Sacral extradural arachnoid cyst: a rare cause of low back and perineal pain.

Sacral extradural arachnoid cysts are rare. The clinical and radiological features of this condition are characteristic. One such rare case with low back and perineal pain is presented and the literature is reviewed. This patient presented with pain in the low back and perineal region, which was aggravated by standing, walking and straining. The patient also had numbness in both lower limbs, precipitated by standing and walking. Both the symptoms were relieved by lying down. Magnetic resonance imaging (MRI) revealed a sacral extradural arachnoid cyst. Sacral laminectomy with opening of the arachnoid cyst and ligation of the fistulous tract was done. Postoperatively, there was complete clinical recovery. Though rare, this entity should be considered in the differential diagnosis of low back and perineal pain. Surgical treatment is curative.