Perineural Cyst as a Rare Cause of L5 Radiculopathy

Abstract

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.Figure 1.: A, T2-weighted axial MRI at the L4–5 intervertebral disc level. B, Area targeted by the first MRI.Figure 2.: A, T1-weighted axial MRI demonstrating a perineural cyst at the L5 vertebral level. B, T2-weighted axial MRI at the same level. C, Area targeted by the second MRI.Perineural cysts occur most frequently at the sacral level. Sacral perineural cyst, so-called Tarlov cyst, was first described by Tarlov in 1938.1 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 directly responsible for symptoms.2 Perineural cysts may be a rare cause, but should be considered in the differential diagnosis of radiculopathy. Mayumi Takatori, MD Munetaka Hirose, MD Toyoshi Hosokawa, MD Kyoto Prefectural University of Medicine Department of Anesthesiology 465 Kajiicho, Kamigyo-ku Kyoto 602-8566, Japan [email protected]