Reversible cervical cord compression in Hirayama disease: Three-position dynamic MRI in a single session

Hirayama disease is an uncommon, self-limiting myelopathy of the lower cervical cord that predominantly affects young males. The condition arises from a length mismatch between the vertebral column and the posterior dura, leading to anterior dural displacement and cord compression during neck flexion. We present the case of a 19-year-old male with a two-year history of progressive right-hand weakness and forearm wasting. Clinical examination showed the oblique amyotrophy sign, cold paresis, and intact sensory function without pyramidal findings. We performed a single-session dynamic cervical MRI covering three neck positions: neutral with intravenous gadolinium, flexion at approximately 48 degrees, and gentle hyperextension. In the neutral position, T2-weighted sequences revealed loss of cervical lordosis with asymmetric right hemicord atrophy at C6–C7, and post-contrast images demonstrated a crescentic enhancing structure in the posterior epidural space from C3 to C6, consistent with an engorged posterior internal vertebral venous plexus. Flexion images showed posterior dural detachment spanning C3 to T1, marked enlargement of this epidural crescent, anterior displacement of the cord, and near-total effacement of the posterior subarachnoid space. On extension imaging, all of these compressive changes reversed almost completely, with the dural wall returning to laminar apposition and the subarachnoid space restored to its normal caliber. This three-position approach yielded a complete mechanistic picture of the flexion-dependent pathology and allowed a confident diagnosis without recourse to electrophysiological testing.