Dorsal arachnoid web. A rare cause of myelopathy

•Dorsal arachnoid web corresponds to a band of arachnoid tissue that extends from dura mater to the posterior surface of the cord and causes cord compression.•Remnants of a previous arachnoid cyst, arachnoid adhesions due to prior surgery or trauma, inflammatory changes or idiopathic are possible causes of dorsal arachnoid web development.•Enlargement of the posterior subarachnoid space, anterior cord displacement with focal cord indentation “scalpel sing” are typical imaging findings of dorsal arachnoid web observed on CT myelogram and/or spine MRI.•Differential diagnosis of dorsal arachnoid web includes anterior cord herniation and arachnoid cyst.