Situs ambiguous with polysplenia: Computed Tomography, Magnetic Resonance and diffusion-weighted imaging findings

Clinical History

Patient presented with a 2-day history of abdominal pain. Her electrolytes, liver function tests and leukocyte count were within normal limits. Physical examination revealed anatomically placed cardiac apex beat on the right side of chest. She had no congenital heart disease, bowel obstruction related to malrotation, or immune deficiency disorders.

Imaging Findings

Abdominal ultrasound showed absence of the spleen, with multiple round or oval, well-circumscribed nodules of echogenicity similar to that of splenic parenchyma located in the epigastrium (Fig. 1). Contrast-enhanced CT showed multiple spleens in right upper quadrant and the midline, with no splenic tissue in left upper quadrant. CT also showed dextrocardia, and interruption of the inferior vena cava with prominent azygos vein. The pancreas was truncated and the superior mesenteric vessels inverted. The liver and the gallbladder were both midline. The jejunum appeared in the right side of the abdomen and the caecum in the left (Figs. 2, 3).
MR images demonstrated signal intensity and enhancement characteristics of nodules similar to those of normal spleen on all sequences (Fig. 4). Splenic parenchyma demonstrated restricted diffusion with high signal intensity on diffusion-weighted images (Figs. 5a-c) and corresponding low signal intensity on the ADC map (Fig. 6).

Discussion

The term situs refers to the anatomic position of the heart and viscera relative to midline. Situs anomalies manifest most commonly in the paediatric population where they present with congenital heart disease, immune deficiency, or bowel obstruction due to malrotation. In adults, situs anomalies usually are incidental findings in patients undergoing imaging evaluation for unrelated conditions, such as cholecystitis or appendicitis.
Situs ambiguous or heterotaxia is a congenital anomaly defined as the abnormal arrangement of organs and vessels as opposed to the orderly arrangement typical of situs solitus and situs inversus [1]. Affected patients have a 50-100% prevalence of congenital heart disease. Indeed, situs ambiguous encorporates a spectrum rather than a single set of abnormalities. The two major subcategories of situs ambiguous are situs ambiguous with polysplenia and situs ambiguous with asplenia.
Situs ambiguous with polysplenia, often referred to as left isomerism or bilateral left-sidedness, is characterized by midline or ambiguous location of the majority of the abdominal organs and multiple spleens [1, 2]. Although this anomaly does not have pathognomonic characteristics, a sufficient number of findings allows for diagnosis. Imaging evaluation with sonography, CT and MR imaging has greatly improved the detection and characterisation of abnormalities. Most commonly, multiple spleens of variable size are located in either the left or right side of the abdomen. The liver and gallbladder are usually midline. The pancreas may appear truncated with only the pancreatic head and/or portion of the pancreatic body being present. Position of the pancreatic head and body are also variable. The stomach may be right- or left-sided. Levocardia or dextrocardia may be present, while the position of the stomach and the cardiac apex may be discordant [1]. The position of the aorta is variable being right, left or midline. Position of the inferior vena cava (IVC) is variable as well. Absence of portion of the IVC with azygous or hemiazygous continuation may be present. Abnormalities of bowel rotation may be seen. The small bowel is primarily right-sided and the colon left-sided.
Knowledge of situs anomalies may have important clinical implications as the patient’s pain typically does not correlate with the expected locations of solid organs, or the gastrointestinal tract. Indeed, major alterations in anatomy associated with situs ambiguous may result in confusing imaging findings when seen in conjunction with acquired diseases. Therefore, it is important for radiologists to recognise and report situs anomalies especially when planning surgical or endoscopic interventions.

Differential Diagnosis List

Final Diagnosis

Situs ambiguous with polysplenia

URL:	https://www.eurorad.org/case/11492
DOI:	10.1594/EURORAD/CASE.11492
ISSN:	1563-4086