Ligamentum Flavum Hematoma in a Fused Lumbar Spine After Oblique Lateral Interbody Fusion: An Unusual Case Report

Hematoma in the ligamentum flavum (HLF) is rare and may mimic symptoms of spinal cord or nerve root compression, as seen in degenerative conditions such as intervertebral disc herniation or spinal stenosis. In this report, we describe a unique case of HLF that developed after long-segment lumbar fusion in a patient with no history of trauma. A 66-year-old man underwent oblique lateral interbody fusion (OLIF) with percutaneous pedicle screw fixation from L2 to S1 for multilevel degenerative lumbar spinal stenosis. Postoperative magnetic resonance imaging (MRI) showed effective spinal canal decompression, and the patient reported marked improvement in low back pain. However, 9 months after surgery, he developed severe left-sided sciatica with symptoms suggestive of dural compression. Subsequent MRI revealed an extradural mass originating from the ligamentum flavum at the left L5–S1 level. Revisional endoscopic hemipartial laminectomy with flavectomy was performed, and a dark brown hematoma was identified within the ligamentum flavum. Histopathological examination of the surgical specimen confirmed the diagnosis of HLF. This case demonstrates that rare complications such as intraligamentous bleeding can occur at any time after spinal fusion and highlights the importance of considering HLF in patients with unexpected neurological deficits after OLIF.