See if you can solve this before scrolling down to see the answer and explanation!

A 20-year-old male died suddenly and unexpectedly while playing basketball. An autopsy is performed, and a gross photograph of his heart, opened to reveal the left ventricle, is shown here. What is the diagnosis in this case?

A. Aortic stenosis

B. Hypertrophic cardiomyopathy

C. Aortic dissection with extension into heart

D. Dilated cardiomyopathy

E. Myocardial infarction

The diagnosis in this case is hypertrophic cardiomyopathy (HCM). Hypertrophic cardiomyopathy is a disorder in which the heart becomes massively hypertrophied, often with a disproportionate thickening of the septum as compared to the rest of the heart. The chamber size of the left ventricle is reduced, leading to impaired ventricular filling during diastole, decreased stroke volume, and decreased cardiac output. Sometimes the septum becomes so thickened that it leads to outflow obstruction, placing further strain on the heart.

A leading cause of sudden death in young, seemingly healthy patients, HCM is caused, in some cases, by an autosomal dominant genetic defect, most commonly in the beta-myosin heavy chain gene on chromosome 14 (but mutations in other genes encoding sarcomeric proteins have been described too). If you look at the cardiac myocytes under the microscope, they look very big and kind of messed up (the more official way to say this is that the cells show extreme hypertrophy with branching and disarray). There’s also a lot of interstitial fibrosis between the myocytes.

Clinically, patients may exhibit atrial fibrillation, intractable cardiac failure, and ventricular arrhythmias. Presenting symptoms may be things like shortness of breath or fainting. The disorder carries an increased risk of sudden death, particularly when it occurs in children or adolescents. However, many patients have no disability and a normal life expectancy.