CASE REPORTS Posterior Circulation Positional Transient Ischaemie Attacks due to Persistent Primitive Hypoglossal Artery with Redundancy Abstract A persistent primitive hypoglossal artery was the sole identifiable stroke risk factor for a patient presenting with positional, posterior circulation ischaemie episodes. Diagnosis was made by magnetic resonance arteriography and verified by conventional angiography. Tortuosity and coiling of the hypoglossal artery was also present. Dynamic transcranial Doppler sonography was normal and SPECT brain scanning revealed an area of posterior hemisphere hypoperfusion. Redundancy of the primitive hypoglossal artery is the postulated mechanism of cerebral ischaemia. Michael Hoffmann* MBBCh, FCP(SA)Neurol Peter Corr+ MBChB, FFRad(D)SA, FRCR,MMed (UCT) • Department of Vascular Surgery, Cerebrovascular section, Department of Medicine; Stroke Unit, Entabeni Hospital + Department of Radiology, University of Natal 20 SAJOURNAL OF RADIOLOGY. May 1996 Introduction Four different primitive arteries connect future anterior and posterior circulations in the embryonic state,' The trigeminal, otic, hypoglossal or proatlantal arteries normally regress and are replaced by the posterior communicating arteries but may persist in adult life. These four arteries may persist with differing frequencies and varying com- plications such as cerebral aneurysms? cra- nial nerve palsies' and as a route of anterior to posterior circulation embolism.' Brain ischaemia and infarction have recently been described with such primitive anastomoses without any other cause of embolism or in association with carotid stenosis at the pre- sumed donor emboligenie site.>? Hypoglossal arteries are said to be present in 0.05 % of cerebral angiograms and have been reported to be associated with aneu- rysms'" arteriovenous malformations, 10-12 moyamoya disease!' and Arnold Chiari malformation." Cerebral ischaemia has been describedinone case." The mere pres- ence of the congenital anomaly alone is in- sufficient to imply causation. A relatively young patient, free of cerebrovascular risk factors is presented with a hypoglossal ar- tery with the additional abnormality of ex- tensive coiling (redundancy) of the vessel in the neck. Case report A 48 year old right handed, white woman reported a sudden onset of bilateral visual impairment lasting several minutes, fol- lowed by intermittent shaking on both sides of her body lasting about 2 hours. Episodes of the body becoming "spastic" every 4-5 minutes were observed by her husband, lasting about 5 minutes at a time. He described the attacks as the arms and legs extending, and her lifting off the bed. The neck would become very stiff and she would arch her spine consistent with opisthotonic posturing. She was totally topage22 THINK WIDE! 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Pins and needles were perceived on both sides but more on the right. Numbness of the tongue, partial deafness of the right ear and dizzy spells were other frequent intermit- tent symptoms. A second similar attack occurred one week later. Of note is that turning her head to the left for more than 1-2 minutes invariably provoked dizziness. Looking down, such as when going down stairs and turning her head to either side would provoke dizziness. Tinnitus was in- variable. No headache, weakness, diplopia or imbalance was associated. Her past his- tory was notable in that she was diagnosed to have had a right sided "Bell's palsy" (of sudden onset) on the 20 July 1995 which lasted about 2 weeks. She had no cerebrovascular risk factors. General and neurological examination was normal save for mild dysmnesia and visuospatial impair- ment, the latter tested with the Rey Com- plex Figure Test. The clinical assessment at time of first visit included a differential of posterior circulation ischaemia, partial sei- zures or cardiac dysrhythmias. The basic cerebrovascular relevant blood screen, chest radiograph, electrocar- diogram, electroencephalogram, computer- ised tomography brain scan and cardiac in- vestigations including cardiac echogram were normal. The magnetic resonance imaging (MRI) brain scan showed a very small hyperintense focus in the left frontal region of dubious significance. An abnor- mal signal void due to a carotid basilar anastomosis was detected (Figure 1). This anastomosis was confirmed on time of flight magnetic resonance (MR) angiography as a very dilated tortuous hypoglossal artery with an aplastic right vertebral and hypoplastic left vertebral ar- tery (Figure 2). Selective angiography con- firmed the MR angiogram findings (Figure 3). The single photon computed tomography (SPEeT) brain scan showed Figure 1: A T2 weighted axial scan demonstrates a signal void from the carotid basilar anastomosis (arrow). left hemisphere hypoperfusion to visual inspection and semiquantitative analysis (Figure4). The asymmetry index was cal- culated as 22%, significantlydifferent to the normal controls (n=5) with a mean value of 4.2% for the pariete-occipital region (standard deviation± 2.7, range 0 - 9.5). Figure 2: MR angiogram demonstrates the tortuous left hypoglossal artery (arrow). Note the aplastic right vertebral artery (arrowhead). The cerebral vasomotor response was tested with intravenous Diamox without any further abnormalities noted on the SPECT scan. Transcranial Doppler sonography including dynamic studies with head rotation and flexion was normal. Specifically basilar artery velocity was un- changed with head rotation to the right and left for 2 minutes each. She was treated 22 SAJOURNAL OF RADIOLOGY. May 1996 Figure 3: Selective left vertebral angiogram confirms the tortuous left hypoglossal arterial anastomosis (arrow). withAspirin 150 mg daily and presently remains well at 2 months follow up. Figure 4: SPEeT scan showing significant ieft parieto·occipital hypopertusion (arrowheads). Discussion A series of case reports has implicated primitive caroticovertebral arteries in stroke and cerebral ischaemia. There is also a known stroke risk associated with cervicocephalic redundancy, with vari- ous mechanisms such as thrombosis and embolism postulated and dissection signifl- cantlyassociated." Thernostlikelymecha- nisrn of ischaemia in our patient is a tran- sient hypoperfusion or thromboembolism from the redundant coils of the primitive to page 23 Posterior Circulation Positional Transient Ischaemie Attacks hypoglossal arterywhich was the main pos- terior circulatory supply vessel in this pa- tient. When these primitive arteries per- sist, aplasia or hypoplasia of the vertebrobasilar system is usual as in the pa- tient under discussion. Positionalischaemia in anatomically normal vessels and atherostenosis with neck turning is well described by Sturzenegger et al.l? Inour pa- tient, head turning to either side but more to the left as well as flexion provoked dizzi- ness. Both embolic and haemodynamic mechanisms could be pathomechanisms with the normal dynamic trans cranial Doppler study marshalling evidence against the latter. This could be a mecha- nism of ischaemia especially as the abnor- mal hypoglossal artery served as the sole posterior circulation supply without the benefit of the normally dual vertebral arte- rial supply. Although no posterior circula- tion infarct was imaged with the aid of an MRI brain scan, functional imaging with SPEeT scanning revealed left posterior hemisphere hypoperfusion, a finding that would correlate well with the symptomatology: The reported Bell'spalsy was more likely to have been a minor pontine infarct as the clinical presentation was compatible with brain stem ischaemia. Although surgicalreconstruction of carotid redundancy has been reported to abolish symptoms of cerebrovascular insufficiency, such treatment would theoretically be contraindicated in our patient inview of the anatomically abnormal posterior circu- lation. This case demonstrates the utility of MR angiography in the detection of un- common vascular abnormalities in patients with unexplained transient ischaemie at- tacks. The hypoglossal arterywhen present is usually the only functional artery to the brain stem and cerebellum and is associated with aplasia or hypoplasia of the vertebral arteries as demonstrated in our patient," To our knowledge, this is the first reported instance of a primitive, persistent hypoglossal artery associated with redun- dancy without other identifiable cause of positional cerebral ischaemia/infarction. The causal relationship of these dual stroke riskfactors seems certain. The need to ex- elude such vasculopathy in patients pre- senting with posterior circulation insuffi- ciency is emphasised as the mechanism is amenable to treatment. Diagnosis by non- invasive magnetic resonance angiography should suffice. References 1. Padget DH. The development of the cranial arteries in the embryo. Contrib Embryo/1948;212:259-261. 2. Fortner AA, Smoker WRK. Persistent primitiv trigeminal artery aneurysm evaluated by MR imaging and angiography. 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