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. 2009 Feb 26;2009:bcr07.2008.0486. doi: 10.1136/bcr.07.2008.0486

Ultrasound findings of bilateral hypoplasia of the vertebral arteries associated with a persistent carotid-hypoglossal artery

Annette Janzen 1, Christine Robert Steinhuber 2, Ulrich Robert Bogdahn 1, Gerhard Robert Schuierer 2, Felix Schlachetzki 1
PMCID: PMC3029923  PMID: 21686784

Abstract

We present a 31-year-old female who was admitted to our neurology department for vertigo, partial left-sided hemihypesthesia and nuchal headache of subacute onset. Colour-duplex ultrasound disclosed bilateral low flow with a high resistance flow pattern in both vertebral arteries in the V2 segments, while the basilar artery had normal flow. CT angiography and MRI ruled out any ischaemic cerebral infarct and disclosed a persistent hypoglossal artery (PHA) originating from the left internal carotid artery (ICA). The patient was eventually treated for cervicobrachialgia. Persistent carotid-basilar anastomosis such as PHA may account for an atypical stroke pattern in carotid disease, aneurysms and arterovenous malformations. In retrospect, PHA is amendable to colour-Duplex investigation due to an abnormal ICA flow and a discrepancy between the vertebral and basilar flow patterns. Ultrasound investigation of the vertebrobasilar system remains a challenge as variants appear frequently; hypoplasia of the vertebral arteries should thus be confirmed using CT or MR angiography.

BACKGROUND

Hypoplasia of the vertebral artery (VA) is normally associated with a dominant contralateral VA or posterior cerebral arteries arising directly from the posterior communicating artery. Due to the high resistance flow profile on routine ultrasound examination, vertebral hypoplasia is an important differential diagnosis to distal VA occlusion or dissection. We present a case with extreme bilateral VA hypoplasia with normal flow in the basilar artery due to a persistent carotid-hypoglossal artery.

CASE PRESENTATION

A 31-year-old female was admitted to our department because of a sudden onset of vertigo, nausea and left-sided pain of the neck suggestive of VA dissection. Additionally, she developed paraesthesia of the left face, arm and leg. Her medical and ENT examinations were normal. Neurological examination only showed paraesthesia in the area of the second and third branches of the trigeminal nerve.

INVESTIGATIONS

To exclude a dissection of the VAs, extra- and transcranial colour-coded duplex sonography (ECCS and TCCS) was performed using a colour duplex system (Sonoline Elegra, Siemens Medical Systems, Erlangen, Germany) equipped with a linear and phased array transducer (L7.5, PL2.5). For better grey scale differentiation, tissue harmonic imaging sequences were used to measure the lumen diameter of the VAs. The lumen diameter was 0.1 cm in the left and 0.22 cm in the right VA in the intervertebral segment. Flow velocity in the left VA was considerably decreased and flow resistance was increased. The peak flow velocity in the right VA was 30 cm/s and resistance index (RI) was 0.86, while peak flow velocity in the left VA was 12 cm/s and RI was 1. Surprisingly, transnuchal colour-coded duplex sonography showed a normofrequent signal in the intradural segment of the left VA. Both carotid arteries were initially read to be normal. ECCS identified the additional ICA bifurcation with PHA and, in retrospect, detected a more pronounced area of flow separation in the common carotid artery bifurcation as compared to the right side. All major ultrasound findings are shown in fig 1.

Figure 1.

Figure 1

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Sonographic findings of a persistent hypoglossal artery (PHA) with bilateral hypoplasia of the vertebral artery. (A) Right vertebral artery with resistance index (RI) of 0.75 and lumen diameter of 0.21 cm. (B) Left vertebral artery with RI of 1 and lumen diameter of 0.09 cm. (C) Origin of the PHA from the left internal carotid artery. (D) Transnuchal sonography of the PHA. (E) Flow in the internal carotid artery distal to the PHA and (F) flow in the PHA at its origin, which is typically lower in the posterior circulation.

Computed tomography with angiography was performed to rule out VA dissection or occlusion and revealed a PHA arising from the left ICA and running through an enlarged hypoglossal canal to the basilar artery. The left VA was more hypoplastic than the right VA and both ended in the posterior inferior cerebellar arteries. The following day, cerebral ischaemia and dissection of the VAs were excluded by MR imaging including diffusion weighted imaging, two-dimensional time of flight angiography and axial images of the VAs. CT and MRI results are shown in fig 2.

Figure 2.

Figure 2

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Computed tomography angiography (CTA) and magnetic resonance angiogram (MRA). (A) Sagittal reconstruction of CTA source data showing the carotid bifurcation and the PHA arising from the internal carotid artery (arrow). (B) Source image from CTA showing an enlarged anterior condyloid foramen on the left side with the PHA (arrow). Note both dot-like VAs below. (C) Time-of-flight MR angiography (anteroposterior maximum intensity projection) showing the circle of Willis with absence of posterior communicating arteries, the VAs ending in the posterior inferior cerebellar arteries and the PHA continuing into the basilar artery. (D) Contrast-enhanced MRA revealing the origin of the PHA in the ICA and the extreme hypoplasia of the left VA.

OUTCOME AND FOLLOW-UP

Additional examination including nerve conduction studies and x ray of the neck classified the patient’s problems as cervicobrachialgia and tension type headache, which were treated successfully with non-steroidal anti-inflammatory therapy.

DISCUSSION

First described by Batujeff in 1889, PHA is a rare vascular anomaly with an angiographic frequency of 0.02–0.1% with the basilar artery arising from the ICA.1–3 Clinical symptoms with relevant PHA are aneurysms of the basilar artery and carotid artery stenosis.4–9 We here present sonographic findings of bilateral hypoplasia of the VAs associated with PHA; however CT or MR angiography are needed to correctly classify the embryonic variant.

Next to the primitive trigeminal artery (PTA), primitive otic artery (POA) and the posterior communicating artery, the PHA connects the primitive ICA and the longitudinal neural artery, which later becomes the basilar artery. After its origin from the extracranial ICA at the C2 level, PHA joins the hypoglossal nerve, enters the posterior cranial fossa via the anterior condyloid foramen and the hypoglossal canal, and forms the basilar artery with and without anastomosis with the contralateral VA. Persistence of these primitive anastomoses may compensate for inappropriate development of the vertebrobasilar system.10 In 79% of 80 cases of PHA, hypoplastic VAs were found ipsilateral or bilateral.11 Various definitions for VA hypoplasia exist and the largest study on healthy volunteers addressing this issue has been published by Jeng et al.12 Hypoplasia of a VA can be assumed using two main criteria: a VA diameter of <0.22 cm and an ipsilateral RI of ⩾0.75. Supporting criteria were the contralateral VA diameter (side-to-side parameter difference) of ⩾0.12 cm and flow volume (side-to-side flow volume ratio) of ⩾5. In our case, both VAs fulfil the main criteria of VA (right VA: RI 0.75, diameter 0.21 cm; left VA: RI 1, diameter 0.09 cm). Unlike PTA or POA, PHA could be scanned via the transnuchal approach as well as at its origin at the ICA; however, only further vascular imaging using CT angiography and MRA provided a final diagnosis.

The clinical relevance of persistent carotid-basilar anastomosis in asymptomatic patients is as yet ill defined as it is based on case reports in symptomatic patients. The presence of PHA has clinical relevance in patients as neurological symptoms can occur in multiple vascular territories in case of atherosclerotic disease of the ICA.13–15 Therefore, carotid-basilar anastomosis has to be kept in mind as clamping of the internal carotid artery during carotid thrombendarterectomy may lead to a significant decrease in brainstem perfusion. Probably the most serious and life-threatening complication with immediate consequences for therapy in patients with carotid-basilar anastomosis is subarachnoid haemorrhage from a ruptured basilar artery or PHA aneurysm.4,5,9,11 Knowledge of the exact vascular variants in these cases is of great importance to guide endovascular treatment.

In conclusion, PHA and other carotid-basilar anastomoses are rare entities and need to be considered in patients with extreme bilateral VA hypoplasia and with complex clinical symptoms of the anterior and posterior circulation.

LEARNING POINTS

  • Rare anatomical variations pose difficulties for routine ultrasound.

  • Inconclusive findings warrant additional neurovascular imaging.

  • Persistent carotid-basilar anastomosis may be associated with embolisation into the posterior circulation from carotid artery stenosis or aneurysms/subarachnoid haemorrhage.

Footnotes

Competing interests: none.

Patient consent: Patient/guardian consent was obtained for publication.

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