The histological features of arterialized medullary vein (MV) in spinal dural arteriovenous fistulas (SDAVF) were studied in five consecutive patients who presented with progressive congestive myelopathy. Retrograde venous filling on preoperative angiography was recognized as being severe in 3 cases and moderate in 2 cases. Direct intradural interruption of the arterialized MV was performed in all patients. The arterialized MV was sampled and examined histologically to determine the percentage of the hyperplasia of venous wall (hypertrophic ratio). Histological examination of arterialized MV showed that hypertrophic alteration of venous wall structure was due to hyperplasia of elastic fibers, ranging from 41 to 82%. Patients with angiographically severe venous hypertension tended to have a higher hypertrophic ratio than patients with moderate venous hypertension. Our observations support the clinical concept that long-standing arterial stress in the spinal venous circulation causes histological alterations of spinal vascular structure associated with the progression of venous hypertension. We suggested that possibly the histological parameter can be used for predicting neurological recovery after occlusion of the fistulas.