Posterior Inferior Cerebellar Artery Infarction Originating at C1-2 after C1-2 Fusion

A vertebral artery (VA) injury is a serious complication that can occur during upper cervical spine surgery and lead to brain infarction, which may cause neurologic deficit or death.1, 2, 3, 15) The VA injury rate in cervical spine surgery is reportedly 0.07–1.4%7, 8, 9, 12, 14) The VA is divided into four segments where C1-2 is included in the V3 segment and occasionally shows anatomical variants and causes congenital or acquired osseous lesions.18) Computed tomography (CT) or magnetic resonance angiography (MRA) should be performed preoperatively to screen for vessel variations and prevent perioperative VA injury.

The posterior inferior cerebellar artery (PICA) originates intracranially from the first branch originating in the VA.17) The extracranial PICA, which originates from the foramen magnum, accounts for 5–20% of all PICA origins.5) Among these extracranial origins, those at the C1-2 level are even rarer, accounting for 1.1–1.3% of all PICA origins.11, 16, 18) Here, we report a case of cerebellar infarction due to C1 lateral mass screw insertion during C1-2 fusion in a patient with a PICA originating at C1-2.

This study was approved by the Institutional Review Board (IRB) of Gyeongsang National University Hospital (IRB No. 2019-09-010). Due to the retrospective design of the study, consent was neither required by the IRB nor by the study team.

A 71-year-old woman presented with a 3-year history of posterior neck pain and a tingling sensation on the bilateral hands. A physical examination revealed normal motor power and a positive Hoffman sign on the left side. Atlanto-axial instability with canal involvement was evident on C-spine plain radiography, and cord compression with right foraminal stenosis at C1-2 was visible on magnetic resonance image (MRI). CT angiography of the brain with the C-spine was taken to confirm the VA anatomy prior to the surgery (FIGURE 1). Considering the VA origin, a pars screw on right C2, a pedicle screw on left C2, and both C1 lateral mass screws were inserted. C1 laminectomy was performed for decompression of the spinal cord, and rods were fixed (FIGURE 2). On the first postoperative day, the patient showed left sixth nerve palsy and diplopia. A brain MRI revealed no significant abnormalities. Four days later, the patient's mental status deteriorated to drowsy. A follow-up diffusion and perfusion MRI demonstrated an acute infarction in the left cerebellum. The previous images were retrospectively reviewed. On the preoperative CT angiography, the left posterior inferior cerebellar artery was visible at the C1-2 level but the same was not seen on the postoperative CT angiography (FIGURE 3). The patient was treated conservatively in the intensive care unit and regained consciousness after several hours. The diplopia, left sixth nerve palsy, and dizziness gradually recovered over 2 weeks; she was then discharged.

FIGURE 1
Preoperative images. (A) C-spine plain radiography, lateral view (ADI = 5 mm, PADI = 10.4 mm). (B, C) C-spine magnetic resonance image T2 sagittal and T2 axial view showing cord compression with right foraminal stenosis on C1-2.
ADI: atlanto-dens interval, PADI: posterior atlanto-dens-interval.

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FIGURE 2
Postoperative plain radiographics. (A) Anteroposterior view and (B) Lateral view.

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FIGURE 3
Postoperative brain magnetic resonance images and computed tomography angiography images taken on postoperative day 4. (A) Diffusion-weighted image, (B) Mean transit time image showing acute infarction at the left cerebellum, and (C, D) Comparison with preoperative image (arrow). The left posterior inferior cerebellar artery is not shown (arrowhead).

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The reported incidence rates of VA injuries vary. Previous studies reported the incidence of VA injury in cervical spine surgery from 0.07–1.4%.7, 8, 9, 12, 14) Most studies reported that posterior cervical spine approaches are more prone to the risk of VA injuries than anterior approaches.7, 8, 12) Especially in posterior C1-2 instrumentation, the rates are higher than total VA injuries, reportedly between 1.3% and 8.2%.8, 10, 12, 19) The studies about vertebral artery injury incidence are summarized in TABLE 1.

TABLE 1
A summary of previous studies on vertebral artery injury incidence

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VA anomalies in the V3 segment are common in acquired disorders such as rheumatoid arthritis and in congenital disorders such as Down syndrome or Klippel-Feil syndrome.18) However, our patient did not have any acquired nor congenital disorders. The VA variations observed at the C1-2 level include persistent first intersegmental artery (FIA), fenestration of the VA above and below C1 (FEN), PICA from C1-2, and high-riding VA (HRVA) (FIGURE 4).18) FIA, in which the VA enters the spinal canal at the C1-2 intervertebral space, comprises 1.8–3.2% of all VA cases.16, 18) FEN, in which the VA is divided into C1 above and below, accounts for 0.9–1.3% of all cases. PICA originating between C1 and C2 comprises 1.1–1.3% of all extracranial PICA cases.16, 18) PICA is usually of intracranial origin, arising from the VA, but 5–20% of PICAs are of extradural origin.5) An HRVA seen in approximately 10% of all VA involves the VA loop running more medial, posterior, and cranial than normal.18)

FIGURE 4
Schemas of vertebral artery variation observed at the C1-2 level (left lateral view). (A) Persistent first intersegmental artery, (B) Fenestration of the vertebral artery above and below C1, (C) Posterior inferior cerebellar artery (white arrow) originating from the C1-2 level, and (D) High-riding vertebral artery.

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In our case, postoperative CT angiography did not reveal the left PICA. After the surgery, we compared pre- and postoperative CT angiography, and the patient's left PICA was discovered, which originated at the C1-2 level (FIGURE 4C). Although no arterial bleeding occurred during dissection or screw insertion, the PICA may have been injured or compressed by the left C1 lateral mass screw insertion (FIGURE 5).

FIGURE 5
Comparisons between preoperative and postoperative images (day 4) of computed tomography angiography. (A) The left posterior inferior cerebellar artery begins between the C1-2 and progresses cephalad towards the cerebellum in the preoperative image (white arrow). (B) The left posterior inferior cerebellar artery may be injured or compressed by the left C1 lateral mass screw (white arrow), and the artery is not seen on the postoperative image (white arrowhead).

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Other studies reported that stroke and its sequelae were observed in 12.7–25.6% of the cases after VA injury.6, 9, 13) Our patient completely recovered without any sequelae. We considered that the patient recovered by conservative treatment alone due to the following reasons: The location of the vascular injury was PICA rather than VA. If VA injury occurred, brain infarction including the brain stem would be more severe and the patient might have serious sequelae. Another reason is that the range of infarction was small, and therefore, the swelling was not severe. The patient was able to recover without further invasive treatments, such as external ventricular drainage or decompressive suboccipital craniectomy.

Previous studies showed that the use of preoperative CT angiography scans might help minimize vascular injury when determining the artery's location and path, as well as the appropriate screw trajectory.4) Prior to C1-2 fusion, preoperative CT angiography of the brain and neck should always be performed to determine the relationship between the vessel and bony structures and confirm the various VA variations.

During C1 lateral mass screw insertion, vascular injury may occur due to rare VA variations such as C1-2 origin PICA. Therefore, the patient's VA anatomy and origin of PICA should be confirmed prior to C1-2 fusion, and precise methods for screw fixation are important to prevent vessel injuries during C1-2 fusion.