Lipomatous hypertrophy of interatrial septum

Clinical History

A 54-year-old female patient arrived in our department to perform a CT staging examination for colorectal cancer. CT examination showed, as a collateral finding, a cardiac mass that was further investigated with ultrasound (images not available) and MRI examinations.

Imaging Findings

CT scan showed a hypodense, well-circumscribed, homogeneous, cardiac formation with fat density values, likely arising from the interatrial septum (Fig. 1), with a thickness of about 3, 5 cm and measuring about 5, 5 cm cranio-caudally. The lesion showed no contrast enhancement. CT coronal reconstructions show mild compression of the inferior vena cava (Fig. 4).
MRI showed high signal of the lesion in T1-weighted black blood sequences and dark signal in fat-suppression T2-weighted sequences (Fig. 2, 3), confirming the fatty nature of the lesion, isointense with subcutaneous fat tissue.

Discussion

Lipomatous hypertrophy of the interatrial septum (LHIS) is a rare entity characterised by the excessive deposition of fat tissue in the interatrial septum, with a thickness of at least 2 cm [1]. LHIS was first described at a post-mortem examination in 1964 [2, 3] and it was first diagnosed in a living patient in 1982 [2]. It consists of an unencapsulated accumulation of mature fat tissue. Histologically the lesion is made of mature adipocytes and vacuolated fat cells with hypertrophied myocytes dispersed within the fat; mitoses are absent, distinguishing this lesion from a malignancy [2]. LHIS is usually observed in elderly and obese patients [3] and it can be associated with metabolic disorders such as cerebrotendinous xanthomatosis; long-term parenteral nutrition seems to be a predisposing factor [1]. Incidence of LHIS is not known; diagnosis of LHIS is rarely made during lifetime due to a lack of typical clinical symptoms, while the reported incidence of LHIS in autopsy studies is about 1% [1]. LHIS is often an incidental finding but a variety of rhythm disturbances such as atrial fibrillation, supraventricular tachycardia, up to sudden death, can be present; in rare cases the lesion can protrude into the right atrium and superior vena cava, causing haemodynamic impairment [1, 3]. Transthoracic and, even if more invasive, transoesophageal echocardiography are the first level diagnostic tools of choice [2, 4] as they can reveal a hyperechogenic mass in the interatrial septum which is thickened. CT and MRI are valuable tools to confirm the diagnosis as they can demonstrate the fatty and unencapsulated nature of the lesion, which typically derives from the upper and/or lower part of the interatrial septum with sparing of the fossa ovalis, giving the lesion the characteristic dumbbell shape; contrast enhancement is usually absent [1]. A common additional finding is an increase in the amount of epicardial and mediastinal fat [5]. LHIS can develop in other regions than the interatrial septum; it can be diffuse and the free wall of the right atrium may be completely infiltrated with fatty tissue [2]. Differential diagnosis of LHIS from other cardiac neoplasms might be difficult; myxomas are mostly peduncolated and arise from the interatrial septum in the vicinity of the foramen ovale [1], lipomas are more frequent in younger patients and encapsulated. In the setting of LHIS, surgery should be limited to patients with severe superior vena cava or right atrium obstruction.

Differential Diagnosis List

Final Diagnosis

Lipomatous hypertrophy of interatrial septum

URL:	https://www.eurorad.org/case/10717
DOI:	10.1594/EURORAD/CASE.10717
ISSN:	1563-4086