Abnormal course of the vertebral artery at the craniovertebral junction in patients with Down syndrome visualized by three-dimensional CT angiography

Abstract

In planning surgery in patients with Down syndrome with symptomatic atlantoaxial subluxation and a congenital skeletal anomaly at the CVJ, we should consider the possible presence of VA anomalies. Preoperative 3DCTA allows us to precisely identify an anomalous VA and evaluate the possible risk of intraoperative VA injury in advance.

Anatomical anomalies of the V3 segment of the vertebral artery in the Polish population

“…Under normal circumstances, these arteries disappear during the development of the vertebral artery which finally arises from fusion of primitive anastomoses between cervical intersegmental arteries. The presence of fenestration may be accidental or may be part of genetic aberrations like, e.g., Down syndrome [9,10].…”

Risk stratification of vertebral artery vulnerability during surgery for congenital atlanto-axial dislocation with or without an occipitalized atlas

“…If the primary VA fails to regress, it is associated with "fenestration." [8,9] In our study, the incidence of persistent first intersegmental artery was high (approximately 30%) and mainly occurred in patients having an AAD with the occipitalized atlas. Tokuda identified three types of VA anomalies: (a) VA turned posteromedially after exiting C2 FT and entered the spinal canal between C1-2, not passing through C1 FT (0.67%); (b) VA duplicated after leaving C2 FT with one fenestration continuing its course normally while the second entering the spinal canal between C1-2 and joining the former at the cranial side of C1 (1%); and (c) VA being normal in course but with a "low-lying" PICA emerging from its extradural portion (between atlas and axis) and entering the spinal canal from the caudal side of C1 (0.67%) or from its proximal intradural portion (at the level of foramen magnum).…”

“…Type 2 (based on variations in its course): (a) Having a normal course [ Figure 4]; (b) having a cranial entry through a congenital foramen between the occipital bone and occipitalized atlas [ Figure 5a]; and when present as (c) a persistent first intersegmental artery [ Figure 5b and c], (d) a fenestrated VA [ Figure 5d] or, (e) a low-lying posterior inferior cerebellar artery (PICA) emerging from the VA below the foramen magnum and crossing the C1-2 joint [ Figure 6a]. [8][9][10] Type 3 (based on anomalous medial deviation of its third segment) showing (a) an absence; or, (b) presence of looping of V3 segment towards the midline [ Figure 6b and c]. Type 4 [based on the type of isthmus of the axis above the loop of VA in the C-2 FT; determination of "safe zone" was done by measuring the parameter 'a' that is the vertical distance from the apex of VAG to the upper facet joint surface and parameter 'e' that is the horizontal distance from the entrance of VAG to the lateral margin of the vertebral canal [5] [ Figure 7a]: (a) When the isthmus was wide [ Figure 7b] or, (b) when the isthmus was narrow (less than or equal to 4.5 mm) and the VA was high riding [ Figure 7c; resulting in a situation where transarticular and transpedicular screw placement were extremely risky], (c) narrow but with a low-lying VA related to it or, (d) when the isthmus was wide and associated with a highly placed VA (all three variations in the anatomy of axis, therefore, leaving an adequate amount of isthmus of the axis for transarticular and transpedicular screw placement).…”

“…The anatomical variations that helped in risk stratification included the presence of a persistent first intersegmental artery, a fenestrated VA, or a low-lying PICA: [8][9][10] An anomalous medial deviation of the third segment of VA; a high-riding VA with a narrow C2 isthmus; [5] a rotational deformity or a tilt at the occipital-C1-2 level that again resulted in a medial deviation of VA; [4] and, unilateral dominance of VA. [2] These anatomical variations coexisting with CVJ anomalies are not coincidental but have a definite embryological basis. Persistent first intersegmental artery and fenestration occur in 0.67 and 1% patients without CVJ anomaly [10] but in 19 and 36.4% patients, respectively, with bony anomalies like occipitalization of atlas, Klippel Feil syndrome or os odontoideum.…”

A case of vertebral artery duplication at the level of atlas: anatomical description

“…Like in our case, arms of local duplication have origin in different embryonic vascular trunks. Such atypical development may be accidental, but may have also complex genetic basis, as such variations in the vertebral artery course are more frequently seen in patients with Down syndrome examined because of atlanto-axial subluxation [12]. To our best knowledge, there are only two cases of vertebral artery passing between the atlas and axis together with the C2 spinal nerve described in contemporary literature and verified by anatomical dissection [7,13,14].…”