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ARTICLE IN PRESSG ModelEURAD-891; No. of Pages 10

Journal of Neuroradiology xxx (2020) xxx–xxx

Available online at

ScienceDirectwww.sciencedirect.com

eview

eyond plaque: A pictorial review of non-atheroscleroticbnormalities of extracranial carotid arteries

ohn C. Bensona,∗, Vance T. Lehmana, Carrie M. Carra, John T. Walda, Harry J. Clofta,iuseppe Lanzinob, Waleed Brinjikji a

Mayo Clinic, Department of Neuroradiology, Rochester, MN, USAMayo Clinic, Department of Neurosurgery, Rochester, MN, USA

a r t i c l e i n f o

rticle history:vailable online xxx

a b s t r a c t

The common carotid artery (CCA) and extracranial internal carotid artery are subject to a wide varietyof non-atheromatous pathologies. These entities are often overshadowed in both research and clinical

eywords:arotid arteryeb

issectionseudoaneurysm

realms by atherosclerotic disease. Nevertheless, non-atherosclerotic disease of the carotid arteries mayhave profound, even devastating, neurologic consequences. Hence, this review will cover both commonand uncommon forms of extracranial carotid artery pathologies in a pictorial format, in order to aid thediagnostician in identifying and differentiating such pathologies.

© 2020 Elsevier Masson SAS. All rights reserved.

ysgenesislowout

ntroduction

Numerous inflammatory, iatrogenic, heritable, and develop-ental disease processes affect the common carotid artery (CCA)

nd extracranial internal carotid artery (ICA). Unfortunately, theppearances of these entities on diagnostic imaging are often sim-lar, leading to misdiagnosis and confusion. The purpose of thisaper is to provide a pictorial overview of non-atherosclerotic enti-ies that involve the cervical carotid vasculature, with an emphasisn the expected appearance of each entity and useful tactics toifferentiate between each abnormality.

ebs

Carotid webs are thin intraluminal shelves made up of non-theromatous tissue [1]. Many authors have opined that websepresent an intimal subtype of fibromuscular dysplasia, and patho-ogic evidence of this exists [2–4]. However, a recent study alsooted the de novo formation of a web from an intimal dissec-ion, offering another possible pathogenesis of webs [5]. These

embrane-like abnormalities project from the arterial wall, withinhe carotid bulb or at or immediately past the origin of the cervical

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CA [4,6] Recently, webs have been increasingly recognized as thetiology of some ischemic strokes, particularly in young patientsnd African American women [4,6–9]. A recent study by Kim et al.

∗ Corresponding author.E-mail address: benson.john3@mayo.edu (J.C. Benson).

https://doi.org/10.1016/j.neurad.2020.02.003150-9861/© 2020 Elsevier Masson SAS. All rights reserved.

found a web in the same vascular territory as a cryptogenic strokein 22.7% of patients 18–60 years old [10]. It is hypothesized thatthe mechanism by which this occurs is related to stasis of blood,ultimately leading to thromboembolism [6]. Webs are often refrac-tory to treatment with antiplatelet or anticoagulation therapy, withhigh rates of recurrent strokes reported [11,12]. Increasingly, websare instead being treated with stents, with favorable results [11].A literature review by Zhang et al. found no recurrent strokesor complications among 70 patients with symptomatic webs thatunderwent revascularization (50% with stent, 50% with endarterec-tomy; median follow up 10.7 ad 14 months, respectively) [12].

On imaging, webs will appear as a smooth defect extendingfrom the posterior wall in oblique sagittal planes, and as a sep-tum on axial planes [13]. (Fig. 1) The location and appearance ofwebs can help avoid mistaking these entities for dissections andatherosclerotic plaque. Most acute dissections occur in the mid ordistal cervical ICA, and will rarely, if ever, involve the carotid bulbunless they extend from the more proximal common carotid artery.Dissections also have irregular margins, and may be associated witha pseudoaneurysm [14]

Multiple imaging features can also help distinguish webs fromshelf-life atherosclerotic plaque. Atherosclerotic plaques are oftencalcified; webs should not be associated with calcification. Plaquessometimes have some associated thickening or positive remodel-ing of the vessel wall, while no such changes will be observed in

torial review of non-atherosclerotic abnormalities of extracranial.2020.02.003

webs [15]. (Fig. 2) Finally, plaques may enhance following admin-istration of contrast and/or have intrinsic T1 hyperintensity on MRif hemorrhagic; such findings are lacking in webs [16].

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2 J.C. Benson et al. / Journal of Neuroradiology xxx (2020) xxx–xxx

Fig. 1. Carotid web. 38 year old female with a history of recurrent right hemispheric strokes. Axial CTA (A), reformatted CTA neck MIP (B), reformatted MRA neck withgadolinium (C), and DSA (D) demonstrate a thin, regular, shelf-like deformity of the right ICA origin causing focal arterial narrowing.

Fig. 2. Shelf-like atherosclerosis. 71 year old male with a history of prior radiation therapy for tonsillar carcinoma who underwent carotid imaging after presenting witha he nea ve artp

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maurosis fugax. Axial CTA (A), sagittal MIP CTA (B), and reformatted CTA (C) of trrows). The presence of a focal calcification along this abnormality as well as positiatient’s right ICA is chronically occluded (curved arrow, A).

issections

Arterial dissections occur as the result of an intimal tear, inhich blood enters the vessel wall through the defect and forms an

ntramural hematoma called the false lumen [17]. The effect on theumen depends on the location of the intramural hematoma: steno-is develops if the intramural hematoma is located between theedia and intima, and aneurysmal dilatation occurs if the blood col-

ects between the adventitia and media [18]. The inciting event maye spontaneous, iatrogenic, related to trauma, or due to an under-

ying connective tissue disorder [19]. The extracranial portions ofhe carotid arterial vasculature are more susceptible to dissectionhan their intracranial counterparts, likely related to the increased

obility and higher risk of traumatic contact with adjacent osseoustructures [17].

Clinically, patients often present with neck or head pain withr without Horner’s syndrome; an acute-onset painful Horner’syndrome is considered nearly pathognomonic of a carotid dis-ection [20]. Neurologic deficits generally occur hours or daysfter symptom onset, although they can occur up to a monthater [21]. Dissections are a common cause of stroke among

Please cite this article in press as: Benson JC, et al, Beyond plaque: A piccarotid arteries, J Neuroradiol (2020), https://doi.org/10.1016/j.neurad

oung and middle-aged patients, responsible for 10-25% of strokesn this age group [17,22]. Strokes may occurs as a result ofrterial stenosis and/or occlusion as well as distal embolization23].

ck show a thin defect extending into the lumen of the proximal left ICA (straighterial remodeling suggest that this represents atherosclerosis rather than a web. The

CTA, MRA, and angiography can be used to diagnose dissections.DSA is the gold standard, although the pathognomonic “double-lumen” sign or an intimal flap are apparent in the minority of cases[24]. Instead, dissections typically appear as an irregular steno-sis about 2–3 cm distal to the carotid bulb, with extension to theintracranial segment occurring in only 17% of cases [25]. (Fig. 3)Complete carotid occlusion appears as a tapering stenosis (“flamesign”), while high-grade stenosis appears as the “string sign”; otherappearances include eccentric arterial wall thickening, the pres-ence of an associated pseudoaneurysm, and dilatation distal to afocal stenosis (“string and pearl sign”) [25,26]. On MRA, intramuralhematomas classically appear as eccentric signal around the ves-sel lumen, with T1 and T2 intensity dependent on the chronicity ofthe dissection [27]. These will appear as crescent-shaped densitieson corresponding NCCTs [26]. Intramural hematomas can also beseen on CTAs, although they can be readily missed - typically, theouter wall of the vessel will appear as slightly more dense than thehematoma.

One potential pitfall is a “flame sign” mimic that occurs in thesetting of an ICA terminus occlusion. Slow flow caused by an occlu-sive thrombus within the distal ICA may cause the vessel to beincompletely visualized on the arterial phase CT imaging (i.e. a

torial review of non-atherosclerotic abnormalities of extracranial.2020.02.003

CTA). This slow flow will be easily apparent on angiography. Fol-lowing mechanical thrombectomy, the vessel again may appearpatent.

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ig. 3. Carotid dissection. 40 year old male who presented with a four day histobrupt narrowing of the distal right ICA (straight arrows). A non-enhancing abnormyperintense on axial FLAIR MRI (C).

seudoaneurysms, true aneurysms, and carotid blowout

seudoaneurysms

Pseudoaneurysms occur as the result of loss of integrity of allhree layers of the arterial wall, in contrast to true aneurysms28]. This defect allows blood to dissect into the peri-vascular softissues, forming a blood-filled sac that communicates with theumen [29]. Often, they are asymptomatic and discovered inciden-ally; some undergo spontaneous thrombosis [29]. Nevertheless,seudoaneurysms can be complicated by arterial occlusion, throm-oembolism, local mass effect, and rupture [30].

Endovascular therapy with covered stents has supplantedurgery as first line therapy in recent years [30]. Such stents preventurther extravasation into the pseudoaneurysm, while allowingntravascular flow to continue unobstructed. Prior to any interven-ion, it is important to obtain imaging of the circle of Willis in ordero assess the patency of collateral flow.

Multiple characteristic imaging features of pseudoaneurysmsxist. DSA is the gold standard for diagnosis, can provide usefulnformation about the morphology of the aneurysmal sac and neck,nd allows for concomitant therapy if desired [29]. CT angiogra-hy will typically showed contrast within the pseudoaneurysm sac;artial or complete filling of the sac with low-attenuation materialay represent some degree of thrombosis. On Doppler sonog-

aphy, pseudoaneurysms demonstrate “to-and-fro” waveforms,orresponding to blood flow into and out of the pseudoaneurysmuring systole and diastole, respectively [31]. The “yin-yang” sign islso frequently cited as an indicator of a pseudoaneurysm, thoughhis can also be seen in true aneurysms [31].

Trauma is the most common cause of carotid pseudoaneurysms28]. Most commonly, they are due to motor vehicle accidentsapproximately 70% of cases), leading to shearing of the artery nearhe carotid canal or compression and/or stretching of the arterylong the lateral mass of C1 [32]. Iatrogenic causes include carotidndarterectomy, central venous cannulations, and head and neckurgery [33]. (Fig. 4) Anatomic variants may also play a role; multi-le publications have suggested that an elongated styloid processEagle syndrome) may be associated with the pathogenesis of someissections and pseudoaneurysm formation [34].

Mycotic aneurysms can arise from spread of bacteria into the

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asa vasorum of the vascular walls, direct spread of the vessel wallrom infection of the adjacent soft tissues, and inoculation fromenetrating trauma. Staphylococcus and Streptococcus species ofacteria are the most common offending agents [35]. In most cases,

Horner’s syndrome. Axial (A) and sagittal MIP CTA (B) of the neck demonstratewas seen within the wall of the vessel on both CTA (curved arrows, A), which was

clinical history is sufficient to differentiate mycotic aneurysms fromtraumatic/iatrogenic. In addition, imaging often shows inflamma-tory changes around a pseudoaneurysm, appearing as fat strandingon CT or hyperintensity on T2WI. In some cases, coalescent inflam-matory soft tissue abnormalities are present. Peri-arterial gas hasbeen reported, but is a rare finding [35]. The area may be hyper-metabolic on FDG PET/CT and demonstrate radiotracer uptake onIn-111 scans.(Fig. 5)

Carotid blowout

Carotid blowout syndrome (CBS) results from the sudden lossof integrity of the carotid artery wall. This nearly always occurs inpatients with and neck cancer, and can occur as the result of necro-sis related to radiation therapy, surgical resection, wound infection,pharyngo-cutaneous fistula, or direct neoplastic invasion [36]. Theresults can be devastating: neurologic mortality is estimated to beas high as 40% [37].

CBS is categorized by severity, ranging from threatened blowout(inevitable hemorrhage without corrective action), impendingblowout/sentinel hemorrhage (transient bleeding that resolve withpressure), and acute CBS (profuse bleeding uncontrolled by packingor pressure). Threatened blowout is recognized either clinically orby imaging as being exposure of the carotid artery, often from tis-sue breakdown [38]. The presence of a pseudoaneurysm, contrastextravasation, and exposed arteries were the highest predictors ofimpending blowout on CBS [37]. (Fig. 6)

True aneurysms

In contrast to pseudoaneurysms, true aneurysms of theextracranial carotid artery (ECAA) are extremely rare, making upunder 1% of peripheral artery aneurysms [39]. They appear asfocal dilatation of the vessel lumen at least 50% greater than thenormal carotid size [40]. Multiple etiologies of ECAAs exist, includ-ing atherosclerosis (most common) fibromuscular dysplasia, andEhlers-Danlos syndrome [41]. Most ECAAs are fusiform, thoughsaccular aneurysms have also been reported [42].

Although multiple treatments exist for ECAAs, the preferredmanagement remains controversial [43]. Invasive therapies havefavorable outcomes, with good long-term results [44].The most

torial review of non-atherosclerotic abnormalities of extracranial.2020.02.003

common side effect is that of cranial nerve damage; a literaturereview by Welleweerd et al. noted nerve injury in 11.8% of patientsafter surgery [43]. Left untreated, larger ECAAs are high-risk abnor-malities, causing strokes in as many as 50% of conservatively treated

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Fig. 4. Iatrogenic pseudoaneurysm. 72 year old male who presented with a palpable right neck mass. He had undergone a carotid endarterectomy 6 years prior to presentationfor a high-grade stenosis. Axial (A), coronal MIP (B), and 3D reformatted (C) CTA images of the neck demonstrate a large pseudoaneurysm at the right carotid bifurcation(short straight arrows) enclosed by low-density soft tissue (long straight arrows). There are luminal irregularities of the ICA immediately distal to the pseudoaneurysm(curved arrow).

Fig. 5. Infected pseudoaneurysm. 64 year old male with a complex history of squamous cell carcinoma of the tonsil status post chemo- and radiation therapy, as well ass t to bea am (B)( s). Th

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tenting of the left CCA and ICA for stenosis. He developed MSSA septicemia, thoughnd an In-111 WBC scan (A), and had marked erythema of the overlying skin on excurved arrows), with development of a pseudoaneurysm at the site (straight arrow

atients with atherosclerotic ECAAs [45]. ECAAs are also associatedith cranial nerve compression and rupture [46].

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ibromuscular dysplasia

Fibromuscular dysplasia (FMD) is a non-atherosclerotic andon-inflammatory process that primarily affects renal, carotid, and

secondary to infection of the stent; this was avid on both an FDG-PET (not shown). Subsequent DSA (C) and ultrasound (D) showed discontinuity between his stentse pseudoaneurysm was confirmed on axial (E) and reformatted (F) CTA imaging.

vertebral arteries [47]. Its prevalence within the cervico-encephalicarteries has been estimated at 0.3–3.0%, although an extensivereview of ICAs from autopsy specimens only found FMD in 0.02%of patients [47,48]. The pathophysiological mechanism by which

torial review of non-atherosclerotic abnormalities of extracranial.2020.02.003

FMD remains unknown, also some authors have postulated thathormones may be involved, given its proclivity to affect females[47]. Tobacco use, mechanical factors, and genetics may also play arole [49].

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ig. 6. Carotid blowout. 65 year old female with a history of follicular thyroid carcinrom a pharyngocutaneous fistula. Initial CTA on presentation was read as a pseudoa).

Often, patients with FMD are asymptomatic, or present withelatively mild symptoms such as headache or pulsatile tinnitus50]. However, patients can also present with neurologic deficits,ften related to thromboembolism or spontaneous dissection of theffected artery [2]. The association between FMD and intracranialneurysms has been reported in the past but is controversial [51].

study by Cloft et al. of 498 patients found the rate of intracranialneurysms to be approximately 7%, much lower than the previouslyeported rates of 21-51% [52].

FMD is classified based on the arterial wall layer most involvedy the disease process, divided into intimal, medial, and perime-ial/subadventitial types. Intimal FMD is usually found in pediatricatients, and appears as a smooth stenotic region that is either focalr segmental. Medial FMD is the most common type, making up0–70% of cases. Abnormalities are typically segmental, and com-only appear as a “string of beads” made up of focal stenoses and

ilatations [2]. Perimedial FMD is similar to the medial type, but hasewer dilatations (“beads”) which do not exceed to the diameter ofhe normal arterial lumen [47].

Findings associated with FMD include vascular ectasia,neurysms, and/or dissections may also be noted [53–55]. (Fig. 7)ortuous vessels - characterized by kinks, coils, and loops - are com-only seen, but are not specific to FMD [56]. Mild FMD may not be

een on CTA.

onnective tissue disorders

Connective tissue disorders (CTDs) include a number oferitable syndromes, including Marfan’s syndrome, Loeys-Dietzyndrome (LDS), Ehlers-Danlos syndrome (EDS), pseudoxanthomalasticum, and osteogenesis imperfecta. Although CTDs have signif-cant phenotypic variability, each of the disorders can lead to severend potentially disastrous neurovascular complications [57]. On

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maging, dilatation of the aorta and tortuosity of the peripheralrterial vasculature are common findings. The identification ofervical arterial tortuosity with co-existent aortic root dilatationhould therefore raise the suspicion for a CTD.

nd squamous cell carcinoma of the tongue who presented with significant bleedingsm (straight arrow, A). Subsequent DSA confirmed a carotid blowout (curved arrow,

Ehlers-Danlos syndrome is related to a mutation of COL3A1,which encodes a peptide in type III collagen. The result of thisdefect is arterial fragility, among many other systemic manifes-tations [58]. Of the subtypes of EDS, neurovascular abnormalitiesare most commonly seen in type IV (so-called “vascular” EDS) [59].Vascular EDS is associated with significant abnormalities of bothmedium- and large-sized arteries throughout the body, includ-ing the carotid vasculature. The vessels are prone to dissection,rupture, and aneurysmal dilatation [59,60]. Though the carotidvasculature involvement of vEDS occurs, neurovascular complica-tions typically result from intracranial abnormalities: most notablycarotid-cavernous fistula and intracranial aneurysms [59].

LDS is characterized by a triad of arterial tortuosity andaneurysms, hypertelorism, and cleft palate or bifid uvula [61].Carotid arterial manifestations include dissections, aneurysms, andtortuosity. One study noted arterial tortuosity in 100% of patientswith head and neck CTA imaging; aneurysms, pseudoaneuysms,and dissections were also noted, though less frequently (Fig. 8) [62].The severity of carotid tortuosity in LDS patients has been proposedto hold prognostic value, as it is correlated with the rate of aorticroot growth and need for aortic root replacement [63]. On imag-ing, most patients with LDS have a wide angulation of the carotidbifurcation, often with co-existent bulbous dilatation of the carotidbulb, in what has been proposed as the “Chalice sign.” In addition,the majority of patients (90% in a study by Kono et al.) have markedtortuosity of the vertebral arteries [64].

Marfan’s syndrome is an autosomal dominant disorder causedby a mutation in the gene encoding fibrillin 1, a glycoprotein thatserves as a scaffold for elastin [65]. Mortality in Marfan’s syndromeis typically from related to its proclivity for cardiovascular compli-cations: aortic insufficiency, aortic dissection, and aortic dilatation[66]. As such, the most common neurovascular manifestations ofMarfan’s are related to extension of arterial dissection into the

torial review of non-atherosclerotic abnormalities of extracranial.2020.02.003

carotid arteries from the aorta [66,67]. Extracranial carotid arteryaneurysms and isolated dissections have been reported in patientswith Marfan’s syndrome, though the number of such cases remainsrare [68].

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Fig. 7. Fibromuscular dysplasia. Reformatted MRA (A) and CTA (B) of the neck demonstrate string-of-beads appearance of the ICAs and vertebral arteries. A focal dissectionwith superimposed pseudoaneurysm of the distal left ICA is present, best seen on the reformatted sagittal CTA (curved arrow, C).

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ig. 8. Loeys-Dietz syndrome in a 26 year old patient. Reformatted CTA images oarotid bifurcations (long straight arrows). Also noted are coils of the right ICA (shoeft ICA (dashed arrow). A focal dissection is seen in the left ICA, confirmed on axial

asculitides

ayakasu arteritis

Takayasu arteritis (TA) is a large-vessel granulomatous vas-ulitis that affects the aorta and its major branches. Almost 20%f patients with TA experience neurologic involvement, includingeadache, seizure, and stroke [69]. The inflammatory changes in TA

nvolve all layers of the vascular walls, resulting in arterial stenosisnd/or occlusion, dilatation and aneurysm formation [70]. Affectedessels will demonstrate significant mural thickening, with or with-ut the aforementioned changes (Fig. 9).

The most common imaging feature of TA is concentric

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ural thickening. This mural thickening is transmural, has high-ttenuation on pre-contrast imaging, and may have a “doubleing” of enhancement on post-contrast imaging, in which theuter layer enhances more than the inner layer [70]. The adjacent

ight (A) and left (B) carotid arteries demonstrate markedly obtuse angles of bothight arrow, A) and left CCA (short straight arrow, B), as well as an aneurysm of the

mages (curved arrows).

periadventitial soft tissues may also enhance. Similarly, vessel wallenhancement of the affected arteries can be seen on MR [72]. Themural thickening may also calcify, which is typically transmuraland should be differentiated from intimal (and often eccentric)calcification seen in atherosclerosis [73]. Such changes can be asso-ciated with arterial stenosis and occlusion, as well as dilatationand aneurysms. FDG PET/CT may demonstrate hypermetabolismin the affected walls, which can identify affected vessels priorto stenotic narrowing and hence can be an early diagnostic tool[74].

The distribution of vascular involvement is characteristic; TAaffects large arteries, most commonly the aorta, subclavian, carotid,pulmonary, and coronary arteries [71]. The most common imaging

torial review of non-atherosclerotic abnormalities of extracranial.2020.02.003

finding of extracranial arteries is common narrowing of the CCA(seen in approximately 60% of patients with TA) [75]. ICA narrow-ing, conversely, is relatively rare, occurring in only 22.8% of patients.Importantly, according to Bond et al., ICA stenosis is only seen with

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Fig. 9. Takayasu’s arteritis. 43 year old female with a known history of Takayasu arteritis, who underwent imaging to evaluate for the cause of left upper and lower extremityweakness. CT images at the level of the upper mediastinum (A) and lower neck (B) show marked mural thickening around the origins of the aortic branches (straight arrow)as well as marked narrowing of the right CCA (curved arrow).

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ig. 10. Bilateral ICA agenesis. Axial CT images of the skull base showed absence of

he ICAs and enlargement of both vertebral arteries (B). The anterior circulation wa

o-existent CCA involvement, and does not exist as an isolated find-ng [75].

iant cell arteritis

Giant cell arteritis (GCA) is a vasculitis characterized by involve-ent of large- and medium-sized arteries. Patients are typically

50 years old, and may often present with a headache and/or visionoss, temporal tenderness, and elevated ESR [76]. In contrast to TA,he superficial temporal (STA), ophthalmic, and vertebral arteriesre the most commonly severely affected [77].

The most useful imaging modality to assess for GCA is CTA,hich can evaluate the presence and severity of arterial narrow-

ng. Close attention should be paid to the STA, which often requires

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ultiplanar reformatted images to accurately assess the arteryn plane. On ultrasound, the “halo” sign - peri-vascular hypoe-hogenicity - has been shown to be both sensitive and specific forCA [78]. Although the temporal arteries are typically assessed on

rotid canals bilaterally (A). Reformatted MRA of the neck demonstrated agenesis oflied via large posterior communicating arteries (C).

sonography, the halo sign has also been reported in carotid arteries[79].

Vessel wall imaging (VWI) on MRI has good to excellent accu-racy in the diagnosis of GCA. This could be performed with imagingsequences acquired perpendicular to the orientation of the ves-sels, with pre-contrast spin-echo T1 sequences and fat-saturatedimages obtained with gadolinium. Attention is paid to the frontaland parietal branches of the STA, as well as the occipital arteries.Diagnostic criteria is set on a 4-point scale, based on the degree ofmural enhancement [80,81]. Fat stranding can sometimes be alsoseen adjacent to affected vessels on T2WI. Such findings on MRImay be useful to direct arterial biopsies.

Involvement of the extracranial ICA is rare. Nevertheless, severecases of GCA can involve the carotid arteries, and in extreme cases

torial review of non-atherosclerotic abnormalities of extracranial.2020.02.003

can lead to cerebral infarction [82–84]. VWI has shown involve-ment of the intradural carotid arteries and distal vertebral arteries[85]. Stenoses are located at or near the point of dural entry[86].

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evelopmental anomalies and normal variants

uplication and fenestration

Carotid artery duplication is a rare anatomic variant in whichwo embryologically distinct carotid vessels remain. Some authorsave opined that the embryologic pathogenesis of this anomalyay be related to abnormalities of the third aortic arch, which is

ormed by multiple channels in its early stage [87]. By definition,uplicated arteries have separate origins, and converge into a single

umen at some distal point [88]. In carotid artery duplication, theccessory channel often represents an enlarged tympanic branchf the ascending pharyngeal artery, which exists in the same spaces the cervical ICA. This accessory artery enters the tympanic cav-ty and ultimately anastomoses with the petrous ICA [89]. Hence,he distinguishing imaging feature is that only one artery entershe skull base at the normal location of the ICA, while the acces-ory lumen follows the expected course of the anterior pharyngealrtery. The duplicated arteries typically involve the entire length ofhe extracranial ICAs [87]. In some cases, co-existent aberrant ICAsave been noted [90,91].

Unlike duplication, fenestration refers to multiple vascularumens within the confines of a single arterial segment [89]. Fen-strations typically involve shorter segments of the vessels thanuplicated arteries [87]. Carotid fenestration is extremely rare,ith only a few case reports existing in the literature [92,93].

ome authors have opined that, in contrast to the basilar andertebral arteries, there is no embryologic mechanism by which

cervical ICA fenestration would occur [94]. Furthermore, therere many overlapping findings between fenestrations and theignificantly more common dissections. Such dissections, termedseudo-fenestrations, represent the most significant diagnostic pit-all; care must be taken to not confuse dissection for this extremelyare anatomic variant [94].

CA dysgenesis

ICA hypoplasia and congenital ICA absence are rare develop-ental anomalies, occurring in 0.01–0.13% of patients [95,96]. The

pectrum ranges from incomplete developmental (hypoplasia) too development with or without the presence of developmentalrecursors (agenesis and aplasia, respectively) [97]. Most patientsre asymptomatic because of collateral flow; communication at theevel of the circle of Willis, branches of the ECA, and persistentmbryologic arteries all may make up for the carotid insufficiency95,98,99]. Nevertheless, patients can present with a variety ofymptoms, including TIA/stroke, migraine headache, and pulsatileinnitus [100,101]. In addition, there is a higher rate of intracra-ial aneurysms among patients with ICA dysgenesis [102,103] Zinkt al., for example, found aneurysms in 27.8% of patients with eitherplasia or hypoplasia of the ICA, compared with 2–4% in the generalopulation [104].

Imaging findings are variable, and depend on the severity (i.e.ypoplasia versus aplasia) and extent (i.e. unilateral versus bilat-ral) of abnormalities (Fig. 10). Close evaluation of the skull baseoramina may help distinguish dysgenesis from acute findings suchs dissection and atherosclerotic occlusion. Demonstration of a nor-al bony carotid canal effectively rules out developmental ICA

nomalies [105]. The foramen spinosum may be enlarged, likelyndicating compensatory hypertrophy of the middle meningealrtery. On CTA, an enlarged ascending pharyngeal artery is some-

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imes seen as an associated finding in patients with ICA dysgenesis.n cases of bilateral ICA anomalies, intracranial blood flow mayepend on the posterior circulation, leading to marked enlarge-ent of the vertebral arteries [97]. Identification of ICA dysgenesis

PRESSadiology xxx (2020) xxx–xxx

should therefore prompt an analysis of collateral vasculature andskull base foramina.

Conclusions

Non-atherosclerotic processes of the extracranial carotid vas-culature include both common and uncommon entities withmany overlapping features on diagnostic imaging. Differentiat-ing between these pathologies may be uniquely challenging,particularly for radiologists less familiar with vascular imaging.Nevertheless, accurate diagnosis of arterial pathology is neces-sary to ensure prompt and targeted therapy. The onus is thereforeon radiologists to have a robust knowledge of the expectedappearances of the iatrogenic, inflammatory, and developmentalabnormalities that can affect the carotid arteries.

Disclosure of interest

The authors declare that they have no competing interest.

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