DOI: 10.1148/rg.226025016
(Radiographics. 2002;22:1439-1456.)
© RSNA, 2002
Abdominal Manifestations of Situs Anomalies in Adults1
Ann S. Fulcher, MD and
Mary Ann Turner, MD
1 From the Department of Radiology, Medical College of Virginia of Virginia Commonwealth University, 401 N 12th St, Rm 3-407B, Richmond, VA 23298-0615. Recipient of a Cum Laude award for an education exhibit at the 2001 RSNA scientific assembly. Received February 4, 2002; revision requested March 14 and received April 1; accepted April 1. Address correspondence to A.S.F. (e-mail: asfulche@hsc.vcu.edu).
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Abstract
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A study was made of 19 adults with situs anomalies (situs inversus [n = 10], situs ambiguous with polysplenia [n = 8], situs ambiguous with asplenia [n = 1]). No patient had congenital heart disease, bowel obstruction related to malrotation, or immune deficiency disorders. All 10 patients with situs inversus had mirror-image location of the abdominal organs relative to situs solitus; nine had dextrocardia, and one had levocardia. The eight adults with situs ambiguous with polysplenia demonstrated a spectrum of abnormalities. All had some degree of abdominal heterotaxy, including midline livers and gallbladders (n = 5), right-sided stomachs and spleens (n = 3), and rotational abnormalities of the small bowel and colon (n = 7). Other findings included multiple spleens (n = 7), interruption of the inferior vena cava (IVC) with azygous or hemiazygous continuation (n = 7), truncation of the pancreas (n = 6), and ipsilateral location of the aorta and IVC (n = 1). In the one patient with asplenia, a midline liver, right-sided stomach, bowel rotation abnormality, IVC interruption, and pancreatic truncation were noted. Recognition of the spectrum of situs anomalies is important because the altered anatomy associated with these anomalies may result in confusing imaging findings when seen in conjunction with acquired diseases.
© RSNA, 2002
Index Terms: Anatomy, situs anomalies, 50.165, 50.166, 50.167, 70.147 • Heart, diseases, 51.191 • Spleen
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LEARNING OBJECTIVES FOR TEST 4
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After reading this article and taking the test, the reader will be able to:
- Recognize situs anomalies (situs inversus, situs ambiguous with polysplenia, situs ambiguous with asplenia) in adults.
- Describe the hepatic, splenic, pancreatic, biliary, gastrointestinal tract, and vascular findings associated with situs anomalies.
- Discuss the challenge of diagnosing disease processes such as appendicitis and cholecystitis in patients with situs anomalies.
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Introduction
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Much has been written about the imaging features of situs anomalies in the pediatric population because most children with these anomalies come to clinical and imaging attention due to severe congenital heart disease, immune deficiency, or bowel obstruction related to malrotation (1–11). In contrast, there is scant information in the radiology literature about the abdominal manifestations of situs anomalies in adults (12–17). In part, this is because adults with situs anomalies undergo imaging less frequently than children due to the absence of congenital heart disease, immune disorders, and other conditions that affect the pediatric population (1,2). In fact, situs anomalies are often detected incidentally in adults during imaging evaluation for unrelated conditions such as cholecystitis and appendicitis. Technical advances in sonography, computed tomography (CT), and magnetic resonance (MR) imaging have greatly enhanced our ability to detect and characterize these anomalies (18–20).
One might postulate, based on the differing prevalences of underlying abnormalities such as congenital heart disease in pediatric and adult patients with situs anomalies, that situs ambiguous with asplenia, which is often associated with severe congenital heart disease, would be detected infrequently in adults, whereas situs ambiguous with polysplenia, which is associated with less severe or no congenital heart disease, would be detected more often. In this article, we describe and illustrate the abdominal manifestations of situs anomalies in adults, including situs inversus, situs ambiguous with polysplenia, and situs ambiguous with asplenia, and discuss clinical scenarios in which these anomalies present diagnostic challenges.
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Terminology
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Situs anomalies are often considered confusing, in part because of the overlapping features of some anomalies such as situs ambiguous with polysplenia and situs ambiguous with asplenia. The literature also contributes to this confusion because some authors use the terms situs inversus and situs ambiguous interchangeably. Greater understanding can be achieved by defining the terms commonly used to describe situs anomalies (1,2).
The term situs refers to the position of the heart and viscera relative to midline. Situs solitus represents the normal position of the heart and abdominal viscera, with the cardiac apex, spleen, stomach, and aorta located on the left and the liver and inferior vena cava (IVC) located on the right (Fig 1a). Congenital heart disease occurs in less than 1% of individuals with situs solitus (21).
Situs inversus indicates mirror-image location of the viscera relative to situs solitus. There are two major subcategories of situs inversus: situs inversus with dextrocardia and situs inversus with levocardia. Situs inversus with dextrocardia is more common and is characterized by mirror-image location of the heart and viscera relative to situs solitus, with the cardiac apex, spleen, stomach, and aorta located on the right and the liver and IVC located on the left (Fig 1b). Congenital heart disease occurs in 3%–5% of cases (21). In contrast, situs inversus with levocardia is an extremely rare variant that is characterized by mirror-image location of the viscera relative to situs solitus and a left-sided cardiac apex. Nearly all affected individuals have congenital heart disease (21).
Situs ambiguous, or heterotaxia, is defined as the abnormal arrangement of organs and vessels as opposed to the orderly arrangement typical of situs solitus and situs inversus. In contrast to individuals with situs solitus or situs inversus with dextrocardia, those with situs ambiguous have congenital heart disease in 50%–100% of cases (3,21). Situs ambiguous is not characterized by a single set of abnormalities but by a spectrum of abnormalities. The two major subcategories of situs ambiguous are situs ambiguous with polysplenia and situs ambiguous with asplenia.
Situs ambiguous with polysplenia (also known as left isomerism or bilateral left-sidedness) is characterized in general by midline or ambiguous location of the majority of the abdominal organs and multiple spleens (Fig 1c). However, there is no single anomaly that is pathognomonic for this condition (2). Affected patients have a lower prevalence of congenital heart disease (50%– 90%) and less severe defects than do those with situs ambiguous with asplenia (3,21).
Situs ambiguous with asplenia (right isomerism or bilateral right-sidedness) is characterized by ambiguous location of the abdominal organs and absence of the spleen (Fig 1d). Affected patients have a 99%–100% prevalence of congenital heart disease that is much more severe than that seen with polysplenia and the other situs anomalies (21).
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Patients and Procedures
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From August 1973 through November 2001, 19 adults (12 men, 7 women) ranging in age from 18 to 70 years (mean, 42 years) with situs anomalies underwent imaging or imaging consultation at our institution. These patients underwent imaging for evaluation of abdominal pain (n = 9), malignancies (n = 5), trauma (n = 1), splenomegaly (n = 1), nausea and vomiting (n = 1), and a pancreatic abnormality suspected at CT (n = 1) and as part of pretransplantation evaluation (n = 1). The malignancies included cervical carcinoma (n = 2), lymphoma (n = 1), hepatocellular carcinoma (n = 1), and thyroid carcinoma (n = 1). Two abdominal radiologists (A.S.F., M.A.T.) reviewed in consensus the CT scans, ultrasonographic images, MR images, barium examination images, intraoperative cholangiograms, angiograms, and conventional radiographs obtained in these patients (Table). An assessment was made for the location of the solid and hollow organs of the abdomen; the location of the cardiac apex, aortic arch, abdominal aorta, and IVC; the presence and number of spleens; the appearance of the pancreas; the presence of vascular anomalies such as interruption of the IVC with azygous or hemiazygous continuation; and the presence of underlying disease processes. An assessment could not be made for each of these factors in all patients because some patients did not undergo cross-sectional imaging.
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Situs Inversus
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Situs inversus is a rare anomaly that is characterized by mirror-image location of the abdominal organs and, in most cases, the cardiac apex relative to situs solitus. This anomaly is important in that its recognition may help avoid mishaps at surgery or other interventions, particularly in the emergency setting (22). A review of 1,551,047 patients registered at the Mayo Clinic from 1910 through 1947 revealed that 76 patients (1 in 20,000) had situs inversus (23). The findings observed in the 10 patients in our series with situs inversus are summarized in the Table.
Solid Organs and Heart
The majority of patients with situs inversus demonstrate mirror-image location of the solid organs and a right-sided cardiac apex (situs inversus with dextrocardia) (Figs 2, 3). Unlike with situs ambiguous with polysplenia and situs ambiguous with asplenia, the pancreas is not truncated. The prevalence of associated congenital heart disease ranges from 3% to 5% (21). An extremely rare variant of situs inversus is situs inversus with levocardia. In this anomaly, there is mirror-image location of the abdominal organs with a left-sided cardiac apex. This variant is almost always associated with congenital heart disease (21). Only a few cases of situs inversus with levocardia and no associated congenital heart disease appear in the literature (15,24). Not surprisingly, nine of the 10 adult patients with situs inversus in our series had dextrocardia and no congenital heart disease. The remaining patient had levocardia but no associated congenital heart disease. Presumably, situs inversus with levocardia is rarely identified in the adult population, not only because it is a rare anomaly, but also because most affected patients succumb early in life to complications related to congenital heart disease.
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Figure 2a. Situs inversus in a 30-year-old man. (a) Conventional supine abdominal radiograph shows the air-filled stomach (S) in the right upper quadrant and the liver (L) in the left upper quadrant. (b) Transverse contrast material-enhanced CT scan of the abdomen demonstrates mirror-image location of the abdominal structures relative to situs solitus (normal). The liver (L) is located in the left upper quadrant, whereas the spleen (S) and stomach are located in the right upper quadrant. (c) CT scan obtained 30 mm caudad to b demonstrates a left-sided gallbladder (GB) and a right-sided pancreatic tail (P) in the region of the splenic hilum. (d) CT scan obtained 70 mm caudad to b reveals inversion of the SMV (arrow) and SMA (arrowhead). The jejunum (J) is in the right side of the abdomen. The pancreatic head (P) and uncinate process lie to the left of midline.
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Figure 2b. Situs inversus in a 30-year-old man. (a) Conventional supine abdominal radiograph shows the air-filled stomach (S) in the right upper quadrant and the liver (L) in the left upper quadrant. (b) Transverse contrast material-enhanced CT scan of the abdomen demonstrates mirror-image location of the abdominal structures relative to situs solitus (normal). The liver (L) is located in the left upper quadrant, whereas the spleen (S) and stomach are located in the right upper quadrant. (c) CT scan obtained 30 mm caudad to b demonstrates a left-sided gallbladder (GB) and a right-sided pancreatic tail (P) in the region of the splenic hilum. (d) CT scan obtained 70 mm caudad to b reveals inversion of the SMV (arrow) and SMA (arrowhead). The jejunum (J) is in the right side of the abdomen. The pancreatic head (P) and uncinate process lie to the left of midline.
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Figure 2c. Situs inversus in a 30-year-old man. (a) Conventional supine abdominal radiograph shows the air-filled stomach (S) in the right upper quadrant and the liver (L) in the left upper quadrant. (b) Transverse contrast material-enhanced CT scan of the abdomen demonstrates mirror-image location of the abdominal structures relative to situs solitus (normal). The liver (L) is located in the left upper quadrant, whereas the spleen (S) and stomach are located in the right upper quadrant. (c) CT scan obtained 30 mm caudad to b demonstrates a left-sided gallbladder (GB) and a right-sided pancreatic tail (P) in the region of the splenic hilum. (d) CT scan obtained 70 mm caudad to b reveals inversion of the SMV (arrow) and SMA (arrowhead). The jejunum (J) is in the right side of the abdomen. The pancreatic head (P) and uncinate process lie to the left of midline.
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Figure 2d. Situs inversus in a 30-year-old man. (a) Conventional supine abdominal radiograph shows the air-filled stomach (S) in the right upper quadrant and the liver (L) in the left upper quadrant. (b) Transverse contrast material-enhanced CT scan of the abdomen demonstrates mirror-image location of the abdominal structures relative to situs solitus (normal). The liver (L) is located in the left upper quadrant, whereas the spleen (S) and stomach are located in the right upper quadrant. (c) CT scan obtained 30 mm caudad to b demonstrates a left-sided gallbladder (GB) and a right-sided pancreatic tail (P) in the region of the splenic hilum. (d) CT scan obtained 70 mm caudad to b reveals inversion of the SMV (arrow) and SMA (arrowhead). The jejunum (J) is in the right side of the abdomen. The pancreatic head (P) and uncinate process lie to the left of midline.
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Figure 3a. Situs inversus in a 63-year-old man. (a) Coronal half-Fourier rapid acquisition with relaxation enhancement (RARE) image of the abdomen and chest shows the liver, gallbladder, and bile duct in the left upper quadrant. The fluid-filled stomach (arrow) is identified in the right upper quadrant. The cardiac apex (arrowhead) is directed toward the right (dextrocardia), and the distal bile duct drains into the junction of the second and third portions of the duodenum. The jejunum (J) is noted in the right midabdomen. (b) Coronal half-Fourier RARE image obtained 8 mm posterior to a shows a right-sided aorta (solid arrow) and a left-sided IVC (arrowhead). A right aortic arch (open arrow) is also noted. (c) Coronal 70-mm-thick RARE MR cholangiopancreatogram shows the biliary tract (arrow) and gallbladder (GB) in the left upper quadrant and the pancreatic duct (arrowheads) coursing toward the right. The high-signal-intensity focus in the right upper quadrant (S) represents fluid in the stomach. (d-f) Unenhanced fat-suppressed T1-weighted MR images reveal the pancreatic tail (arrow in d) medial to the spleen (S), the body (arrowheads in e) crossing the midline, and the pancreatic head and uncinate process (solid arrow in f) medial to the duodenum (D). The uncinate process lies posterior to the SMV (open arrow in f). (g) Selective digital subtraction angiogram shows mirror-image branching of the common hepatic artery (CHA) directly into the right hepatic artery (RHA) and left hepatic artery (LHA). GDA = gastroduodenal artery.
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Figure 3b. Situs inversus in a 63-year-old man. (a) Coronal half-Fourier rapid acquisition with relaxation enhancement (RARE) image of the abdomen and chest shows the liver, gallbladder, and bile duct in the left upper quadrant. The fluid-filled stomach (arrow) is identified in the right upper quadrant. The cardiac apex (arrowhead) is directed toward the right (dextrocardia), and the distal bile duct drains into the junction of the second and third portions of the duodenum. The jejunum (J) is noted in the right midabdomen. (b) Coronal half-Fourier RARE image obtained 8 mm posterior to a shows a right-sided aorta (solid arrow) and a left-sided IVC (arrowhead). A right aortic arch (open arrow) is also noted. (c) Coronal 70-mm-thick RARE MR cholangiopancreatogram shows the biliary tract (arrow) and gallbladder (GB) in the left upper quadrant and the pancreatic duct (arrowheads) coursing toward the right. The high-signal-intensity focus in the right upper quadrant (S) represents fluid in the stomach. (d-f) Unenhanced fat-suppressed T1-weighted MR images reveal the pancreatic tail (arrow in d) medial to the spleen (S), the body (arrowheads in e) crossing the midline, and the pancreatic head and uncinate process (solid arrow in f) medial to the duodenum (D). The uncinate process lies posterior to the SMV (open arrow in f). (g) Selective digital subtraction angiogram shows mirror-image branching of the common hepatic artery (CHA) directly into the right hepatic artery (RHA) and left hepatic artery (LHA). GDA = gastroduodenal artery.
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Figure 3c. Situs inversus in a 63-year-old man. (a) Coronal half-Fourier rapid acquisition with relaxation enhancement (RARE) image of the abdomen and chest shows the liver, gallbladder, and bile duct in the left upper quadrant. The fluid-filled stomach (arrow) is identified in the right upper quadrant. The cardiac apex (arrowhead) is directed toward the right (dextrocardia), and the distal bile duct drains into the junction of the second and third portions of the duodenum. The jejunum (J) is noted in the right midabdomen. (b) Coronal half-Fourier RARE image obtained 8 mm posterior to a shows a right-sided aorta (solid arrow) and a left-sided IVC (arrowhead). A right aortic arch (open arrow) is also noted. (c) Coronal 70-mm-thick RARE MR cholangiopancreatogram shows the biliary tract (arrow) and gallbladder (GB) in the left upper quadrant and the pancreatic duct (arrowheads) coursing toward the right. The high-signal-intensity focus in the right upper quadrant (S) represents fluid in the stomach. (d-f) Unenhanced fat-suppressed T1-weighted MR images reveal the pancreatic tail (arrow in d) medial to the spleen (S), the body (arrowheads in e) crossing the midline, and the pancreatic head and uncinate process (solid arrow in f) medial to the duodenum (D). The uncinate process lies posterior to the SMV (open arrow in f). (g) Selective digital subtraction angiogram shows mirror-image branching of the common hepatic artery (CHA) directly into the right hepatic artery (RHA) and left hepatic artery (LHA). GDA = gastroduodenal artery.
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Figure 3d. Situs inversus in a 63-year-old man. (a) Coronal half-Fourier rapid acquisition with relaxation enhancement (RARE) image of the abdomen and chest shows the liver, gallbladder, and bile duct in the left upper quadrant. The fluid-filled stomach (arrow) is identified in the right upper quadrant. The cardiac apex (arrowhead) is directed toward the right (dextrocardia), and the distal bile duct drains into the junction of the second and third portions of the duodenum. The jejunum (J) is noted in the right midabdomen. (b) Coronal half-Fourier RARE image obtained 8 mm posterior to a shows a right-sided aorta (solid arrow) and a left-sided IVC (arrowhead). A right aortic arch (open arrow) is also noted. (c) Coronal 70-mm-thick RARE MR cholangiopancreatogram shows the biliary tract (arrow) and gallbladder (GB) in the left upper quadrant and the pancreatic duct (arrowheads) coursing toward the right. The high-signal-intensity focus in the right upper quadrant (S) represents fluid in the stomach. (d-f) Unenhanced fat-suppressed T1-weighted MR images reveal the pancreatic tail (arrow in d) medial to the spleen (S), the body (arrowheads in e) crossing the midline, and the pancreatic head and uncinate process (solid arrow in f) medial to the duodenum (D). The uncinate process lies posterior to the SMV (open arrow in f). (g) Selective digital subtraction angiogram shows mirror-image branching of the common hepatic artery (CHA) directly into the right hepatic artery (RHA) and left hepatic artery (LHA). GDA = gastroduodenal artery.
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Figure 3e. Situs inversus in a 63-year-old man. (a) Coronal half-Fourier rapid acquisition with relaxation enhancement (RARE) image of the abdomen and chest shows the liver, gallbladder, and bile duct in the left upper quadrant. The fluid-filled stomach (arrow) is identified in the right upper quadrant. The cardiac apex (arrowhead) is directed toward the right (dextrocardia), and the distal bile duct drains into the junction of the second and third portions of the duodenum. The jejunum (J) is noted in the right midabdomen. (b) Coronal half-Fourier RARE image obtained 8 mm posterior to a shows a right-sided aorta (solid arrow) and a left-sided IVC (arrowhead). A right aortic arch (open arrow) is also noted. (c) Coronal 70-mm-thick RARE MR cholangiopancreatogram shows the biliary tract (arrow) and gallbladder (GB) in the left upper quadrant and the pancreatic duct (arrowheads) coursing toward the right. The high-signal-intensity focus in the right upper quadrant (S) represents fluid in the stomach. (d-f) Unenhanced fat-suppressed T1-weighted MR images reveal the pancreatic tail (arrow in d) medial to the spleen (S), the body (arrowheads in e) crossing the midline, and the pancreatic head and uncinate process (solid arrow in f) medial to the duodenum (D). The uncinate process lies posterior to the SMV (open arrow in f). (g) Selective digital subtraction angiogram shows mirror-image branching of the common hepatic artery (CHA) directly into the right hepatic artery (RHA) and left hepatic artery (LHA). GDA = gastroduodenal artery.
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Figure 3f. Situs inversus in a 63-year-old man. (a) Coronal half-Fourier rapid acquisition with relaxation enhancement (RARE) image of the abdomen and chest shows the liver, gallbladder, and bile duct in the left upper quadrant. The fluid-filled stomach (arrow) is identified in the right upper quadrant. The cardiac apex (arrowhead) is directed toward the right (dextrocardia), and the distal bile duct drains into the junction of the second and third portions of the duodenum. The jejunum (J) is noted in the right midabdomen. (b) Coronal half-Fourier RARE image obtained 8 mm posterior to a shows a right-sided aorta (solid arrow) and a left-sided IVC (arrowhead). A right aortic arch (open arrow) is also noted. (c) Coronal 70-mm-thick RARE MR cholangiopancreatogram shows the biliary tract (arrow) and gallbladder (GB) in the left upper quadrant and the pancreatic duct (arrowheads) coursing toward the right. The high-signal-intensity focus in the right upper quadrant (S) represents fluid in the stomach. (d-f) Unenhanced fat-suppressed T1-weighted MR images reveal the pancreatic tail (arrow in d) medial to the spleen (S), the body (arrowheads in e) crossing the midline, and the pancreatic head and uncinate process (solid arrow in f) medial to the duodenum (D). The uncinate process lies posterior to the SMV (open arrow in f). (g) Selective digital subtraction angiogram shows mirror-image branching of the common hepatic artery (CHA) directly into the right hepatic artery (RHA) and left hepatic artery (LHA). GDA = gastroduodenal artery.
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Figure 3g. Situs inversus in a 63-year-old man. (a) Coronal half-Fourier rapid acquisition with relaxation enhancement (RARE) image of the abdomen and chest shows the liver, gallbladder, and bile duct in the left upper quadrant. The fluid-filled stomach (arrow) is identified in the right upper quadrant. The cardiac apex (arrowhead) is directed toward the right (dextrocardia), and the distal bile duct drains into the junction of the second and third portions of the duodenum. The jejunum (J) is noted in the right midabdomen. (b) Coronal half-Fourier RARE image obtained 8 mm posterior to a shows a right-sided aorta (solid arrow) and a left-sided IVC (arrowhead). A right aortic arch (open arrow) is also noted. (c) Coronal 70-mm-thick RARE MR cholangiopancreatogram shows the biliary tract (arrow) and gallbladder (GB) in the left upper quadrant and the pancreatic duct (arrowheads) coursing toward the right. The high-signal-intensity focus in the right upper quadrant (S) represents fluid in the stomach. (d-f) Unenhanced fat-suppressed T1-weighted MR images reveal the pancreatic tail (arrow in d) medial to the spleen (S), the body (arrowheads in e) crossing the midline, and the pancreatic head and uncinate process (solid arrow in f) medial to the duodenum (D). The uncinate process lies posterior to the SMV (open arrow in f). (g) Selective digital subtraction angiogram shows mirror-image branching of the common hepatic artery (CHA) directly into the right hepatic artery (RHA) and left hepatic artery (LHA). GDA = gastroduodenal artery.
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Bowel and Mesenteric Vessels
Patients with situs inversus demonstrate mirror-image location, not only of the solid organs and heart, but also of the bowel and mesenteric vessels. The stomach, jejunum, and descending colon are located on the right, and the ligament of Treitz, ileum, and ascending colon are located on the left (Fig 4). The orientation of the bowel is reversed rather than malrotated relative to situs solitus. In our series, the stomach was right-sided in all 10 patients. In eight of 10 patients, the colon could be located with certainty and showed reverse rotation. In seven of 10 patients, the location of the small bowel could be determined. The jejunum was shown to lie primarily to the right of midline and the ileum to the left. Inversion of the superior mesenteric artery (SMA) and superior mesenteric vein (SMV) was noted in all six patients who underwent CT, MR imaging, or angiographic correlation (Fig 2d).
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Figure 4a. Situs inversus in a 47-year-old man. (a) Conventional supine abdominal radiograph reveals that the descending colon (D), located in the right side of the abdomen, is cephalad to the ascending colon (A), located in the left side of the abdomen. The triangular cecum (C) lies in the left lower quadrant. This represents the mirror-image location of bowel relative to situs solitus. (b) Radiograph from an upper gastrointestinal study shows that the stomach (S) is located in the right side of the abdomen along with the jejunum (J). (c) Delayed radiograph from an upper gastrointestinal study helps confirm the location of the descending colon (D), ascending colon (A), and cecum (C) (cf a).
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Figure 4b. Situs inversus in a 47-year-old man. (a) Conventional supine abdominal radiograph reveals that the descending colon (D), located in the right side of the abdomen, is cephalad to the ascending colon (A), located in the left side of the abdomen. The triangular cecum (C) lies in the left lower quadrant. This represents the mirror-image location of bowel relative to situs solitus. (b) Radiograph from an upper gastrointestinal study shows that the stomach (S) is located in the right side of the abdomen along with the jejunum (J). (c) Delayed radiograph from an upper gastrointestinal study helps confirm the location of the descending colon (D), ascending colon (A), and cecum (C) (cf a).
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Figure 4c. Situs inversus in a 47-year-old man. (a) Conventional supine abdominal radiograph reveals that the descending colon (D), located in the right side of the abdomen, is cephalad to the ascending colon (A), located in the left side of the abdomen. The triangular cecum (C) lies in the left lower quadrant. This represents the mirror-image location of bowel relative to situs solitus. (b) Radiograph from an upper gastrointestinal study shows that the stomach (S) is located in the right side of the abdomen along with the jejunum (J). (c) Delayed radiograph from an upper gastrointestinal study helps confirm the location of the descending colon (D), ascending colon (A), and cecum (C) (cf a).
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Biliary Tract and Gallbladder
The branching pattern of the biliary tract and the location of the gallbladder in situs inversus are mirror image relative to situs solitus (Figs 3a, 3c, 5). In a study by Mayo and Rice (23), seven of 76 patients with situs inversus had abnormalities of the biliary tract or gallbladder (23). Two of the seven patients were infants with biliary atresia, and five were adults with cholelithiasis and cholecystitis. In our series, two of 10 patients had acute cholecystitis and another had a small, asymptomatic gallstone. The remaining seven patients had no diseases of the biliary tract or gallbladder.
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Figure 5. Situs inversus in a 23-year-old man. Intraoperative cholangiogram shows the right hepatic duct (RHD) and left hepatic duct (LHD) as well as the extrahepatic bile duct in the left upper quadrant. The cystic duct remnant (arrow) inserts into the right hepatic duct rather than the extrahepatic bile duct. Note the nasogastric tube in the right upper quadrant.
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Pulmonary and Sinus Disease
Pulmonary and sinus disease may be associated with situs inversus. A subset of patients with situs inversus may demonstrate bronchiectasis and sinusitis, a constellation of findings often referred to as Kartagener syndrome and first described by Kartagener and Stucki in 1962 (25). Kartagener syndrome has been reported to occur in approximately 17% of patients with situs inversus (23). No patient in our series had Kartagener syndrome.
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Situs Ambiguous with Polysplenia
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Situs ambiguous with polysplenia, often referred to as left isomerism or bilateral left-sidedness, is a subcategory of situs ambiguous that is usually characterized by an abnormal arrangement of the solid organs and bowel and the presence of multiple spleens. However, it should be remembered that this anomaly does not have a fixed set of characteristics that are present in all cases. For example, even abdominal heterotaxy is not always present, nor are multiple spleens (1,3,9–11). Although this anomaly has no pathognomonic feature, a sufficient number of associated findings occur in the majority of patients to allow the diagnosis to be established. The most frequently encountered findings are discussed later. The findings seen in the eight patients with situs ambiguous with polysplenia in our series are summarized in the Table.
Spleen
Although situs ambiguous with polysplenia is associated with multiple discrete spleens in the majority of patients, some studies (including our own) report patients with situs ambiguous who have a single, lobulated spleen or even a normal spleen (1,9,10). Nevertheless, the majority of patients have multiple spleens of variable size and number that may be located in either the left or right side of the abdomen (Figs 6–8) (1,3). In our series, the number of spleens in an affected patient ranged from one to 10 (mean, six). The spleens were located on the right side in three patients, on the left side in five patients, and adjacent to the stomach in all eight patients. The consistent relationship between the spleens and the stomach has been noted in other series and is explained by the fact that splenic tissue develops in the dorsal mesogastrium (26).
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Figure 6a. Situs ambiguous with polysplenia in a 67-year-old man. (a) Transverse contrast-enhanced CT scan of the abdomen shows a midline liver, multiple spleens (S) in the right upper quadrant adjacent to the collapsed stomach (St), and IVC interruption with azygous continuation (arrow). The low attenuation of the spleens is related to infarctions, which cause liquefaction and subcapsular hematomas. Note the absence of splenic tissue in the left upper quadrant (*). (b) Transverse CT scan through the midabdomen reveals a midline gallbladder (GB). (c) Transverse CT scan through the lower abdomen reveals small bowel (SB) in the right lower quadrant and colon in the left lower quadrant. The cecum (C) lies near the midline, a finding that indicates incomplete fixation. (d) Conventional abdominal radiograph shows a nasogastric tube that courses through the stomach in the right upper quadrant and enters the duodenum. Note the reversal of the duodenal C shape (arrows). (e, f) Frontal (e) and left lateral decubitus (f) images from a double-contrast barium enema examination reveal that the majority of colon is located left of midline and that the position of the cecum (C) changes, a finding that indicates incomplete fixation of the cecum.
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Figure 6b. Situs ambiguous with polysplenia in a 67-year-old man. (a) Transverse contrast-enhanced CT scan of the abdomen shows a midline liver, multiple spleens (S) in the right upper quadrant adjacent to the collapsed stomach (St), and IVC interruption with azygous continuation (arrow). The low attenuation of the spleens is related to infarctions, which cause liquefaction and subcapsular hematomas. Note the absence of splenic tissue in the left upper quadrant (*). (b) Transverse CT scan through the midabdomen reveals a midline gallbladder (GB). (c) Transverse CT scan through the lower abdomen reveals small bowel (SB) in the right lower quadrant and colon in the left lower quadrant. The cecum (C) lies near the midline, a finding that indicates incomplete fixation. (d) Conventional abdominal radiograph shows a nasogastric tube that courses through the stomach in the right upper quadrant and enters the duodenum. Note the reversal of the duodenal C shape (arrows). (e, f) Frontal (e) and left lateral decubitus (f) images from a double-contrast barium enema examination reveal that the majority of colon is located left of midline and that the position of the cecum (C) changes, a finding that indicates incomplete fixation of the cecum.
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Figure 6c. Situs ambiguous with polysplenia in a 67-year-old man. (a) Transverse contrast-enhanced CT scan of the abdomen shows a midline liver, multiple spleens (S) in the right upper quadrant adjacent to the collapsed stomach (St), and IVC interruption with azygous continuation (arrow). The low attenuation of the spleens is related to infarctions, which cause liquefaction and subcapsular hematomas. Note the absence of splenic tissue in the left upper quadrant (*). (b) Transverse CT scan through the midabdomen reveals a midline gallbladder (GB). (c) Transverse CT scan through the lower abdomen reveals small bowel (SB) in the right lower quadrant and colon in the left lower quadrant. The cecum (C) lies near the midline, a finding that indicates incomplete fixation. (d) Conventional abdominal radiograph shows a nasogastric tube that courses through the stomach in the right upper quadrant and enters the duodenum. Note the reversal of the duodenal C shape (arrows). (e, f) Frontal (e) and left lateral decubitus (f) images from a double-contrast barium enema examination reveal that the majority of colon is located left of midline and that the position of the cecum (C) changes, a finding that indicates incomplete fixation of the cecum.
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Figure 6d. Situs ambiguous with polysplenia in a 67-year-old man. (a) Transverse contrast-enhanced CT scan of the abdomen shows a midline liver, multiple spleens (S) in the right upper quadrant adjacent to the collapsed stomach (St), and IVC interruption with azygous continuation (arrow). The low attenuation of the spleens is related to infarctions, which cause liquefaction and subcapsular hematomas. Note the absence of splenic tissue in the left upper quadrant (*). (b) Transverse CT scan through the midabdomen reveals a midline gallbladder (GB). (c) Transverse CT scan through the lower abdomen reveals small bowel (SB) in the right lower quadrant and colon in the left lower quadrant. The cecum (C) lies near the midline, a finding that indicates incomplete fixation. (d) Conventional abdominal radiograph shows a nasogastric tube that courses through the stomach in the right upper quadrant and enters the duodenum. Note the reversal of the duodenal C shape (arrows). (e, f) Frontal (e) and left lateral decubitus (f) images from a double-contrast barium enema examination reveal that the majority of colon is located left of midline and that the position of the cecum (C) changes, a finding that indicates incomplete fixation of the cecum.
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Figure 6e. Situs ambiguous with polysplenia in a 67-year-old man. (a) Transverse contrast-enhanced CT scan of the abdomen shows a midline liver, multiple spleens (S) in the right upper quadrant adjacent to the collapsed stomach (St), and IVC interruption with azygous continuation (arrow). The low attenuation of the spleens is related to infarctions, which cause liquefaction and subcapsular hematomas. Note the absence of splenic tissue in the left upper quadrant (*). (b) Transverse CT scan through the midabdomen reveals a midline gallbladder (GB). (c) Transverse CT scan through the lower abdomen reveals small bowel (SB) in the right lower quadrant and colon in the left lower quadrant. The cecum (C) lies near the midline, a finding that indicates incomplete fixation. (d) Conventional abdominal radiograph shows a nasogastric tube that courses through the stomach in the right upper quadrant and enters the duodenum. Note the reversal of the duodenal C shape (arrows). (e, f) Frontal (e) and left lateral decubitus (f) images from a double-contrast barium enema examination reveal that the majority of colon is located left of midline and that the position of the cecum (C) changes, a finding that indicates incomplete fixation of the cecum.
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Figure 6f. Situs ambiguous with polysplenia in a 67-year-old man. (a) Transverse contrast-enhanced CT scan of the abdomen shows a midline liver, multiple spleens (S) in the right upper quadrant adjacent to the collapsed stomach (St), and IVC interruption with azygous continuation (arrow). The low attenuation of the spleens is related to infarctions, which cause liquefaction and subcapsular hematomas. Note the absence of splenic tissue in the left upper quadrant (*). (b) Transverse CT scan through the midabdomen reveals a midline gallbladder (GB). (c) Transverse CT scan through the lower abdomen reveals small bowel (SB) in the right lower quadrant and colon in the left lower quadrant. The cecum (C) lies near the midline, a finding that indicates incomplete fixation. (d) Conventional abdominal radiograph shows a nasogastric tube that courses through the stomach in the right upper quadrant and enters the duodenum. Note the reversal of the duodenal C shape (arrows). (e, f) Frontal (e) and left lateral decubitus (f) images from a double-contrast barium enema examination reveal that the majority of colon is located left of midline and that the position of the cecum (C) changes, a finding that indicates incomplete fixation of the cecum.
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Figure 7a. Situs ambiguous with polysplenia in a 42-year-old woman. (a) Contrast-enhanced CT scan of the lower chest reveals dextrocardia and a prominent azygous vein (A). (b) CT scan of the upper abdomen reveals a midline liver (L) and multiple spleens in the left upper quadrant that lie lateral to the stomach. A 2-cm enhancing structure (arrow) representative of a left IVC courses posterior to the stomach and was seen on other images to enter the suprahepatic portion of the IVC. Note the slightly enlarged azygous vein (A) and the normal-sized hemiazygous veins (HA). (c, d) CT scans obtained 2.4 cm (c) and 4.8 cm (d) caudad to b reveal that the left IVC (arrow) courses through the retroperitoneum and is continuous with the renal vein (arrowhead). A midline gallbladder (GB) is also noted. (e) CT scan obtained 2.4 cm below the left renal vein reveals duplication of the infrarenal IVC (arrows).
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Figure 7b. Situs ambiguous with polysplenia in a 42-year-old woman. (a) Contrast-enhanced CT scan of the lower chest reveals dextrocardia and a prominent azygous vein (A). (b) CT scan of the upper abdomen reveals a midline liver (L) and multiple spleens in the left upper quadrant that lie lateral to the stomach. A 2-cm enhancing structure (arrow) representative of a left IVC courses posterior to the stomach and was seen on other images to enter the suprahepatic portion of the IVC. Note the slightly enlarged azygous vein (A) and the normal-sized hemiazygous veins (HA). (c, d) CT scans obtained 2.4 cm (c) and 4.8 cm (d) caudad to b reveal that the left IVC (arrow) courses through the retroperitoneum and is continuous with the renal vein (arrowhead). A midline gallbladder (GB) is also noted. (e) CT scan obtained 2.4 cm below the left renal vein reveals duplication of the infrarenal IVC (arrows).
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Figure 7c. Situs ambiguous with polysplenia in a 42-year-old woman. (a) Contrast-enhanced CT scan of the lower chest reveals dextrocardia and a prominent azygous vein (A). (b) CT scan of the upper abdomen reveals a midline liver (L) and multiple spleens in the left upper quadrant that lie lateral to the stomach. A 2-cm enhancing structure (arrow) representative of a left IVC courses posterior to the stomach and was seen on other images to enter the suprahepatic portion of the IVC. Note the slightly enlarged azygous vein (A) and the normal-sized hemiazygous veins (HA). (c, d) CT scans obtained 2.4 cm (c) and 4.8 cm (d) caudad to b reveal that the left IVC (arrow) courses through the retroperitoneum and is continuous with the renal vein (arrowhead). A midline gallbladder (GB) is also noted. (e) CT scan obtained 2.4 cm below the left renal vein reveals duplication of the infrarenal IVC (arrows).
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Figure 7d. Situs ambiguous with polysplenia in a 42-year-old woman. (a) Contrast-enhanced CT scan of the lower chest reveals dextrocardia and a prominent azygous vein (A). (b) CT scan of the upper abdomen reveals a midline liver (L) and multiple spleens in the left upper quadrant that lie lateral to the stomach. A 2-cm enhancing structure (arrow) representative of a left IVC courses posterior to the stomach and was seen on other images to enter the suprahepatic portion of the IVC. Note the slightly enlarged azygous vein (A) and the normal-sized hemiazygous veins (HA). (c, d) CT scans obtained 2.4 cm (c) and 4.8 cm (d) caudad to b reveal that the left IVC (arrow) courses through the retroperitoneum and is continuous with the renal vein (arrowhead). A midline gallbladder (GB) is also noted. (e) CT scan obtained 2.4 cm below the left renal vein reveals duplication of the infrarenal IVC (arrows).
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Figure 7e. Situs ambiguous with polysplenia in a 42-year-old woman. (a) Contrast-enhanced CT scan of the lower chest reveals dextrocardia and a prominent azygous vein (A). (b) CT scan of the upper abdomen reveals a midline liver (L) and multiple spleens in the left upper quadrant that lie lateral to the stomach. A 2-cm enhancing structure (arrow) representative of a left IVC courses posterior to the stomach and was seen on other images to enter the suprahepatic portion of the IVC. Note the slightly enlarged azygous vein (A) and the normal-sized hemiazygous veins (HA). (c, d) CT scans obtained 2.4 cm (c) and 4.8 cm (d) caudad to b reveal that the left IVC (arrow) courses through the retroperitoneum and is continuous with the renal vein (arrowhead). A midline gallbladder (GB) is also noted. (e) CT scan obtained 2.4 cm below the left renal vein reveals duplication of the infrarenal IVC (arrows).
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Figure 8a. Situs ambiguous with polysplenia in a 31-year-old woman. (a) Contrast-enhanced abdominal CT scan shows the liver in the right upper quadrant and multiple spleens in the left upper quadrant immediately lateral to the stomach. Interruption of the IVC with azygous continuation is also noted. (b) CT scan obtained at the level of the renal hila shows a truncated pancreas (arrows). Note the small bowel (SB) in the right side of the abdomen and the colon (C) in the left side.
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Figure 8b. Situs ambiguous with polysplenia in a 31-year-old woman. (a) Contrast-enhanced abdominal CT scan shows the liver in the right upper quadrant and multiple spleens in the left upper quadrant immediately lateral to the stomach. Interruption of the IVC with azygous continuation is also noted. (b) CT scan obtained at the level of the renal hila shows a truncated pancreas (arrows). Note the small bowel (SB) in the right side of the abdomen and the colon (C) in the left side.
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Liver, Gallbladder, and Biliary Tract
In the eight patients in our series with situs ambiguous with polysplenia, the liver and gallbladder were midline in five and right-sided in three (Figs 6, 7). A recent review that included 10 pediatric patients with polysplenia reported midline livers in five patients, right-sided livers in four, and a left-sided liver in one (1). In a larger review of 146 patients with polysplenia, an abnormal arrangement of the abdominal organs was present in only 56% (3).
Intraoperative cholangiography was performed in one of the patients in our series and demonstrated mirror-image branching of an otherwise normal biliary tract. Gagner et al (27) reported a quadruplication anomaly of the bile ducts and choledocholithiasis in an adult with polysplenia. Biliary abnormalities including biliary atresia have been reported in pediatric patients (9).
Pancreas
In six of the eight patients in our series with situs ambiguous with polysplenia, the pancreas was truncated. Only the pancreatic head was present in five of these six patients, and only the pancreatic head and a small portion of the pancreatic body was present in the remaining patient. The head was located to the right of midline in five patients and was midline in one (Figs 8, 9). In one of the six patients, the pancreas demonstrated a cleft created by vessels traversing the gland. Little information appears in the radiology literature regarding the appearance of the pancreas in patients with polysplenia. Hadar et al (16) reported incidental detection of a short pancreas in two adult patients with polysplenia who underwent CT for evaluation of unrelated disease. In both patients, CT revealed absence of the pancreatic body and tail with a normal-sized pancreatic head located to the right of midline, findings similar to those detected in the six patients in our series. Hatayama and Wells (28) described a short, "stubby" pancreas in six pediatric patients with polysplenia and congenital heart disease. The association between a short pancreas and polysplenia is interesting, and indeed, knowledge of this association may be clinically relevant. When only a short portion of the pancreatic duct is opacified at endoscopic retrograde cholangiopancreatography in a patient with polysplenia, it is important to attribute this finding to a truncated pancreas rather than to pancreas divisum or a mass obstructing the pancreatic duct.
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Figure 9. Situs ambiguous with polysplenia in a 51-year-old woman. Contrast-enhanced fat-suppressed T1-weighted MR image of the abdomen shows a truncated pancreas (P). The pancreatic parenchyma terminates at the level of the distal pancreatic body (arrow). No pancreatic parenchyma lies anterior to the majority of the splenic vein (arrowheads).
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IVC Interruption with Azygous or Hemiazygous Continuation
Besides being associated with duplication of left-sided structures such as the spleen, situs ambiguous with polysplenia (bilateral left-sidedness) is associated with absence of right-sided structures such as a portion of the IVC. IVC interruption with azygous or hemiazygous continuation was present in seven of the eight adults with polysplenia in our series (Figs 6–8). The infrahepatic IVC was right-sided in five of seven patients with IVC interruption, left-sided in one, and duplicated in one. In the patient with a duplicated infrahepatic IVC, the right IVC was interrupted and associated with azygous continuation, whereas the left IVC coursed through the left side of the retroperitoneum and entered the suprahepatic IVC (Fig 7). IVC interruption with azygous or hemiazygous continuation has been reported in at least four additional adults with polysplenia in whom the anomaly was incidentally detected (13,14,17). In two series of pediatric patients with polysplenia, this vascular anomaly was seen in 65% and 80% of cases, respectively (1,3).
Abdominal Aorta
In our series, the aorta was located to the left of midline in seven of eight patients, including the patient with a left-sided IVC. The aorta was located to the right of midline but between the right and left infrahepatic IVCs in the patient with duplication of the infrahepatic IVC.
Cardiac Apex and Congenital Heart Disease
Levocardia was present in seven of eight patients in our series and dextrocardia in the remaining patient. In four of eight patients (50%), the stomach and the cardiac apex were discordant. A similar frequency of discordance was reported by Applegate et al (1) in their series of pediatric patients.
None of the patients with situs ambiguous and polysplenia in our series had congenital heart disease, which in part explains their survival into adulthood. In contrast, only three of 10 pediatric patients in the study by Applegate et al (1) had no evidence of congenital heart disease.
Gastrointestinal Tract
In our series, the stomach was right-sided in three patients and left-sided in five. In each of the three patients with a right-sided stomach, the third portion of the duodenum was directed from right to left. Abnormalities of bowel rotation were observed in seven of the eight patients with polysplenia in our series (Figs 6, 8). The small bowel was primarily right-sided and the colon primarily left-sided in five of seven patients with rotational abnormalities. One patient had evidence of an incompletely fixed cecum. No patient in our series had a history of bowel obstruction related to anomalous bowel rotation. In a study of six pediatric patients with polysplenia, Ditchfield and Hutson (6) reported that all six had anomalies of bowel rotation and one developed midgut volvulus.
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Situs Ambiguous with Asplenia
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Situs ambiguous with asplenia is a second subcategory of situs ambiguous that is generally characterized by an abnormal arrangement of the abdominal organs and absence of the spleen. This anomaly occurs more frequently in males than in females, with approximately two-thirds of all reported cases occurring in males (26). Because congenital heart disease complicates this anomaly in up to 99%–100% of patients, most present as neonates with symptoms of congenital heart disease and have a much higher mortality rate than those with polysplenia (21). Others also have immune deficiency, in part due to absence of the spleen. In fact, death occurs in the 1st year of life in up to 95% of cases owing to congenital heart disease and abnormalities in immune status (26). Thus, it is not surprising that situs ambiguous with asplenia is rarely encountered in adults. Applegate et al (1) reported that 11 (52%) of 21 pediatric patients with situs ambiguous had asplenia and that all 21 had congenital heart disease. In contrast, of the nine patients with situs ambiguous in our series, only one had asplenia, and this patient had no history of congenital heart disease. Although it is difficult to draw strong conclusions based on the imaging findings in only one patient (Fig 10), these findings are summarized in the Table and will be discussed in the following subsections.
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Figure 10a. Situs ambiguous with asplenia in a 48-year-old man. (a) Transverse contrast-enhanced CT scan of the lower chest shows dextrocardia and azygous continuation of the IVC. The aorta is located to the right of the enlarged azygous vein (arrow). Left lower lobe collapse and a left pleural effusion are also noted. (b) CT scan obtained 15 mm caudad to a shows the stomach (S) and colon (C) in the expected location of the spleen. Hypoplasia of the anterior segment of the right hepatic lobe is noted and allows cephalic migration of the colon. (c) On another CT scan obtained caudad to b, the gallbladder (GB) is midline. The SMV lies anterior to the truncated pancreas (P), whereas the SMA lies posterior to it. (d) CT scan obtained at the level of the right renal hilum reveals that the cecum (C) is located in the left lower quadrant. Note the terminal ileum (TI) entering the colon.
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Figure 10b. Situs ambiguous with asplenia in a 48-year-old man. (a) Transverse contrast-enhanced CT scan of the lower chest shows dextrocardia and azygous continuation of the IVC. The aorta is located to the right of the enlarged azygous vein (arrow). Left lower lobe collapse and a left pleural effusion are also noted. (b) CT scan obtained 15 mm caudad to a shows the stomach (S) and colon (C) in the expected location of the spleen. Hypoplasia of the anterior segment of the right hepatic lobe is noted and allows cephalic migration of the colon. (c) On another CT scan obtained caudad to b, the gallbladder (GB) is midline. The SMV lies anterior to the truncated pancreas (P), whereas the SMA lies posterior to it. (d) CT scan obtained at the level of the right renal hilum reveals that the cecum (C) is located in the left lower quadrant. Note the terminal ileum (TI) entering the colon.
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Figure 10c. Situs ambiguous with asplenia in a 48-year-old man. (a) Transverse contrast-enhanced CT scan of the lower chest shows dextrocardia and azygous continuation of the IVC. The aorta is located to the right of the enlarged azygous vein (arrow). Left lower lobe collapse and a left pleural effusion are also noted. (b) CT scan obtained 15 mm caudad to a shows the stomach (S) and colon (C) in the expected location of the spleen. Hypoplasia of the anterior segment of the right hepatic lobe is noted and allows cephalic migration of the colon. (c) On another CT scan obtained caudad to b, the gallbladder (GB) is midline. The SMV lies anterior to the truncated pancreas (P), whereas the SMA lies posterior to it. (d) CT scan obtained at the level of the right renal hilum reveals that the cecum (C) is located in the left lower quadrant. Note the terminal ileum (TI) entering the colon.
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Figure 10d. Situs ambiguous with asplenia in a 48-year-old man. (a) Transverse contrast-enhanced CT scan of the lower chest shows dextrocardia and azygous continuation of the IVC. The aorta is located to the right of the enlarged azygous vein (arrow). Left lower lobe collapse and a left pleural effusion are also noted. (b) CT scan obtained 15 mm caudad to a shows the stomach (S) and colon (C) in the expected location of the spleen. Hypoplasia of the anterior segment of the right hepatic lobe is noted and allows cephalic migration of the colon. (c) On another CT scan obtained caudad to b, the gallbladder (GB) is midline. The SMV lies anterior to the truncated pancreas (P), whereas the SMA lies posterior to it. (d) CT scan obtained at the level of the right renal hilum reveals that the cecum (C) is located in the left lower quadrant. Note the terminal ileum (TI) entering the colon.
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Spleen
The spleen is absent in virtually all patients with asplenia. A rudimentary spleen may rarely be detected (26). In the one case of asplenia in our series, no splenic tissue was detected at CT.
Liver, Gallbladder, and Biliary Tract
In the one patient with asplenia in our series, the liver and gallbladder were midline in location. The anterior segment of the right hepatic lobe was hypoplastic, which allowed cephalic migration of the colon. Applegate et al (1) noted midline livers in 10 of 11 pediatric patients with asplenia. In another series of patients with asplenia, Freedom and Fellows (4) reported that some degree of heterotaxia was present in all patients at autopsy, even when it was not suggested by radiologic findings.
Pancreas
As mentioned earlier, in the one patient in our series with asplenia, the pancreas was truncated, with only the pancreatic head present. The pancreatic head was midline in location and was interposed between the inverted SMA and SMV. An autopsy series of 32 patients with asplenia revealed that the pancreas was intraperitoneal in location in some patients; however, the report made no mention of truncation of the pancreas (4).
IVC Interruption with Azygous or Hemiazygous Continuation
IVC interruption with azygous continuation was present in the one patient with asplenia in our series. However, it was not present in any of the 11 pediatric patients in the series by Applegate et al (1) and in only one of 32 pediatric patients in the autopsy series by Freedom and Fellows (4). In a study of patients with asplenia and polysplenia syndromes, Van Mierop et al (26) noted that IVC interruption with azygous continuation in asplenia syndrome is very rare.
Abdominal Aorta and Infrarenal IVC
An ipsilateral location of the aorta and IVC has been reported to be a consistent finding in asplenia (26,29). However, this finding was not present in our patient with asplenia. Instead, the abdominal aorta was located slightly to the right of midline and the IVC slightly to the left of midline along their entire lengths. Furthermore, in their series of 11 pediatric patients with asplenia, Applegate et al (1) noted that the aorta and IVC were ipsilateral in only six patients.
Cardiac Apex and Congenital Heart Disease
In a pediatric series, the cardiac apex was noted to lie contralateral or discordant relative to the stomach in six of 11 patients with asplenia (1). However, in the patient in our series with asplenia, the cardiac apex and stomach were concordant.
The one patient with situs ambiguous with asplenia in our series had no history of congenital heart disease, which in part explains his survival into adulthood. In an extensive review of cardiac anomalies in asplenic patients, Phoon and Neill (5) noted that not only does congenital heart disease occur in virtually all patients with this anomaly, but that multiple defects are frequently present.
Gastrointestinal Tract
In our patient with asplenia, the stomach and the majority of the small bowel were located in the right side of the abdomen and the majority of the colon in the left side. The patient had no history of bowel obstruction. Variable forms of intestinal rotational abnormalities have been described in asplenic pediatric patients and include nonrotation, incomplete rotation, and reversed rotation (1,4,6). In fact, rotational abnormalities occur in most patients with asplenia. In the most severe cases, there is lack of rotation and retroperitonealization of the bowel such that the colon lies inferior and posterior to the jejunum and ileum (26).
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Disease Processes in Adults with Situs Anomalies
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The incidental detection of situs anomalies in adults usually indicates that these individuals have not been affected by congenital heart disease, bowel obstruction, or deficiencies of the immune system. Rather, these patients come to clinical attention as a result of diseases that occur in the general population, such as appendicitis, cholelithiasis, cholecystitis, cirrhosis, and malignancy. Because individuals with situs anomalies may develop neoplasias such as hepatocellular carcinoma and lymphoma, the anomalies may be identified at imaging conducted for staging or surveillance. Diseases identified in the 19 patients in our series included appendicitis (Fig 11), ureteropelvic junction obstruction (Fig 12), uncomplicated acute cholecystitis, acute cholecystitis complicated by intraperitoneal abscesses resulting in duodenal obstruction (Fig 13), cholelithiasis without acute cholecystitis, hepatocellular carcinoma, infarction of multiple spleens (Fig 14), splenic laceration (Fig 15), lymphoma (Fig 16), and splenomegaly, with each disease being found in one patient. Cervical carcinoma was detected in two patients.
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Figure 11. Situs inversus in a 22-year-old man who presented with fever, vomiting, and left lower quadrant pain. Conventional radiograph of the pelvis shows a 1.5-cm appendicolith (arrow) and a smaller adjacent appendicolith. Appendicitis and the presence of appendicoliths were confirmed surgically.
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Figure 12. Situs inversus in a 56-year-old woman with left flank pain. Coronal unenhanced fat-suppressed T1-weighted MR image of the abdomen reveals a left ureteropelvic junction obstruction (arrow). The liver (L) is located in the left upper quadrant, and the stomach (S) and spleen (not shown) are located in the right upper quadrant. Dextrocardia (arrowhead) is also noted.
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Figure 13a. Situs ambiguous with polysplenia in a 24-year-old man with midline abdominal pain and fever. (a) Transverse contrast-enhanced abdominal CT scan shows that the liver (L) crosses the midline and lies in the right and left upper quadrants. Fluid (arrow) is noted adjacent to the midline gallbladder and was shown to be centered around the gallbladder on multiple images (not shown), raising the possibility of acute cholecystitis. (b) CT scan obtained 6 cm caudad to a reveals one of several abscesses containing air and fluid (arrow) that occurred due to acute cholecystitis complicated by gallbladder perforation. The location of the patient’s pain was atypical due to the midline location of the gallbladder. Note the inversion of the SMA and SMV posterior to the pancreas. (c) Radiograph from an upper gastrointestinal study shows that the stomach (S) is located in the left side of the abdomen. However, the third and fourth (arrow) portions of the duodenum are located in the right upper quadrant. Barium did not pass distal to the duodenum, a finding that indicated an obstruction. Surgery revealed that the obstruction was caused by the right upper quadrant abscesses.
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Figure 13b. Situs ambiguous with polysplenia in a 24-year-old man with midline abdominal pain and fever. (a) Transverse contrast-enhanced abdominal CT scan shows that the liver (L) crosses the midline and lies in the right and left upper quadrants. Fluid (arrow) is noted adjacent to the midline gallbladder and was shown to be centered around the gallbladder on multiple images (not shown), raising the possibility of acute cholecystitis. (b) CT scan obtained 6 cm caudad to a reveals one of several abscesses containing air and fluid (arrow) that occurred due to acute cholecystitis complicated by gallbladder perforation. The location of the patient’s pain was atypical due to the midline location of the gallbladder. Note the inversion of the SMA and SMV posterior to the pancreas. (c) Radiograph from an upper gastrointestinal study shows that the stomach (S) is located in the left side of the abdomen. However, the third and fourth (arrow) portions of the duodenum are located in the right upper quadrant. Barium did not pass distal to the duodenum, a finding that indicated an obstruction. Surgery revealed that the obstruction was caused by the right upper quadrant abscesses.
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Figure 13c. Situs ambiguous with polysplenia in a 24-year-old man with midline abdominal pain and fever. (a) Transverse contrast-enhanced abdominal CT scan shows that the liver (L) crosses the midline and lies in the right and left upper quadrants. Fluid (arrow) is noted adjacent to the midline gallbladder and was shown to be centered around the gallbladder on multiple images (not shown), raising the possibility of acute cholecystitis. (b) CT scan obtained 6 cm caudad to a reveals one of several abscesses containing air and fluid (arrow) that occurred due to acute cholecystitis complicated by gallbladder perforation. The location of the patient’s pain was atypical due to the midline location of the gallbladder. Note the inversion of the SMA and SMV posterior to the pancreas. (c) Radiograph from an upper gastrointestinal study shows that the stomach (S) is located in the left side of the abdomen. However, the third and fourth (arrow) portions of the duodenum are located in the right upper quadrant. Barium did not pass distal to the duodenum, a finding that indicated an obstruction. Surgery revealed that the obstruction was caused by the right upper quadrant abscesses.
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Figure 14. Situs ambiguous with polysplenia in a 67-year-old man with sudden onset of right upper quadrant pain. Contrast-enhanced CT scan of the abdomen shows low-attenuation material replacing the spleens. This appearance is related to infarctions, which caused splenic liquefaction (S). A midline liver and IVC interruption with azygous continuation (arrow) are also noted.
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Figure 15. Situs inversus in a 24-year-old man with right upper quadrant pain who had been injured in a motor vehicle accident. Transverse contrast-enhanced abdominal CT scan shows multiple splenic lacerations (arrows) and hemoperitoneum (*). The liver (L), gallbladder, and duodenum (d) are located in the left upper quadrant. Note the right-sided aorta and left-sided IVC.
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Figure 16. Situs inversus in a 69-year-old woman with lymphoma. Transverse contrast-enhanced abdominal CT scan shows that the aorta (Ao) is located to the right of midline and the IVC to the left of midline. Multiple enlarged retroperitoneal lymph nodes are identified adjacent to the aorta and IVC. In fact, one node (arrow) mimics the appearance of a right-sided IVC. It is conceivable that the IVC could be mistaken for an enhancing node at percutaneous biopsy due to its left-sided location. The liver (L) is noted on the left as well.
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Although situs anomalies do not in themselves usually cause symptoms in adults, their presence often creates a confusing clinical picture, especially in the setting of diseases such as appendicitis, cholecystitis, and splenic infarction when the patient’s pain does not correlate with the expected locations of the appendix, gallbladder, and spleen (30). Likewise, situs anomalies may lead to diagnostic dilemmas on imaging examinations if radiologists are not aware of the spectrum of findings associated with these anomalies. Confusion may occur, not only in the evaluation of solid organ abnormalities, but also in the evaluation of abnormalities of the gastrointestinal tract such as volvulus and Crohn disease. Finally, the recognition and correct characterization of situs anomalies is important in planning and performing surgical, radiologic, and endoscopic interventions (20,22).
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Conclusions
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As the use of imaging increases, situs anomalies will likely be detected with greater frequency in adults. Therefore, it is important for radiologists to become familiar with these anomalies, the spectrum of their manifestations, and their significance. This information is crucial in diagnosing disease and planning interventional procedures.
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Footnotes
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Abbreviations: IVC = inferior vena cava,
RARE = rapid acquisition with relaxation enhancement,
SMA = superior mesenteric artery,
SMV = superior mesenteric vein
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References
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