Lipomatous hypertrophy of the interatrial septum in a dog: echocardiographic, gross pathologic, and histologic findings.

LHIAS should be considered a differential for interatrial septal thickening in dogs with echocardiographic anomalies.

This case report describes the first documented occurrence of lipomatous hypertrophy of the interatrial septum (LHIAS) in a dog, a condition well established in human cardiology but previously unreported in veterinary medicine. A 12-year-old male Cocker Spaniel presented with acute marked weakness and was found to have concurrent myxomatous mitral valve disease (MMVD) with moderate left atrial dilation and a sustained narrow QRS complex tachycardia consistent with focal atrial tachycardia. Two-dimensional echocardiography identified a hyperechoic, multifocal thickening of the interatrial septum measuring up to 10 mm, raising differential diagnoses of neoplasia, intracardiac thrombosis, and mural endocarditis. Despite intensive care hospitalization and combination antiarrhythmic therapy, the tachyarrhythmia remained refractory, and euthanasia was elected. Postmortem examination confirmed MMVD and excluded neoplasia, thrombosis, and endocarditis. Histopathology revealed abnormal infiltration of the interatrial septum by mature adipose tissue causing full-thickness separation and dissociation of septal myofibers, consistent with LHIAS. Clinicians should be aware that LHIAS may occur in dogs and can present as an incidental or clinically relevant echocardiographic finding. Its hyperechoic septal appearance may mimic more serious pathologies. Whether LHIAS contributed to the arrhythmogenesis in this case remains speculative but plausible, as septal myofiber disruption by adipose tissue could predispose to aberrant conduction. This report expands the known spectrum of interatrial septal pathology in dogs and underscores the value of histopathologic confirmation.

This summary was distilled by AI and may occasionally misinterpret data. Confirm critical details with the primary literature before clinical application.