Symptomatic Idiopathic Noncommunicating Intradural Arachnoid Cyst of the S1 Nerve Root

Study Design. A case report of a rare symptomatic, idiopathic, noncommunicating intradural arachnoid cyst (IAC) of the proximal part of the S1 nerve root (NR). Objective. To discuss the possible pathophysiology, clinical and magnetic resonance imaging (MRI) presentation, intraoperative fi ndings, and follow-up of IAC of the proximal part of the S1 NR. Summary of Background Data. Rare variety of the Nabors’s Type 3 spinal IAC. The etiopathogenesis are uncertain. Surgical NR decompression with extirpation of the cyst is the treatment of choice. Methods. A 37-year-old woman clinically presented as monoradiculopathy with a 9-month history of progressive, posture-dependent radicular pain, paresthesia and hypoesthesia in the right S1 dermatome, and mild weakness of the ipsilateral plantar fl exors. Magnetic resonance imaging (MRI) showed a noncommunicating IAC of the proximal part of the S1 NR on the right side. Surgical exploration through the ipsilateral L5-S1 hemilaminectomy was performed with microsurgical arachnolysis of the compressed and stretched S1 NR fascicles that surrounded the cyst, during which the cyst spontaneously collapsed. The remnant of the cyst wall was extirpated and histopathology confi rmed the diagnosis. Results. After surgery an excellent clinical outcome was archived: the leg pain was no longer present and the paraesthesia, hypoesthesia, and motor weakness were resolved within 3 months. At 12 months of follow-up, the patient continues to be completely asymptomatic with no evidence of recurrence on MRI.