"Stretched loop sign" of the vertebral artery: a predictor of vertebrobasilar insufficiency in atlantoaxial dislocation.
BACKGROUND
Vertebrobasilar territory infarction is one of the rarer presentations of CVJ anomalies. A new radiologic sign due to stretching of the short third segment of VA detected on MRA/DSA may identify patients of AAD at risk of developing VBI.


METHODS
Seven patients who presented with VBI were found to have a coexisting mobile (n = 6) or fixed (n = 1) AAD. None of these patients had the presence of any of the known risk factors for cerebrovascular disease. On identification of VBI on CT/MRI, DSA (n = 7) and MRA (n = 1) were performed to assess bilateral vertebral arteries. The course of normal VA was also studied in 5 control patients without AAD or VBI.


RESULTS
Digital subtraction angiography/MRA showed obstruction of VA at the C1 through C2 level on one side in each of these cases. The third segment of the contralateral VA showed a shortened and straighter loop termed as the stretched loop sign of the VA. On DSA, the latter manifested as (a) opening of the distal loop of the VA as it emerges from the foramen transversarium of the atlas and traverses on the dorsum of the posterior arch of atlas (n = 3), (b) shortened and stretched VA that runs laterally and posteriorly forming the proximal loop after emerging from the foramen transversarium of the axis (n = 2), or (c) both (n = 2). All patients presented with the clinical manifestations of VBI. Only 2 of these had preexisting myelopathy and long tract signs conventionally attributable to AAD.


CONCLUSIONS
Vertebrobasilar territory infarction in AAD may occur because of the obstruction of the third segment of VA. A shorter and straighter loop of the third segment of VA coexisting with an abnormal translational mobility between the atlas and the axis may be the etiopathogenetic factor.
Sawlani
Vijay
V
Department of Neuroradiology, Morriston Hospital, Swansea, SA6 6NL, UK.
Behari
Sanjay
S
Salunke
Pravin
P
Jain
Vijendra K
VK
Phadke
Rajendra V
RV
D000328:Adult; D015901:Angiography, Digital Subtraction; D001268:Atlanto-Axial Joint / Q000002:abnormalities / Q000000981:diagnostic imaging / Q000293:injuries*; D020526:Brain Stem Infarctions / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology; D015984:Causality; D002526:Cerebellar Diseases / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology; D002533:Cerebral Angiography; D005260:Female; D006801:Humans; D004204:Joint Dislocations / Q000150:complications* / Q000000981:diagnostic imaging / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D019838:Neck Injuries / Q000150:complications / Q000000981:diagnostic imaging / Q000503:physiopathology; D011237:Predictive Value of Tests; D013123:Spinal Fusion / Q000592:standards; D013124:Spinal Injuries / Q000150:complications* / Q000000981:diagnostic imaging / Q000503:physiopathology; D014057:Tomography, X-Ray Computed; D014711:Vertebral Artery / Q000002:abnormalities / Q000000981:diagnostic imaging / Q000293:injuries*; D014715:Vertebrobasilar Insufficiency / Q000175:diagnosis* / Q000209:etiology* / Q000503:physiopathology