Effect of coil packing proximal to the dilated segment on postoperative medullary infarction and prognosis following internal trapping for ruptured vertebral artery dissection

Abstract

Introduction: Medullary infarction is an important complication of internal trapping for vertebral artery dissection. This study investigated risk factors for medullary infarction following internal trapping of ruptured vertebral artery dissection.

Methods: We retrospectively studied 26 patients with ruptured vertebral artery dissection who underwent endovascular treatment and postoperative magnetic resonance imaging between April 2001 and March 2013. Clinical and radiological findings were analyzed to identify factors associated with postoperative medullary infarction.

Results: Ten of the 26 patients (38%) showed postoperative lateral medullary infarction on magnetic resonance imaging. Multivariate logistic regression analysis revealed that medullary infarction was independently associated with poor clinical outcome (odds ratio (OR) 17.01; 95% confidence interval (CI) 1.68-436.81; p=0.032). Univariate analysis identified vertebral artery dissection on the right side and longer length of the entire trapped area as risk factors for postoperative medullary infarction. When the trapped area was divided into three segments (dilated, distal, and proximal segments), proximal segment length, but not dilated segment length, was significantly associated with medullary infarction (OR 1.55 for a 1-mm increase in proximal segment length; 95% CI 1.15-2.63; p=0.027). Receiver operating characteristic analysis showed that proximal segment length offered a good predictor of the risk of postoperative medullary infarction, with a cut-off value of 5.8 mm (sensitivity 100%; specificity 82.3%).

Conclusions: Longer length of the trapped area, specifically the segment proximal to the dilated portion, is associated with a higher incidence of medullary infarction following internal trapping, indicating that this complication may be avoidable.

Keywords: Vertebral artery dissection; internal trapping; medullary infarction; subarachnoid hemorrhage.

Figure 1.

Schema of the vertebrobasilar artery following internal trapping for VAD, which is located proximal to the origin of the PICA. Bidirectional arrow A+B+C indicates the length of the entire trapped area. Bidirectional arrow A indicates the length of the dilated segment of the VAD. Bidirectional arrow B indicates the length of the segment distal to the dilated portion. Bidirectional arrow C indicates the length of the segment proximal to the dilated portion. Bidirectional arrow D indicates the length from the distal end of the trapped area to the union of the VAs. Bidirectional arrow E indicates the length from the proximal end of the trapped area to the lower edge of the foramen magnum (arrow). AICA, anterior inferior cerebellar artery; ASA, anterior spinal artery; BA, basilar artery.

Figure 2.

Proximal segment length according to infarction and non-infarction groups and the receiver operating characteristic curve. (a) Mean length of the proximal segment was significantly longer in the infarction group (9.9±4.1 mm) than in the non-infarction group (2.8.±3.7 mm; p = 0.001). (b) Receiver operating characteristic curve of proximal segment length in patients with and without medullary infarction. The cutoff point indicates that the threshold at the proximal segment length can predict medullary infarction with optimal sensitivity and specificity.

Figure 3.

Images of the representative case. (a) Preoperative right vertebral angiogram shows pearl-and-string sign in the intracranial VA and absence of an ipsilateral PICA. The length of the dilated segment (bidirectional arrow a) is 13.0 mm. Postoperative right (b) and left (c) vertebral angiograms show complete obliteration of the affected segment. The distance to union of the VAs (bidirectional arrow d) is 13.1 mm. (d) Radiograph in working projection shows the shape of the coil mass. Lengths of the entire trapped area (bidirectional arrow a+b+c), distal segment (bidirectional arrow b), and proximal segment (bidirectional arrow c) are 30.1 mm, 3.3 mm, and 13.8 mm, respectively. (e) Lateral radiograph shows the positional relationship of the coil mass and foramen magnum (arrow). The length to the foramen magnum is 2.8 mm (e). (f) Diffusion-weighted image from the day after coil embolization shows right lateral medullary infarction.

Figure 4.

Schema of perforators arising from the vertebrobasilar artery as viewed from the front. The lateral area of the medulla is perfused by perforators from the PICA arising from the intracranial VA, and by perforators from the proximal VA (A: ellipse). The medial area of the medulla is perfused by perforators arising from the vertebrobasilar artery at approximately 14 mm proximal and 16 mm distal from the union of the vertebral arteries (B: circle). AICA, anterior inferior cerebellar artery; ASA, anterior spinal artery; BA, basilar artery.