Persistent trigeminal artery (PTA) associated with a cavernous carotid aneurysm.

Posted By Jeremy Lam
Persistent trigeminal artery (PTA) associated with a cavernous carotid aneurysm.

Gender, Age

Female, 71

Diagnosis

Persistent trigeminal artery (PTA) associated with a cavernous carotid aneurysm.

History

A 71 year-old woman of Chinese origin presented with symptoms of transient bilateral up-per visual field defects. The physical examination was unremarkable. Her symptoms were initially attributed to amaurosis fugax or a transient ischemic attack.

Findings

Magnetic Resonance Image (MRI) of the brain shows no evidence of acute infarct. Time-of-Flight Magnetic Resonance Angiography (TOF-MRA) shows the presence of a large wide-necked saccular aneurysm arising from the cavernous segment of the right internal carotid artery (ICA). It measures approximately 1.3 x 1.2 x 0.9 cm causing expansion of the right cavernous sinus with mass effect on the adjacent pituitary gland. Computed Tomography Angiogram of the Circle of Willis (CTA COW) shows the presence of a persistent right trigeminal artery arising just proximal to the superomedially directed right cavernous ICA aneurysm. There are persistent fetal origins of the bilateral posterior cerebral arteries (PCAs) whilst the bilateral vertebral arteries end as the posterior inferior cerebellar arteries (PICA). The basilar artery proximal to the carotid-vertebrobasilar anastomosis is hypoplastic and hence the bilateral superior cerebellar arteries were supplied by the PTA. This corresponds to a Saltzman type II PTA. As part of the pre-treatment evaluation, a catheter angiogram was performed. The case was subsequently discussed at the multi-disciplinary meeting. There were potential risks for endovascular treatment with coil embolization due to the considerable size of the aneurysm. Endovascular stenting was considered with placement of a suitable size flow-diversion stent across the aneurysm although there were potential risks for inadvertent occlusion of the PTA at its origin due to its close proximity to the cavernous ICA aneurysm. The potential treatment options of surgical clipping and endovascular treatment were dis-cussed with the patient. The decision was eventually made for conservative management and close monitoring. The patient remained asymptomatic for more than 2 years of follow-up in the outpatient clinic.

Discussion

There are four persistent fetal anastomoses between the carotid and vertebrobasilar circulations. These primitive anastomoses represent non-obliterated remnants of the pre-segmental dorsal arteries which comprise the persistent primitive trigeminal (PTA), persistent hypoglossal (PHA), persistent otic (acoustic) artery (POA), and proatlantal intersegment arteries (PIA). The four primitive carotid-vertebrobasilar anastomoses occasionally persist into the adult period and may be detected incidentally. In the early embryonic stage, the blood supply to the hindbrain is via the four carotid-vertebrobasilar anastomoses. The primitive carotid-vertebrobasilar anastomoses then regress within a week as the posterior communicating and vertebrobasilar arteries begin to develop. Rarely, there is failure of regression and the trigeminal artery is not obliterated in the embryonic stage and persists into adulthood. The PTA is the most common of the four carotid-vertebrobasilar anastomoses with a prevalence of 0.1-0.6%, and represents up to 85% of the persistent embryological anastomoses. It originates from the ICA distal to its exit from the carotid canal and forms an anastomosis with the basilar artery. The basilar artery caudal to the anastomosis is usually diminutive. The persistent hypoglossal artery (PHA) is the second most common carotid-vertebrobasilar arterial anastomosis with a prevalence of 0.02%–0.10%. The PHA usually originates from the cervical ICA distal to the carotid bifurcation between C1 and C3, and it enters the hypoglossal canal before anastomosing with the basilar artery. The PTA may be classified into the lateral or medial subtype, both of which are equally common. In the lateral subtype, the PTA follows a posterolateral course associated with the trigeminal nerve roots and neural structures. In the medial subtype, the PTA courses posteromedially from its origin with an intra-sellar or trans-hypophyseal course. In such cases, the PTA is in close proximity to the pituitary gland with mass effect on its stalk which may result in hypopituitarism. The PTA may also be classified according to the Saltzman classification system which is based on the configuration of the ipsilateral posterior cerebral artery (PCA). In Saltzman type 1, the PTA supplies the entire vertebrobasilar system cranial to the anastomosis. The posterior communicating artery is either absent or poorly opacified. In Saltzman type 2, the PTA joins the basilar artery caudal to the origins of the superior cerebellar arteries, and blood supply to the posterior circulation is predominantly via the posterior communicating arteries rather than via the PTA as in Saltzman type 1. As in our case, the radiological diagnosis of PTA is made on MRA, CTA and conventional cerebral angiography. On all three imaging modalities, the PTA is shown as an anomalous vessel arising from the posterior aspect of the ICA, coursing posteriorly towards the basilar artery. The configuration of the h

Pearls

PTA is the most common of the persistent carotid-vertebrobasilar anastomosis. While most cases are incidental, rarely, patients may present with symptoms of neurovascular conflict, cranial nerve compression, PHaCE syndrome, cerebral aneurysm or posterior circulation stroke, hence, it is imperative to promptly recognize the imaging features of PTA.

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