Persistent Primitive Hypoglossal Artery in a 55-Year-Old Woman with Recurrent Dizziness, Identified on Ultrasound and Computed Tomography Imaging

Introduction

Persistent primitive hypoglossal artery (PPHA) is a rare vascular anatomical variation and is the second most common persistent embryonic carotid-basilar anastomosis (after the persistent trigeminal artery), with an angiographic incidence of 0.027–0.1% and a higher prevalence in left-sided locations (65%) and female patients [1]. PPHA has 3 distinct anatomical segments [1,2]: 1) Proximal segment: originates from the posterolateral wall of the internal carotid artery (ICA) at the C1–C3 vertebral level (most commonly C1–C2); 2) Middle segment: ascends dorsomedially, passing through the hypoglossal canal to enter the posterior fossa; 3) Distal segment: connects to the caudal third of the basilar artery (BA), often continuing as the BA itself. Common associated anatomical anomalies include: hypoplastic or absent bilateral vertebral arteries (VAs) and posterior communicating arteries (PCoAs) [1].

Most PPHA cases are asymptomatic and incidentally detected during routine imaging. Symptomatic cases may present with dizziness, hypoglossal nerve palsy, subarachnoid hemorrhage (due to associated aneurysms), or cerebral infarction (from plaque rupture/embolism at the PPHA-ICA bifurcation) [1,2]. Nagarajan et al [3] reported 3 PPHA cases: a 30-year-old man with PPHA, absent septum pellucidum, and periventricular heterotopia; a 4-year-old child with PPHA and hypoplastic corpus callosum; and a 9-year-old child with PPHA and growth hormone deficiency. These cases underscore PPHA’s potential association with parenchymal and endocrine anomalies, although most adult cases present with isolated vascular findings [1,3].

Brismar et al [2] established 3 standard diagnostic criteria for PPHA: 1) an extracranial branch arising from the ICA at the C1–C3 vertebral level; 2) passage through the hypoglossal canal to enter the skull; and 3) connection to the BA, with the posterior circulation primarily supplied by the ipsilateral ICA. While current diagnosis relies mostly on magnetic resonance angiography (MRA) or computed tomography angiography (CTA) [4], descriptions of PPHA’s ultrasonographic features remain scarce, despite carotid Doppler ultrasound (CDU) and transcranial color-coded sonography (TCCS) being increasingly used as first-line head-neck artery screening tools (advantages include being affordable, radiation-free, and real-time) [5,6]. Thus, this report describes the case of a 55-year-old woman presenting with dizziness due to a PPHA identified on ultrasound (CDU and TCCS) and CTA. The novelty of this case lies in the initial diagnosis of PPHA through combined CDU and TCCS screening, followed by confirmation via CTA. It aims to highlight the ultrasonographic features of PPHA and promote the use of CDU/TCCS as a first-line screening tool.

Case Report

A 55-year-old woman presented with a 2-year history of recurrent dizziness (3–4 episodes monthly, each lasting 10–15 minutes, triggered by head turns). She had no history of hypertension, diabetes, or smoking. Physical examination revealed normal vital signs, no focal neurological deficits (including intact hypoglossal nerve function), and normal bilateral carotid pulses. The initial differential diagnoses included vestibular disorders (eg, benign paroxysmal positional vertigo), posterior circulation ischemia, and vascular anatomical anomalies (eg, PPHA, persistent trigeminal artery).

Initial CDU revealed the dilated left ICA (9.2 mm vs 5.0 mm on the right) with increased peak systolic velocity (PSV) (69 cm/s vs 58 cm/s on the right) (Figure 1A, 1B). An anomalous branch vessel was observed at the distal end of the left ICA (Figure 1A), ascending toward the skull base but not visualized further due to acoustic shadowing from the cranial bone. The bilateral extracranial VA segments were hypoplastic (1.4 mm on the left and 1.6 mm on the right) (Figure 1C, 1E) and exhibited high-resistance flow patterns (resistive index=0.75) (Figure 1D, 1F). Next, TCCS showed no intracranial VA flow and reduced bilateral posterior cerebral arteries (PCAs) PSV (right PCA: 45→22 cm/s; left PCA: 48→20 cm/s) upon left common carotid artery (CCA) compression (Figure 2A, 2B). Based on findings from CDU combined with TCCS, the presence of a left-sided PPHA was suspected, and further imaging was recommended.

Subsequent CTA of the head and neck revealed a dilated left ICA at the C1–C2 vertebral level, from which an anomalous vessel originated, traversed the hypoglossal canal (consistent with PPHA), and connected to the BA (Figure 3A, 3B) –fulfilling Brismar’s diagnostic criteria for left-sided PPHA [2]. Additionally, bilateral PCoAs were absent (Figure 3C), and the intracranial segment of the left VA was not visualized (suggestive of severe stenosis/occlusion), which aligns with common PPHA-associated vascular anomalies [1].

Finally, the patient received conservative treatment (aspirin 100 mg/day, atorvastatin 20 mg/day) and was advised to avoid sudden head turns. At 3-month follow-up, her dizziness episodes had decreased to 1 episode monthly, indicating a positive therapeutic response.

Discussion

This case offers 2 key lessons: 1) PPHA presents with characteristic ultrasonographic findings (dilated ICA with anomalous branch, hypoplastic VAs, posterior circulation dependence on ipsilateral ICA) that can be detected via CDU and TCCS; and 2) CDU/TCCS, as an accessible, radiation-free tool, can serve as a first-line screening modality for PPHA, reducing reliance on costly radiation-based angiography (CTA/MRA) for initial suspicion.

Our patient’s recurrent dizziness aligns with Vasović et al’s report of dizziness as the most common symptomatic presentation of PPHA – attributed to reduced posterior circulation reserve (due to VA hypoplasia) [1]. Unlike Nagarajan et al’s cases (which presented with seizures, developmental delay, or growth hormone deficiency) [3], our case had no non-vascular symptoms, reflecting the typical adult PPHA phenotype (asymptomatic or isolated cerebrovascular symptoms) [1].

PPHA arises from the ICA with a vascular bifurcation, which – due to anatomical and hemodynamic factors – increases the risk of atherosclerotic plaques [7]; plaque rupture or embolization here can cause simultaneous anterior-posterior circulation ischemia and rapid disease progression [8]. PPHA also often associated with intracranial aneurysms [1]. Thus, early PPHA identification is critical, as it optimizes surgical/endovascular planning and avoids iatrogenic injury or postoperative complications [9].

Reports on the ultrasonographic diagnosis of PPHA are scarce. Our patient had suspected PPHA based on findings from CDU combined with TCCS and confirmed by head and neck CTA. A review of the imaging data and the literature [1,3,10] revealed several diagnostic clues. We propose that PPHA can be suspected when the following 4 criteria are met: 1) A branch vessel originating from the C1 segment of the ICA is observed, ascending but not entering the foramen magnum; 2) The ipsilateral ICA is dilated in diameter and exhibits increased blood flow; 3) Bilateral or unilateral VAs are congenitally hypoplastic; 4) Compression of the CCA reveals that the posterior circulation is primarily supplied by the ipsilateral ICA. PPHA can be easily confused with type I persistent primitive proatlantal intersegmental artery (PPPIA), as both originate from the C1 segment of the ICA and share similar hemodynamic characteristics. The following features can help differentiate these 3 conditions: 1) Type I PPPIA originates from the ICA at the C2–C3 vertebral level, and occasionally at the C4 level, which is lower than the origin of PPHA; 2) PPHA has a longer vertical ascending segment compared to type I PPPIA; 3) PPHA enters the cranium through the hypoglossal canal, whereas type I PPPIA enters through the foramen magnum [11].

Our diagnostic pathway (CDU/TCCS→CTA) mirrors the “screening-confirmation” approach recommended by Vasović et al [1]. The CDU findings (dilated ICA, anomalous branch, VAs hypoplasia) and TCCS findings (PCAs PSV reduction on CCA compression) are consistent with the ultrasound clues proposed in recent PPHA reports [3]. CTA confirmation (fulfilling Brismar’s 1976 criteria) further validates our initial ultrasound suspicion, highlighting the utility of non-invasive imaging.

The patient’s positive response to conservative treatment (aspirin + atorvastatin) aligns with Vasović et al’s [1] recommendation for medical management in asymptomatic or mildly symptomatic PPHA cases. Unlike Nagarajan et al’s [3] pediatric cases, which required multidisciplinary care for associated anomalies, our patient had a straightforward clinical course, suggesting that adult PPHA with no concurrent anomalies has a favorable prognosis.

Conclusions

This report presents a rare congenital vascular anomaly, PPHA, in a 55-year-old woman with recurrent dizziness, and aims to raise awareness of this condition. It highlights the approach to diagnosis using ultrasound (CDU and TCCS) for initial screening and CTA for confirmation.