Full endoscopic decompression of ligamentum flavum cyst causing thoracic myelopathy: illustrative case.

BACKGROUND: Ligamentum flavum cysts are benign lesions arising from the ligamentum flavum. Although rare in the thoracic spine, they can cause significant spinal cord compression and myelopathy. While open surgical decompression is well described, the role of full endoscopic spine surgery (FESS) in the thoracic spine remains limited due to technical and anatomical challenges. The authors present a rare case of thoracic myelopathy secondary to a facet joint cyst treated with FESS, together with a focused literature review. OBSERVATIONS: A 57-year-old male presented with progressive gait instability, recurrent falls, bilateral lower limb weakness, and mild urinary incontinence. MRI of the thoracic spine demonstrated a 1.0 × 1.0-cm posterior epidural cyst at T11-12 causing severe canal stenosis and spinal cord compression with signal changes suggestive of myelomalacia. He underwent successful right-sided T11-12 uniportal endoscopic decompression and cyst marsupialization, with resolution of his symptoms postoperatively. LESSONS: FESS is an emerging minimally invasive technique for neural decompression. Despite technical challenges in the thoracic spine, it offers advantages including improved visualization, reduced blood loss, and shorter hospital stay. FESS represents a promising treatment option for selected thoracic facet cysts and other compressive pathologies, although further studies are required to better define its role. https://thejns.org/doi/10.3171/CASE26441.