Surgical Management of a Large Multiloculated Thoracolumbar Spinal Extradural Arachnoid Cyst via Decompressive Laminectomy With Selective Foraminal Fenestration: A Case Report.

Spinal extradural arachnoid cysts (SEACs) are rare, benign, non-neoplastic lesions arising from focal dural defects, most frequently reported in the thoracic spine. Large multilocular with intraforaminal extension SEACs represent a challenging surgical case, as attempts for complete resection may result in dural defect and cerebrospinal fluid (CSF) leakage. The optimal surgical approach in the setting of adherent foraminal involvement remains an area of debate. We report a 32-year-old woman who presented with a three-month history of progressive low back pain, bilateral lower limb pain and weakness, paresthesia, and intermittent urinary incontinence. Magnetic resonance imaging (MRI) demonstrated a large, lobulated, extradural arachnoid cyst extending across the thoracolumbar junction from lower T10 to upper L2, measuring approximately 116 × 61 × 21 mm, with marked anterior displacement of the spinal cord and lateral foraminal extension in the left T11/T12, T12/L1, and L1/L2 levels. The patient underwent partial laminectomy of the inferior half of T10, complete laminectomy of T11 to T12, and partial laminectomy of the superior half of L1 with near-total cyst resection. The adherent intraforaminal component at the left T11/T12 level was selectively fenestrated to avoid the risk of postoperative dural injury, CSF leakage, or injury to the nerve root. Histopathological examination was consistent with a benign arachnoid cyst, negative for malignancy. Postoperative MRI confirmed complete resolution of all extradural cystic lesions at 10-month follow-up. Pain scores were obtained preoperatively and postoperatively from the patient using the 0-10 numeric rating scale, improved from 9/10 preoperatively to 4/10 at 10-month follow-up; paresthesia and urinary incontinence were reported as fully resolved.