Situs inversus is a congenital abnormality in which organs in the thorax and the abdomen are opposite to their normal positions. The normal arrangement of organs is known as situs solitus. Situs inversus is the mirror-imaged arrangement of the organs. (The anatomical left lung is in the right hemithorax and the anatomical right lung is in the left hemithorax.
The stomach and spleen are on the right, the liver on the left. The heart is on the right.) Situs inversus is categorised under heterotaxy syndromes, which results from failure of the developing embryo to establish normal left-right asymmetry and is associated with a wide range of cardiac and extracardiac congenital anomalies. During the embryological development, a 270 degree clockwise rotation instead of normal 270 degree anti-clockwise rotation of the developing thoraco-abdominal organs results in mirror image positioning of the abdominal and thoracic viscera.
Situs inversus is a hereditary syndrome, which is estimated to occur in 1 in 8,000 to 25,000 individuals. It was reported as one in 5,000–20,000 births. Situs inversus totalis is usually an autosomal recessive disorder, and may sometimes be X-chromosome-related. There is no established gender or ethnic difference in its incidence, but genetic predisposition and familial occurrence point towards multiple inheritance patterns. Most cases are caused by ciliary abnormalities (the primary ciliary dyskinesia disorders). Cilia also are responsible for determining proper visceral laterality in utero.
Thus, during embryogenesis in patients with primary ciliary dyskinesia, visceral laterality will be determined at random, and half of these patients will have situs inversus totalis. Situs inversus totalis is associated with right-sided heart (dextrocardia). Situs inversus may be abdominal, thoracic, or both. Most patients are asymptomatic and maintain their normal life.
The association of situs inversus totalis with syndromes such as Kartagener syndrome (i.e. situs inversus, primary ciliary dysfunction (PCD), chronic sinusitis and bronchiectasis), cardiac anomalies, spleen malformations, mucociliary dysfunction, and airway anomalies makes the clinical management difficult for the anaesthesiologist.
There is a significantly higher incidence of heart defects in this group compared to normal hearts. Situs inversus totalis is associated with numerous cardiac anomalies such as atrial septal defect, ventricular septal defect, transposition of great vessels, abnormal atrioventri-cular valves, absent coronary sinus, conduction abnormalities, double-outlet right ventricle, total pulmonary venous defect and pulmonary valve stenosis. Dextrocardia with complete situs inversus occurs in approximately 2 of 10,000 births. The most prevalent cardiac defects associated with situs inversus are ventricular septal defect and transposition of the great vessels. There are limited reports of sick sinus syndrome diagnosed in patients with dextrocardia. In general, heart rhythm disturbance is not a significant finding in patients with situs inversus compared to situs solitus.
The extracardiac anomalies that most frequently challenge the anesthesiologist are gastro-intestinal abnormalities, hepatic dysfunction, splenic dysfunction, respiratory abnormalities, and associated midline defects.
Situs inversus is associated with primary ciliary dyskinesia (Kartagener syndrome) in 20–25 % of cases. Kartagener syndrome occurs with the triad of bronchiectasis, chronic sinusitis (as symptoms of PCD) and situs inversus and should be excluded by a carefully obtained medical history. Situs inversus totalis is present in 50 % of individuals with Kartagener syndrome. The patients are prone to an increased probability of developing respiratory complications. Aggressive pre-operative optimisation and treatment of infection is required. A history of intermittent respiratory tract infections, especially during the winter season, should be watched.
The coexistence of situs inversus and congenital duodenal obstruction is an extremely rare situation. A relationship between ectopic thyroid and situs inversus totalis was reported. Most patients with ectopic thyroid show clinical features of euthyroid, while a few patients show clinical features of hyperthyroidism. Thyroid function tests are useful for the pre-operative diagnosis.
Spinal dysrapism, which includes all forms of neural tube defects from thickened filum terminalis to meningomyelocele, is an important abnormality that is associated with situs inversus regarding neuraxial blocks.
There is some association between situs inversus and renal abnormalities. Kidney function should be tested pre-operatively if situs inversus with Kartagener syndrome is suspected. Biliary atresia may occur in 28 % of infants born with situs inversus as compared to the
0.01 % of the general population. The anaesthetic concerns include managing the abnormalities related to liver pathology (deranged metabolism, coagulation problems). Situs inversus is also a very rare feature of Bardet-Biedl syndrome.