The myelopathy may have a subacute or saltatory evolution, presumably from fluctuating venous congestion within the cord. A claudicatory syndrome has also been reported. Characteristically, activities that increase venous pressure (Valsalva maneuver, exercise) transiently amplify the symptoms or produce irreversible, stepwise worsening. One remarkable such case involved a baritone opera singer whose legs gave way repeatedly while singing (Khurana et al). A few of our patients have reported transient symptoms upon standing. Many cases occur, however, without a stepwise progression or elicitable worsening. As mentioned, many reported cases have been painless, although most of our patients have had a moderate spinal ache or sciatica. In contrast to the larger parenchymal arteriovenous lesions, these bleed only rarely. The spinal fluid is normal or shows a slight elevation of protein.
The disease can be inferred from the MRI appearance of a characteristic swelling of one or a few adjacent segments of the lower cord that represents venous congestion and edema as discussed further on.
Intramedullary AVM The true spinal cord AVM, previously referred to as angioma racemosum venosum or dorsal extramedullary arteriovenous malformation, is typically located on the dorsal surface of the lower half of the spinal cord and occurs most often in middle-aged and elderly men (23 of 25 of Logue’s patients were male). However, this lesion may occur at any age and at any location in the cord and may be quite widespread. In a few cases has there been an overlying dermatomal nevus.
The clinical picture was well described by Wyburn-Mason. Acute cramp-like, lancinating pain, sometimes in a sciatic distribution, is often a prominent early feature. It may occur in a series of episodes over a period of several days or weeks; sometimes it is worse in recumbency. Almost always there is weakness or paralysis of one or both legs and numbness and paresthesias in the same distribution with a highly variable duration of evolution; an abrupt apoplectic onset is known or the neurologic signs may appear over months, most cases conforming to the middle of these extremes. Wasting and weakness of the legs may introduce the disease in some instances, with uneven progression, sometimes in a series of abrupt episodes. Severe disability of gait is usually present within 6 months, and half of the patients described by Aminoff and Logue were chair-bound within 3 years; the average survival in the past was 5 to 6 years, but the disorder has rarely been fatal in our patients. These lesions only infrequently give rise to intramedullary or subarachnoid hemorrhage. The spinal fluid shows high protein but little or no cellular reaction.
When viewed directly, the dorsal surface of the lower cord may be covered with a tangle of veins, some involving roots and penetrating the surface of the cord. The progression of symptoms is presumably a result of chronic venous hypertension and secondary intramedullary ischemic changes, and the abrupt episodes of worsening are attributed to the thrombosis of vessels, all on uncertain grounds because angiographic studies sometimes show only a single or a few such dilated draining vessels. Furthermore, there is insufficient pathologic material to determine whether some of the more prominent venous anomalies represent true venous angiomas (probably they do not).