Mass-like hypertrophic cardiomyopathy

Mass-like or tumefactive hypertrophic cardiomyopathy is a morphological variant or phenotype of hypertrophic cardiomyopathy (HCM).

Epidemiology

Mass-like or tumefactive hypertrophic cardiomyopathy is rare and accounts for less than 2% of cases ^1-4.

Associations

Mass-like or tumefactive hypertrophic cardiomyopathy can be sometimes associated with left ventricular outflow obstruction if the affected segment is located in the basal region near the left ventricular outflow tract ¹.

Pathology

This phenotype is characterized by asymmetric focal left ventricular thickening simulating a cardiac tumor but with otherwise typical features of hypertrophic cardiomyopathy.

Microscopic appearance

Microscopically the hypertrophic segment is characterized by the following features ¹:

• cardiomyocyte hypertrophy
• myocardial fiber disarray
• interstitial fibrosis or replacement fibrosis
• bizarre enlarged nuclei nuclear hyperchromasia and pleomorphism

Radiographic features

Mass-like hypertrophic cardiomyopathy is characterized by a focally thickened segment.

Echocardiography

Echocardiography might serve as a first-line imaging modality for the detection of the lesion ⁴.

Speckle tracking echocardiography can be used to assess cardiac contractility which might be variable but should be present.

CT

On cardiac CT the cardiac segments affected by mass-like hypertrophic cardiomyopathy should look like the remainder of the myocardium with similar contrast enhancement and without calcifications ².

MRI

Cardiac MRI characteristics of mass-like hypertrophic cardiomyopathy feature a similar signal intensity as the normal uninvolved myocardium and relative preservation of myocardial contractility unlike real cardiac tumors which need to be distinguished from the condition ^1-5:

• cine imaging: focal mass-like thickening
• cardiac strain imaging: variable contractility
• cardiac tissue characterization​
  • T2/STIR black blood: should look like normal myocardium
  • T1 mapping: mildly increased native T1 values
  • ECV: mildly increased
• perfusion imaging: normal first-pass perfusion
• IRGE/PSIR:
  • fan-shaped or patchy mesocardial late gadolinium enhancement
  • indicating replacement fibrosis or myocardial scarring

Radiology report

The radiological report should include a description of the following:

• location, extent, contractility and contrast enhancement of the hypertrophic wall segment
• cardiac volumes and measurements including left ventricular mass
• cardiac wall motion abnormalities
• presence of myocardial crypts
• signs of myocardial fibrosis, focal replacement fibrosis or myocardial fiber disarray
• mitral annular plane systolic excursion (MAPSE)
• left ventricular outflow obstruction
• systolic anterior movement of the mitral valve

Differential diagnosis

Conditions that might mimic the clinical presentation or imaging appearance of mass-like or tumefactive hypertrophic cardiomyopathy include ^1-5:

• cardiac tumors (e.g. fibroma, rhabdomyoma, lymphoma)
• asymmetric hypertrophic cardiomyopathy
• midventricular hypertrophic cardiomyopathy
• apical hypertrophic cardiomyopathy (Yamaguchi syndrome)
• cardiac sarcoidosis