Our patient is very unusual in terms of the anatomy and aetiological classification of his cardiac mass, which to the best of our knowledge has not previously been described. Initially, the mass was deemed to be a congenital aneurysm, or a diverticulum protruding through the crux of the heart. There is frequently debate over distinguishing these two types of out-pouching. A review of the literature indicates that a sac with a short communicating neck, composed of well differentiated muscular layers, and showing synchronous contraction with the ventricular mass as documented by the presence of a systolic pattern of flow from the mass to the ventricular cavity,1,2
as well as an association with midline defects,3
would favor the diagnosis of a ventricular diverticulum. In contrast, aneurysms frequently have a wider neck, lack muscular layers, and show a paradoxal or absent pulsatilty, resulting in systolic flow from the ventricular cavity into the mass. In lesions of this type described thus far, there is a stronger association with congenital or acquired abnormalities, such as a perimembranous ventricular septal defect or coronary arterial disease.4
The pathological findings from our specimen, rather than supporting either the diverticular or aneurysmal aetiology, suggest the differential diagnosis to be between a defect in embryogenesis or a monophasic teratoma. Cardiac teratomas are uncommon at any age, but nearly two-thirds of those reported have been diagnosed in infants.5,6
Most have been described as located in the pericardium or near the base of the great vessels. Intracardiac teratomas are consistent with similar tumours in other locations, frequently consisting of a cystic area lined by a variety of epithelium and solid areas that are composed of neuralgic tissue, pancreas, thyroid, bone, or muscle.5
Although this mass was consistent with a monophasic teratoma, it is difficult to establish a distinction from a defect in embryogenesis. Its unusual composition, as well as its location, makes it atypical for an intracardiac teratoma. Consequently, a defect in embryogenesis may be the most likely cause of this mass.
A pre-operative concern for our patient was the possibility of rupture of the mass. Due to its unusual location, had the mass not remained intact, rupture could have occurred either into the pericardial cavity or to the right atrium. Had it ruptured to the right atrium, it would have produced the variant of atrioventricular septal defect also known as the Gerbode defect, namely a left ventricular-right atrial communication through the fibrous atrioventricular septum which may be either congenital or acquired. Whether acquired or congenital, this defect differs from the atrioventricular shunting frequently found in atrioventricular septal defects with common atrioventricular junction in that the essence of the Gerbode defect is the presence of discrete right and left atrioventricular junctions.7
The congenital form of the defect occurs in less than 0.1% of all patients with congenitally malformed hearts.8
The acquired Gerbode defect, also exceedingly rare, has been described as the result of endocarditis, aneurysm, trauma, myocardial infarction, and replacement of either the mitral or aortic valves.8
We have been unable, however, to find a report of an intact or ruptured defect comparable to the arrangement observed in our patient. Fortunately, in our patient, the mass remained intact until surgery. Resection has now resolved both the cardiomegaly and extra-systolic contractions, even if not answering all of the questions regarding the aetiology of the mass.