Ventral cord herniation
10 months right lower limb weakness. New left lower limb numbness.
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At the level of a chronic T5 vertebral compression fracture, there is a focal C-shaped anterior displacement of the cord, which is mildly rotated and closely applied to the left anterolateral dura with obliteration of the anterior CSF plane. This is associated with T2 hyperintensity and atrophy of the left hemicord at adjacent levels. There is no obstruction to CSF flow in the enlarged posterior CSF space.
MR findings are characteristic of ventral cord herniation, in which Brown-Sequard syndrome (ipsilateral motor, fine touch and proprioception defect with contralateral pain, temperature and gross touch defect) is the most common presentation.
The major imaging differential diagnosis is dorsal arachnoid cyst or (rarely) dorsal arachnoid web. If there is diagnostic uncertainty, high resolution T2 sequences and cine flow studies or CT myelogram could be performed in an attempt to define a cyst wall or obstruction to CSF flow produced by a dorsal arachnoid cyst.