Extensive Lipomatous Hypertrophy of the Interatrial Septum with Involvement of the Right Atrium

An 81-year-old man with hypertension, diabetes, paroxysmal atrial fibrillation, and history of remote ischemic stroke underwent workup for abdominal pain, revealing a renal cell carcinoma with tumor thrombus extending into the hepatic inferior vena cava (IVC). He was referred to our institution for nephrectomy and IVC thrombectomy. Perioperative cardiac evaluation included a transthoracic echocardiogram from the referring institution that reported a mass in the right atrium (RA). After induction of general anesthesia, we performed a transesophageal echocardiogram (TEE) to characterize the mass before proceeding with surgery. The midesophageal bicaval view revealed a massively thickened interatrial septum (IAS) (maximal thickness 3.5 cm) (Fig. 1). (Video 1, see Supplemental Digital Content 1, https://links.lww.com/AA/A58. Midesophageal bicaval view showing massively thickened interatrial septum. LA = left atrium; IAS = interatrial septum; IVC = inferior vena cava; SVC = superior vena cava; RA = right atrium.) Rotation of the multiplane TEE probe to 123° demonstrated thickening of the upper and lower portions of the IAS, with sparing of the fossa ovalis, a pattern characteristic of lipomatous hypertrophy, and a 2.5-cm mass of similar echogenicity in the RA, adjacent to the IVC. (Video 2, see Supplemental Digital Content 2, https://links.lww.com/AA/A59. Midesophageal modified bicaval view showing lipomatous hypertrophy of the interatrial septum and a 2.5-cm mass of similar echogenicity in the RA. An atrial septal aneurysm can be seen, with septal movement >10 mm from baseline. LA = left atrium; IAS = interatrial septum; RA = right atrium; LH = lipomatous hypertrophy of the interatrial septum; IVC = inferior vena cava; SVC = superior vena cava.) The mass appeared to be continuous with the lipomatous hypertrophy of the IAS and was of similar echogenicity (Fig. 2). Pulsed wave, color flow, and continuous wave Doppler analysis of the IVC and of the cavoatrial junction demonstrated that the mass was unrelated to the tumor in the IVC and did not cause obstruction to atrial inflow. An atrial septal aneurysm (septal movement >10 mm from baseline by M-mode Doppler analysis) and patent foramen ovale were incidentally noted.Figure 1.: Midesophageal bicaval view showing massively thickened interatrial septum (IAS). LA = left atrium; IVC = inferior vena cava; SVC = superior vena cava; RA = right atrium.Figure 2.: Midesophageal bicaval view demonstrating continuity between the right atrial mass and the lipomatous hypertrophy (LH) of the interatrial septum (IAS). LA = left atrium; RA = right atrium; IVC = inferior vena cava; SVC = superior vena cava.Based on the TEE findings, we advised the surgical team that the right atrial mass likely represented lipomatous hypertrophy, and that surgical intervention was unnecessary because the mass did not cause hemodynamic compromise. The planned nephrectomy and thrombectomy proceeded uneventfully, and the patient recovered well. Postoperatively, cardiac magnetic resonance imaging was performed to verify the TEE-based diagnosis and revealed massive thickening of the IAS and right atrial wall. The lesions were bright on T1-weighted imaging and illuminated on fat-saturation sequences, confirming the diagnosis of lipomatous hypertrophy (Fig. 3).Figure 3.: T1-weighted fat-saturation magnetic resonance imaging demonstrating saturation in areas of extensive lipomatous hypertrophy of the interatrial septum and the right atrium (RA). RV = right ventricle; LA = left atrium; LV = left ventricle.Lipomatous hypertrophy is a histologically benign proliferation of adipose tissue that appears echocardiographically as a hyperechoic enlargement of the upper and/or lower part of the IAS but sparing the fossa ovalis, resulting in a characteristic bilobar, dumbbell-shaped morphology.1 Although no uniform size criteria have been established, a thickness of ≥2 cm is frequently cited. Lipomatous hypertrophy is well visualized in the midesophageal bicaval and 4-chamber views, but variable probe rotation and multiplane angles may be necessary for optimal imaging. Lipomatous hypertrophy is a relatively common lesion, particularly in the cardiac surgical population, where its prevalence has been found to be as high as 43% (compared with 1%–8% in the general population).2,3 Several TEE findings suggested that this patient's mass represented an extension of lipomatous hypertrophy into the RA. First, the mass had similar echogenicity to the lipomatous hypertrophy of the IAS and appeared on several views to be continuous with it. Second, because IVC stenosis is associated with a 3- to 4-fold increase in flow velocity,4 the absence of flow acceleration in the IVC on Doppler interrogation, and the absence of luminal narrowing in short- and long-axis views of this vessel, proved that IVC tumor thrombus did not extend above the liver and was therefore unrelated to the right atrial mass. Finally, the well-circumscribed border of the mass, uniform echogenicity without cystic elements or calcification, and absence of associated thrombus, vegetation, or pericardial effusion were all consistent with a benign process. Although lipomatous hypertrophy is histologically benign, surgical intervention should be considered for lesions causing intractable arrhythmias or hemodynamically significant obstruction. Supraventricular tachyarrhythmias or various degrees of heart block can arise from lipomatous involvement of the atrial wall or atrioventricular conduction pathways.1 Rare cases causing symptomatic obstruction (with apparent narrowing of the superior cavoatrial junction on TEE) have been reported.5,6 Although Doppler flow profiles were not described in these reports, separate Doppler studies demonstrated that obstruction at the cavoatrial junction results in turbulent flow, increased velocity downstream of the obstruction, and loss of the normal biphasic (systolic and early diastolic) pattern of superior vena cava flow.7 In this patient's case, surgical intervention was avoided because the mass did not cause hemodynamically significant obstruction. In summary, TEE and Doppler analysis proved valuable in diagnosing a right atrial mass as an extension of lipomatous hypertrophy of the IAS, documenting its independence from the IVC tumor, providing supporting evidence of its benign origin, and analyzing its hemodynamic profile. A diagnosis of lipomatous hypertrophy should be considered when bilobar enlargement of the IAS is observed, and surgical intervention considered for patients with intractable arrhythmias or symptoms of obstructive physiology. ACKNOWLEDGMENTS The authors thank Mr. Dashiell Reinhardt for his expert assistance in preparing and annotating the echocardiographic images. The first author (TCH) called the patient at his home phone number on March 22, 2009, to obtain his permission for publication. The patient gave his full support for the presentation of this case in Anesthesia & Analgesia Echo Rounds.