Bilateral leg weakness + bladder dysfunction + loss of both pain and vibration sense means every tract in the cord is involved, i.e. a transverse (whole-cross-section) lesion such as transverse myelitis. Anterior spinal artery occlusion is the tempting choice (paraplegia, pain/temperature loss, sphincter loss) but it spares the dorsal columns, so vibration and proprioception are preserved. Cauda equina syndrome typically has low back pain, saddle anaesthesia and lost ankle reflexes; sagittal sinus thrombosis is intracranial.