The most common residual manifestation of persistent carotid-vertebrobasilar anastomosis is persistent trigeminal artery (PTA), with a prevalence rate of approximately 0.2% (0.1-0.6%) [19]. Salas et al. [28] classified PTAs into the medial (sphenoidal) and lateral (petrosal) types based on their course on angiography. Among aneurysms associated with PTA, those occurring at the trunk of the medial-type PTA are rare [2,11,31].

Trigeminal neuralgia is an uncommon clinical presentation among aneurysms. Four following mechanisms for trigeminal neuralgia associated with an aneurysm have been reported : direct compression of the trigeminal nerve, indirect trigeminal nerve distortion, cavernous sinus compression, and third nerve compression (existence of sensory fibers with a trigeminal origin) [26]. We present a unique case of an aneurysm located at the trunk of the medial-type PTA associated with facial pain. We also discuss the probable pathomechanisms of facial pain.

In our institution, case reports are exempt from the informed consent process; therefore, a consent form is not required. This study was reviewed and approved by the Institutional Review Board (IRB) under the exemption from the informed consent process.

Padget described the presence of four channels between the carotid and vertebrobasilar arteries during embryonic development, which from the cranial to caudal, the trigeminal, otic, hypoglossal, and proatlantal intersegmental arteries [23]. These anastomoses, named based on their associated anatomy, exist in early fetal life (4- to 5-mm embryonic stage) [18]. The PTA is the most common and largest of the persistent fetal carotid-vertebrobasilar arteries.

The PTA exhibits variations, initially categorized by Saltzman based on the posterior circulation configuration and proximal vertebrobasilar system contribution [4,29]. In this case report, the patient’s condition corresponded with Saltzman type I, characterized by the absence of bilateral PComAs. The PTA supplies the BA, posterior cerebral arteries, and superior cerebellar arteries (SCAs). The BA segment proximal to the PTA insertion may be hypoplastic. When considering treatment alternatives for the lesion associated with Saltzman type I PTA, sacrificing the PTA is not recommended because the blood flow from the ICA to the PTA is essential for maintaining posterior circulation. In Saltzman type II, the PTA joins the BA below the SCA origin, mainly supplying the SCA territory. In Saltzman type III, the PTA terminates as the cerebellar artery.

Salas et al. [28] described two PTA types (lateral or petrous and medial or sphenoidal) based on their relationship with the abducens nerve. The medial-type reflects the direct perforation of the central portion of the dorsum sellae and forms an anastomosis with the BA. The lateral-type courses along the lateral portion of the dorsum sellae, turns toward the center, and forms an anastomosis with the BA [31,32]. The medial-type is rare, comprising approximately 10% PTAs [4]. Furthermore, the Salas type has implications in neurosurgical procedures. Medial-type PTAs associated with a pituitary adenoma have been reported [1,16,24]. Failure to recognize such anomalous vessels within the sella may lead to major complications during transsphenoidal surgery [12]. Ekinci et al. [8] reported a case of hyperprolactinemia caused by a medial-type PTA compressing the pituitary stalk. As the lateral-type PTA runs close to Meckel’s cave, a risk of hemorrhagic complications exists during a percutaneous Gasserian ganglion procedure for treating trigeminal neuralgia in patients with lateral-type PTA [20,34]. The incidence of in situ thrombosis-associated infarction in lateral-type PTA is higher than in the medial type, as brainstem perforators often arise from the PTA with lateral cisternal courses [33].

The anatomical characteristics and prevalence of PTA have been analyzed [4,18,22,28]. However, only a few PTA aneurysm cases have been reported, and their actual prevalence is controversial. Initial studies report that 14% patients with PTA may have aneurysms [9]. Contrastingly, studies focusing on a series of patients selected using an unbiased method, rather than published case reports, indicate that the prevalence rate of PTA aneurysm is 3-4%, which is not higher than that in the general population [22]. The medial-type PTA aneurysm is only observed in one of 40 cases according to a review [7]. Furthermore, the incidence rate of ruptured PTA aneurysms was high at 50%, with 20 ruptured aneurysms, nine (45%) of which presented with subarachnoid hemorrhage. Unruptured PTA aneurysms are rare (21%), and PTA aneurysms at the trunk are uncommon. However, these rates may be overestimated because of unreported unruptured asymptomatic PTA aneurysms. Kai et al. [11] reported 18, 12, and three PTA aneurysms detected at the ICA-PTA junction, PTA trunk, and PTA-BA junction, respectively. The case described herein with an aneurysm at the medial-type PTA trunk is the third reported occurrence at this location [2,32]. To the best of our knowledge, this is the first case of treating an aneurysm arising from the medial-type PTA trunk. Previous cases were found incidentally, and patients were observed closely without surgery or endovascular treatment.

Diana et al. [7] recommended that the best alternative for symptomatic patients with unruptured PTA may be parent-vessel occlusion. However, the patient in this case has Saltzman type I PTA. Thus, PTA preservation should be considered when selecting treatment strategy. Cases of aneurysms at the PTA trunk were successfully treated with simple coil embolization, with symptom amelioration [14,35]. In the present case, a simple coil embolization procedure might be adequate as the narrow neck of the aneurysm was completely riding on the PTA. For wide-neck aneurysms associated with PTA in Saltzman type I, stent-assisted coil embolization, involving stent deployment in the PTA to preserve the parent artery would be appropriate [21,27]. Flow diverter placement can be an alternative strategy if sacrifice of PTA is challenging.

Cranial nerve palsy, particularly involving the abducens nerve, is the most common symptom in patients with unruptured PTA aneurysms [14]. The presence of localized headache or facial is typically associated with aneurysms compressing the trigeminal nerve, and these are commonly lateral-type PTAs [5,14,17]. Considering the anatomical features and the postoperative T2-weighted MR imaging results of our patient, the medial-type PTA was unlikely to cause cranial nerve compression (Fig. 3C and Fig. 3D) [6,12].

In this case, the most plausible cause of facial pain may have been dura mater irritation due to aneurysm pulsation. The C1, C2, and C3 spinal nerves innervate the dura mater in the posterior cranial fossa, along with intradural structures such as the arteries [30]. The stimulation of the posterior fossa dura, on the clivus in this case, can usually cause pain in the posterior neck region [13]. However sensory input from the C1 spinal nerve may project to the trigeminal caudal nucleus rather than terminating in the dorsal horns of the spinal cord [3,15]. C1 stimulation is known to result in periorbital and frontal pain [10]. Cerebral aneurysms typically originate from the major cerebral arteries that contain pain nerve fibers, predominantly from the trigeminal nerve (mainly the ophthalmic division, V1) [13,30]. Pain caused by the intracranial artery stimulation can be referred to the ipsilateral temporal, retroorbital, and frontal regions. The pulsatile motion of the aneurysm may also contribute to pain [13]. Regardless of the cause, symptom improvement after endovascular treatment indicates that facial pain may have been relieved by the resolution of irritation, possibly due to the high-velocity pulsatile f low of the aneurysm [25]. However, other contributing factors, such as migraine, could not be ruled out.

We present a rare case of an aneurysm located at the medial-type PTA trunk associated with facial pain. This is the first report involving treatment of an aneurysm in this specific location. The successful endovascular treatment highlights the importance of accurate vascular anatomy evaluation and provides insights into individualized treatment strategies for PTA aneurysms. Significant symptom improvement indicates a possible association between medial-type PTA aneurysms and facial pain. Further studies are necessary to understand the pathophysiology of symptoms associated with PTA aneurysms and optimize treatment protocols to improve outcomes in similar rare presentations.