Background

The trigeminal arteries have their origin in the embryonic vessels that connect the cavernous portion of the developing internal carotid arteries (ICA) and the paired longitudinal neural arteries that will later form the basilar artery (BA) [1, 2]. While the trigeminal artery usually involutes after the development of the posterior communicating artery (PcoA) there are cases, for reasons still unclear, where it remains persistent [2]. The PTA is the most common persistent embryonic carotid–basilar anastomosis [1]. Prevalence varies from 0.12 to 1% in studies using magnetic resonance angiography imaging or classical angiography [3,4,5,6,7,8]. In this paper we will briefly explain what is a PTA and to what pathologies it can be associated, we will review the meaning of a PTA in a posterior circulation stroke through a clinical case and we will present a table that summarizes the PTA related strokes reported in literature.

The different variations of the PTA can be cataloged using the Saltzman classification (Fig. 1), [1, 9, 10]. In Saltzman type 1, also called fetal PTA, the PTA insertion in the BA is distal to the anterior inferior cerebellar artery (AICA) and proximal to the superior cerebellar artery (SCA) and, in some cases, the BA proximal to the insertion of the PTA may be hypoplastic and the PcoA of the same side may be absent. In the Saltzman type 2 there is usually no hypoplasia of the BA, the PTA inserts proximally to the SCA, supplying them, and the PCAs are predominantly supplied by the PcoA. In the Saltzman type 3 variant, the PTA inserts directly into one of the cerebellar arteries, without having an anastomosis with the BA. In the case of Slatzman type 3 there are 3 variants: the type 3a variant that terminates in SCA; the type 3b variant, and the the most common one, that terminates into AICA; and type 3c variant that terminates into posterior inferior cerebellar artery (PICA) [1, 2]. In one study of 4.650 patients that underwent brain MRA, the prevalence of each type using the Saltzman classification was as follows: type I, 24%; type II, 16%; type III, 60% [7].

Fig. 1
figure 1

– Schematic representation of the vertebrobasilar system, a) without PTA, b) with Saltazman type 1 PTA, showing BA hypoplasia proximal to the PTA, c) with Saltazman type 2 PTA, showing the PCAs predominantly supplied by the PcoA. BA – basilar artery, ICA – internal carotid artery, PCA – posterior cerebral artery, PcoA – posterior communicating artery, PTA – persistent trigeminal artery, VA – vertebral artery

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The PTA is linked to several pathologies, including vascular nerve compression syndromes, like trigeminal neuralgia (more prevalent in patients with PTA) [11, 12] or ophthalmoplegia due to oculomotor or abducens palsy [12,13,14]. It is also linked to hypopituitarism due to compression of the pituitary stalk [14, 15], spontaneous or traumatic intracavernous fistula [16] and brain aneurysms. Although there is no agreement that brain aneurysms are more prevalent in patients with PTA [4, 7, 17], the PTA itself is prone to aneurysms due to its bifurcation [1]. Finally, the PTA is also related to ischemic stroke, although, to our knowledge it has never been linked to TIA by vertebrobasilar insufficiency [18,19,20,21,22,23,24,25,26,27,28,29,30]. We present in Table 1 a structured summary of the PTA related stroke cases reported in literature.

Table 1 Summary description of PTA related stroke episodes found upon literature review, cases are ordered according to patient’s age at symptom onset
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Case presentation

An 82-year-old man, presented to the emergency department, on February 2018, after sudden onset of left hemiparesis and vertigo. Symptoms started during a period of greater physical effort, upon participation in a zumba class. His past medical history included transient episodes of vertigo during exercise in the previous months, an anterior circulation right hemispheric stroke in 2015, that left no sequels, and hypertension controlled with a combination of 10 mg lisinopril and 2.5 mg amlodipine. The neurologic examination revealed mild left hemiparesis with facial involvement and crural predominance, vertical nystagmus, right internuclear ophthalmoplegia, dysarthria and dysmetria on the left arm. The total National Institutes of Health Stroke Scale (NIHSS) score was 6.

The plain brain CT scan was normal and a CT angiography showed hypoplasia of both vertebral arteries, the left terminating as the PICA, while the right gave origin to the BA. The BA had a filiform aspect in its proximal two thirds, having a normal caliber in the distal remaining third, after receiving a communicating artery from the cavernous segment of the left internal carotid artery, a PTA (Fig. 2). No abrupt stop of flow was identified. Echocardiogram showed severe dilation of the left auricle, as well as mild dilation of the right auricle and a 35 mm dilation of the proximal portion of the ascending aorta. Electrocardiogram was normal and a 48 h cardiac telemetry monitoring didn’t show any periods of arrhythmia. Lipid profile showed borderline high low density lipoprotein level, at 139 mg/dL.

Fig. 2
figure 2

– Head CT scan showing the PTA, a) volume rendering technique showing PTA anastomosing the left ICA with de the terminal portion of the BA, b) arrow indicating PTA originating from the left ICA, c) arrow showing hypoplastic BA proximal to the anastomosis. IC – internal carotid artery, T – trigeminal artery, B – basilar artery, P – posterior cerebral artery

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The patient underwent treatment with recombinant tissue plasminogen activator (rt-PA) at two hours of symptom onset, this decision was based on the clinical presentation and in the absence of hemorrhage in the CT scan. Shortly after treatment the NIHSS score was 2, maintaining a slight paresis of the left leg and dysmetria on the left arm. Months later, the patient showed no neurologic sequelae.

Discussion and conclusions

PTA can be associated with many different vascular events. Patients with PTA and vertebrobasilar hypoplasia have a tendency to have a decreased vascular supply to the posterior fossa [19], this fact renders them susceptible to ischemic events. In this context, in the case of a stenosed carotid artery, a steal phenomenon can occur, and this can lead either to vertebrobasilar insufficiency or hemodynamic brain stem infarction [31]. In the case of BA occlusion however, if the occlusion is proximal to the insertion of the PTA, the PTA can have a protective effect in the distal territory [25]. In the case of an anterior circulation thrombus, the PTA can lead to migration of the thrombus to the BA, possibly causing a posterior circulation stroke [20, 24]. Finally, in BA hypoplasia, PTA also opens the possibility for thrombectomy in the posterior circulation [26, 27].

Despite all the variety of ischemic events related with PTA, thrombosis of this vessel remains a rare phenomenon, although there is a case report of PTA thrombosis related with internal carotid dissection [18].

Our patient had a congenital Saltzman type 1 PTA variant and presented with symptoms suggestive of acute brainstem infarction that partially resolved after the administration of rt-PA. The clinical manifestations are compatible with an ischemic lesion of the basis pons, causing an ataxic hemiparesis syndrome, and extending to the tegmental region, affecting the longitudinal medial fasciculus. This suggests that the most affected territory was dependent from the small perforating vessels of the BA. Furthermore, the patient was exposed to extenuating exercise when the symptoms started, this favors the possibility that the event was due to a steal phenomenon, but the fact that the patient had no great artery disease and the fact that the patient improved after rt-PA suggests that the mechanism could also have been thromboembolic. Upon literature review both mechanisms seem possible. We would also like to emphasize that the reported episodes of vertigo probably corresponded to previous transient ischemic attacks (TIA) in the same area, possibly being the first sign of vertebrobasilar insufficiency. To our knowledge this is the first case study to point out the possibility of having several transient episodes (in this case of vertigo) compatible with vertebrobasilar insufficiency as a premonitory sign of PTA related stroke.