Occult vascular malformations of the spinal cord: report of four cases not detected by angiography.

Angiographically occult vascular malformations (AOVMs) are reported. Although cavernous malformations, the most common type among the spinal intramedullary AOVMs, have been well documented, the natural history and clinical features of non-cavernous type AOVMs of the spinal cord remain obscure. We have evaluated four cases of non-cavernous AOVMs in the past 9 years. Although the clinical features and magnetic-resonance imaging (MRI) of three cases were similar to those previously reported, the other one had unusual features of insidious onset with limb asymmetry. The natural history of intramedullary occult AVMs remains enigmatic. One speculation for the neurological deterioration is that it results from repeated hemorrhages around the vessels or from intralumenal thrombosis.