Type 2 Proatlantal Intersegmental Artery
Type 2 Proatlantal Intersegmental Artery: (~40%)
Corresponds to the second segmental artery
Arises from the external carotid artery
Rarely (~5%) it arises from the common carotid artery
Irrespective of their origin, the artery passes through the foramen magnum and joins the vertebral artery. If large then the ipsilateral vertebral artery is small or absent 1).
Case reports
see https://radiopaedia.org/cases/type-ii-proatlantal-artery
Whole-Brain Perfusion via Right Common Carotid Artery With Type 2 Proatlantal Intersegmental Artery 2).
A 48-year-old man with type 2 persistent primitive proatlantal intersegmental artery found incidentally on imaging. It is one of the rare persistent carotid-vertebrobasilar anastomoses in which the anomalous vessel arises from the external carotid artery and enters the skull through the foramen magnum 3)
Uchino A. Type 2 proatlantal intersegmental artery. Surg Radiol Anat. 2018 May;40(5):605. doi: 10.1007/s00276-017-1958-0. Epub 2017 Dec 8. PMID: 29222578 4).
Occurrence of a type 2 proatlantal intersegmental artery during carotid endarterectomy for symptomatic stenosis 5).
An 83-year-old man with cerebral infarctions underwent cerebral MR imaging, and head and neck MR angiography using a 1.5 T imager. MR angiography was obtained using the standard non-contrast three-dimensional time-of-flight technique.
MR angiography showed aplasia of the proximal left VA and a large anastomotic artery between the left ECA and distal left VA that passed through the foramen magnum, indicative of a type 2 PIA. This patient also had an anastomosis between the precavernous segment of the left ICA and midbasilar artery via a lateral course, indicative of a lateral-type persistent TA.
They presented the first case of type 2 PIA associated with ipsilateral lateral-type persistent TA diagnosed by MR angiography. MR angiography should be performed including the carotid bifurcation to find more frequently extracranial arterial variations, including type 2 PIAs 6).
A 60-year-old woman who presented with cerebellar ataxia, homonymous hemianopia, and aphasia. Both Doppler scan and magnetic resonance angiography (MRA) showed agenesis of both vertebral arteries, 80% stenosis of the left internal carotid artery (ICA), and an anastomotic vessel between the left external carotid artery (ECA) and the left vertebral artery (LVA) with a tight stenosis at the origin. It was thought to be a type II PA. Both lesions were successfully treated by ICA endarterectomy and common carotid artery to PA bypass. This case demonstrates the clinical significance of persistent PA in the evolution of an ischemic cerebrovascular disease 7).
Type II proatlantal intersegmental artery associated with objective pulsatile tinnitus 8).