Sacral perineural cysts (Tarlov cysts) are cysts of the sacral nerve roots. They rarely become symptomatic, but have been associated with lumbar and sacral pain, pseudoradicular and radicular symptoms, and bowel and bladder dysfunction [1–5, 7, 10, 11]. Perineural cysts, most of which were asymptomatic, showed a prevalence of 1.5% to 4.6% in radiological studies [6, 9]. Their etiology remains unclear (reviewed in [5]). Micro-communications at the distal dural sleeve of the nerve root functioning as a valve that allows CSF influx while restricting CSF efflux is thought to be one possible underlying pathomechanism of perineural cyst growth [8]. Cyst expansion may eventually lead to irritation or compression of the affected or adjacent nerve roots, and erosion of surrounding bone with consecutive irritation of periostal pain fibers.
Cystic lesions of the sacral region can be diagnosed by CT or MRI. The presence of a communication between the cyst and thecal sac differentiates perineural cysts from other cystic lesions [8]. These micro-communications can be demonstrated by myelography and postmyelographic CT. Delayed contrast filling of the cystic lesion indicates the presence of micro-communications and hence a possible valve mechanism [1, 2, 7, 8, 11].
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