A rare case of near-complete resolution of extensive cervicothoracic syrinx following bilateral cerebellar tonsillar resection in Chiari malformation type I.

Chiari malformation type I (CM-I) often leads to syringomyelia (SM) through impaired cerebrospinal fluid (CSF) flow at the craniocervical junction, resulting in progressive neurological deficits. A 27-year-old woman presented with a 6-month history of severe occipital headaches, neck pain, bilateral upper limb numbness, quadriparesis (MRC 3/5), and ataxia. MRI revealed 23-mm cerebellar tonsillar herniation and an extensive syrinx from C2 to T3 (maximal diameter 11 mm). She underwent suboccipital craniectomy, C1 laminectomy, bilateral subpial tonsillectomy, and expansile duraplasty with autologous fascia lata graft. Intraoperative Valsalva confirmed restored CSF flow. Postoperatively, headaches and neck pain resolved immediately. At 1 month, strength improved to MRC 4/5 with reduced numbness; by 3 months, full neurological recovery (MRC 5/5, no ataxia or sensory deficits) was achieved. Follow-up MRI showed near-complete syrinx resolution (< 3 mm residual cavity) and normalized CSF dynamics, without complications like cerebellar ptosis. This case demonstrates the efficacy of a comprehensive surgical approach incorporating bilateral tonsillectomy in severe CM-I with extensive SM, yielding rapid radiological and clinical improvement within 3 months.