Situs Inversus

A 50 year old lady presented to our tertiary hospital with abdominal pain of a non-specific origin. It was decided by the ED consultant to order an abdominal CT scan (otherwise known as a ‘grope-a-gram’). Although there was no obvious pathology detected to explain her symptoms, I was still showed the abdominal slices to look for an interesting finding:

“Who is the fairest of them all?”

I will post a short precis on this condition (and its classification) in a few hours leaving some for the Twitterverseto have a gander. I wonder how long it takes you to find it, I remember it being well over 30 seconds for me!! ===============================================================

So after my almost minute of searching through the above grey/white/black image for subtle fat stranding, flaps of aortic lining and pancreatic abscess, it hit me. “Oh s**t. The liver isn’t supposed to be on that side.” My heart sank when a medical student came up and said straight away “this CT looks weird” and without missing a beat exclaimed “everything’s on the wrong side.” A few terms of colorectal surgery and general medicine had me looking for minutia. I’d failed to see the forest for the trees, or leaves even! The more thoracic slices were easier to pick:

Put your hand on your heart….other side please

What we had was a case of situs inversus. This condition can also be known as situs transversus, situs oppositus or situs organsaroundthewrongwayus*. Their internal organs are mirrored across the sagittal plane, or more simply: things usually on the right side of the body (liver, gall bladder, caecum) are found on the left and vice versa.

*Term made up by me, just now.

So what is the first thing you should think of when you see a CT like this? No the answer shouldn’t be situs inversus. Common things happen commonly. Mislabelling or image mirroring of the CT may be to blame. Then if you are confident this is not the case, time to delve into the rarefied air of such genetic abnormalities. Rare, yes. But the classification of position of internal organs is quite simple. It is not clearly essential knowledge, however very good for impressing cerebral physicians…

Total flips of the heart

  • Situs solitus (‘normal’) – How most of us and the anatomy text books are put together/drawn
  • Situs inversus with dextrocardia (situs inversus totalis) – Most common form of inversus which has a right sided heart, in keeping with the switch
  • Situs inversus with levocardia (situs inversus incompletus) – A much more rare form of an already rare condition in which the heart remains on the left (normal) side of the thorax
  • Situs ambiguous (heterotaxy syndrome) – Any combination of the above that does not fit a pattern of complete solitus or inversus. Calling it ‘incomplete’ situs inversus probably explains it better, but sounds too much like the latter.

Basically your insides are all topsy-turvey…

Situs inversus is thought to have a prevalence of 1 in 10,000 people. It is inherited in an autosomal recessive manner and is usally associated with other congenital heart defects (most commonly transposition of great vessels, TGV). Interestingly, although Leonardo Da Vinci was the first to describe dextrocardia, it was Matthew Baillie who described situs inversus and TGV. He was a Scottish physician who in 1793 wrote the best titled text I have come across: The Morbid Anatomy of Some of the Most Important Parts of the Human Body.

Interestingly 25% of patients with situs inversus have an underlying diseased called Primary Cilia Dyskinesia (PCD). Cilia are tasked with placing organs in their appropriate positions during embryogenesis and this is where things can go wrong. If patients have the triad of chronic sinusitis, bronchiectasis and situs inversus, then this is known as Kartaneger syndrome. Perhaps its worth conducting a thorough listen to the chest (or ECG) for those patients with recurrent sinusitis and mucousy coughing?! These conditions pose interesting anomalies, but what are the practical consequences for the patient sitting across from you?

  • ECG interpretation: If you attach the leads (correctly!!) and see strange axis deviation, p-waves inversions and a decrease in QRS voltage across to V6, then there may be inversus. To confirm this, swap all of the leads across to the right chest, including limb leads. The lesson though, is always double check lead placement lest you end up diagnosing ‘technical dextrocardia’

RA lead goes on the left lower limb?

  • General surgery 101

    Pain/Tenderness: We are taught in surgical training to know that for pain or tenderness in the abdomen, think about the underlying structures to help differentiate causes. Clearly if things are mirrored it will change your thinking. LIF pain could be appendicitis, RIF pain could be sigmoid diverticulitis and LUQ pain could be gall bladder related. Bruising over the right flank might mean you are worried about a splenic rupture.

  • Organ transplantation: The vast majority of organ donors will have anatomy orientated in the usual way. However if a patient with situs inversus needs a transplant, problems arise. Not only are arteries and veins in different positions, but the physical shape of the organs will not match up. In fact, an American patient with situs inversus underwent a heart transplant in 2007. The six-hour long operation was likened to solving a “three dimensional Rubix cube” (actually not sure what other dimensions Rubix cubes come in…but here is one solved in 30 seconds)

Thanks for reading and contributing. Clearly this is not a common presentation or finding, but hopefully if you happen across an interesting CT, CXR or ECG, you will have some background knowledge of these rare and fascinating disorders.

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4 Comments

Filed under Emergency Medicine, General Practice, Radiology

4 responses to “Situs Inversus

  1. I bet the cardiac exam would have been a challenge.

  2. ivan

    that is awesome!! never seen a CT of one before 🙂

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