Spontaneous perineural hematoma of a lumbar nerve root presenting as radiculopathy successfully treated with needle aspiration: illustrative case.

backgroundSpinal hemorrhagic disorders are relatively uncommon. Hematomas occurring outside the spinal canal, particularly around the spinal nerve root, are especially rare. To date, reported cases have been limited to a single case associated with a nerve root block procedure and 9 cases of Tarlov cyst hemorrhage. OBSERVATIONS: A 35-year-old woman presented with acute right L5 radiculopathy and extensor hallucis longus weakness. MRI demonstrated a septated cystic lesion in the right L5-S1 extraforaminal region adjacent to the L5 nerve root. Fluoroscopy-guided aspiration yielded a dark red liquefied hematoma with immediate symptom relief and radiographic reduction. The patient experienced recurrence 10 days later with worsened weakness; repeat aspiration of xanthochromic fluid resulted in rapid recovery. No recurrence was observed during 3 years of follow-up. This appears to be the first reported case of spontaneous perineural hematoma involving a spinal nerve root. LESSONS: Acute unilateral lower limb radicular pain is commonly attributed to lumbar disc herniation. However, MRI may reveal an atypical lesion adjacent to the nerve root. Perineural hematoma should be included in the differential diagnosis of acute radiculopathy. Fluoroscopy-guided needle aspiration may offer a minimally invasive treatment option. Early MRI evaluation is important for accurate diagnosis and timely management. https://thejns.org/doi/10.3171/CASE26413.