Age / Sex : 17 / M

Hirayama disease

Discussion

Findings:

 MR - On T2 sagittal image, focal spinal cord atrophy with myelomalacic change at C6-7 level. On fully flexed position of neck, forward displacement of dural sac with enlarged vascular space in posterior epidural area at C5~C7 level.

Differential Diagnosis:

 Myelomaiacia caused by other insults such as trauma or ischemia
 

Diagnosis: 

 Hirayama disease = Nonprogressive juvenile spinal muscular atrophy of distal upper arm
 

Discussion: 

* Clinical feature

- Predominantly males in 2nd or early 3rd decade

- Muscular weakness and atrophy in hand and forearm, usually unilateral involvement, but asymmetric and symmetric bilateral involvement  also observed

- Insidious onset & steadily progressive 

* Pathomechanism

 - Debated, but postulates that insufficient growth of the dura relative to the spinal column during puberty allows forward displacement of the dura in flexion with compression of the spinal cord, possibly leading to ischemia of the anterior horn cells at C8 and T1 

 * MR findings

 - LOA(loss of attachment) of the dura to the lamina, asymmetric lower cervical spinal cord atrophy, spinal cord T2 hyperintensity, loss of cervical lordosis in the neutral position, and forward displacement of the dura with flexion

References:

1. Gandhi D, Goyal M, Bourque PR, Jain R. Case 68. Hirayama disease. Radiology 2004 Mar;230(3):692-6
2. Lehman VT, Luetmer PH, Sorenson EJ, Carter RE, Gupta V, Fletcher GP, Hu LS, Kotsenas AL. Cervical spine MR imaging findings of patients with Hirayama disease in North America: a multisite study. AJNR Am J Neuroradiol. 2013 Feb;34(2):451-6.