Situs ambiguous-polysplenia syndrome: Torsion splenunculus – A rare cause of acute abdomen pain

INTRODUCTION

“Heterotaxy syndrome” also known as “situs ambiguous” is derived from two Greek words; heteros – meaning other and taxis implies arrangement. This rare congenital condition can either present with the left isomerism (polysplenia syndrome) or right isomerism (asplenia syndrome). The prognosis of former better is due to less severe cardiac abnormalities. Polysplenia is generally asymptomatic, but can present with various acute complications like torsion in rare instances.

CASE REPORT

A 3-year-old boy presented to pediatric outpatient department with a complaint of acute onset of abdomen pain localized to the right hypochondrium associated with fever. There was no complaint of cough, vomiting, loose stools, or constipation. Peripheral blood smear of the patient showed thrombocytosis (platelet count 719,000 cells/cc), lymphocytosis (54%), and microcytic hypochromic anemia with mild anisocytosis (Hemoglobin 8.3 g%).

The patient was referred to ultrasound (USG). USG showed a well-defined hypoechoic lesion with internal low level septations [Figure 1] with possibilities of necrotic node or omental torsion. Contrast computed tomography (CT) of the abdomen and chest was suggested for further evaluation. Contrast-enhanced CT revealed multiple splenunculi in the right hypochondrium with absent parent spleen. One of the splenunculi was relatively hypodense with only marginal and peripheral enhancement, measured (4 × 3.8 × 3.7 cm). Situs ambiguous with the right-sided liver, dorsal pancreatic agenesis, aorta on the right side, inferior vena cava (IVC) on the left side, altered superior mesenteric vein superior mesenteric artery – axis, and left side ileocecal junction were also noted [Figure 2]. However, the right side lung was trilobed and the left lung was bilobed with corresponding number of bronchi [Figure 2]. The diagnosis of situs ambiguous-polysplenia syndrome with torsion splenunculi was made.

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Figure 1:

(a) Ultrasound (USG) B mode shows a well-defined hypoechoic lesion with internal low -level septations with possibilities of necrotic node or omental torsion (b) USG color Doppler show no uptake of color flow.

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Figure 2:

(a) Contrast-enhanced CT (CECT) of abdomen and pelvis coronal section shows multiple splenunculi (yellow arrow) in the right hypochondrium with absent parent spleen. One of the splenunculi was relatively hypodense with only marginal and peripheral enhancement, measured (4 × 3.8 × 3.7 cm) (green arrow). (b) CT lung window shows, trilobed right side lung (green arrow) and bilobed left lung (yellow arrow) with corresponding number of bronchi. (c) CECT axial section of abdomen shows aorta on the right side (yellow arrow) and inferior vena cava (IVC) (brown arrow) on the left side. (d) Contrast-enhanced CT axial section of the chest shows azygos continuation of IVC (red arrow). CT: computed tomography.

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Laparoscopic excision of the infarcted splenunculus done with prophylactic pneumococcal vaccination. Pre-operative cardiac evaluation, however, did not show any congenital heart disease in this case.

DISCUSSION

Heterotaxy syndrome is characterized by an abnormality in the distribution of the thoracic and intra-abdominal contents. It differs from situs inversus as the former does not entirely correspond to the mirror image seen in latter.^[1] It occurs from the early embryological developmental disturbance with most cases being sporadic in distribution.^[2] The incidence of heterotaxy syndrome is rare, which is around 1/8000–25,000 live births.^[1]

Radiological features of heterotaxy syndrome are extremely complex. There may be duplication of the left- or right-sided intra-thoracic contents with associated changes below the diaphragm. Classically, there is malposition of liver, stomach, and spleen. In addition, the vascular anatomy can be altered. Congenital heart diseases are often associated with this condition.^[1,3] Polysplenia can be seen in 2.5/100,000 of live births which is approximately seen in 55% of cases with the left isomerism.^[1] Interrupted IVC is the second most consistent associated finding next to polysplenia, although extremely rare (1%).^[3]

Embryologically, spleen arises from mesenchymal buds in the dorsal mesogastrium during the 5^th week of gestation. Incomplete fusion results in splenunculi and when associated with situs ambiguous, they are seen on the right side of the abdomen. They however are still vascularized by the branches of splenic artery.^[4] The most common sites of accessory spleen are splenic hilum (75%), followed by pancreatic tail (20%).^[4] Usually asymptomatic, they can rarely get complicated with torsion, infarction, and ruptured with bleeding.^[4]

The first case of splenunculi torsion was reported by Alexander and Romanes^[5] and since then only very few cases are reported in the literature.^[4] Imaging plays a very important role in accurate diagnosis of this complication.^[4,6] Twisting of the vascular pedicle when present can be diagnostic.^[7] Venous congestion can result in enlargement of the torsed spleen, with reduced enhancement of the surrounding fat. There is usually an intensely enhancing capsule supplied by the patent capsular arteries and characterized by the peripheral enhancement of the torsed spleen.^[7] The differential diagnosis includes wandering spleen, necrotic nodes, omental infarction, and chronic encapsulated fat necrosis. Awareness of this syndromic association is essential to suspect this rare cause of acute abdomen pain.

Necrotic nodes, commonly seen in tuberculosis (TB), are often conglomerate due to periadenitis which is classical of TB. They are often seen in multiple sites. Encapsulated fat necrosis is characterized by fat attenuation in center (Hounsfield units-10–20) with peripheral rim of calcification, unlike the central necrosis in splenunculus torsion.^[8] Omental infarction is evidenced by inflammatory fat stranding and fat inflammation characterized by altered normal homogeneous fat signals of omentum.^[9] Wandering spleen is a condition in which spleen is normally fused and formed but located at lower abdomen which can rarely undergo torsion due to long course of artery supplying it.

DIFFERENTIAL DIAGNOSIS

The Differential Diagnosis is listed in Table 1.

It can also be associated with heterotaxy syndrome but splenunculi are not seen.^[10]

CONCLUSION

It is important to be aware of types of isomerism and complications associated with it as they are very rarely seen in clinical practice. Differentiation from situs inversus is important and imaging the chest can be helpful in the diagnosis. Cardiac anomalies are very common with he terotaxy syndromes, and hence, screening echocardiography is mandatory before any surgical interventions.

TEACHING POINTS

1. Polysplenia is characteristic of situs ambiguous (left isomerism).

2. Torsion of splenunculi should be kept as a differential diagnosis in cases of polysplenia presenting with acute abdominal pain.

3. Congenital heart diseases should be ruled out as they are closely associated with heterotaxy syndrome.

MCQs

1. Which of the patients have a better prognosis among heterotaxy syndrome?

   1. Left isomerism

   2. Right isomerism

   3. Both

   4. None

   Answer Key: a

2. All are associations of heterotaxy syndrome (left isomerism) except

   1. Polysplenia

   2. Asplenia

   3. Intestine malposition

   4. Azygos continuation of IVC

   Answer Key: b

3. All are differential diagnosis for torsion of splenunculi except

   1. Omental infarction

   2. Necrotic nodes

   3. Encapsulated fat necrosis

   4. Pseudo-aneurysm

   Answer Key: d