Bilateral lower limb dysfunction due to acute hematoma in the lumbar ligamentum flavum

RATIONALE: There have been several reports of lumbar yellow ligament hematomas leading to cauda equina and/or nerve root compression. However, based on clinical history and histological findings, most of these cases involve chronic hematomas. Acute lumbar yellow ligament hematomas causing nerve compression are relatively rare. PATIENT CONCERNS: A 71-year-old male presented with an 8-day history of sudden-onset lower back pain without an identifiable trigger, which progressively worsened with new-onset pain and numbness in both lower extremities. Physical examination revealed muscle strength of the quadriceps femoris left IV/right V, tibialis anterior left IV/right IV, and extensor hallucis longus left V/right V. DIAGNOSES: Magnetic resonance imaging on the 8th day after symptom onset revealed severe stenosis of the L4/5 spinal canal and cauda equina compression caused by a posterior mass, which appeared hyperintense on T1-weighted images and hypointense on T2-weighted images with nodular and ring-like hyperintense signals. Histopathological and immunohistochemical examination confirmed ligamentum flavum hematoma with recent angiogenesis and hemorrhage in the degenerated yellow ligament. INTERVENTIONS: Surgical exploration and resection of the extradural mass were performed on the 9th day after symptom onset. An endoscopic-assisted posterior spinal decompression, laminectomy, and spinal fusion with internal fixation at the L4/5 level were performed. OUTCOMES: The surgical treatment was successful, and the severe bilateral lower limb dysfunction improved immediately after surgery. Two weeks after surgery, at follow-up, muscle strength had been restored to grade 5 with no recurrence of symptoms. LESSONS: Acute ligamentum flavum hematoma can occur without trauma and should be included in the differential diagnosis for sudden bilateral lower limb deficits. MRI is crucial for early recognition, and prompt surgical intervention can yield rapid, complete recovery, underscoring the importance of timely diagnosis and decompression to prevent permanent neurologic injury and inform evidence-based management.