Brain imaging abnormality Forward displacement of posterior cervical dura mater on neck flexion 2025-03-01T11:10:50Z Flexion MRI (imaging with neutral and flexed about 30-40 degrees neck position) reveals an anterior shift of the cervical dural sac from the lamina in the region of C4 to C7. This finding is characteristic of Monomelic amyotrophy (Hirayama disease) is a rare motor neuron disorder characterized by progressive weakness and atrophy in the distal upper extremities, typically beginning during adolescence. The condition involves asymmetric muscle atrophy in the hand and forearm, sparing the brachioradialis muscle, and is attributed to increased laxity in the dura mater, which causes the spinal cord to shift forward during neck flexion. Increased laxity of the dura mater from its superior anchors on the dorsal surfaces of C2 and C3, harbingering forward cord movement during cervical flexion. Increased laxity allows the spinal cord to shift forward, leading to repeated subclinical trauma and microischemia in the anterior horn during cervical flexion. Trauma and microischemia eventually lead to myelopathy and degeneration, as evidenced by asymmetric lower cervical cord thinning within the C7 and C8.