Iliopsoas hematoma presenting with sudden knee extensor weakness

Rationale: Hematoma of the iliopsoas muscle is a rare condition. Prolonged pressure conditions due to hematoma of the femoral nerve can cause severe pain in the affected groin, hip, and thigh, and quadriceps weakness. We report a rare case of a spontaneous iliopsoas muscle hematoma that caused sudden femoral neuropathy. Patient concerns: A 71-year-old woman presented sudden left hip pain and knee extensor weakness. The pain was aggravated with left hip extension. She had a bilateral total hip replacement surgery due to avascular necrosis. She was diagnosed as mild stenosis of the cerebral artery and took aspirin to prevent cerebral artery atherosclerosis. Diagnosis: A hip computed tomography scan demonstrated a suspicious fluid collection at the left iliopsoas bursa. We considered the possibility of lower limb weakness due to neuralgic amyotrophy and performed electromyography and enhanced lumbosacral magnetic resonance imaging (MRI). Electromyography finding showed left femoral neuropathy of moderate severity around the inguinal area was diagnosed. On MRI, left iliopsoas bursitis or hematoma, and displacement of the left femoral nerve due to the iliopsoas bursitis/hematoma were observed. Intervention: Ultrasonography (US)-guided aspiration of the left iliopsoas hematoma was performed. We started steroid pulse therapy for 8 days. Outcomes: After US-guided aspiration and steroid pulse therapy, the patient's knee extension motor grade improved from grade 1 to 2, and the pain was slightly reduced. At 3 weeks after the aspiration procedure, her hip flexion motor grade had improved from grade 3+ to 4 at follow-up. Lessons: Imaging studies are fundamental to diagnose of iliopsoas hematoma. Electromyography examination plays an important role in determining the prognosis of patients and lesion site. Despite the negligible change in sitting position, hematoma can develop. Physicians should consider hematoma that cause femoral neuropathy.