerve compression.2 Larger cysts greater than 1.5 cm are more likely to be associated with symptoms of nerve root impingement such as radicular pain, paresthesia, and bowel or bladder dysfunction.1,2
An MRI is the best imaging study to view a Tarlov cyst; the next best imaging modality is a computed tomography (CT) myelography to help demonstrate communication of the cyst with CSF. The majority of Tarlov cysts are clinically irrelevant and radicular pain is much more likely to be caused by other pathologies such as lumbar disc herniation and lumbar stenosis.2 Initial treatment is conservative unless the patient presents with bowel or bladder dysfunction. Surgical excision is reserved for patients who have progressive neurologic deficits or severe pain that has failed conservative treatment.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor in chief of the Journal of Orthopedics for Physician Assistants.
References
1. Acosta FL Jr, Quinones-Hinojosa A, Schmidt MH, Weinstein PR. Diagnosis and management of sacral Tarlov cysts: case report and review of the literature. Neurosurg Focus. 2003;15(2):E15. doi:10.3171/foc.2003.15.2.15
2. Langdown AJ, Grundy JR, Birch NC. The clinical relevance of Tarlov cysts. J Spinal Disord Tech. 2005;18(1):29-33. doi:10.1097/01.bsd.0000133495.78245.71
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