Angiographically Occult Dorsal Extramedullary Spinal Arteriovenous Malformations: Report of 4 Cases With Atypical Preoperative Findings and Postoperative Course Review of Classifications
Objectives: Presenting 4 cases of spinal arteriovenous malformations (SAVMs) with typical spinal magnetic resonance imaging (MRI) and myelogram, but negative complete selective spinal angiography (SAG) and a "hard to explain'' postoperative course. Materials and Methods: All were male patients of 40 to 50 year of age presenting with progressive paraparesis and sphincter disturbance. MRI, spinal myelography, multislice spinal computed tomographic angiography, and digital subtraction selective SAG was performed. The surgical treatment is described and the videos of 2 cases are demonstrated. Even though all the patients had slow and acceptable improvement in the short postoperative course but in longer follow-up, the clinical improvement continued slowly in 1 case, plateaued in 1 case, and paraplegia recurred in 2 cases. Results: Low intensity intramedullary ellipsoid shadow in T1-weighted spin echo MRI, turning to a homogenous bright high signal intensity lesion in T2-weighted sequence with flow void serpentine images located in the dorsal aspect of the spinal cord in multiple levels were the typical findings. Ill-defined filling defects visualized in myelography was present in all 4 cases. Digital subtracted selective SAG did not show any abnormal vessels in any of the cases. Conclusions: (a) There are still unusual variants of SAVMs that neurosurgeons should recognize, (b) there should be an acceptable explanation for the lesions being angiographically invisible, and (c) the natural course and outcome of the angiographically occult SAVM is not known and unexpected events can be anticipated in long-term follow-up of similar cases.