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Neuroradiology Case of the Week

Case 46

George Manglasseril and José A. Echeverri, MD

Clinical Presentation: A 76-year-old male presented with left-sided weakness and sudden, progressive onset of bilateral lower extremity paraplegia. MRI showed a spinal dural arteriovenous fistula. Further evaluation of the AVM was requested. Conventional angio confirmed the fistula, which was subsequently embolized with n-butilcyanoacrylate (n-BCA). Immediately after the procedure the patient noted some improvement in his lower extremity weakness, and thereafter improved progressively.

Radiological Findings:

Diagnosis: Spinal Dural Arteriovenous Fistula (SDAVFs)

Discussion:  Spinal Dural AVFs, most common type of spinal vascular malformation constituting 80% of spinal AVMs [1]. There are three basic types of AVFs - extradural, dorsal intradural, and ventral intradural [3]. Dorsal intradural AVFs have been given a number of alternate names including long dorsal, angioma racemosum, dorsal extramedullary, angioma racemosum venosum, and Type I. The current literature supports use of term Type I [3]. Type I is further classified into subtypes A and B to designate AVMs with single or multiple feeding arteries, respectively [3]. These dural AVFs are malformations that most commonly occur in the thoracic region [1].
   The dural AVFs consist of an abnormal communication between a radicular artery and a radicular vein within the dural sleeve of a nerve root [1]. The vein communicates with the coronal venous plexus along the surface of the spinal cord. The clinical manifestation of patients with this miscommunication is the insidious development of venous hypertension induced-progressive myelopathy [1]. Venous congestion produces progressive neurological deterioration that can manifest as sensory disturbances, paraparesis, and sphincter dysfunction [2,3]. The pathognomonic MR imaging studies is a pencil-like hyperintensity in the spinal cord on a T2-weighted image [2]. Aminoff and Logue detailed the clinical prognosis of 60 cases of dural AVFs [3]. Seven patients with acute onset symptoms had no progression of neurological dysfunction. The 53 other patients had symptom progression with acute neurological episodes, and lower extremity impairment. Within three years of developing impairment the patients became severely disabled [3]. This and similar outcomes has led to the rule that elimination of dural AVFs will halt the progressive neurological deterioration [1,3].
   The eliminations of dural AVFs can be performed through endovascular or surgical therapy. Endovascular therapy consists of embolization with liquid acrylic embolic material into the AVF and/or the proximal draining vein [1]. Surgical therapy involves microsurgical ligation of AVF draining vein and excision of affected dura1. Literature has supported the use of endovascular therapy as initial treatment with awareness of a 39% failure rate that should be followed up with definitive surgical therapy [1].

References:

1. Eskandar EN, Borges LF, et al. Spinal dural arteriovenous fistulas: Experience with endovascular and surgical therapy. J. Neurosurg (Spine 2) 96: 162-167, 2002.
2. Kataoka H, Miyamoto S, et al. Venous congestion is a major cause of neurological deterioration in spinal arteriovenous malformations.
   Neurosurgery 48:1224-1230, 2001.
3. Spetzler RF, Detwiler PW, et al. Modified classification of spinal cord vascular lesions. J. Neurosurg (Spine 2) 96:145-156, 2002.