[Pure motor monoparesis of a lower limb due to head injury: a case report].

A 70-year-old woman sustained a head injury after a motor vehicle accident. Physical examination conducted on admission revealed pure motor monoparesis (PMM) and pathological reflexes in the right lower extremity. Her left lower extremity and upper extremities were intact. Computed tomography showed a spotty high-density lesion in the left precentral gyrus and a subgaleal hematoma in the left occipital region. Magnetic resonance imaging was performed on the next day. Fluid-attenuated inversion recovery (FLAIR) imaging demonstrated a high-intensity lesion in the left precentral gyrus, and T₂ imaging revealed a low-intensity lesion suggesting a small hemorrhage in the same area. The small hemorrhage and perifocal edema were identified on diffusion-weighted images in which low- and high-intensity lesions were observed in the anterior and posterior left precentral gyrus, respectively. Subsequent neurological examinations over 2 weeks showed improvement. We discuss the clinical presentation, diagnosis, and treatment of PMM due to head injury. We concluded that FLAIR and T₂ and diffusion-weighted imaging may be useful techniques for diagnosing PMM due to head injury.