CASE 15835 Published on 07.06.2018

Lipomatous hypertrophy of the interatrial septum (ECR 2018 Case of the Day)

Section

Cardiovascular

Case Type

Clinical Cases

Authors

L. Schneider*1, P.A. Poncelet*2, L. Monnier-Cholley3, Y. Menu3

1Medizinische Universität, Innsbruck, Österreich
2Cliniques Universitaires Saint-Luc, Bruxelles, Belgium
3Hôpital Saint-Antoine, Paris, France
*Both authors share first co-authorship
Patient

60 years, female

Categories
Area of Interest Cardiac ; Imaging Technique PET, PET-CT
Clinical History

A 60-year-old woman was diagnosed with epidermoid carcinoma of the right palatine tonsil.
A FDG-PET was performed in order to rule out secondary localisations. This examination showed expected high FDG uptake of the right palatine tonsil and a hypermetabolic cardiac mass (Fig. 1-3).

Imaging Findings

Figure 1: FDG-PET shows a hypermetabolism of the right palatine tonsil and a high FDG uptake of a cardiac mass.
Figure 2: CT-scan showing a spontaneous hypodense mass (mean density: -41HU) of the interatrial septum with sparing of the fossa ovalis.
Figure 3: Fused PET-CT image showing a hypermetabolic mass of the interatrial septum (mean SUV: 8).

Discussion

Lipomatous hypertrophy of the interatrial septum (LHIS) is a benign infiltration of fat between the myocardial fibres of the atrial septum which spares the fossa ovalis. This condition is estimated to be present in 2-3% [1] of the general population and is classically associated with older age and obesity, but was also reported in association with long-term corticotherapy. [2, 3] Although LHIS is a benign process, it can induce several complications like atrial arrhythmia, obstruction of the superior vena cava, sudden death. It can also be an obstacle for cardiac interventional procedures. [4]

Histologically, LHIS presents as a non-encapsulated mix of mature adipose tissue, brown fat cells, hypertrophied myocytes and fibrous tissue. The fibrous fibres are responsive of a disruption of the myocardial fibres which can lead to electric perturbation and cardiac arrhythmia. [3, 5]
LHIS has a dumbbell appearance on cross-sectional imaging with spontaneous negative density on CT-scan and fat signal on MR. [2, 5] Sparing of the fossa ovalis is a diagnostic sign specific for LHIS when combined with a fat signal/density. [5] LHIS may show the illusion of a pseudo-capsule by the anatomical structures such as the atrial wall itself.
On FDG-PET, LHIS classically presents an increased uptake of FDG which can lead to a misdiagnosis for a malignant tumour. [1, 5] An explanation for this hypermetabolism is the presence of brown fat cells. [5] This theory is subject to controversy [4] and other hypotheses have been proposed such as an inflammatory process. [6]

Differential diagnosis of LHIS includes: primary cardiac tumours (lipoma, liposarcoma, myxoma, rhabdomyoma, lymphoma, fibroma, fibroelastoma, mesothelioma) but also metastasis (frequent with melanoma and leukaemia). [4] Misdiagnosis between LHIS and one of these lesions can lead to wrong therapeutic decisions of capital importance. Hypermetabolism on FDG PET-CT can be found in many of the conditions and is not necessarily a synonym of a malignant lesion.
To conclude, this case aims to raise awareness on the existence of LHIS and its hypermetabolism on FDG-PET in order to avoid wrong diagnosis of malignancy and, consequently, wrong therapy.

Differential Diagnosis List
Lipomatous hypertrophy of the interatrial septum
Liposarcoma
Lipoma
Lymphoma
Lipomatous hypertrophy of the interatrial septum
Metastasis
Final Diagnosis
Lipomatous hypertrophy of the interatrial septum
Case information
URL: https://eurorad.org/case/15835
DOI: 10.1594/EURORAD/CASE.15835
ISSN: 1563-4086
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