It’s 11 PM, Do You Know Where Your Organs Are?

Biology concepts – situs inversus, situs ambiguous, dextrocardia, dextroposition, isomerism, canalization

Catherine O’Hara has situs inversus, but she doesn’t have any strange stories to tell about it as do Dr. No and Donny Osmond. On the other hand, a weird movie like Beetlejuice deserves a star with a strange anatomical quirk.

Being an arch criminal has its good points and its bad points. You have a lot of disposable income, but then again a lot of people are trying to kill you. Criminality is sort of a mirror image of polite society, so perhaps it fits into our discussion of situs inversus (mirror image organs) last week.

Dr. No of the James Bond stories was the quintessential bad guy, but he still had a congenial relationship with 007. During a discussion over tea, or perhaps as Bond hung over a pool of sharks, Dr. No explained to James that he once survived an assassination attempt when a his would be murderer tried to stab him in the heart.

Little did the assassin realize that Dr. No had situs inversus. Even though he was stabbed on the left side, right where his heart should have been, Dr. No laughed it off and then cut up the poor guy with a laser. It helps to have an edge that people don’t know about.

Then again, sometimes situs inversus can be a pain. Donny Osmond, of the Osmond Brothers and then later of Donny and Marie, had situs inversus. As a child he had a bout of lower left abdominal pain. Nothing special is located in the lower left abdomen, so his family ignored it - so did the doctors. When they arrived in England, he had to have emergency surgery because of appendicitis. His situs inversus meant that his appendix was on the opposite side.

In the cases mentioned above, the condition was situs inversus totalis, but it isn’t always totalis. This is rare, but it happens, and most often it involves the heart. Even when it comes to location, the heart wants what the heart wants.

We’re talking about looking for horses instead of zebras and we’re talking about hearts, so why not zebrafish hearts? It turns out that zebra fish can regenerate their heart after injury, as can many animals. A new paper is showing how the cells can change into the cell type they need and then proliferate.

One of the tenets of medical training is that when you hear hoof beats behind you, think horses not zebras. Another way of saying the same thing – common things occur commonly. So if a patient presents in your clinic, you should expect that their organs are where they most commonly are. However, they could be situs inversus totalis; this would be a Shetland pony instead of a horse.

But zebras do exist, and you have to know that they exist and what they look like. One zebra is called isolated levocardia (levo= left, and cardio = heart). If situs inversus is rare (1in about 10,000 live births), then isolated levocardia is very rare (in about 25,000 live births). Levocardia means that the apex (the bottom of the heart comes to a blunt point) is directed to the left – this is normal. But in isolated levocardia, the rest of the organs are situs inversus, only the heart is in the normal orientation.

Remember that the lungs are designed to fit around the heart. The left lung has a cardiac notch for the apex of the organ. If the lungs are switched, then the cardiac notch is on the right lung; this is fine if the heart is mirrored as well. But in isolated levocardia, the right lung has room for the heart apex, but the heart is point to the left.

The top left image is the normal arrangement. B shows something called dextroposition. This happens with congenital malformations of the chest or sometimes in injury. The heart points left but is moved to the right side of the chest. C is dextrocardia without situs inversus, there are often congenital heart defects in this condition. D is situs inversus totalis. The heart works fine because everything is switched.

This in itself is a problem, but not a huge one. The problems really come because there are often congenital heart defects that accompany the change of orientation. The valves of the heart may be misshapen so they don’t close completely (called a heart murmur), the muscle fibers may not align for efficient pumping. None of these problems allow for maximal blood flow through the body.

The prognosis of patients with isolated levocardia is not good, only 5-13% live beyond the age of five years. This is usually due to severe cardiac defects. The problems with the vessels may be a part of it, but these patients often have defects of the heart organ itself. The chambers may be transposed or the septa between the chambers could have holes or other defects.

Situs inversus with a normal heart position is one exception, but how about the opposite exception? Can all the organs be in the normal orientation except the heart? Yes – it’s called dextrocardia. If you want to be picky, dextrocardia refers to any situation where the apex of the heart points to the right instead of to the left, but the vast majority of these cases occur in situs inversus. What we are talking about is an isolated dextrocardia, although the terms in dextrocardia get somewhat muddled. I prefer dextrocardia without situs inversus or dextrocardia with situs solitus (situs solitus is the normal organ arrangement).