Lipomatous hypertrophy of the atrial septum – a benign heart anomaly causing unexpected surgical problems: a case report

Lipomatous hypertrophy of the atrial septum is a rare but increasingly recognized non-neoplastic benign abnormality of the heart. Since the first mention in literature in 1964, fewer than 300 cases of LHAS have been described, most of which were based on autopsy studies. Lipomatous lesion derives entirely from the upper and/or lower part of the atrial septum, typically sparing the fossa ovalis, giving a characteristic, considered by some to be pathognomonic, an hourglass-shaped image, with a tendency to bulge into the right atrium, which may be related with a thickening of crista terminalis (Fig. 3). The first descriptions of LHAS in vivo were made on the basis of echocardiography, and in 1983 Fyke et al. published the first diagnostic guidelines [16]. Currently, TTE, TEE, CT (preferred multislice CT – MSCT) and MRI are used for diagnostics. Transthoracic echocardiography, usually performed first, is not a very accurate diagnostic tool with limited imaging of the heart structures, however, transesophageal examination (TEE) is much more precise and shows the pathological mass quite well. CT scans enable the visualization of adipose tissue. Lipomatous changes also demonstrate minimal contrast enhancement, which allows us to exclude the other suspected pathologies. The typical localization, shape, and image, including the density of changes in CT, allows to differentiate LHAS from heart tumors and make a diagnosis without first confirming in histopathological examination [8, 17]. The actual incidence of LHAS in the population is not known. This is due to its asymptomatic course, and the lack of well-targeted diagnostics. Previously described in the literature cases were based on autopsy, surgery and clinical imaging incidental findings or were associated with the symptomatic course of the disease. Among the rare risk factors of LHAS are emphysema with steroid therapy, in which the predisposition to the mediastinal and intracardiac deposition of adipose tissue is observed, cereberotendinous xantomatosis, mediastino-abdominal lipomatosis and long-term parenteral nutrition [1, 11]. Arrhythmia, rarely associated with LHAS, was first observed in 1969 by Kluge [18]. The mechanism of its formation has not been explained, however, it seems to be related with the infiltration of adipocytes interfering with the structure of the atrial myocytes, and thus the normal conduction pathways are interrupted [11, 19]. Arrhythmia manifests mainly in atrial fibrillation, atrial premature complexes, supraventricular arrhythmias, ectopic and junctional rhythm. It is also presumed that the incidence of atrial arrhythmia is related to septal thickness [20]. Dickerson et al. presented a case of the patient with symptomatic LHAS who had atrial flutter, and following complete resection of the lesion, the symptoms completely resolved [21]. The mechanism in which the removal of LHAS resulted in the return of the sinus rhythm is unclear, although the authors speculate that the area of arrhythmogenic foci involved the right atrial wall with the crista terminalis, and as a result of resection, the pathological path between the superior vena cava (SVC) and the right atrium was discontinued, just like in the Cox-Maze procedure.

LHAS can cause undesirable consequences due to its size and localization. An abundant volume causing atrial septum bulging into the atrial cavities may cause symptoms, but most importantly may render some surgical and percutaneous interventions particularly challenging. Therefore, while pre-interventional recognition of LHAS in certainly important for cardiac surgery, this is even more important for invasive cardiological interventions involving transseptal catheterization access. This approach is commonly used in interventional cardiology, to treat number of anatomical defects of the heart, such as closure of atrial septal defects (ASDs), patent foramen ovales (PFO) or correction of the functional mitral regurgitation through percutaneous “edge-to-edge” mitral valve repair, as well as in interventional electrophysiology to treat left atrial arrhythmias through commonly used transseptal puncture [6]. A very rare problem related to the size of the mass and the anatomy of the right atrium are technical difficulties, as described above, during the bicaval cannulation, when commencing the CPB and difficulties in accessing the operated heart structures. In the presented case, resistance was encountered while inserting the venous cannulas. Based on the standardly performed intraoperatively TEE, as well as by analyzing the chest X-ray (Fig. 1) and CT scans, a diagnosis of LHAS was made (Figs. 4 and 5). Choosing the smaller cannula sizes allowed for an effective cannulation and transition to cardiopulmonary bypass in order to perform the surgery. Access from the left atrium to the operated mitral valve was significantly impeded, and the transseptal approach, without disturbing the LHAS structure, could not be possible.

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In the presented case, a complex cardiac surgery was successfully performed. Asymptomatic LHAS does not require cardiac surgery. Surgical treatment of LHAS should be limited only to cases of patients with marginal obstruction of the SVC or the right atrium, which is an indication for a resection of the lesion with simultaneous interatrial septum plasty. The performed procedure may be a beneficial therapeutic option in patients with arrhythmia [1, 9, 21]. Long-term benefits of the surgery and the risk of recurrence have not been investigated [2].

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