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PICTORIAL ESSAY
2011
:1;
51
doi:
10.4103/2156-7514.86666
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Non-Coronary Cardiac Findings and Pitfalls in Coronary Computed Tomography Angiography

Address for correspondence: Dr. Noriko Oyama-Manabe, Department of Diagnostic and Interventional Radiology, Hokkaido University Hospital, N15 W7, kita-ku, Sapporo, Japan norikooyama@med.hokudai.ac.jp
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Abstract

Non-coronary incidental findings are not rare. Kirsch et al found 67% non-coronary abnormalities with coronary computed tomography angiography (CCTA). Radiologists are expected to identify the extracoronary, intra- and para-cardiac anatomical structures and distinguish them from pathologic processes in CCTA. We have reviewed 2000 CCTA studies done at our institution with 64-MDCT. This pictorial essay presents case studies of non-atherosclerotic cardiovascular findings to recognize cardiac anatomic structures and how to distinguish them from pathologic processes. Correct interpretation of benign, clinically insignificant findings is crucial to avoid unnecessary additional imaging tests.

Keywords

Coronary computed tomography angiography
incidental non-coronary cardiac findings
intra-cardiac shunt
paracardiac structures
non-coronary cardiac structures

INTRODUCTION

Coronary computed tomography angiography (CCTA) is widely used in clinical practice. Clinicians, especially radiologists are expected to evaluate all extra-coronary, intra-, and para-cardiac anatomical structures and distinguish them from pathologic processes in coronary CCTA. Non-coronary incidental findings are not rare. Kirsch et al found 67% non-coronary abnormalities with CCTA.[1] Understanding the anatomy of the cardiac and para-cardiac structures is a key in assessing non-coronary cardiac incidental findings. It is important to identify the intra-cardiac anatomical structures that can mimic a disease and distinguish them from pathologic processes using reformatted images. This pictorial essay describes the anatomy of the cardiac and para-cardiac structures and reviews the appearance of non-coronary incidental findings and pitfalls in CCTA.

METHODS

We have reviewed 2000 CCTA studies performed at our institution with 64-MDCT scanner and present non-atherosclerotic cardiovascular findings to recognize cardiac anatomic structures and how to distinguish them from pathologic processes.

Coronary computed tomography angiography scan protocol

Dose of the non-ionic contrast used intravenously was 350 mgI/mL over a duration of 12 s. The average flow rate was 4.1 ± 2.8 mL/s and total amount of the contrast was 50.2 ± 10.3 mL. This was followed by 0.9% saline solution at a fixed duration of 7 s and the same flow rate as the contrast material.

If the heart rate was less than 60 beats per minute (bpm), CCTA was performed using the step and shoot (Snapshot Pulse) sequence. In patients with heart rate of more than 60 bpm, CCTA was performed using the helical technique with low helical pitch (cardiac helical). Patients with irregular heart rates or heart rates more than 60 bpm received intravenous beta-blocker. The dose administered was IV metoprolol in 5 mg doses, up to a maximum of 20 mg. The aim was to keep the heart rate below 60 bpm.

Coronary computed tomography angiography parameters used

Snapshot pulse

0120 kV variable mA 0.35 s/rot. temporal resolution 230 ms, 0.625 mm slice, 0.625 mm interval, R-R interval 75% (center) padding time 150 ms.

Cardiac helical

120 kV variable mA 0.35 s/rot. temporal resolution variable, 0.625 mm slice, 0.625 (or 0.312) mm interval, beam pitch variable (0.16-0.20) HR60-65: ECG dose modulation (R-R 65-85%).

Images were analyzed on a CT post-processing workstation (Advantage Windows, GE Healthcare) using commercially available software. Standard axial images acquired during end-diastole, volume rendering images and corresponding 2D multiplanar reformations were used for image interpretation.

Non-coronary-related intra-cardiac findings

It is important to pay attention to the cardiac chambers and myocardium in addition to coronary arteries to assess for congenital and anatomical variants that may mimic an abnormality. There are several normal variants as described below.

Cor triatriatum: mimicking the left atrial mass

This congenital anomaly was first described by Church in 1868, as a rare congenital heart defect, accounting for 0.1% of all congenital heart diseases.[2] It is characterized by the presence of a fibromuscular membrane [Figures 1a and 1b] dividing the left atrium into two chambers: A posterosuperior chamber into which the pulmonary veins drain, and an anteroinferior chamber that communicates with the left atrial appendage and the mitral valve.[3]

Figure 1: (a) 47-year-old woman with suspected coronary artery disease. Axial CT image shows spotty low density area in the left atrium. (b) 3D endocardial view shows membrane.
Figure 2: 42-year-old man with no symptom. Axial CT image shows spotty low density area on the right wall in the right atrium.

Crista terminalis: mimicking the right atrial mass

A vertically orientated fibromuscular ridge at the posterolateral region of the right atrium Figure 2, formed by the junction of the sinus venous and primitive right atrium. Besides mimicking right atrial mass, crista terminalis is an important anatomic structure responsible for paroxysmal atrial fibrillation and atrial flutter by initiating ectopic atrial beats.[4]

Ventricular diverticula

The incidence of congenital ventricular diverticula was reported to be as high as 0.4% in an autopsy series of patients with cardiac diseases.[5] The diverticula ranged from 0.2 to 1.4 cm in maximum dimension. The diverticula showed contractile properties, appearing smaller in systolic phases than in diastolic phases, which indicated that the tissue surrounding the diverticula was primarily muscle tissue.[6]

On the other hand, ventricular septal aneurysms show a paradoxical expansion in systole. Diverticula can be seen in both ventricles [Figures 3 and 4].[7]

Figure 3: 70-year-old woman with angina. MPR image shows long-axis view of diverticulum in diastolic phase.
Figure 4: 53-year-old man with angina. MPR images show protrusion of the contrast media to the septum, representing the right ventricular diverticulum.

Ventricular septal aneurysm

Ventricular septal aneurysms are defined by bowing of the septum 10-15 mm to either side. The size of the base of the aneurysm is important and must be more than 15 mm but not involve the entire septum.[8]

The prevalence of cardiac septal aneurysms is 0.2-3% in the general population. Myocardium surrounds the contrast media indicating aneurysm [Figures 5a and 5b], while ventricular septal defect [Figure 6] shows left to right contrast shunt without muscle wall.

Figure 5: 81-year-old man with suspected coronary artery disease, (a) Four chamber view, (b) Short axis view of the ventricles. Myocardium surrounds the contrast media protruding toward right ventricle (RV) indicates aneurysm.
Figure 6: 62-year-old man with known ventricular septal defect. Ventricular septal defect shows left ventricle (LV) to right ventricle (RV) contrast shunt (arrow) without muscle wall.

Patent foramen ovale

A patent foramen ovale (PFO) is a persistent valvular-like connection between the left and right atrium [Figures 7a and 7b]. During the first months of life, adhesions between the septum primum and secundum form, closing this embryological connection. In approximately 25% of the general population, this connection persists into adult life, resulting in a potential right-to-left shunt.[9] In some patients, the PFO may be the pathway through which thrombotic emboli, air emboli, desaturated blood are shunted into the left-sided cardiac chambers. ECG-gated CCTA performed with a 64-MDCT scanner can be used to reliably detect and evaluate size and shunt grade of the PFO.[1011]

Williamson et al described the CT criteria for diagnosing PFO. The criteria are:

  1. Presence of a distinct flap in the left atrium at the expected location of the septum primum.

  2. Presence of a continuous column of contrast material between the septum primum and septum secundum.

  3. Presence of a jet of contrast material from the column into the right atrium.

Using above described three CT criteria results in 100% specificity for the diagnosis of PFO.[10]

Figure 7: 49-year-old woman with angina pectoris. (a) Coronal oblique view. Coronal oblique CT image shows characteristic findings of patent foramen ovale (PFO) with left atrial flap (arrow), continuous contrast column connecting the left (LA) and right atria (RA), (b) Four chamber view. A left-to-right PFO shunt is visible with contrast media jet (arrow) through foramen ovale.

Left appendage / Left atrial thrombus

Rhythm abnormalities, such as atrial fibrillation, and various cardiac chamber and valvular abnormalities have been associated with the formation of left atrial appendage thrombi.[12] An intracardiac thrombus is depicted as a filling defect on CCTA [Figures 8a and 8b]. The pseudo-filling defects seen on CT images represent incomplete mixing of CT contrast material and blood [Figures 9a and 9b]. Two-phase cardiac CT angiography can be used to differentiate thrombus from circulatory stasis, which may cause a pseudo-filling defect on early-phase CT images. [13]

Figure 8: 69-year old man with chronic atrial fibrillation showed consistent filling defect in LAA, indicating LAA thrombus (a) Early-phase CT image shows triangular filling defect (arrow) in LAA, (b) Late-phase CT angiographic image shows no filling defects in LAA.
Figure 9: Pseudo-filling defect: 51-year-old man with chronic atrial fibrillation (a) Early-phase CT image shows triangular filling defect (arrow) in LAA, b) Late-phase CT angiographic image shows no filling defects in LAA.

Coronary artery related, but non stenotic findings

It is also important to pay attention to assess variants of coronary arteries in a CCTA study.

Anomalies of the coronary arteries may be found incidentally in 0.3%-1% of healthy individuals.[14]

Kim et al classified the coronary artery anomalies into anomalies of origin, course, and termination.[15]

Anomalous origin

High take off: “High take off” refers to the origin of either the RCA [Figure 10a] or the LCA at a point above the junctional zone between its sinus and the tubular part of the ascending aorta.[15]

Figure 10: 61-year-old woman with suspected coronary artery disease (a) On VR, the RCA demonstrates a high take-off above the sinotubular junction, (b) On axial CT image, the RCA (arrow) shows inter-arterial course between aorta (Ao) and pulmonary artery (PA), (c) The stretch view (left) and the trans-axial view (right) show narrowing of the proximal RCA.

Multiple ostia: Separate ostia (multiple ostia) of the LCA and LCx artery may occur in a small percentage (0.41%) of individuals with otherwise normal anatomy [Figure 11].[16]

Figure 11: 70-year-old woman with suspected coronary artery disease. VR image shows separate ostia of the LAD and LCX arteries.

Single coronary artery: In the anomalous situation of a single coronary artery, only one coronary artery arises with a single ostium from the aortic trunk. This is an extremely rare congenital anomaly that is seen in only 0.0024%-0.044% of the population.[17]

Anomalous origin and course

In terms of clinical importance, recognized hemodynamically significant coronary artery anomalies are anomalous origins arising from the pulmonary artery; inter-arterial courses that indicate malignancy between the aorta and pulmonary artery [Figures 10a10c]. Hemodynamically insignificant or courses that indicate benignity of the coronary arteries are retroaortic, prepulmonic, and subpulmonic locations.[15]

Myocardial bridging

Myocardial bridging is a congenital anomaly that results in abnormal positioning of the coronary artery and most commonly occurs in the mid LAD [Figure 12]. Jacobs et al reported the prevalence of 10.4% on CCTA.[1819] Myocardial bridging is generally regarded to be a benign condition; however, myocardial bridging has been reported in association with myocardial ischemia and infarction, conduction abnormalities, and sudden death.[20] The length and depth of the tunnelled arterial segment have been shown to correlate with the presence of myocardial ischemia and sudden death.[21]

Figure 12: 62-year-old woman with suspected coronary artery disease. Curved MPR shows long segment of myocardial bridging of mid LAD.

Anomalous termination

Coronary artery fistula

Coronary artery fistula is a condition in which a communication exists between one or two coronary arteries and either a cardiac chamber [Figures 13a and 13b], the coronary sinus, the superior vena cava, or the pulmonary artery [Figures 14a and 14b][15] Coronary artery fistulas are found in 0.1-0.2% of patients who undergo coronary angiography.[22]

Figure 13: 79-year-old man with suspected coronary artery disease (a) VR image shows tortuous right ventricular branch (arrow) from the RCA, (b) Short axis image of the ventricles shows contrast flow into the right ventricle (arrow: shunt sign).
Figure 14: 65-year-old man with diabetes mellitus (a) VR image shows multiple tortuous communicating vessels originating from the proximal LAD artery, (b) The communicating vessels drain into the main pulmonary artery (PA). Note that contrast flow into the PA (arrow: shunt sign).
Coronary artery aneurysms

Coronary artery aneurysms are defined as segments with a diameter greater than 1.5 times the normal adjacent artery segment and can be classified as fusiform or saccular.[23] Coronary artery aneurysms are small and thick walled and have a low risk of spontaneous rupture.[24] Giant aneurysms are rare and usually congenital in origin. Another cause of giant aneurysms is Kawasaki's disease [Figures 15a and 15b].Kawasaki's disease is the most frequent cause of coronary aneurysms worldwide, whereas atherosclerotic coronary disease is the most common cause in the United States. The prognosis of coronary artery aneurysm is related to the severity of concomitant obstructive coronary disease.[25]

Figure 15: 26-year-old man with Kawasaki disease. VR (Figure 15a) and CPR (Figure 15b) images show partly calcified thrombosed saccular aneurysm in proximal LAD. He has another fusiform aneurysm in the right coronary artery.

Other non-coronary findings

Pericardial disease

A spectrum of abnormalities involving pericardium exists, ranging from small defects to total absence of the pericardium. Left-sided absence of the pericardium allows interposition of lung tissue between the aorta and the main segment of the pulmonary artery.[26]

Pericarditis

The causes of pericarditis are numerous, including postsurgical, postradiation, posttraumatic, and postinfectious. However, idiopathic pericarditis is most common. Thickening of the pericardium, often with and without calcifications, can be clearly depicted with CT.[26] Pericardial enhancement may indicate active inflammation [Figure 16]. Pericardial calcifications, bi-atrial enlargement, and pleural effusions are highly suggestive of constrictive pericarditis resulting in impaired ventricular filling.

Figure 16: 55-year-old man with fever up. Axial CT shows enhanced pericardial thickening without calcification (arrow). Open biopsy of pericardium revealed tubercular pericarditis.

Abnormal coronary sinus

The unroofed coronary sinus (UCS) is a spectrum of cardiac anomalies in which part or entire common wall between the coronary sinus (CS) and the left atrium is absent [Figures 17a and 17b].[2728] In a normal case, a normal-sized coronary sinus runs parallel to the posterolateral branch [Figure 17c]. A dilated CS and its relationship with coronary arteries are clearly depicted by CCTA.

Figure 17: 71-year-old woman with pulmonary-to-systemic blood flow ratio (Qp:Qs) more than 3 (a) The roof of the coronary sinus (CS) was partially absent (arrow). VR image shows dilated, partially unroofed CS and its relationship to the left atrium (LA). Note the distal CS is normal in size, (b) Axial CT image shows the dilated CS, (c) Another 76-year-old man with coronary artery disease. VR shows normal sized CS (arrow).

CONCLUSION

It is important for the practicing radiologist to be familiar with the imaging appearances of unusual cardiac anomalies during the interpretation of CCTA. Normal anatomical variants can cause confusion to the inexperienced observer and must be recognized to avoid unnecessary intervention. Knowledge of the CCTA appearance of various coronary artery and non-coronary artery cardiac anomalies is essential for accurate diagnosis.

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