Interventional Radiology: Presurgical Selective Angiographic Embolization (SAE) in Hypervascular Cervical Spine Tumours

The spinal cord and dura mater have a united and functionally indissociable vascularization. Characteristic of the intramedullary vessels of the spinal cord is to maintain their embryonal metameric disposition, which occasionally disappears in the arterial and venous extramedullary vessels.

The vascular structures feeding the rachis and spinal cord was first described by Adamkiewicz, Corbin, Crock and Lazorthes. There are however significant differences between vascularization at cervical level and vascularization in other portions of the rachis, where the metameric disposition is more evident. In the cervical region, the ascending branches of the right and left subclavian arteries feed the vertebro-medullary region, from where the inferior thyroid and ascending cervical, vertebral and deep cervical arteries take their origin.

Below are listed the three cervical axes:

Anterior or prevertebral, arising from the inferior thyroid and ascending cervical arteries (vertebral body and vertebral arch)
Median or latero-vertebral, arising from the vertebral artery (anterior and posterior spinal arteries)
Posterior, arising from the deep cervical artery (anterior and posterior spinal arteries)

The three axes anastomose with each other through horizontal intra-rachideal or paravertebral branches that provide blood supply to the vertebrae. At cervical level, the spinal axis receives most of the arterial vessels.

At high cervical level, up to C3, there are no anterior radiculomedullary arteries, and two anastomosing spinal arteries, arising from the vertebral ones, feed the anterior spinal axis.

At medium-low cervical level, the anterior axis is supplied blood by 2–4 anterior radiculomedullary arteries, randomly originating either on the right or on the left side from the vertebral or deep cervical arteries.

Two main radiculomedullary arteries are often present, one originating from the vertebral artery at the level of the foramen of conjugation (C5-C6 or C4-C5) and the other arising from the deep cervical artery and entering the spinal canal through the C7-T1 foramen. The anterior radiculomedullary arteries enter the spinal canal following the nervous root course.

Blood supply is provided to the posterior spinal axes by 4–6 slender posterior radiculomedullary arteries, arising from the vertebral artery, which runs between C3-C6. These small arteries penetrate into the spinal canal through the conjugation foramen, following the radicular course.

4.1.2 Anatomy of the Anterior Spinal Artery (ASA) at Cervical Level

The anterior spinal artery (ASA) course completely follows the median line of the spinal cord (Fig. 4.1).

Fig. 4.1

Anterior spinal artery (ASA) (A) AP and (B) LL views of right vertebral artery angiography. ASA follows the median line of the spinal cord (arrows), arising from branches of the vertebral artery

It arises from two branches of the vertebral arteries in the superior cervical region, a little behind the origin of the basilar trunk. Both branches descend anteriorly to the bulb and unite forming the descending, median and anterior spinal trunks or the anterior spinal artery (ASA). The latter runs along the median anterior fissure, usually ending at the level of the fifth pair of the cervical nerves. At this level, 6–10 anterior radicular arteries, each of them feeding one descending and one ascending branch, form the anterior spinal trunk.

4.1.3 Anatomy of the Cervical Posterior Spinal Arteries

There are two cervical posterior spinal arteries, one located on the left-hand and the other on the right-hand side. They originate from the vertebral arteries and run posteriorly to the bulb and spinal cord, reaching the lateral aspect of the median posterior sulcus. Along their descending course, a variable number of posterior radicular arteries (10–23) reinforce them. Each spinal segment of the cervicodorsal region of the spinal cord averagely receives one or two tributaries.

4.1.4 Radicular Arteries or Lateral Spinal Arteries at Cervical Level

Even though of variable origin, most of the radicular arteries arise from the arteries running along the spinal roots to reach the vertebral canal. With segmental course, in the neck, they originate from the vertebral and cervical ascending arteries.

4.2 Diagnostic Angiography of Spinal Cord: Technique

Diagnostic angiography prior to SAE is necessary for the following purposes:

(a)

To accurately evaluate the pathological circle
(b)

To identify possible presence of arteries ending in the spinal cord, which are not eligible for SAE (AKA, ASA, ASPL)
(c)

For a safe embolization, to obtain stable selective catheterization, prior to selective micro-catheterization

We routinely employ 4 F introducers, with the exception of presurgical embolization of the vertebral arteries, where 6 F catheters are necessary. All diagnostic angiographic procedures of the vertebro-medullary tracts are performed using 4 F catheters (Glidecath Terumo^®, Tokyo, Japan o Tempo Aqua Codman^®, J&J, MA, USA).

Catheters with “curve” distal extremities are preferably used, because they guarantee a more stable catheterization, independently of vascular site and anatomical features of the region of interest. We use a curve catheter type “vertebral” for the study of the cervical district (vertebral, thyrocervical and costocervical arteries).

In case of cervical lesions, the vertebral arteries are examined at angiography on the two orthogonal planes. To study the vertebral arteries is necessary to identify possible feeders of the lesion, as well as presence of medullary links or anastomoses with regional arteries (ascending and deep cervical arteries). The study of thyrocervical and costocervical trunks usually necessitates use of the anteroposterior projections alone. The latero-lateral projections are fundamental for lesions of the inferior cervical tract (C5-C7), to distinguish the pathologic circle of origin of the thyrocervical trunk from the normal circle of the thyroid. In case of presurgical embolization of a vertebral artery, a bilateral examination of the internal carotid arteries is necessary, to identify possible presence of carotid-vertebral compensatory vessels at the level of the vertebral artery to be treated.

To summarize, diagnostic angiography must include the study of the following districts:

Vertebral arteries
Thyrocervical trunks
Costocervical trunks
Internal carotid artery (only in case of presurgical vertebral artery embolization)
External carotid, bilaterally (lesions affecting C1-C2)

4.2.1 Technical Considerations on Super-Selective Catheterization

Catheterization is optimal if performed as super-selectively as possible within the arteries feeding the lesion of interest. Super-selective catheterization is carried out with 4 F catheters and coaxial catheterization technique (micro-guide, micro-catheter, carrier catheter). In our experience, we routinely use micro-catheters (Renegade^®18 HI-FLO™) and micro-guides (Transcend EX .014; Stryker, USA). Both devices guarantee accurate navigation through vessels, albeit mobile and tortuous. Remodelling of micro-guide tip is often necessary to adapt it to the variable course of the arteries supplying blood to the lesion. The micro-catheters employed in our experience had a straight tip, and no remodelling was necessary. Road mapping provided by the carrier catheter is fundamental. Diagnostic angiography with 4 F catheters is necessary prior to injection of embolic agent and is performed through the micro-catheter. The injection is carried out at high pressure and with small syringes (3 ml). The preliminary angiography provides important morphological and haemodynamic information, since it allows:

Visualization of the pathological circle
Exclusion with reasonable certainty of presence of vessels ending in the spinal cord

Another advantage offered by injecting at high pressure through the micro-catheter is the visualization of possible metameric anastomoses, which in turn may help diffuse embolic agent to medullary feeders originating from the adjacent metameric levels.

4.2.2 Embolic Agents and Techniques

Embolic agents now available for SAE of tumours of the spine are listed below:

Particles
Acrylic glue (Glubran 2)
Coils

4.2.2.1 Micro-particles

Particles or micro-particles are the most widely used material for embolization. They are of two different types:

Stable
Absorbable

Stable particles are non-absorbable tris-acryl gelatin microspheres, with calibre ranging from 50 to 1000 μ. In our experience, we employed Embosphere^® Biosphere Medical, Roissy France, and Embozene^® CeloNova BioSciences, San Antonio, Texas, USA.

Due to their flexibility, stable particles can be used for vessels with calibre inferior to their diameter. Stable particles do not significantly aggregate within the proximal tract of the main vessel. The particles mainly used in our experience ranged in diameter from 250 to 700 μ.

Stable particles are chosen for the following reasons: