Hamartoma of mature cardiac myocytes

Last revised by Joachim Feger on 26 Dec 2021

Hamartomas of mature cardiac myocytes (HMCM) are benign tumors arising from mature striated cardiac myocytes.

Terms that are not recommended include ‘cardiac hamartoma’ or ‘hamartoma of adult cardiac myocytes’ 1.

A hamartoma of mature cardiac myocytes is a very rare cardiac tumor, which has been found in a wide age range but more commonly in younger patients. There is a clear male predilection 1.

The final diagnosis is based on histology.

Most tumors are incidentally detected on imaging studies or autopsy 1.

An essential diagnostic criterion according to the WHO classification of bone tumors (2020 - blue book) is a cardiac mass formed by nodular collections of disorganized cardiac myocytes.

A further desirable criterion is the admixture of adipose tissue and nerves 1.

Clinical signs and symptoms if present revolve around arrhythmia including palpitations, dizziness, syncope, dyspnea, chest pain and variable abnormalities on ECG 1.

Hamartomas of mature cardiac myocytes might be complicated by the following 1:

Hamartomas of mature cardiac myocytes are benign cardiac tumors made up of disorganized differentiated mature cardiomyocytes 1.

The exact etiology of hamartomas of mature cardiac myocytes is unknown 1.

Hamartomas of mature cardiac myocytes are usually found within the walls of the ventricles and rarely in the atria. They can occur as multiple lesions 1.

Macroscopically hamartomas of mature cardiac myocytes are poorly defined tumors that are closely interlinked to the adjacent myocardium with a pale white-tannish grey appearance and a firm consistency 1,2.

Histologically hamartomas of mature cardiac myocytes are characterized by the following features 1,2:

  • a disorganized pattern of enlarged or hypertrophied striated cardiac myocytes
  • sarcoplasmic vacuolization
  • bizarre nuclei
  • myocyte disarray with herringbone, whorled or haphazard arrangement
  • associated with interstitial fibrosis

Immunohistochemistry stains are usually positive for muscular markers such as desmin, troponinmuscle-specific actin and/or myosin 1.

Echocardiography might show a homogeneous intramyocardial mass 3.

Thoracic CT or cardiac CT might show an enhancing well-circumscribed mass 4.

On cardiac MRI the appearance has been described as well-delineated homogeneous and intramural 3,4.

  • T1: isointense to mildly hyperintense
  • T2: mildly hypointense to hyperintense
  • STIR: hyperintense
  • T1C+ (Gd): early avid enhancement

The radiological report should include a description of the following:

  • location and extent
  • relation to other chambers and valves
  • relation to adjacent structures
  • associated myocardial fibrosis

Hamartomas of mature cardiac myocytes are benign but can cause arrhythmias and sudden cardiac death 1. Management includes surgical excision in symptomatic tumors, which has been proven to be effective in treating arrhythmia and obstruction 1.

Hamartomas of mature cardiac myocytes were first reported by a Japanese pathologist, Akira Tanimura, and his colleagues in 1988 2,6.

Conditions or tumors that might mimic the appearance of hamartomas of mature cardiac myocytes include 1:

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