LE Rueff MD MPH; MB Srichai MD; JE Jacobs MD; L Axel PhD MD; RP Lim MBBS MMed FRANZCR.
CT and MRI appearances of cardiac pseudotumours
Article first published online: 25 JUL 2012
© 2012 The Authors; Journal of Medical Imaging and Radiation Oncology © 2012 The Royal Australian and New Zealand College of Radiologists
Journal of Medical Imaging and Radiation Oncology
Volume 57, Issue 5, pages 582–588, October 2013
How to Cite
Rueff, L. E., Srichai, M. B., Jacobs, J. E., Axel, L. and Lim, R. P. (2013), CT and MRI appearances of cardiac pseudotumours. Journal of Medical Imaging and Radiation Oncology, 57: 582–588. doi: 10.1111/j.1754-9485.2012.02411.x
Conflict of interest: No conflicts of interest to disclose.
Grants and Support: None.
- Issue published online: 13 OCT 2013
- Article first published online: 25 JUL 2012
- Manuscript Accepted: 28 FEB 2012
- Manuscript Received: 15 DEC 2011
- magnetic resonance imaging;
- multi-detector CT ;
Cardiac anatomic variants, vascular abnormalities and non-neoplastic mass lesions may be misinterpreted as tumours, potentially leading to inappropriate intervention. This article discusses the complementary role of multi-detector computed tomography and magnetic resonance imaging in the work-up of suspected masses. The cross-sectional imaging appearance of common or distinctive anatomic variants and pseudotumours, including ‘don't touch’ lesions, are reviewed.
Anatomic variants and pseudotumours can potentially be misinterpreted as cardiac tumours. This may cause significant morbidity or mortality if a benign finding or anatomic variant is mistaken for a pathologic or aggressive lesion, triggering inappropriate intervention. In particular, differentiation between thrombus and neoplasm is vital, as well as identification of lesions that are best left alone.
Echocardiography, with high axial spatial resolution and real-time capabilities, is often the means by which unsuspected mass lesions are first discovered. However, it is highly operator dependent, and restrictions in the acoustic window may limit visualisation of some structures. Therefore, computed tomography (CT) and magnetic resonance imaging (MRI) are increasingly being used to differentiate pseudotumours from true neoplasms. This pictorial essay reviews the strengths and weaknesses of CT and MRI in the evaluation of suspected cardiac mass lesions. The CT and MRI appearance of a number of common pseudotumours are reviewed, including anatomic structures, embryologic remnants, fat-containing lesions, vascular pathology and other non-neoplastic masses.
CT or MRI?
Understanding the strengths and limitations of CT and MRI helps determine subsequent work-up. With either modality, electrocardiographic (ECG)-gating for suppression of cardiac motion, and intravenous contrast, for differentiating enhancing neoplasms from vascular pathology or non-enhancing thrombi or vegetations, are essential.
In general, MRI, with excellent soft tissue contrast and temporal resolution of the order of 50 ms, is the preferred next step in the evaluation of a true or suspected mass. It offers a comprehensive assessment, encompassing morphology and function, without ionising radiation. Breath-hold, ECG-gated T1- and T2-weighted fast spin echo images, combined with double inversion-recovery to null blood signal, provide excellent tissue characterisation. T1-weighted imaging is particularly useful for identifying fat or subacute haemorrhage, and T2-weighted imaging can identify oedema and inflammation. Cine gradient-echo imaging allows evaluation of mass mobility and relationships with adjacent structures. Vascularity and/or fibrosis can be assessed with post-contrast T1-weighted imaging, including early dynamic and delayed inversion-recovery sequences. For vascular lesions, CT coronary angiography currently offers superior spatial resolution to balanced steady state free precession (bSSFP) MR angiography.
Multi-detector CT (MDCT)
MDCT offers high speed, sub-millimetre spatial resolution and large field of view imaging. It is very sensitive for identifying calcification, and is the modality of choice for patients with implanted devices where MRI is contraindicated, or in patients unable to lie supine for a relatively extended period of time. Prospectively gated images are sufficient for mass work-up, when functional information is not required, with an estimated 77% lower radiation dose compared with retrospectively gated imaging, which can impart a dose of up to 32 mSv without radiation reduction measures. Dynamic contrast-enhanced MDCT imaging may be considered to assess enhancement patterns of a known mass; however, this entails an additive radiation dose.
Anatomic structures and embryologic remnants
The crista terminalis (Fig. 1) is a fibromuscular ridge separating the smooth-walled posterior right atrium from the trabeculated right atrial appendage. The eustachian ridge (Fig. 2) is a contiguous embryologic remnant of the inferior vena cava (IVC) valve between the IVC orifice and coronary sinus. These normal structures may be mistaken for echogenic mass lesions at echocardiography. The Chiari network is another embryologic remnant, consisting of fibrous threads, commonly attached to the right atrial wall in relation to the IVC orifice. Due to its nature of very fine, fenestrated, mobile fibres, spatial resolution limitations can limit visualisation with MRI or CT.
Ventricular structures that may masquerade as a mass include a prominent septomarginal trabeculum (moderator band) or other prominent trabeculations (Fig. 3), identifiable by characteristic location and continuity with normal myocardium.
Epicardial fat, particularly atrioventricular groove fat (Fig. 1) may mimic a cardiac mass at echocardiography, but is easily identified by location outside of the myocardium and the embedded epicardial coronary arteries. Lipomatous hypertrophy of the interatrial septum (LHIS) is a developmental variant in which unencapsulated adipose tissue accumulates in the atrial septum. Generally asymptomatic, LHIS has been associated with atrial arrhythmias. It is confined to the interatrial septum, with smooth margins. It is often thicker cephalad with characteristic sparing of the fossa ovalis, giving a dumb-bell-shaped appearance. There is no enhancement, with homogenous fat attenuation at CT, and homogeneous T1 hyperintensity at MRI (Fig. 4). Fat-suppression sequences are confirmatory.
A number of vascular lesions may masquerade as a mass, and are important to correctly identify, as biopsy of a vascular lesion can be catastrophic. Interatrial septal aneurysms (ISA) are saccular deformities with focal atrial septal membrane deviation of greater than 10 mm into the left or right atrium. ISA can be associated with a patent foramen ovale or atrial septal defect, and paradoxical embolism. The cross-sectional imaging appearance is distinctive, with segmental outpouching of the interatrial septum into either atrium (Fig. 5).
A cardiac pseudoaneurysm is a saccular outpouching of the cardiac wall following contained ventricular rupture, most often secondary to myocardial infarction (Fig. 6). Pericardium forms the wall of a pseudoaneurysm. Large or recently formed pseudoaneurysms have a propensity to rupture, with ensuing tamponade and high mortality, requiring expedient surgical intervention. An imaging feature of pseudoaneurysms is non-visualisation of epicardial fat adjacent to the cavity. The superior soft tissue contrast of MRI allows differentiation of pericardium from myocardium, even with pericardial effusion. If thrombus is present within the pseudoaneurysm, this may appear as a non-enhancing filling defect.
Coronary artery aneurysm is defined as a 50% or greater increase in coronary arterial diameter compared with normal adjoining arterial segments (Fig. 7). It can present as a pseudotumour if its continuity with the epicardial coronary arteries is not appreciated. CT is able to depict calcification and plaque morphology, and may show heterogeneous enhancement in the arterial phase due to flow turbulence. Bright blood bSSFP MR angiography with or without contrast provides a radiation-free alternative. 3D reformations for either modality can clarify spatial relationships with adjacent anatomic structures for preoperative planning.
Other, less common, aneurysms that may be mistaken for a tumour include bypass graft aneurysms/pseudoaneurysms, intervalvular fibrosa pseudoaneurysms and sinus of Valsalva aneurysms. Morphology and location of these lesions is characteristic at MRI and CT. Bypass graft aneurysms or pseudoaneurysms arise from venous aortocoronary or arterial bypass grafts (Fig. 8). Intervalvular fibrosa pseudoaneurysms are in communication with the left ventricle, and arise from the intervalvular fibrosa, the junction point of the aortic and mitral valves, often secondary to infection or valve surgery (Fig. 9). In contrast, sinus of Valsalva aneurysms are more commonly congenital than acquired, and arise from one of the three sinuses of Valsalva, most commonly the right coronary sinus, above the aortic annulus (Fig. 10).
Non-neoplastic mass lesions
Intracardiac thrombus causes approximately 20% of ischaemic strokes, and accurate identification is important for stroke prevention. It most commonly occurs in patients with atrial fibrillation or infarcted myocardium, arising in regions of impaired myocardial motion. The key finding distinguishing thrombus from tumour is lack of contrast uptake at both CT and MRI. Thrombi appear as non-enhancing hypoattenuated lesions on CT (Fig. 11), although acute thrombi may be hyperattenuating. On MRI (Fig. 12), thrombus signal is variable on T1- and T2-weighted imaging, depending on its chronicity. Delayed inversion-recovery post-contrast images, with a long inversion time to null avascular thrombus, has been reportedly useful in thrombus identification, superior to cine gradient-echo imaging.
Extracardiac lesions may be inadvertently mistaken for a cardiac tumour, including congenital cystic lesions (pericardial, bronchogenic or duplication cysts) or hiatus hernia at plain film. A pericardial cyst is a congenital outpouching of the pericardial sac, typically asymptomatic. Uncommonly, life-threatening complications such as cardiac tamponade or bronchial obstruction may occur, necessitating percutaneous drainage or resection. These are well-circumscribed lesions attached to the pericardium, at the right cardiophrenic angle in up to 70% of cases. They are generally of simple fluid attenuation or signal (Fig. 13). Proteinaceous or haemorrhagic fluid content may increase CT density and appear T1 hyperintense at MRI. Bronchogenic cysts are most commonly found along the course of the tracheobronchial tree, whereas duplication cysts are more posteriorly located. Both bronchogenic and duplication cysts have similar imaging features to pericardial cysts at CT or MRI. Gas may be found within these cysts when they communicate with the aerodigestive tract or are complicated by infection.
Familiarity with the CT and MRI characteristics of anatomic variants and non-neoplastic mass lesions is essential for accurate differentiation from true neoplasms and appropriate patient management.
The authors wish to thank Martha Helmers for her expertise in compiling the figures.
- 2Cardiovascular MRI: Physical Principles to Practical Protocols. Lippincott Williams and Wilkins, Philadelphia, 2006..
- 5Langman's Medical Embryology, 10th edn. Lippincott Williams & Wilkins, Baltimore, 2006..