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Cardiovascular

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Incidental findings of vascular anatomic variants oncomputed tomography Alejandro Rodriguez, Ricardo Cobeñas, Juan Cruz Gallo, Alejandra Salamida, Nebil Larrañaga, Shigeru Kozima

ResumenIntroducción. El hallazgo de variantes anatómicas vas-culares en estudios de tomografía computada (TC)puede generar confusiones, diagnósticos incorrectos eincluso la solicitud de nuevos estudios complementa-rios más invasivos.El conocimiento de estas variantes, además, es impor-tante porque pueden estar asociadas a otras anomalías,como cardiopatías, poliesplenia o síntomas como dis-fagia o disnea.Objetivo. El objetivo de esta publicación es describirlas variantes anatómicas vasculares halladas inciden-talmente en estudios de tomografía computada.Materiales y Métodos. Se revisaron 3586 estudios, rea-lizados desde junio de 2010 hasta junio de 2011, contomografía computada multicorte de 16 y 64 detecto-res. Entre los estudios analizados, se encontraron: arcoaórtico derecho (AAD), subclavia derecha aberrante,vena cava superior izquierda, vena subclavia izquier-da aberrante, vena cava inferior (VCI) izquierda, venarenal izquierda doble, vena cava inferior doble, venarenal circumaórtica, vena renal izquierda retroaórtica,vena subhepática e interrupción de la vena cava infe-rior con continuación en ácigos/hemiácigos.Conclusión. Las variantes anatómicas vasculares sonhallazgos que se encuentran con relativa frecuencia enforma incidental en estudios solicitados por otras razo-nes. Su conocimiento puede evitar confusiones y larealización de estudios complementarios innecesarios,así como también nos obliga a analizar la presencia deotras anomalías que podrían estar asociadas.Palabras clave. Tomografía computada multidetector.Variantes anatómicas vasculares. Tomografía computada.

AbstractIncidental findings of vascular anatomic variants oncomputed tomography.Introduction. Incidental findings of vascular anatomicvariants on computed tomography scans (CT) may causeconfusion, misdiagnosis and lead to even more invasivecomplementary exams. The knowledge of these variants is also important becausethey can be associated with other anomalies such as heartdiseases or polysplenia, and symptoms like dysphagia ordyspnea.Purpose. The aim of this study is to describe the vascularanatomical variants incidentally found on computed tomog-raphy imaging.Materials and Methods. A total of 3586 scans were per-formed between June 2010 and June 2011 with 16-row anda 64-row Multidetector CT scanners. Findings included:right aortic arch, aberrant right subclavian artery, aberrantleft subclavian vein, left superior vena cava, left inferiorvena cava, double inferior vena cava, circumaortic renalvein, retroaortic left renal vein, subhepatic vein and azy-gous continuation of the inferior vena cava. Conclusion. Vascular anatomical variants are found withrelative frequency on CT scans requested for other reasons.To be familiar with these anomalies may prevent confusions,diagnostic errors and unnecessary complementary examsand forces us to search for other associated anomalies. Keywords. Computed tomography multidetector. Vascularanatomical variants. Computed tomography.

INTRODUCTION

Given the extended use of computed tomography(CT) for the evaluation of the most varied symptomsand/or pathologies, and the use of intravenous con-trast in these studies, the evaluation of the differentvascular anatomic variants has become routine forradiologists.

A proper analysis of a CT scan requires knowled-ge of the vascular anatomy of the scanned area.Furthermore, it is important to check the correctarrangement of vessels and their filling defects in the

case of intravenous contrast-enhanced CT scans, bothfor future surgery planning and to account forsymptoms reported by the patient.

At the time of interpretation of CT findings, it isnot only necessary to consider the various anatomicvariants that may occur, but also to have the knowled-ge of their different classifications, relationship withdifferent symptoms and their association with otheranomalies.

Ignorance of these vascular variants may lead toserious problems for the patient and it may even havemedical and legal implications.

Departamento de Diagnóstico por Imágenes, CEMIC, Buenos Aires,Argentina.Correspondencia: Dr. Ricardo Cobeñas - [email protected]

Recibido: enero 2012; aceptado: septiembre 2012Received: january 2012; accepted: september 2012©SARdoi: 10.7811/rarv77n1a03

RAR - Volumen 77 - Número 1 - 2013 Página 1

Incidental findings of vascular anatomic variants

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The aim of this study is to describe the vascularanatomical variants incidentally found on CT imaging.

MATERIALS AND METHODS

A total of 3586 scans performed from June 2010 toJune 2011 with 16-row and 64-row multidetector CTscanners were reviewed. The age of patients involvedranged from 2 to 93 years old, with a mean age of 68years. Males were 2110, with an age range between 4and 90 years and a mean age of 65 years, while fema-les were 1476, with an age range between 2 and 93years and a mean age of 68 years. Indications werevaried; some of the most common included abdomi-nal pain, tumor staging and follow-up, evaluation ofrenal and hepatic cysts, arterial and venous thrombo-sis, CT-urography, CT enterography (CTE) and ultra-sounds that were difficult to read because of overlap-ping bowel gas.

Intravenous contrast was administered at a doseof 1.5 ml/kg of body weight, by infusion pump at anapproximate rate of 2.5 to 4 ml per second. A triphasicprotocol was used, with series at 30 seconds, 70seconds and 5 minutes for visualization of the bran-ches of the celiac trunk and superior mesentericartery, and of the origin of the hepatic, splenic, leftgastric and gastroduodenal arteries.

Furthermore, for studying abdominal conditions,2066 patients received an oral intake of 1000 ml ofwater mixed with 30 ml of iodinated contrast an hourprior to the scan, for better visualization of the diges-tive tract.

Patients were required to fast for at least 6 hoursprior to the scan in order to prevent gastrointestinalcomplications from intravenous contrast injection.

Oral or intravenous contrast was not administeredin patients who had a previous history of atopy.

RESULTS

Out of 3586 patients evaluated, 23 had vascular ano-malies; i.e., 0.64% (Table 1).We founded a total of five thoracic and eighteen abdo-minal vascular anomalies: Thoracic: 1 right aortic arch(RAA), 2 aberrant right subclavian arteries, 1 left infe-rior vena cava (IVC) and 1 aberrant left subclavianvein. Abdominal: 4 left inferior vena cava (IVC), 3double renal veins, 3 circumaortic left renal veins, 4retroaortic left renal veins, 1 double IVC, 1 accessorysuprahepatic vein and 2 interruption of the inferiorvena cava with direct continuation towards the aci-gos/hemiacigos vein.

DISCUSSION

Vascular anatomic variants are abnormalities in the

usual arrangement of vessels, which are found withrelative frequency on contrast CT imaging for reasonsunrelated to these abnormalities (1).

Right aortic arch

RAA is a rare and asymptomatic entity that isusually diagnosed incidentally. On plain chest radio-graph (X-ray), it may be confused with widening ofthe anterior and superior mediastinum and usuallydiagnosed after a chest CT scan (Fig. 1). Symptomsassociated with this congenital anomaly arise fromcompression of the airway and, less frequently, of theupper digestive tract, resulting in recurrent respira-tory tract infections, dry cough and dyspnea. This isa congenital malformation occurring during embryo-logic development as a consequence of a completeobliteration of the left 4th aortic arch and of the leftdorsal aorta (1,2).

Vascular anatomic variants N %

Thoracic 5 22,5%RAA 1 4,5%Aberrant right subclavian artery 2 9%Aberrant left subclavian artery 1 4,5%Left SVC 1 4,5%

Abdominal 18 77,5%Left IVC 4 17%Double renal vein 3 13%Circumaortic renal vein 4 17%Retroaortic renal vein 4 17%Accessory suprahepatic vein 1 4,5%IVC with azygos 1 4,5%Double IVC 1 4,5%

RAA: right aortic arch; SVC: superior vena cava; IVC: inferior vena cava.

Table 1: Number and percentages of thoracic andabdominal vascular variants found.

Fig. 1: Chest CT scan without IV contrast showing the aorta on theright (arrow).

Alejandro Rodriguez et al.


a b

Fig. 2: Aberrant right subclavian artery arisingfrom the posterior region of the aortic arch (arrow):(a) axial view, (b) coronal reconstruction, (c) volu-me rendering.

c

Aberrant right subclavian artery

Aberrant right subclavian artery is a malformationof the aortic arch, with an incidence of 0.5 % to 1.8 %.It is a distal branch arising from an otherwise normalaortic arch. It courses behind the trachea and esopha-gus, crossing the mediastinum obliquely from left toright (Fig. 2) (1,3-7).

Aortic arch with aberrant left subclavian artery

This is a rare anomaly, which is associated with aright aortic arch. It has an aortic diverticulum at itsorigin, the so-called Kommerell’s diverticulum. It maybe associated with the tetralogy of Fallot, approxima-tely in 3 % of cases (1-3,5).

Isolated left vertebral artery

The isolated left vertebral artery originates directlyfrom the aortic arch. It is one of the most common aor-tic arch branch anomalies, occurring in about 4% of thegeneral population (1,8).

Anomalous course of the right brachiocephalicvein trunk

Tortuosity and low position of the brachiocephalicvein relative to the aortic arch, in elderly patients, maysimulate a mediastinal mass (1).

Persistent left SVC

It rarely occurs in the general population and it isassociated with congenital cardiac malformations.The left subclavian and jugular veins directly draininto this abnormal SVC. It passes lateral to the aorticarch and main pulmonary artery, draining close to theright atrium, into the coronary sinus, posterior to theright ventricle (1,3) (Fig. 3).

Accessory left gastric artery

The accessory left gastric artery arises from the lefthepatic artery and is a variant gastric artery that sup-plies the cardias and fundus of the stomach. The inci-dence of this variant has been reported to be 3-14 % inangiographic studies (3,9,10).



a b

Fig. 3: (a) Chest CT scan without IV contrast showing persistent leftSVC. Catheter present inside (arrow). (b) 3D reconstruction showingleft superior vena cava (arrow) to the left of the aortic arch, draining intothe right atrium. (c) MIP (Maximum Intensity Projection) coronalreconstruction showing left superior vena cava (arrow), descending tothe left of the aortic arch.

c

a b

Fig. 4: (a) Axial view of the abdomen with presence of a retroaortic left renal vein (arrow). (b) Coronal view of the abdomen showing the retroaor-tic left renal vein (arrow).

Common hepatic artery not arising from theceliac trunk

The presence of a common hepatic artery supplyingthe entire liver parenchyma and not originating fromthe celiac trunk has been reported with an incidence of

2% to 5%. The most common anatomical variations inhepatic artery are an accessory left hepatic artery arisingfrom the left gastric artery in 3.0 % and an accessoryright hepatic artery branching off the superior mesente-ric artery in 12 % of cases (3,9,11).



a b

Fig. 5: (a) Coronal view showing 2 right renal veins entering into the IVC (arrows). (b) 3D reconstruction with posterior view, showing two rightrenal veins entering into the IVC (arrows). The right renal artery is seen between them.

Fig. 6: Abdominal CT scan with IV contrast evidencing the presence ofcircumaortic left renal vein (arrow).

Fig. 7: Abdominal CT scan without IV or oral contrast, showing dou-ble inferior vena cava (arrow).

Variations of celiac trunk

Variations in one of the three arteries of the celiactrunk are associated with another vascular anatomicalvariation in the rest of the body in 61-64 % of cases.

The rate of vascular variations findings in thisregion ranges between 30 % and 47% according tovarious reviews (9,10).

Renal vessels anomalies

The anatomy of left renal vessels is very importantbecause it is the preferred side for resection in kidneytransplantation donors.

One variant is the retroaortic left renal vein (Fig.4), which passes behind the aorta and drains into the

IVC. It can be seen either at the same level as a normalleft renal vein or as low as the confluence of iliac veinsto form the IVC (1,12-14).

Multiple renal veins are the most common variant,occurring in 15-30 % of individuals (Fig. 5).

The most common left renal vein variant is the cir-cumaortic vein (Fig. 6). It is a vascular ring around theaorta. Generally, the additional retroaortic vein con-nects to the IVC one to two vertebrae below the levelof the preaortic vein.

Left inferior vena cava

Left inferior vena cava results from persistence ofthe left supracardinal vein with regression of the rightsupracardinal vein. The infrarenal inferior vena cava


is located to the left of the aorta. Over the left renalvein, it crosses anterior to the aorta joining to the rightrenal vein to form a normal IVC to the right andupwards, until draining into the right atrium.

A direct association has been reported between thepresence of this vascular anomaly and an increasedincidence of deep venous thrombosis (1,14-18).

Double inferior vena cava

Both IVC can be equal in diameter or either ofthem may be dominant, and therefore have a largercaliber. In general the union of both IVCs occurs at thelevel of renal veins and it can be clearly seen both inaxial and coronal planes (Fig. 7) (1,14-18).

Azygos continuation of the inferior vena cava

When the subcardinal vein fails to join the hepaticveins during the sixth week of fetal life, blood returnsto the heart from the postrenal segment via the azygosor hemiazygos system, and hepatic veins drain intothe right atrium. This finding is usually associatedwith other abnormalities, such as asplenia or polys-plenia (1,3,16-18).

The retrohepatic segment of the IVC, usually loca-ted anterior to the right diaphragmatic crus and pos-terior to the hepatic caudal segment, is absent (1,3,9,14-18).

The widened azygos vein is usually seen on oneside of the aorta (Fig. 8) and the hemiazygos vein onthe other.

Thus, knowledge of any variation in vascular ana-tomy becomes essential in the preoperative evaluationof potential candidates for abdominal or endovascularsurgical procedures.

Accessory subhepatic or suprahepatic vein

This is an hepatic vein draining directly into theIVC, beneath the usual termination of suprahepaticveins. From the surgical viewpoint, this finding isimportant in cases of partial hepatectomy, as ligationof these vessels is necessary when performing resec-tion of segments drained by such accessory veins (19).

CONCLUSION

Vascular anatomical variants are incidentallyfound with relative frequency on imaging studiesrequested for other reasons.

Knowledge of these anomalies may prevent con-fusions and unnecessary complementary exams, andalso lead us to search for other associated anomalies.

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Fig. 8: Chest axial image where the upper arrow indicates the IVC, adja-cent to the liver, entering the right atrium, and the lower arrow showsa dilated azygos vein on one side of the aorta.


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The authors declare no conflicts of interests.

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