Perineural Cyst as a Rare Cause of L5 Radiculopathy

To the Editor: We report a rare case presenting with a cyst that was observed in the lumbar spine and caused L5 radiculopathy. A 34-yr-old woman presented with a 6-yr history of left lower back pain and left lower extremity pain. Physical examination was unremarkable except for a positive straight leg-raising test on the left side. Magnetic resonance imaging (MRI) was reported to be within normal limits except for slightly bulging discs at L4–5 and L5–S1 (Fig. 1). No lumbosacral transitional vertebrae were identified. Several epidural blocks decreased pain but left L5 radiculopathy remained. L5 selective nerve root block alleviated pain temporarily. Epidurography showed a filling defect in the L5 vertebral level. We suspected the presence of epidural adhesions and performed diagnostic epiduroscopy. The endoscope was introduced into the sacral hiatus and advanced into the epidural space but could not be advanced into the area of the filling defect. We realized a space-occupying lesion might be present. MRI was carefully performed again, targeted to the L5 vertebral level. Imaging revealed the presence of an extradural cyst located along the left L5 nerve root (Fig. 2). Cyst resection was performed successfully and histopathological examination confirmed the cyst as a perineural cyst. Perineural cysts occur most frequently at the sacral level. Sacral perineural cyst, so-called Tarlov cyst, was first described by Tarlov in 1938. Langdown et al. reported Tarlov cysts as a relatively common finding on lumbosacral MRI with a prevalence of 1%–2%, and only 13% of cysts were Figure 1. A, Ultrasonographic view of LFCN before injection. (FL fascia lata, FI fascia iliaca, Sart. M. sartorius muscle, n LFCN). B, Ultrasonographic view of LFCN after injection. (FL fascia lata, FI fascia iliaca, Sart. M. sartorius muscle, n LFCN, LA local anesthetic and steroid spreading around LFCN).