Introduction

A persistent trigeminal artery (PTA) is the most frequent carotid-vertebrobasilar anastomosis and usually arises from the cavernous or precavernous segment of the internal carotid artery (ICA). According to its course, the PTA is classified as either lateral or medial. Its incidence on magnetic resonance (MR) angiography has recently been reported as 0.34% [20]. Although the reason is unclear, there is left-side predominance [11, 20].

We report a case of left lateral-type PTA that arises from an arterial ring/fenestration of the cavernous segment of the ICA that we examined by both MR angiography and selective catheter angiography. To our knowledge, no similar cases have been reported.

Case report

A 50-year-old Japanese woman with severe headache underwent cerebral MR imaging and MR angiography using a 3-tesla MR scanner. We observed no evidence of subarachnoid hemorrhage but found three aneurysms at the siphon of the left ICA and lateral-type left PTA. We made partial maximum-intensity projection (MIP) images of the MR angiography to see them more clearly and noted an anomalous small artery in the left cavernous sinus lateral to the cavernous segment of the ICA that formed a large arterial ring/fenestration and a lateral-type PTA arising from the posterior end of the arterial ring/fenestration (Fig. 1). Subsequent selective catheter angiography confirmed these findings (Fig. 2). The posterior communicating artery was absent, but we did visualize the anterior choroidal artery, which was hyperplastic. Three months later, we successfully treated the largest aneurysm using Guglielmi detachable coils. Figure 3 is schematic illustration of this anomaly.

Fig. 1
figure 1

Magnetic resonance angiography obtained using a 3-tesla scanner. Lateral (a), slightly superolateral (b), and inferior (c) projections of partial maximum-intensity projection images of the left ICA and its source image (d) show lateral-type PTA that arises from the cavernous segment of the ICA. The PTA shares a common trunk with the anomalous artery that connects with the carotid siphon, forming a large fenestration in the cavernous segment of the left ICA. The anterior choroidal artery is hyperplastic. There are 3 aneurysms at the carotid siphon (1 lateral-type PTA, 2 anomalous artery lateral to the normal cavernous segment, 3 common trunk of 1 and 2, 4 hyperplastic anterior choroidal artery, 5 large aneurysm, 6 and 7 small aneurysms)

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Fig. 2
figure 2

Selective catheter angiography. Lateral projection of the left internal carotid angiogram (a) and its anterosuperior left oblique 3D angiogram (b) show PTA (long arrow) and an anomalous artery arising from the common trunk with the PTA that runs anteriorly and connects with the carotid siphon to form a large fenestration (thick arrow). Two aneurysms can be seen (short arrows). There is no posterior communicating artery, but a hyperplastic anterior choroidal artery is seen (arrowhead)

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Fig. 3
figure 3

Schematic illustration of this anomaly in the lateral projection (three aneurysms were deleted) (1 lateral-type PTA, 2 anomalous artery lateral to the normal cavernous segment, 3 common trunk of 1 and 2, 4 hyperplastic anterior choroidal artery)

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Discussion

According to Padget [14], at 5 weeks’ gestation (stage 3–5 mm), there are four types of fetal anastomosis between the carotid and vertebrobasilar arteries. From caudal to cranial, these are the proatlantal intersegmental artery, hypoglossal artery, otic artery, and trigeminal artery. These arteries usually regress. When the primitive trigeminal artery persists, a PTA arises either laterally or medially, with the lateral type 10 times more frequent than the medial [13, 20]. Although the medial type is extremely rare, its recognition is nevertheless clinically very important during transsphenoidal pituitary surgery because of the risk of arterial injury [9]. Traditionally, PTA is also characterized by Saltzman’s classification [15], but we did not find the classification useful [13, 20]. Rarely, a PTA arises from the more proximal segment of the ICA, and these low-lying PTAs have been misdiagnosed as persistent otic arteries [3]. A cerebellar artery that arises directly from the ICA without connecting to the basilar artery is regarded as a PTA variant [18].

PTA or PTA variants with associated cerebral aneurysms at their origin or on their trunk are extremely rare [7, 8, 10, 22]. Rupture of such an aneurysm on the PTA might result in the formation of a PTA-cavernous sinus fistula [21]. Our patient had three aneurysms outside the PTA. True prevalence of cerebral aneurysm associated with PTA is reported as 3% [6], similar to prevalence in the general population, so cerebral aneurysm in a patient with PTA is considered coincidental [2, 13].

The occurrence of PTAs and PTA variants is frequent enough to be clinically significant and merit vigilance to avoid serious complications in surgeries and endovascular therapies [1]. Usually asymptomatic, patients with PTAs and PTA variants rarely experience cranial nerve symptoms, such as trigeminal neuralgia [17] and oculomotor nerve palsy [4].

In our patient, the most important finding was the large arterial ring/fenestration of the cavernous segment of the ICA from which the PTA arose. Fenestration of the distal ICA is most frequently seen at the supraclinoid segment, usually small and slit-like; only one case of ICA fenestration of the cavernous segment has been reported [19]. However, our patient’s duplicated segment was relatively large. Ohshiro and et al. [12] reported an adult autopsy case with lateral-type PTA from which the meningohypophyseal trunk and artery of the inferior cavernous sinus arose. During early gestation, a primitive arterial network is present that generally regresses to form the ICA. Normally, from caudal to cranial, the meningohypophyseal and inferolateral trunks and capsular artery arise from the cavernous segment of the ICA [16]. Because all three are tiny branches, they are not identified on MR angiography. We speculate that the anomalous artery of our patient was formed by persistence of the primitive anastomosis among these three arteries and that the trigeminal artery also persisted. Our patient also demonstrated an ipsilateral hyperplastic anterior choroidal artery, from which the branches of the posterior cerebral artery arose [5].

Conclusions

To our knowledge, this is the first case of PTA arising from the large arterial ring/fenestration of the cavernous segment of the ICA. Detailed knowledge of congenital vascular variations/anomalies is of great importance in managing intracranial vascular pathologies.