Non-compaction of Myocardium Cardiomyopathy

Non-compaction of the ventricular myocardium ("spongy myocardium") is a rare congenital cardiomyopathy of children and adults resulting from arrested myocardial development during embryogenesis. Prior to formation of the epicardial coronary circulation at about 8 weeks of life, the myocardium is a meshwork of interwoven myocardial fibers that form trabeculae and deep trabecular recesses. That increased surface area permits perfusion of the myocardium by direct communication with the left ventricular cavity. Normally, as the myocardium undergoes gradual compaction, the epicardial coronary vessels form. 

In this disorder, echocardiography demonstrates a thin epicardium with extremely hypertrophied endocardium and prominent trabeculations with deep recesses. These features tend to be apically localized since compaction would normally proceed from base to apex, and from epicardium to endocardium. 

Clinical presentation consists of congestive heart failure with depressed left ventricular systolic function, ventricular arrhythmias, arterial thromboemboli from thrombus formation within the inter - trabecular recesses, as well as restrictive physiology from endocardial fibrosis. 

Echo
Transthoracic short axis view showing prominent trabeculations and deep intertrabecular recesses localized to the anterior and antero-lateral segments.

Echo
Short axis view further depicting the trabeculations and intertrabecular recesses in the anterior and anterolateral segments.

Klatskin trichrome stain revealing the prominent myocardial trabeculations with deep intertrabecular recesses. Collagen stains blue. Overlying endocardium is thickened by fibrous tissue. Low power magnification on left and high power on right.

Gross specimen following explantation at time of orthotopic heart transplant reveals the prominent trabeculations and recesses.