Classification of Cardiomyopathies
As classification serves to bridge the gap between ignorance and knowledge, the 1995 World Health Organization (WHO)/International Society and Federation of Cardiology Task Force on the definition and classification of cardiomyopathies defined cardiomyopathies as diseases of the myocardium associated with cardiac dysfunction. ¹ The cardiomyopathies were classified by the dominant pathophysiology or, if possible, by aetiological/pathogenetic factors; four categories of distinct and one category of unclassified cardiomyopathies were classified (see Table 1). Unclassified cardiomyopathies include cases that do not fit into any group (e.g. fibroelastosis, systolic dysfunction with minimal dilatation and mitochondrial involvement, etc.). ¹ Left ventricular non-compaction (LVNC) has not yet been classified as a distinct entity but rather belongs to the group of unclassified cardiomyopathies, although it clearly departs in its morphology from classified cardiomyopathies.

Embryology
In higher vertebrates, the heart develops from a simple tube into a complex organ with four chambers.² The development of the myocardial architecture itself passes through several steps. During early embryogenesis, trabeculations emerge in the luminal myocardial layers of the ventricles enabling the myocardium to increase its mass in the absence of epicardial coronary circulation. Trabeculations effectively increase surface area this developmental step serves to provide adequate oxygenation from the ventricular cavity. ² With the completion of the ventricular septation (eight weeks in human embryos), the trabeculae start to solidify at their basal area and ends at the apex, adding substantially to the thickness of the epicardial compact layer. This compaction process, coinciding with the invasion of the coronary arteries into the myocardium from the epicardium, is more pronounced in the left ventricle (LV) than in the right ventricle (RV) and results in a more trabeculated endomyocardial surface of the RV. ² LVNC is supposed to be the result of an arrest or failure of the compaction process of the myocardial trabeculae during endomyocardial embryogenesis; thus, myocardial non-compaction best characterises the basic nature of this disorder and respects its embryogenesis, ³ although in the past other terms (e.g., spongy myocardium) were used.

Non-compacted myocardium was previously described as persistent intramyocardial sinusoids; however, the latter are associated with congenital obstructive lesions of the left or right ventricular outflow tract, such as pulmonary atresia with intact ventricular septum. ^{4 - 6} In these patients, regression of the embryogenic sinusoids is impaired during ontogenesis by ventricular pressure overload, which results in deep recesses communicating with both the ventricular cavity and the coronary artery system. ^5,7,8

First Descriptions of a New Disease
The first case report about the persistence of left ventricular myocardial 'sinusoids' as an isolated anomaly was published in 1984. ⁹ In 1985, the description of both the angiographic and the echocardiographic characteristic features published in a German radiology journal was the first important step in the research for identification and diagnosis of a new disease. ¹⁰ A year later, Jenni's group reported a third case of a 21-year-old male patient with progressive heart failure (HF) and cardiomyopathy of obscure aetiology. ¹¹ Twodimensional (2-D) echocardiography identified a markedly thickened myocardium with prominent trabeculations and intertrabecular recesses (channellike structures) in the apex and at the posterolateral wall of the severely hypokinetic LV. The same structures were visualised by left ventricular angiography and resembled a honeycomb-like inner contour in both ventricles. In this case, autopsy for the first time confirmed the echocardiographic and angiocardiographic findings. ¹¹