Spinal dural AVFs are rare disease entities, with many different established causes. Although they comprise approximately 60–80% of total spinal malformations, their overall yearly incidence is about 5–10 cases per million . Patients typically experience a slowly progressive course of symptoms, and less commonly rapid progression. The average patient will present 1–3 years prior to a correct diagnosis . At the time of diagnosis, the triad of motor deficits, sensory disturbances and cauda syndrome are present in 70% of patients .
There are 5 types of spinal AV shunts, with the most common type being a Type 1 dural AVF. The typical location for these lesions is in the lower thoracic and the upper lumbar spine [1, 4]. The exact etiology remains unknown, with a small percentage of possible multifactorial causes attributed to infection, syringomyelia, trauma, and surgery . Irrespective of the cause, the disproportionate arterial inflow and venous outflow creates increased subarachnoid venous plexus pressure and congestion of the radial veins draining the spinal cord with resultant cord edema and eventual ischemia .
Although imaging characteristics may be non-specific, the multisegmental centromedullary T2 hyperintense signal with associated subarachnoid flow voids, particularly dorsally, are pathognomonic for this condition. As there is increased venous pressure, cord volume expansion becomes evident. These findings classically span approximately 5–7 vertebral levels . Enhancement is typically present, however, the length of enhancement does not correlate with clinical symptoms. The majority of lesions involve the thoracolumbar junction, and 80% involve the conus . The relatively lower venous outflow channels in the thoracic spine relative to the cervical level may explain why venous congestion is transmitted craniocaudally, and presenting symptoms may be conus medullaris related, even from a shunt higher up . Primary differential diagnoses include transverse myelitis, neuromyelitis optica, vasculitis, demyelinating lesions, or tumors. CSF analysis is helpful in narrowing this differential, with a bland CSF profile excluding several etiologies and favoring a vascular etiology . If the shunt volume is small, the perimedullary vessels may not be seen, or only noted on post contrast timed MRA sequences. First pass contrast enhanced MRA (CE MRA) can demonstrate early venous filling, confirming the shunt. CE-MRA is also useful in localizing the spinal level of the shunt, which can be very helpful in guiding the interventionalist while performing the angiogram to confirm the diagnosis. However, MRAs are often technically limited, limiting interpretation . A pinal angiogram remains the gold standard for localizing and treatment planning of the lesion. Open ligation and endovascular embolization are the mainstays of treatment, currently . The treatment usually stops the progression of symptoms or improves neurological deficits.
We present a case of a patient with suspected transverse myelitis, with worsening symptoms after steroid administration which unmasked an underlying dural arteriovenous fistula as seen on follow-up imaging.