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Ventricular Diverticula on Cardiac CT: More Common Than Previously Thought

¹ All authors: Department of Radiology, New York University School of Medicine, 530 First Ave., HCC-C48, New York, NY 10016.

Received September 15, 2006; accepted after revision November 21, 2006.

 
Address correspondence to M. B. Srichai (srichai{at}alum.mit.edu).

Abstract

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OBJECTIVE. We describe the findings of contrast-enhanced gated cardiac CT in 15 patients with 23 incidentally noted cardiac ventricular diverticula.

CONCLUSION. Cardiac diverticula most commonly occur in the left ventricle but have been reported to occur in all chambers of the heart. Despite reports of their rare occurrence, cardiac ventricular diverticula are fairly common findings in patients undergoing cardiac MDCT angiography.

Keywords: cardiac CT • cardiovascular disease • coronary artery disease • heart • MDCT angiography • ventricular diverticula

Introduction

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Congenital cardiac diverticula are reportedly rare findings, especially when first diagnosed in adults [1, 2]. They are most often found in the left ventricle (LV) but have been reported in all chambers of the heart [1]. Various classification schemes for describing different features associated with cardiac diverticula and prognostic implications have been proposed. We describe our institution's experience using cardiac MDCT angiography (MDCTA) to diagnose cardiac ventricular diverticula.

Materials and Methods

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The reports of all MDCTA examinations of the coronary arteries performed at our institution between November 2004 and August 2006 were retrospectively reviewed, and a search for the diagnosis of "ventricular diverticula" was performed. Once patients were identified, their images were reviewed by two radiologists in consensus, and the following data were recorded: sex and age of the patient; number, location, and size of diverticulum or diverticula present; end-diastolic volume, end-systolic volume, and ejection fraction of the involved ventricle; degree of coronary artery disease; and presence of any other cardiac abnormality.

To distinguish diverticula from trabeculations, we adopted a strict criterion for defining diverticula to ensure that the patients identified from our review had lesions that definitely involved the compacted myocardium. We decided to use involvement of at least half of the compacted myocardial wall thickness in the diastolic phase as the cutoff. Because muscular diverticula may completely compress during systole and hence no longer be visible, we did not use images obtained during systole as part of the diagnostic criteria for diverticulum.

Cardiac MDCTA examinations were performed using a 64-MDCT single-source scanner (n = 567) (Sensation 64, Siemens Medical Solutions) or a dual-source CT scanner (n = 113) (Definition, Siemens Medical Solutions). A volume data set was acquired from the level of the carina through the diaphragm using thin collimation and ECG gating. Imaging was performed after the IV injection of 50–100 mL of 320–370 mg I/mL of nonionic contrast material (either iodixanol [Visipaque 320, GE Healthcare] or iopromide [Ultravist 370, Berlex Imaging]) administered at a rate of 4.0–5.0 mL/s via a power injector.

The volumetric data set was reconstructed using retrospective ECG-gating techniques at 10% phase intervals throughout the cardiac cycle to encompass both systolic and diastolic phases. Studies were reviewed on a 3D workstation equipped with multiplanar and maximum-intensity-projection reformations to visualize the heart along the cardiac axes and to assess cardiac function. The institutional review board at our institution approved the protocol for this study.

Results

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A total of 680 cardiac MDCTA studies were performed in 675 patients during the study period. The indications for MDCTA were suspected coronary artery disease (n = 592), coronary artery anomaly (n =4), coronary artery stent patency (n = 56), and coronary artery bypass graft assessment (n = 34). All cases were retrospectively reviewed, and 15 patients were found to have a diverticulum or diverticula in the LV (2.2% prevalence). A diverticulum was distinguished from an aneurysm by the presence of predominantly myocardial tissue, as opposed to fibrous tissue, surrounding the ventricular outpouching. No case of right ventricular diverticulum was noted.

The patients with LV diverticula included 11 men and four women between the ages of 26 and 84 years old (mean, 54 years). The clinical and imaging characteristics of the patients are shown in Table 1. The patients were referred for several indications including chest pain (n = 8); arrhythmia (n = 1); risk factor assessment (n = 2); known cardiac disease, including valve dysfunction (n = 1), hypertrophic cardiomyopathy (n = 1), and coronary artery bypass graft (n = 1); and prior percutaneous coronary intervention (n = 1). All patients had normal LV function with no evidence of regional wall motion abnormalities.

Twenty-three diverticula were found in these 15 patients. All diverticula were located in the LV and were most common along the inferior or inferoseptal wall, primarily at the right ventricular insertion point (Figs. 1A, 1B, 1C, and 1D). Two diverticula were located at the apical septum (Figs. 2A, 2B, 2C, and 2D), and one was located in the anteroseptal wall. The diverticula were single in nine patients (60%) and multiple in six patients (40%) (Figs. 3A, 3B, 4A, and 4B). When multiple diverticula were present, they were commonly found clustered close to one another. Nine (39%) diverticula had a wide connection with the LV ( 1 cm in any one dimension), and 14 (61%) had a narrow connection with the LV (< 1 cm).

View larger version (92K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A —39-year-old man with single left ventricular diverticulum located at mid ventricle level at inferior right ventricular insertion site (patient 4 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT single-source scanner show long-axis (A and C) and short-axis (B and D) views of diverticulum (arrow, A and B) in diastolic (A and B) and systolic (C and D) phases of cardiac cycle. There is complete closure of diverticulum during systole.

View larger version (118K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B —39-year-old man with single left ventricular diverticulum located at mid ventricle level at inferior right ventricular insertion site (patient 4 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT single-source scanner show long-axis (A and C) and short-axis (B and D) views of diverticulum (arrow, A and B) in diastolic (A and B) and systolic (C and D) phases of cardiac cycle. There is complete closure of diverticulum during systole.

View larger version (86K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1C —39-year-old man with single left ventricular diverticulum located at mid ventricle level at inferior right ventricular insertion site (patient 4 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT single-source scanner show long-axis (A and C) and short-axis (B and D) views of diverticulum (arrow, A and B) in diastolic (A and B) and systolic (C and D) phases of cardiac cycle. There is complete closure of diverticulum during systole.

View larger version (105K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1D —39-year-old man with single left ventricular diverticulum located at mid ventricle level at inferior right ventricular insertion site (patient 4 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT single-source scanner show long-axis (A and C) and short-axis (B and D) views of diverticulum (arrow, A and B) in diastolic (A and B) and systolic (C and D) phases of cardiac cycle. There is complete closure of diverticulum during systole.

View larger version (147K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A —80-year-old man with single left ventricular diverticulum localized to apical septum (patient 5 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT single-source scanner show four-chamber (A and C) and two-chamber (B and D) views of diverticulum (arrows) in diastolic (A and B) and systolic (C and D) phases of cardiac cycle. Diverticulum is contractile but does not completely close during systole.

View larger version (150K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B —80-year-old man with single left ventricular diverticulum localized to apical septum (patient 5 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT single-source scanner show four-chamber (A and C) and two-chamber (B and D) views of diverticulum (arrows) in diastolic (A and B) and systolic (C and D) phases of cardiac cycle. Diverticulum is contractile but does not completely close during systole.

View larger version (143K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C —80-year-old man with single left ventricular diverticulum localized to apical septum (patient 5 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT single-source scanner show four-chamber (A and C) and two-chamber (B and D) views of diverticulum (arrows) in diastolic (A and B) and systolic (C and D) phases of cardiac cycle. Diverticulum is contractile but does not completely close during systole.

View larger version (150K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2D —80-year-old man with single left ventricular diverticulum localized to apical septum (patient 5 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT single-source scanner show four-chamber (A and C) and two-chamber (B and D) views of diverticulum (arrows) in diastolic (A and B) and systolic (C and D) phases of cardiac cycle. Diverticulum is contractile but does not completely close during systole.

View larger version (109K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A —26-year-old woman with multiple left ventricular diverticula (patient 2 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT single-source scanner in diastolic (A) and systolic (B) phases show two diverticula (arrows) located close to one another. Diverticula close completely during systole.

View larger version (112K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B —26-year-old woman with multiple left ventricular diverticula (patient 2 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT single-source scanner in diastolic (A) and systolic (B) phases show two diverticula (arrows) located close to one another. Diverticula close completely during systole.

View larger version (83K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4A —47-year-old woman with multiple left ventricular diverticula (patient 13 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT dual-source scanner in diastolic (A) and systolic (B) phases show three diverticula (arrows) located close to one another. Diverticula close almost completely during systole.

View larger version (83K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4B —47-year-old woman with multiple left ventricular diverticula (patient 13 in Table 1). Multiplanar reformatted MDCT angiography images from 64-MDCT dual-source scanner in diastolic (A) and systolic (B) phases show three diverticula (arrows) located close to one another. Diverticula close almost completely during systole.

Discussion

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A diverticulum is defined as a pouch or sac branching out from a hollow organ or structure, such as the intestine [3]. These malformations were first described in 1816, and surgical resection of these malformations dates back to 1912 [1].The incidence of congenital ventricular diverticula was previously reported to be as high as 0.4% in an autopsy series of patients who had died as a result of cardiac disease, but the incidence was only 0.26% in a population of nonselected patients referred for cardiac catheterization [4]. In a large retrospective echocardiographic study, researchers found a prevalence of only 0.04% [5].

There is no uniform classification system for cardiac ventricular diverticula. In some studies, investigators have classified ventricular diverticula into fibrous and muscular types [6], whereas others have differentiated congenital diverticula from congenital aneurysms on the basis of the size of the connection with the ventricle. In our study, we defined ventricular diverticula as any outpouching from the ventricle that had walls composed of ventricular myocardium; its connection to the ventricle may be wide or narrow.

Depending on the amount of myocardial fibers involved, diverticula may be primarily muscular or fibrous in nature. Muscular forms tend to show synchronous contractile function with the ventricle and the typical features described in the literature for congenital ventricular diverticula. Histologically, muscular diverticula contain all layers of the ventricular myocardium with the myocardial architecture preserved and minimal fibrous tissue [1, 7]. Fibrous forms often show akinetic or dyskinetic contractile function with the ventricle, features typically described in the literature for congenital ventricular aneurysms. Histologically, fibrous diverticula typically have connective tissue composed of reticulin fibers and few or no muscle fibers are present [1].

The sizes of ventricular diverticula described in the literature range from as small as 0.5 cm in diameter to as large as 8–9 cm [1]. Ventricular diverticula are commonly found in the apex and perivalvular area, although diverticula have been reported in nearly all locations of the ventricular wall except the ventricular septum. In the literature, apical diverticula have a high association (> 70%) with other congenital abnormalities, including septal defects, pulmonary stenosis, and dextrocardia [7, 8]; however, in our study, there were two cases of apical diverticula and an associated cardiac anomaly was not detected in either case. Fibrous diverticula with a narrow connection to the ventricle are commonly reported in the subvalvular area and are often associated with valvular incompetence [9].

Congenital ventricular diverticula are often asymptomatic and are usually found incidentally during diagnostic imaging procedures performed for other reasons. No typical or pathognomonic ECG changes are known, and specific laboratory tests for the diagnosis are not available. Symptomatic patients may have ventricular arrhythmias ranging from occasional premature ventricular contractions to sudden cardiac death. In some cases, evaluation for a cardiac source of embolism, atypical chest pain, or nonspecific heart murmur has led to the diagnosis of ventricular diverticulum, although no direct link has been established to our knowledge.

Depending on the size of the diverticulum, radiographic changes in the cardiac silhouette can occasionally be observed, including deviation of the heart's border, abnormal cardiac contour, and cardiomegaly. Transthoracic echocardiography and transesophageal echocardiography, including 3D echocardiography, are more universally available and are commonly used to diagnose ventricular diverticula. Accompanying cardiac malformations can be evaluated on echocardiography, and Doppler sonography can provide additional information about the contractility and myocardial perfusion of the diverticulum [10, 11].

Congenital ventricular diverticula should be differentiated from other causes of acquired ventricular aneurysms such as those that occur after myocardial infarction, myocardial inflammatory disease such as sarcoidosis or myocarditis, infectious endocarditis, or trauma [1]. Additional causes of ventricular aneurysm include connective tissue disease and ventricular dysplasia, as seen in patients with arrhythmogenic right ventricular cardiomyopathy. Often the distinction between fibrous ventricular diverticula and these entities can be made only with knowledge of cardiac history and visualization of an associated abnormality—for example, significant coronary artery disease. However, because aneurysms consist of predominantly fibrous tissues that have replaced myocardium and because aneurysms are associated with abnormal myocardial contour in diastole and myocardial bulging during systole, they usually can be distinguished from muscular diverticula. In particular, three of the patients included in this study were noted to have severe coronary artery disease, but in all cases the diverticula closed completely during systole, which suggests that the diverticula were primarily muscular in all of these cases.

Isolated ventricular noncompaction is another entity that needs to be considered in the differential diagnosis. In cases of isolated ventricular noncompaction, endomyocardial morphogenesis is impaired and hypertrophy of the LV myocardium with prominent trabeculation and deep intertrabecular recesses is present. Although ventricular noncompaction can appear similar to ventricular diverticula, diagnosis of ventricular noncompaction usually requires the finding of more than three deep intertrabecular recesses [12, 13].

The high spatial resolution and high temporal resolution offered by ECG-gated cardiac MDCTA provide a unique opportunity to evaluate the ventricular myocardium in a manner not previously afforded by nongated CT or by alternative imaging techniques such as echocardiography. As the number of patients referred to cardiac MDCTA for evaluation of coronary artery disease increases, there is an opportunity to evaluate a population of patients who may have a higher incidence of ventricular diverticula.

In this study, we found a greater incidence of ventricular diverticula (2.2%) than has previously been reported (0.04–0.4%). The true incidence of ventricular diverticula has likely been underreported in the literature because of limitations inherent in the previously available imaging techniques and differences in the patient populations studied. Because cardiac MDCTA is frequently performed in patients with symptoms of chest discomfort and because chest pain may be a signal of a cardiac abnormality, the incidence of ventricular diverticula is probably higher in this population than in the general asymptomatic population.

The prognostic implications of the diagnosis of small muscular ventricular diverticula are to date unknown. In the current series of cases, no specific interventions other than close clinical follow-up were performed. In addition, no further imaging follow-up has been performed, and whether the size or number of ventricular diverticula already present will increase over time is not clear.

This study has a few limitations. First, ventricular diverticula cases were identified by retrospective review of reports from cardiac MDCTA studies, so the true incidence may be underestimated because this unusual entity is underreported. At our institution, almost all of the cardiac MDCTA studies are prospectively interpreted by two reviewers in consensus to generate the official report and most of the reports were generated by two of the most senior reviewers, so the likelihood of underdiagnosis is low. Second, although we chose a strict criterion for the identification of this entity that is consistent with the pathologic description of ventricular diverticula, pathologic proof of diagnosis was not obtained in any of our patients. However, given that the true prognostic implication of ventricular diverticula is unknown and that treatment of this entity is controversial, there is no indication to pursue an invasive procedure to confirm the diagnosis in these patients.

In summary, this study shows that the incidence of congenital ventricular diverticula is higher than previously reported. Ventricular diverticulum is underdiagnosed in patients with atypical chest pain syndrome or arrhythmia. Although cardiac MDCTA provides a new method for diagnosing this entity, more information about its natural history and prognosis is needed.

References

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