 CES is a devastating condition caused by compression of the cauda equina nerve roots resulting in bowel, bladder and sexual dysfunction with potential lower limb weakness. CES requires urgent surgery and has serious potential morbidity and medico-legal consequences1. Suspected acute CES has a minimum incidence of 11 per 100,000 making it twice as common as multiple sclerosis. However, in the two largest studies both retrospective and from Edinburgh, 43-48 of patients with clinical CES were scan-negative and indeed received no other diagnosis 1,2. 