Custom Cart0

Vertebral Artery Hypoplasia: Ultrasound Appearance and Criteria

Lorem ipsum - excerpt to go here

March 4, 2020 / / Dr. Cristiana Vitale & ABC Vascular staff

Background

The vertebral arteries, which originate from the subclavian arteries and unite to form the basilar artery after branching into the posterior inferior cerebellar arteries, are the primary blood supply for infratentorial brain structures. Congenital variations in the arrangement and size of the vertebral arteries are common, and vertebral artery hypoplasia (VAH) has frequently been recognised among healthy individuals without symptoms of vertebrobasilar insufficiency.

More recently, several studies have shown that VAH, defined both as a vertebral artery of diameter <2 mm or <3 mm, is commonly observed in patients with posterior circulation stroke. Therefore, it has been speculated that VAH can be associated with an increased probability of ischemic stroke.

However, due to its high prevalence and the lack of a consensual definition of VAH, the clinical significance of VAH as an independent risk factor for ischemic stroke is still debated.
   

How to Detect Vertebral Artery Hypoplasia With Ultrasound

Definition

The definition of vertebral artery hypoplasia is still unclear, and several criteria have been suggested. Some ultrasound and angiography studies have defined VAH as a vertebral artery with a lumen diameter below 2 mm, while other studies suggest a below 3 mm cut-off diameter.

An asymmetry ratio between vertebral arteries of equal or greater than 1:1.7 has also been suggested to define VAH by other authors. In addition, the measurement of the volume flow within the vertebral arteries has been used as an additional criteria to define VAH with a cut off value of approximately 100 mL/min (see reference by Seidel et al 1999); yet its application in the routine scanning practice seems limited.

“The definition of vertebral artery hypoplasia is still unclear, and several criteria have been suggested”

Ultrasound Assessment

To identify the vertebral artery with ultrasound, a medium-high frequency linear array is generally used; however, a curvilinear array can also be used, in particular when the vertebral arteries lie deep or in presence of short or thick necks.

In order to identify the vertebral artery, the patient generally lies supine on a couch with the head straight or slightly turned towards the opposite side being scanned. The vertebral artery is identified in longitudinal view.

On B-mode, the vertebral artery appears as an anechoic structure that lies between the transverse processes of the cervical spine with the vertebral vein anteriorly (Figure 1).

Appearance of vertebral artery and vertebral vein
Figure 1: Longitudinal view of the vertebral artery and vertebral vein.

Figure 1 Description: B-mode longitudinal view image of the vertebral artery (VA) and vertebral vein (VV) lying superiorly to the VA.

Using colour Doppler flow, normally the vertebral artery will present the same colour pattern of the ipsilateral common carotid artery and opposite colour of the one of the vertebral vein.

To measure the diameter of the vertebral artery, an optimal B-mode longitudinal view image is needed. In order to clearly evaluate the lumen of the vertebral artery, focus, time gain compensation, overall B-mode gain and eventually other B-mode parameters should be optimised.

Once the lumen of the vertebral artery is identified the measurement callipers are placed over the outer layer of the posterior and anterior vertebral artery walls (Figure 2). The vertebral artery diameter is generally measured at the V2 level, between the transverse processes of the C4 and C5 vertebra.

Comparison right left vertebral arteries
Figure 2: Right and left vertebral arteries viewed side by side.

Figure 2 Description: B-mode longitudinal view of the right and left vertebral artery and the respective diameters measured with callipers measurements. In the right panel the right vertebral artery diameter measures 2 mm (2) while on the left panel the left vertebral artery measures 6.3 mm (1). Additionally, the asymmetry ratio in this particular case is 1:3.15.

Pulsed wave Doppler waveforms are also used as an additional criterion to define VAH. A normal vertebral artery presents antegrade low resistance Doppler flow pattern with a pronounced diastolic component. In presence of VAH the Doppler flow waveform changes with a less pronounced diastolic component reflecting the higher resistance, caused by the smaller diameter.

Complete absence of the diastolic flow and a low peak systolic flow velocity can be suggestive of distal intracranial steno-obstructive disease; therefore, further imaging is usually suggested in these circumstances.

In presence of VAH, the diastolic flow is generally represented even if of small amplitude. As shown in figure 2, while the left (dominant artery) vertebral artery presents a normal low resistance Doppler waveform, the right vertebral artery presents a high resistance pattern with a low diastolic flow.

Doppler analysis right and left vertebral arteries
Figure 3: Doppler flow analysis through the right and left vertebral arteries

Figure 3 Description: Pulsed wave Doppler flow analysis throughout the right (VAH) and left (dominant) vertebral arteries. High resistance flow is noted in the right vertebral artery with small diastolic component shown on the Doppler trace. The left vertebral artery presents a normal antegrade low resistance Doppler flow with pronounced diastolic component.
 

Conclusion

Despite the lack of consensus on diagnostic criteria to define VAH, the most commonly used are:

  • Diameter of the vertebral artery < 2 mm or < 3 mm
  • An asymmetry ratio between vertebral arteries of equal or greater than 1:1.7
  • Volume flow within the vertebral artery < 100 mL/min.

“The most commonly used criteria for VAH (Vertebral Artery Hypoplasia) are:
– Diameter of the vertebral artery < 2 mm or < 3 mm
– An asymmetry ratio between vertebral arteries of equal or greater than 1:1.7
– Volume flow within the vertebral artery < 100 mL/min.”

Related ABC Vascular Courses

Have you considered learning more with these related courses?

Master course on Carotid and Vertebral Arteries 
Info on the “Carotid and Vertebral Arteries” course >

Short course on How to Diagnose Subclavian Steal Syndrome (SSS) 
More on the “How to Diagnose Subclavian Steal Syndrome” course >

Additional Reading

Katsanos AH, Kosmidou M, Kyritsis AP, Giannopoulos S. Is Vertebral Artery Hypoplasia a Predisposing Factor for Posterior Circulation Cerebral Ischemic Events? A Comprehensive Review. Eur Neurol. 2013;70(1-2):78–83. https://www.ncbi.nlm.nih.gov/pubmed/23816871

Perren F, Poglia D, Landis T, Sztajzel R. Vertebral artery hypoplasia: A predisposing factor for posterior circulation stroke? Neurology. 2007;68(1):65–7. https://www.ncbi.nlm.nih.gov/pubmed/17200496

E. Seidel, B.M. Eicke, B. Tettenborn, F. Krummenauer Reference Values for Vertebral Artery Flow Volume by Duplex Sonography in Young and Elderly Adults. Stroke 1999; Dec;30(12):2692-6. https://www.ahajournals.org/doi/pdf/10.1161/01.STR.30.12.2692

Chuang YM, Chan L, Wu HM, Lee SP, Chu YT. The clinical relevance of vertebral artery hypoplasia. Acta Neurol Taiwan. 2012 Mar;21(1):1. https://www.ncbi.nlm.nih.gov/pubmed/22879083

Chi HY, Chen KW, Hsu CF, Shen CY, Chen AC, Su C, Fu WM Ultrasound Findings Disclose the Mutual Impact of Vertebrobasilar Dolichoectasia and Vertebral Artery Hypoplasia. J Ultrasound Med. 2019 Nov;38(11):3037-3042. https://onlinelibrary.wiley.com/doi/abs/10.1002/jum.15011

Kulyk C, Voltan C, Simonetto M, Palmieri A, Farina F, Vodret F, Viaro F, Baracchini C. Vertebral artery hypoplasia: an innocent lamb or a disguise? J Neurol. 2018 Oct. https://www.ncbi.nlm.nih.gov/pubmed/30116939

Share the case studies

related courses

Carotid and Vertebral Arteries

Carotid and Vertebral Arteries

Learn how to conduct an ultrasound examination of the carotid and vertebral arteries.
Imaging ultrasonografico dell’aneurisma dell’aorta addominale

Imaging ultrasonografico dell’aneurisma dell’aorta addominale

Impara come identificare un aneurisma dell’aorta addominale (AAA), come classificarlo con l’ecografia e come misurarne il diametro massimo.
Evaluación de la Placa Aterosclerótica Carotídea

Evaluación de la Placa Aterosclerótica Carotídea

Criterios ecográficos 2D para la caracterización de la placa.
Carotid Atherosclerotic Plaque Assessment

Carotid Atherosclerotic Plaque Assessment

Learn how to detect and characterise a carotid plaque with ultrasound.

Lower Limb Venous System Course

Learn how to conduct an ultrasound examination of the superficial and deep veins of the lower limbs.
Abdominal Aortic Aneurysm Course

Abdominal Aortic Aneurysm Course

Learn how to identify, measure and classify abdominal aortic aneurysms with ultrasound.
Como Diagnosticar Trombosis Venosa Profunda Poplítea Femoral – CME Quiz

Como Diagnosticar Trombosis Venosa Profunda Poplítea Femoral - CME Quiz

Aprender los principales criterios de diagnóstico para ultrasonido.
Screening for AAA during TTE Course

Screening for AAA during TTE Course

Learn how to detect an abdominal aortic aneurysm during a transthoracic echocardiography examination.
How to Diagnose Subclavian Steal Syndrome – CME Quiz

How to Diagnose Subclavian Steal Syndrome - CME Quiz

Learn the ultrasound criteria used to identify different types of steal syndrome.
How to Diagnose a Femoral-Popliteal DVT – CME Quiz

How to Diagnose a Femoral-Popliteal DVT - CME Quiz

Learn the main direct ultrasound diagnostic criteria used to diagnose a femoral-popliteal DVT.

Leave a Comment

Acquire immediately relevant skills

Expand your Medical Career Opportunities