Which Side Are the Organs On?

A 13-day-old male came to clinic for his health supervision visit.
He was breastfeeding, gaining weight well and was past his birth weight. He was breathing and eliminating without problems. The past medical history showed that the baby had had an abnormal prenatal ultrasound that was consistent with an abdominal lateralization defect. After delivery, the baby was well but taken to the neonatal intensive care nursery as a precaution and his evaluation showed a left sided liver with appropriate vasculature and a patent biliary system. His bowel also was rotated, and he had one spleen that was on the left side. He had normal position and anatomy in his thorax.

The pertinent physical exam showed a vigorous infant with no jaundice. His growth parameters were in the 50-75%. His cardiac examination was normal. On abdominal examination his liver was palpable on the left side. The diagnosis of a healthy infant with situs ambiguous was confirmed. “He looks and acts just like any other baby and they told he he may never have any problems. The surgeons are still deciding if anything should be done to prevent a problem though. We are supposed to see them in a couple of weeks,” the parents said. “I’m obviously happy to help you and will help the surgeons or any other specialist if they need it. As you know a lot of baby’s spit up, but with his different anatomy we’ll have to watch that more closely though,” remarked the pediatrician. “Yes, the surgeons are okay with the little baby spit up we’ve seen with our daughter, but if it is more forceful or occurs a lot or doesn’t look like the breastmilk, we’re supposed to call them and go to the emergency room,” the parents stated.

Although externally vertebrates present with bilateral symmetry, this is not necessarily true internally for humans. Humans have a normal left-right asymmetry of their internal organs. For example, the right lung has 3 lobes and is slightly larger than the left lung with 2 lobes. The normal asymmetry is called situs solitus (SS). Complete reversal of the normal abdominal and thoracic organ positions is called situs inversus totalis (SIT). Variations on the laterality between situs solitus and SIT has been referred to by different names including situs ambiguous or heterotaxy. For this case, the term situs ambiguous (SA) will be used. Overall the incidence is 1 in 15,000 for all lateralization defects, with SIT being reported from 1 in 6,500-25,000. Laterality problems are associated with some specific syndromes and genes. Anatomic variations overall are very common and an illustrated atlas can be found here.

Learning Point
Such lateral anatomical variation may never cause any significant problems, but certainly has the potential to do so. Congenital heart defects, respiratory and hepatic problems are usually thought about first as they can cause acute life-threatening problems. However, patients may also have functional asplenia and increased risks of infection. Medical procedures may be more difficult to perform because of the differences in laterality, and imagine the surprise thoughts of the trauma surgeon who must also confront vast anatomical differences in an emergency situation.

SA like SIT is highly associated with cardiac defects. Congenital heart disease is associated with SS is only 0.6%, but is 3-9% for SIT and almost 80% for SA. SA also has many vascular anomalies especially those serving the hepatic system. Biliary atresia is also more common. Polysplenia or asplenia is also associated with SA.

SIT is associated with many different problems including congenital heart disease (e.g. complex and single lesions), gastrointestinal (e.g. biliary problems, anal atresia), respiratory system (e.g. bronchial dysplasia, primary ciliary disease), skeletal system (e.g. thoracic deformities, spinal deformities, polydactyly), urinary system (e.g. chronic kidney disease, uronephrosis, chronic kidney disease), and various others (e.g. dwarfism, cleft lip and palate, hernia, intellectual disability, precocious) among others. SIT is highly associated with various ciliopathies, a review of which can be found here.

Questions for Further Discussion
1. How often have you seen lateralization defects?
2. What is the general pediatrician’s role for patients with rare diseases? A review can be found here

Related Cases

    Disease: Situs Ambiguous | Anatomic Variation | Anatomy

To Learn More
To view pediatric review articles on this topic from the past year check PubMed.

Evidence-based medicine information on this topic can be found at SearchingPediatrics.com and the Cochrane Database of Systematic Reviews.

Information prescriptions for patients can be found at MedlinePlus for this topic: Anatomy

To view current news articles on this topic check Google News.

To view images related to this topic check Google Images.

To view videos related to this topic check YouTube Videos.

Knowles M, Zariwala M, Leigh M. Primary Ciliary Dyskinesia. Clin Chest Med. 2016;37(3):449-461. doi:10.1016/j.ccm.2016.04.008

Chen W, Guo Z, Qian L, Wang L. Comorbidities in situs inversus totalis: A hospital-based study. Birth Defects Research. 2020;112(5):418-426. doi:10.1002/bdr2.1652

Eitler K, Bibok A, Telkes G. Situs Inversus Totalis: A Clinical Review. Int J Gen Med. 2022;15:2437-2449. doi:10.2147/IJGM.S295444

Donna M. D’Alessandro, MD
Professor of Pediatrics, University of Iowa