Subdural arteriovenous fistulas (SDAVF) represent a rare disease of the spinal cord with diverse neurological complains resembling polyneuropathies of myelopathies. Due to the absence of specific clinical signs the diagnosis relies upon the MRI findings, which consists of the following classical triad of 1) dilated vessels in the subdural space, 2) central spinal cord edema and 3) contrast enhancement of the affected segments. A fourth yet inconsistent finding is an enlarged conus medullaris. The triad is however often incomplete and in the absence of the engorged perimedullary vessels the diagnosis can remains elusive for an extensive period of time and until an advanced level of clinical disability is reached. Unlike most other immune of infectious causes of medullary dysfunction, SDAVF is a treatable condition, surgical treatment usually stopping the progression of neurological complains. Therefore, an early diagnosis is the most important factor associated with neurological recovery. The aim of this case report is to illustrate how essential a prompt diagnosis is by presenting two patients with very different clinical outcomes based on the time from the initial complains to the correct diagnosis.