Incidental Detection of a Posterior Inferior Cerebellar Artery (PICA)-Terminating Vertebral Artery Variant During CT Evaluation of Venous Sinus Thrombosis: A Case Report.

A 25-year-old man presented to the emergency department with a sudden alteration in consciousness, characterised by reduced responsiveness to verbal stimuli and impaired neurological status. Baseline laboratory investigations demonstrated no evidence of coagulopathy, with coagulation parameters, prothrombin time (PT), international normalized ratio (INR), activated partial thromboplastin time (aPTT), and platelet count within normal reference ranges. Non-contrast CT of the brain revealed a left temporoparietal intraparenchymal haemorrhage with a left transverse sinus thrombus. Arterial-phase CT angiography demonstrated a hypoplastic left vertebral artery (defined as a luminal diameter ≤2 mm or marked asymmetry relative to the contralateral vertebral artery) terminating as the ipsilateral posterior inferior cerebellar artery (PICA) without contribution to the basilar trunk, consistent with a PICA-terminating vertebral artery variant (PICA-VA). The right vertebral artery was dominant based on a larger calibre relative to the contralateral side and continued as the basilar artery. No posterior-circulation aneurysm or arteriovenous malformation was identified. In normal anatomy, the vertebral arteries fuse at the pontomedullary junction to form the basilar artery, with the PICA arising proximally. In this rare variant, one vertebral artery ends directly as the PICA rather than contributing to the basilar formation, an anatomic configuration that can mimic vertebral occlusion on imaging. Recognition of this pattern is important because it alters posterior circulation haemodynamics and may influence procedural planning or aneurysm risk assessment. In this patient, the PICA-terminating vertebral artery was an incidental finding during evaluation for venous sinus thrombosis. The variant did not alter management but clarified the posterior circulation anatomy and prevented misinterpretation as vertebral occlusion.