|ECR 2019 / C-2783|
|Spinal arteriovenous lesions: anatomical and radiological approach|
Findings and procedure details
Each segment of the spine (metamere) is supplied by paired segmental arteries (left and right) that feed all its components, including the vertebral body, paraspinal muscles, dura, nerves roots and spinal cord. Those segmental arteries have multiple longitudinal and transverse connections at different levels, configuring two network anastomoses: a extraspinal and intraspinal-extradural system (Fig. 1, Fig. 2).
The segmental artery gives a dorsal branch, the dorsal spinal artery. This artery irrigates the posterior elements, giving a dorsal branch and a ventral branch. The dorsal branch of the dorsal spinal artery gives muscles branches that feed the post-transverse anastomotic network that communicates with the adjacent upper and lower levels. The ventral branch of the dorsal spinal artery travels through the neural foramen, sends branches that irrigate the epidural and dural elements, as well as a radicular artery to supply the nerve root (Fig. 2).
In some levels, the radicular artery has greater caliber and reaches the spinal cord, where it contributes to the formation of the anterior spinal artery. This type of radicular artery is known as radiculomedullary artery (Fig. 1).
The number of radiculomedullary arteries that feed the anterior spinal artery is not constant (6 to 10) and its origin is unpredictable. Classically, there are two dominant radiculomedullary arteries, one at the cervical level and the other at the dorso-lumbar level (Adamkiewicz). The Adamkiewicz artery originates in 80% of cases between T9 and L3 on the left side, 15% on the right side and 5% on other levels.
On the anterior surface of the spinal cord, the radiculomedullary arteries form a longitudinal connection called the anterior spinal artery, that travels along the anterior sulcus and predominantly supply the gray matter of the spinal cord. Radiculomedullary arteries, specially the prominent Adamkiewicz artery, present an identifying "hairpin turn" at their anastomosis with the anterior spinal artery.
On the posterolateral surface of the spinal cord, the radiculopial arteries form two longitudinals connections called posterior spinal arteries. They are in fact a discontinuous longitudinal system which predominantly supply the surface of the spinal cord, i.e., the white matter.
In the medullary cone, an "arterial basket" is formed between the anterior spinal artery and the posterior spinal arteries, which anastomose via the “rami cruciantes” (Fig. 3).
The blood of the spinal cord parenchyma is drained by intrinsic veins in a radial and horizontal pattern until the radial veins reach the surface of the cord. At the level of the spinal pia-mater, blood is accumulated in essentially two longitudinal collectors (extrinsic): the anterior and posterior median spinal veins (Fig. 4).
The superficial venous blood collectors drain into the epidural venous plexus through radicular veins. The transition of the midline vessel to the radicular vein forms a hairpin course, similar to the arterial configuration.
CLASSIFICATION OF SPINAL ARTERIOVENOUS LESIONS
Kim and Spetzler proposed a classification of spinal arteriovenous (AV) lesions based on anatomical and pathophysiological factors, as well as intraoperative observations and imaging characteristics, dividing them into:
Arteriovenous fistulas (AVF):
Correspond to AV lesions where there is a direct communication between an artery and a vein, without an interposed capillary network or vascular nidus. They are the most frequent type of spinal AV lesions (70%), and tend to affect older and middle-aged men (> 40 years old). They are presumably acquired and their symptoms are predominantly due to venous hypertension.
According to their location AVF are classified in:
- Extradural AVF.
- Intradural dorsal AVF.
- Intradural ventral AVF.
Arteriovenous malformations (AVM):
Correspond to AV lesions where there is a communication between an artery and a vein with an interposed vascular nidus. They are less frequent (30%), without predilection for gender and tend to affect younger people. They are presumably congenital and their symptoms are predominantly due to hemorrhage, compression, vascular steal and venous congestion.
According to their location they are classified in:
- Extradural-intradural AVM.
- Intramedullary AVM.
- Conus medullary AVM.
Types of AVF:
EXTRADURAL AVF →
Corresponds to a communication between a branch of an extradural artery and a vein of the epidural plexus. There is significant dilatation of the venous plexus, with mass effect and compression of adjacent roots and spinal cord, with subsequent venous hypertension, vascular steal and myelopathy (Fig. 5, Fig. 6) .
INTRADURAL DORSAL AVF →
Corresponds to a communication between the radicular artery and the medullary venous system, at the dural sleeve of the nerve root. It produces obstruction of the venous outflow with arterialization of the venous plexus, venous hypertension and myelopathy (Fig. 7).
INTRADURAL VENTRAL AVF →
Corresponds to a ventral lesion of the midline in the subarachnoid space, with a fistula between anterior spinal artery and a dilated venous network. It produces similar physiopathological alterations than its dorsal counterpart (Fig. 8, Fig. 9). There are 3 subtypes (A, B, C), depending on the size of the lesion.
Types of AVM:
EXTRADURAL – INTRADURAL AVM →
Also known as juvenile or metameric AVM.
INTRAMEDULLARY AVM →
Analogous to an intracranial AVM. Corresponds to an AV lesion with communication between an artery and a vein with an interposed vascular nidus, located completely in the medullary parenchyma. They present one or multiple feeders of the anterior/posterior spinal arteries (figure 9). They are subdivided into compact or diffuse types, depending on the angioarchitecture of the nidus (Fig. 12, Fig. 13).
CONUS MEDULLARY AVM →
Corresponds to a different category AVM, located in the conus medullaris, with a complex angio-architecture characterized by multiple feeders of the anterior and posterior spinal arteries, with direct AV communications, a nidus and markedly dilated veins (Fig. 14 , Fig. 15).
To facilitate the imaging diagnosis, we propose the use of a simplified diagnostic algorithm based on Kim and Spetzler's classification (Fig. 16):
STEP 1: Define the presence / absence of a vascular nidus.
- With nidus→ AVM.
- Without nidus→ AVF.
STEP 2: Evaluate the anatomical location of the lesion to obtain the diagnosis.