The deceased: A 39-year-old man in the United States
The autopsy findings: Medical examiners evaluated the man after a deadly fight, during which a stab wound had punctured a vein in his lungs. They noted that the man's heart was slightly enlarged and that he had moderate atherosclerotic coronary artery disease (CAD) in two vessels. CAD is caused by plaque buildup in the walls of arteries that lead to the heart.
Upon dissecting the man's heart, the examiners noticed an unusual lump around the atrioventricular node, which coordinates electrical signals between the heart's top and bottom chambers. When examiners sliced the node and surrounding tissue into thin sections to investigate the lump, they uncovered a "boomerang-shaped, bony structure" about the size of a black bean, according to a report of the case.
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They identified this structure as the os cordis — a "cardiac bone" rarely, if ever, seen in humans.
What makes the case unique: The os cordis has long been observed in nonhuman mammals, including ruminants such as cows and camels. In animals, it is believed to support the cardiac valves that direct the flow of blood within the heart.
The structure was only recently described in primates, in a report published in 2020, just five years before the case study described above. In that 2020 report, scientists examined 16 chimpanzee hearts and found that three contained an os cordis. Those three chimps also had heart-tissue scarring, leading the researchers to suggest that the development of the bony structure might have been linked to such tissue damage.
Also in 2020, a similar structure was described in seven humans by Dr. Jorge Trainini, a cardiac surgeon and professor at the National University of Avellaneda in Argentina. He and his co-authors dubbed their discovery the "cardiac fulcrum," emphasizing its proposed role in stabilizing heart muscles as they pump against the forces of gravity.
They reported that, unlike the os cordis they saw in cow hearts, the adult human fulcrum was made of cartilage and tendon, not bone. That said, in the team's own analysis, they found that a heart from a 10-year-old did contain bone tissue, and they suggested that the structure might lose its bony nature with age. (The 10-year-old had cardiomyopathy, or disease of the heart muscle, and had undergone a heart transplant. The bony tissue was found in the explanted heart.)
Trainini told Live Science in an interview that the os cordis and the cardiac fulcrum are the same structure. But the case report authors disagreed. They acknowledged Trainini's previous findings, but they maintained that the structure they found in the 39-year-old man was distinct because it was made of bone.
However, the case report authors come to a similar conclusion as Trainini, stating that such a structure may be more common among humans than is currently recognized. They suggested that, since they found the os cordis during a dissection of the heart tissue that was not standard for an autopsy, the feature may typically go unnoticed.
Tranini went so far as to argue that all humans likely have a cardiac fulcrum based on his subsequent investigations of around 100 human hearts.
Though the case report authors didn't know the man's full medical history, they noted that the formation of an os cordis might be linked to his apparent cardiac disease. It's known that age and disease can influence this structure in other animals, too, they added.
For more intriguing medical cases, check out our Diagnostic Dilemma archives.
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