The persistent proatlantal artery: types and subtypes

The persistent proatlantal artery (PPA) is the most caudal of the four persistent carotid–vertebrobasilar anastomoses and is frequently misclassified because “Type I/Type II” terminology variably reflects arterial origin and/or cervical course. To synthesise embryology, imaging criteria, and clinically relevant PPA variants, and to harmonise nomenclature including Cohen’s Type II “spinal” and “occipital” subtypes. A Scale for the Assessment of Narrative Review Articles (SANRA)-guided narrative review of PubMed/MEDLINE and Google Scholar (inception to February 2025) was performed. Data extracted included origin (internal carotid artery, external carotid artery ECA, or common carotid artery), relationship to the C1 transverse foramen, vertebral artery (VA) status, occipital artery (OA) incorporation, and procedural relevance. An illustrative computed tomography angiography (CTA) index case was included. Evidence is dominated by case reports and small series. PPA is very uncommon (reported incidence ~ 0.01% in multi-slice CTA cohorts) and often accompanies ipsilateral VA hypoplasia/aplasia, sometimes providing the dominant posterior fossa supply. Course-forward interpretation distinguishes canonical Type I suboccipital pathways from Type II ECA/occipital-system pathways, including “occipital” Type II channels that bypass transverse foramina and can mimic Type I. In the index case, a 73-year-old woman had an ECA-origin Type II (occipital subtype) PPA that gave rise to the OA and continued as the extracranial VA before entering the skull via the foramen magnum. Standardised, course-based reporting, explicitly documenting origin, transverse foramen traversal, and posterior circulation dependence, reduces diagnostic ambiguity and supports safer planning for ECA interventions, carotid endarterectomy, and craniovertebral junction/skull-base surgery.