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Situs inversus totalis: A mirror-image anatomy discovered incidentally on chest radiograph
*Corresponding author: K. Pushpalatha, Department of Anatomy, JSS Medical College, Mysuru, Karnataka, India. pushpalathak@jssuni.edu.in
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Received: ,
Accepted: ,
How to cite this article: Murugesh K, Pushpalatha K. Situs inversus totalis: A mirror-image anatomy discovered incidentally on chest radiograph. Sri Ramachandra J Health Sci. 2025;5:82-4. doi: 10.25259/SRJHS_7_2025
Abstract
Situs inversus totalis (SIT) is a rare congenital condition characterized by a complete mirror-image reversal of thoracic and abdominal organs. Although often asymptomatic and discovered incidentally, SIT poses significant challenges in clinical diagnosis, imaging interpretation, and surgical procedures. SIT is primarily caused by genetic variations, often inherited in an autosomal recessive pattern. An 18-year-old female presented for evaluation following complaints of mild, intermittent epigastric discomfort. A routine chest radiograph revealed dextrocardia, raising suspicion for situs inversus. Further imaging with abdominal ultrasonography confirmed transposition of visceral organs: The liver and gallbladder were in the left upper quadrant, while the stomach and spleen were visualized on the right side. This case emphasizes the importance of clinical suspicion and appropriate imaging in identifying SIT, especially in emergency and surgical settings. Awareness of such anatomical variations is critical to avoid misdiagnosis, especially in conditions such as appendicitis, myocardial infarction, or during laparoscopic procedures. SIT, while rare and often incidentally detected, has important clinical and surgical implications. Early recognition through imaging and careful documentation is essential to ensure accurate diagnosis and safe medical or surgical intervention.
Keywords
Anatomical variation
Case report
Dextrocardia
Radiological diagnosis
Situs inversus totalis
INTRODUCTION
Situs inversus totalis (SIT) is a rare congenital anomaly characterized by a complete mirror-image reversal of the thoracic and abdominal organs.[1] The term situs inversus originates from the Latin phrase situs inversum viscerum, meaning an inverted arrangement of the visceral organs. In SIT, also referred to as situs inversus with dextrocardia, the heart is positioned in the right hemithorax, the right lung is bilobed, and the left lung is trilobed. The stomach and spleen lie on the right side, while the liver and gallbladder are located on the left.[1,2] The prevalence of SIT is approximately 0.01%, and it is associated with congenital heart defects in 3–5% of affected individuals.[2]
Although SIT may occur as an isolated anomaly, it is also seen in syndromic conditions such as primary ciliary dyskinesia (PCD) and Kartagener’s syndrome.[3] Most individuals with SIT are asymptomatic, and the condition is frequently discovered incidentally during evaluation for unrelated medical complaints. Despite its benign nature, SIT presents significant challenges in clinical diagnosis, radiological interpretation, laparoscopic surgeries, and organ transplantation, owing to its reversed anatomical orientation.[1,3]
The etiology of SIT remains incompletely understood. Proposed contributing factors include autosomal recessive genetic inheritance with incomplete penetrance, maternal diabetes, prenatal cocaine exposure, and rare cases associated with conjoined twinning.[4] SIT is believed to result from altered left-right (L-R) axis determination during embryogenesis. In affected individuals, midgut rotation occurs in a counter-clockwise direction, the reverse of the normal clockwise rotation, resulting in a complete mirror-image arrangement of thoracic and abdominal organs.[5]
Overall, while SIT does not typically reduce life expectancy, its clinical significance lies in the challenges it poses during diagnostic and surgical procedures, necessitating heightened awareness among clinicians.
CASE REPORT
An 18-year-old female presented for evaluation following complaints of mild, intermittent epigastric discomfort. There was no history of fever, vomiting, bowel disturbances, respiratory complaints, or prior surgeries. Despite the mirror-image arrangement of visceral organs, clinical examination revealed no symptoms or abnormal findings, and the patient’s vital signs were within normal limits. A routine chest radiograph revealed dextrocardia [Figure 1], raising suspicion for situs inversus. Further imaging with abdominal ultrasonography confirmed transposition of visceral organs [Figure 2]. The liver and gallbladder were in the left upper quadrant, while the stomach and spleen were visualized on the right side. The aortic arch was right-sided, and echocardiography demonstrated a structurally normal heart with apex directed to the right (dextrocardia), consistent with SIT.
- Chest X-ray showing dextrocardia (yellow arrow).
- Ultrasonography abdomen. Showing spleen and stomach on left side.
There were no associated congenital heart anomalies. Laboratory parameters were within normal limits. The patient was counseled regarding the condition, its implications, and the importance of informing healthcare providers of the anatomical variation before any future medical or surgical procedures. No immediate intervention was required, and she was advised to follow-up.
DISCUSSION
SIT is an uncommon congenital anomaly, seen in approximately 1 in 10,000–50,000 live births.[4,5] It is characterized by a complete mirror-image arrangement of the thoracic and abdominal organs. The condition arises from a disruption in the normal L-R asymmetry established during embryonic development, leading to a global reversal of organ orientation. Although many affected individuals remain asymptomatic, SIT can complicate diagnostic and therapeutic decision-making. Due to its rarity, most clinicians, including surgeons, radiologists, and gastroenterologists, have limited clinical exposure to such cases, and even experienced surgeons may encounter it only once or twice in their careers.[6] According to Orphanet, the overall incidence of laterality defects is about 1 in 15,000 live births, with heterotaxy occurring in roughly 1 in 10,000 cases. SIT itself has been reported to occur at a frequency ranging from 1 in 6,500 to 1 in 25,000 births.
Embryological basis
The development of SIT is linked to errors in establishing the L-R axis during early embryogenesis. Normally, asymmetry first becomes evident during cardiac development, and disturbances in this process can affect not only the heart but also the lungs, gastrointestinal tract, spleen, and great vessels, supporting the idea of a shared embryological mechanism.[7] SIT should be distinguished from intestinal malrotation, which results from an abnormal 270° counterclockwise rotation of the midgut around the superior mesenteric artery. Unlike malrotation, SIT involves a systemic laterality disturbance that affects multiple organ systems and is independent of midgut rotation.[6]
L-R patterning is controlled by a complex signaling network involving genes and molecules such as Nodal, PITX2, serotonin (5HT), and kinesin motor proteins (KIF3A and KIF3B). More than 100 genes have been implicated in laterality disorders, many of which are also associated with PCD.[2] Orphanet estimates further support that the overall prevalence of laterality defects is about 1 in 15,000 live births, with heterotaxy and SIT being the most frequently described presentations.[6]
During embryogenesis, the primitive heart tube normally undergoes a rightward looping process, which is conserved across vertebrates. If this process is disrupted, dextrocardia with a mirror-image arrangement or other cardiac malformations, such as transposition of the great arteries, may result. Although many individuals with SIT remain clinically silent, the condition has important implications in diagnostic imaging, operative planning, and recognition of syndromes such as Kartagener’s syndrome.[7]
The present case underlines the importance of maintaining a high degree of clinical suspicion for SIT and utilizing appropriate imaging modalities for its diagnosis, particularly in emergency and surgical settings. Awareness of this anatomic variation is critical to avoid misinterpretation of clinical signs and to prevent errors in the diagnosis of conditions such as appendicitis, myocardial infarction, or complications during laparoscopic procedures.
CONCLUSION
SIT, while rare and often incidentally detected, has important clinical and surgical implications. Early recognition through imaging and careful documentation is essential to ensure accurate diagnosis and safe medical or surgical intervention.
Ethical approval:
Institutional Review Board approval is not required.
Declaration of patient consent:
The authors certify that they have obtained all appropriate patient consent.
Conflicts of interest:
There are no conflicts of interest.
Use of artificial intelligence (AI)-assisted technology for manuscript preparation:
The authors disclose limited use of ChatGPT (OpenAI) solely for assistance with grammar, sentence restructuring, and language refinement. No clinical decision-making, data analysis, image interpretation, or content generation was performed using AI tools. All scientific content and conclusions were authored and verified by the authors.
Financial support and sponsorship: Nil.
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