Persistent primitive trigeminal artery: An unusual cause of trigeminal neuralgia

A 55-year-old female patient who presented with a 10-year history of left hemiface pain 8 out of 10 in the visual analogue scale. The patient attended multiple physicians who prescribed carbamazepine and nonsteroidal anti-inflammatory drugs (NSAIDs) with no improvement. Due to this condition, a magnetic resonance imaging [MRI] was performed. After the MRI, NSAIDs such as celecoxib were prescribed to control neuralgia.

In the MRI examination, a vascular structure is visualized that originates from the basilar artery and goes to the left and anterior side, forming a loop where it contacts directly with the trigeminal nerve on the left side and anastomoses with the cavernous segment of the left internal carotid artery, compatible with a persistent primitive trigeminal artery [PPTA].

In a parasagittal view, the Greek letter Tau sign can be demonstrated, which is represented by the combination of the vertical and horizontal segments of the internal carotid artery [ICA] and the proximal portion of the trigeminal artery.

The trigeminal artery is the largest of the fetal carotid-basilar anastomotic arteries that connects the cavernous portions of the developing internal carotid arteries with the paired longitudinal neural arteries that later form the basilar artery, and it persists for the longest embryonic period, usually being obliterated by the 11.5 to 14 mm embryonic stage. Its incidence is reported in 0.1 to 0.7% in adults [1,2].

PPTA is classified into the lateral or medial subtype. In the lateral subtype, the PPTA follows a posterolateral course associated with the trigeminal nerve roots and neural structures. In the medial subtype, the PPTA courses posteromedially from its origin with an intra-sellar or trans-hypophyseal course. Also, PPTA can play many roles in vascular lesions, including intracranial aneurysms, brain arteriovenous malformations, trigeminal artery-cavernous fistulas, Moyamoya disease, and large vessel occlusion. PPTA is usually an incidental finding without clinical importance; however, this could be associated with cerebrovascular disease and vascular nerve compression syndromes. Studies have revealed that patients with trigeminal neuralgia have a frequency of 2.2% of PPTA, exhibiting direct contact to the trigeminal nerve. Due to its clinical importance, an understanding of the anatomical and angiographic features of the PPTA is important in the evaluation [2,3].

Diagnosis of PPTA is made with MRI, angiography or contrast material-enhanced computed tomographic angiography [4]. Tau sign can be seen on sagittal MRI; the vertical limb and anterior horizontal limbs of Tau are formed by the ICA and the posterior limb is formed by the proximal portion of PPTA [5].

Treatment of PPTA requires a thorough knowledge of the underlying PPTA anatomy and classification. Treatment in Saltzman type I PPTA should not be realized because this might result in infarction of the posterior circulation, however, type II PPTA could be occluded. Therapeutic techniques such as extracranial artery-ICA bypass, surgical packing of the cavernous sinus, carotid artery ligation and clipping of the aneurysm of the PTA can be performed. Also, endovascular treatment may be performed with coils. Parent vessel occlusion might be the best option also in symptomatic patients with unruptured PTA, while a conservative approach might be the best choice in asymptomatic patients in Saltzman type II and III [6].

Neurological symptoms could be a sign of PPTA. MRI could be an excellent technique to evaluate patients with PPTA. Awareness of PTA could lead to early diagnosis.

Written informed patient consent for publication has been obtained.