Foot Drop of Sudden Onset Caused by Acute Hematoma in the Lumbar Ligamentum Flavum

Abstract

A case report. To describe an unusual case of acute hematoma in the lumbar ligamentum flavum causing foot drop. There have been several reports of hematoma in the lumbar ligamentum flavum causing compression of the cauda equina and/or nerve root. However, the majority of these cases were chronic hematomas, based on clinical history and histologic findings. A 64-year-old man presented with right foot drop of sudden onset and severe sciatica. Magnetic resonance imaging (MRI) on the 10th day after the onset of symptoms revealed spinal stenosis at L4/5 caused by a posterior mass that was isointense on T1-weighted images and hyperintense on T2-weighted images, but was hyperintense on T1-weighted images and hypointense on T2-weighted images 5 days later. Because of these neurologic findings, surgical exploration and excision of the intraspinal mass were performed on the 18th day after onset. Surgical treatment was uneventful, and the severe sciatica improved immediately after surgical treatment. Histologic examination revealed recent extravasation of blood in the degenerated ligamentum flavum. These findings were supported by the 2 consecutive preoperative MRI examinations. At 1 year after surgery, manual muscle testing of the tibialis anterior on the affected side had recovered to grade 4. Consecutive MRI examinations performed 5 days apart in the early stage after the onset of symptoms clearly demonstrated intensity change, indicating acute hematoma of ligamentum flavum as a cause of foot drop of sudden onset.