Bow Hunter Syndrome – A Harbinger of Basilar Stroke

A 29-year-old male with no comorbidities presented with acute-onset left superior-temporal quadrantanopia and right-sided tingling sensation. His cranial CT ruled out any bleed and incidentally showed various cranio-vertebral junction (CVJ) anomalies (occipitalization of CV1, fusion of CV1 and 2, fusion of CV5 and 6, and basilar invagination). Subsequent MRI revealed T2 flair hyperintensities in the right cerebellar hemisphere and diffusion restrictions suggestive of recurrent ischemic changes. CT-angiography showed no vertebral artery (VA) occlusion. His workup for stroke in the young was essentially normal. While being managed with double antiplatelets, he presented again with episodic giddiness and right-sided weakness, which were more pronounced on turning the head to the right. Suspecting a dynamic vascular insult, a provocative digital subtraction angiography (DSA) was planned. He had a sudden onset of giddiness and quadriparesis while shifting for DSA. A swift left subclavian artery catheter angiogram showed proximal basilar occlusion [Figure 1]. Immediate mechanical thrombectomy achieved a mTICI-3 recanalization [Figure 2]. Provocative DSA of right VA (turning the head toward the left) showed no compromise in contrast flow, whereas provocation of left VA (turning the head toward the right) resulted in complete cessation of distal contrast flow into the basilar trunk. The patient was managed thereafter by cervical collar and prevention of provocative maneuvers while he was being planned for elective surgical fixation of the CVJ anomalies.Figure 1: Digital subtraction angiography (DSA) in a basilar artery stroke patient in Anteroposterior (a and c) and lateral (b and d) projections showing complete occlusion of the proximal basilar trunk (arrows in a and b), after mechanical thrombectomy resulted in complete mTICI-3 recanalization of the posterior circulation arteries. Fragmented ~ 1.5 cm clot (e) extracted by thrombectomy was sent for histopathology and was found to be a red blood cell-rich thrombus.Figure 2: Catheter angiography in left sided “bow hunter syndrome” with bilateral vertebral artery (VA) injections with head in neutral position (a–d) and provocation by cranial rotation (e–h) showing normal contrast flow into the basilar artery and distal branches without provocation and complete cessation of contrast flow distal to the left V4 segment VA on provocation (e, f). Provocative angiography from right VA (g, h) did not show any distal contrast flow compromise.Bow hunter syndrome or rotational VA insufficiency is a rare cause of dynamic VA occlusion.[1] It should be suspected in cases of giddiness with positional variability of symptoms. VA is relatively immobile from the C1-transverse process to the atlanto-occipital ligament, thus making it prone to occlusion at this site.[2] Compression may be due to osteophytes, tendinous bands, fractures, or CVJ involvement in pathologies such as achondroplasia.[3,4] Long-term treatment options include surgical fixation of the culprit CVJ anomalies causing dynamic vascular compression for V3 segment or V3-V4 junction involvement. When a relatively straighter segment with a short segment and ligamentous compression is involved, as in the V2 segment of VA, endovascular stenting can also achieve curative results.[5] Repeat catheter angiography after curative therapy with identical provocative maneuvers needs to be offered on follow-up to ensure long-term therapeutic effectiveness. Disclosures This study did not have any sponsorship. None of the authors reports any disclosures relevant to the manuscript. Abbreviations DSA = Digital Subtraction Angiography; NCCT = Non-Contrast Computed Tomography; CVJ = Cranio Vertebral Junction; mTICI = Modified Treatment in Cerebral Infarction Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.