BLOOD VESSELS

The spinal cord receives its blood supply through spinal branches coming from the vertebral artery, the thoracic vertebral artery, the dorsal branches of the intercostal arteries and lumbar arteries. These arteries enter the vertebral canal through the intervertebral foramina.

 

The vertebral artery[1] vascularizes the cervical spinal cord, the thoracic vertebral artery[2] vascularizes the first thoracic segments, the dorsal branches of the intercostal arteries[3] vascularize the rest of the thoracic spinal segments, and the lumbar arteries[4] vascularize the lumbosacral spinal cord.

 

Within the vertebral canal, each spinal branch enters the subarachnoid space to form the dorsal and a ventral spinal artery. These arteries enter the subarcahomid space and run with the dorsal and ventral roots respectively to reach the spinal cord to form an irregular network that surrounds the spinal cord. Occasionally, a dorsolateral artery may be found on each side along the dorsolateral sulcus. Branches from this network (radial arteries) penetrate the spinal cord to vascularize the white matter and the outer regions of the dorsal horn. Ventrally, the network forms the ventral spinal artery that runs longitudinally in the ventral median fissure. It extends into the cranial cavity becoming the basilar artery. Along the spinal cord, it sends off segmental vertical arteries into the ventral median fissure (the vertical arteries) to vascularize most of the gray matter.

The artery of Adamkiewicz is also known as the arteria radicularis magna. It has been described in humans as the primary supply to the lower two-thirds of the spinal cord and enters the spinal canal via an intervertebral foramen[5]. This vessel exhibits significant variability in its anatomy. It derives from a single posterior intercostal artery originating from the aorta between the thoracic vertebra number 9 and the lumbar vertebra number 5, most commonly between T9 and T12[6]

In dogs, the artery of Adamkiewicz is present in half of all the specimens, and arises from the left fifth lumbar artery[7] although the level, side and configuration are variable. In rats and mouse the artery of Adamkiewicz is also present[8]. In the cat, the artery of Adamkiewicz is highly variable although, its origin at the level of the fourth lumbar artery has been described in 80% of the cases, and from the third lumbar in 20% of cases. In most cases is left-sided[9].

In the dissection of the dog in the attached image, the Adamkiewicz artery corresponds to the fourth left ventral root artery and the fifth right ventral root artery. Due to the variability, it is necessary to perform spinal angiography in order to identify the Adamkiewicz artery in subarachnoid, subdural or spinal epidural lesions and in vascular malformations.[10].

The venous drainage is provided by venous capillaries that drain to the network of veins that surrounds the spinal cord in the subarachnoid space. A dorsal and a ventral spinal vein runs longitudinally on the dorsal and ventral aspect of the spinal cord. The ventral spinal vein may be double. The network of spinal veins drain  to a dorsal and a ventral radicular veins that run with the dorsal and ventral roots of the spinal nerves respectively.

 

The radicular veins drain to the internal vertebral venous plexus[11]. It consists of two (left and right) thin- walled valve-less vessels that extend from the skull to the caudal vertebrae, between the outer and inner layer of the spinal dura mater. Each vessel continues into the cranium as the basilar sinus (a venous sinus of the dura mater) inside the condyloid canal. In order to do so, it has to move its position from ventral, in the floor of the vertebral canal, to lateral at the level of the first cervical segments.

 

The dorsal and ventral epidural venous plexuses, together with the external venous plexus, form the Baxton plexus. The dorsal epidural is very small and is only identifiable in dissections of the first cervical segments. The internal vertebral venous plexus reaches the caudal vertebrae where it ends up joining the vertebral body or venules that are continuous with the tail. The two vessels diverge at the level of the intervertebral disc and converge over the vertebral bodies where dorsal and ventral anastomoses in between may be present. These anastomosis are located around the dorsal longitudinal ligament or in the vertebral body[12]. In dogs, the diameter of the internal vertebral venous plexus is larger at the cervical level (being the largest inside the atlas). The diameter reduces at the cervicothoracic region and remains constant until the fourth or fifth lumbar vertebrae where it decreases in size.

The internal vertebral venous plexus receives the basivertebral veins[13] and the spinal veins. Basivertebral veins are veins within the vertebral bodies that communicate with the ventral external vertebral plexus and the ventral internal vertebral plexus. Since the ventral internal vertebral plexus has no valves, the direction of venous blood flow can vary depending on pressure. It acts as a vascular "bypass" during transient increases in thoracolumbar pressure[14],[15]. It can also become a pathway for tumor metastasis.

 

At the level of the interarcuate spaces, the interspinous veins traverse the yellow ligament to enter the vertebral canal and divide to form the interarcuate branches. These join the ventral internal vertebral plexus in the cervical region and the intervertebral veins at the thoracic level. They are caudally absent at T9.

 

The intervertebral veins are located at the intervertebral foramina and connected with the internal vertebral venous plexus. The first intervertebral veins are single but most are double.

At the level of the intervertebral foramen, the spinal artery runs close to the spinal nerve in the rostral portion of the interventricular foramen and the intervertebral vein or veins are located in the caudal aspect of the intervertebral foramen. The intervertebral foramina are closed by a two layer membrane: the outer layer of the dura mater (periosteal dura), and the deep sheet of the thoracolumbar fascia. This membrane is reinforced by crossed transforaminal ligaments and ligaments that attach to the spinal nerves, to the spinal artery and to the intervertebral veins. They serve to protect the nerve roots and vessels mechanically in stretching situations. Foraminal inflammation and fibrotic adhesion may be a potential cause of radicular pain by entrapment of the nerve roots.

The anastomoses between intervertebral veins and interspinous veins form the dorsal external vertebral venous plexus. In cervical and lumbar regions, ventral anastomoses of the intervertebral veins form the ventral external vertebral venous plexus.

Not all the spinal segments receive a dorsal and a ventral root artery and vein. Some lack of radicular veins, some lack of the dorsal or ventral radicular arteries, and some few have no radi

 

[1] This arises from the subclavian artery.

[2] This arises from the costocervical trunk (branch of the subclavian artery).

[3] These arise from the thoracic aorta.

[4] These arise from the abdominal aorta.

[5] Benzon, H.T., Raja, S.N., Fishman, S.M., Liu, S.S. and Cohen, S.P. Essentials of pain medicine, 4th edition 2018.

[6] Hoehmann CL, Hitscherich K, Cuoco JA (2016) The Artery of Adamkiewicz: Vascular Anatomy, Clinical Significance and Surgical Considerations. J Cardiovasc Res 5:6

[7] Pais D, Casal D, Arantes M, Casimiro M, O’Neill JG. Spinal cord arteries in Canis familiaris and their variations: implications in experimental procedures. Braz J Morphol Sci 2007; 24: 224–228

[8] Mazensky, D.., J Radonak, J., Danko. J, Petrovova, E.  and Frankovicova, M. Anatomical study of blood supply to the spinal cord in the rabbit Spinal Cord (2011) 49, 525–528.

[9] Caulkins, E.E., Purinton, P.T. and Oliver, J.E.Jr. (1979) Arterial supply to the spinal cord of dogs and cats. Am. J. Vet. Res. 50:425-430.

[10] William P. Dillon, W., P. and Dowd, C.F., in Aminoff’s Neurology and General Medicine 5th edition 2014 and Ohaegbulam, C. and ,  Eichler, M. in Office Practice of Neurology 2nd edition 2003.

[11] It is also called spinal sinuses or vertebral sinuses.

[12] Page 714 of "Miller's anatomy of the dog" by Evans, H.E. 3rd ed.

[13] The basivertebral veins are usually paired veins. They originate in the vertebral bodies and anastomose with the internal vertebral venous and the ventral external vertebral plexuses. They may be absent in the first segments of the thoracic region. The sacral and caudal vertebrae usually have no basivertebral veins (Page 714 of  “Miller’s anatomy of the dog” by  Evans H. E. 3ª Ed).

[14] Page 713 of "Miller's anatomy of the dog" by Evans, H.E. 3rd Ed.).

[15] Page 34 of "Imaging studies of the canine cervical vertebral venous plexus" by Gómez Jaramillo, M. A. Thesis dissertation 2005.