Introduction

Aneurysms of the spinal arteries are rare lesions responsible for less than 1% of all subarachnoid hemorrhages (SAHs). Since being first described in 1981, fewer than 50 cases of spinal artery aneurysms have been reported in the medical literature. Most have been associated with vascular lesions, including arteriovenous malformations (AVMs), dural arteriovenous fistulas, coarctation of the aorta, bilateral vertebral artery occlusion, and moyamoya disease, in which the anterior spinal artery serves as the collateral blood supply. Spinal artery aneurysms that are not associated with a precipitating factor are called isolated spinal aneurysms and have not been associated with other intracranial aneurysms.

The mean age of patients with spinal artery aneurysms at presentation is 38 years. Most of these aneurysms are small, with a diameter of less than 3 mm. Patients with isolated spinal aneurysms are more likely to present with hemorrhage than those in whom the aneurysm is associated with a vascular malformation ( 1 in algorithm ). The specific clinical presentation of a ruptured spinal aneurysm depends on the level and severity of hemorrhage; however, sudden-onset pain appears to be a universal attribute of this pathology. Given the rarity of these lesions, practice guidelines are ill defined or altogether lacking.

Major controversies in decision making addressed in this chapter include:

1. 
   

   Whether or not treatment is indicated.

   
   
2. 
   

   Open versus endovascular treatment for ruptured and unruptured spinal aneurysms.

   
   
3. 
   

   Management of aneurysms in patients who present with hematoma.

   
   
4. 
   

   Determining which specific surgical technique (e.g., vessel sacrifice, clipping, wrapping, reconstruction, embolization) to use.

Whether to Treat

Most spinal aneurysms are diagnosed only after the patient presents with a symptomatic hematoma or an SAH. Whereas the natural history of intracranial aneurysms is well understood, the natural history and the management paradigm of spinal artery aneurysms are poorly defined. If found incidentally (i.e., unruptured and asymptomatic), these lesions can be managed conservatively with follow-up imaging to evaluate any associated vascular lesions and growth ( 2 in algorithm ). For symptomatic lesions, surgical or endovascular treatment is advised ( 3 in algorithm ).

With ruptured spinal aneurysms, SAH and/or hematoma will also be present. Therefore, early treatment is recommended to avoid devastating outcomes due to mass effect or rerupture. The type of management should be determined by the morphology of the aneurysm and the presence or absence of distal parent vessel flow ( 4 in algorithm ).

Anatomical Considerations

The spinal cord vasculature can be divided into a central system and a peripheral system. The central system derives from the anterior spinal artery and supplies blood to the anterior two-thirds of the spinal cord. In the peripheral system, blood flows centripetally from the posterior spinal arteries and the pial arterial plexus to supply the posterior one-third of the spinal cord.

In the upper cervical spine, the radiculomedullary arteries are fed by intervertebral branches of the vertebral arteries and their descending rami. In the lower cervical spine, the segmental arteries arise from the deep cervical artery, the costocervical artery, or the ascending cervical artery. In the thoracic spinal cord, radiculomedullary arteries originate from intercostal arteries that are derived from the subclavian artery and the aorta. The lumbar region arteries extend from the aorta into the body wall, where the radicular arteries arise from them. In the sacral region, the segmental arteries are supplied with blood from the lateral sacral arteries.

In about half the population, the great radicular artery (i.e., the artery of Adamkiewicz) supplies one-fourth of the spinal cord, and in most cases it travels with T9–T12 roots. The artery of Adamkiewicz is found mostly on the left side, and where it joins the anterior spinal artery, it divides into a small ascending branch and a large descending branch. The lateral spinal arteries arise at the level of the medulla, from either the posterior inferior cerebellar artery or the intradural vertebral arteries, and then descend inferolaterally, anterior to the posterior spinal nerve roots. These arteries supply the spinal accessory nerve and the posterior and lateral surfaces of the spinal cord.

Pathophysiology

As with cranial vascular lesions, the coexistence of spinal aneurysms and spinal cord AVMs has been associated with hemodynamic factors, congenital defects of arterial walls, or some interaction between these factors. Spinal aneurysms are often located on the afferent arteries of AVMs and regress after treatment of the AVM. Spinal aneurysms often occur along the course of an artery but seldom at branching points. Compared with intracranial arteries, spinal arteries have a much smaller caliber and tend to be less affected by atherosclerosis. In addition, most spinal aneurysms are fusiform dissecting dilations that lack a surgical neck. The anterior spinal artery is involved in most cases, but spinal aneurysms can also arise from the posterior spinal arteries, the lateral spinal arteries, and the segmental arteries such as the artery of Adamkiewicz.