**8. Intussusception**

Intussusception is the penetration of the bowel segment, either the small intestine or colon, into the distal lumen and propulsion as luminal content. It is the most common etiology of small bowel obstruction in infants, with a reported incidence of 56 cases per 100,000 hospitalizations per year in the United States [24]. More than 90% of cases present in the first two years after birth and peak age between 3 and 9 months [1, 3, 22]. Depending on the localization, there are two subtypes; ileo-cecal (or ileocolic) comprises 90% of cases and ileo-ileal occurs in about 10% [42]. The most common symptoms are recurrent abdominal pain, vomiting and currant jelly stool. Additionally, previous episodes of infection in the upper respiratory tract or gastroenteritis may occur in the patient's clinical history. Most common localization of ileocecal intussusception is the subhepatic region, followed by upper abdominal midline and left upper quadrant [3]. It consists of three bowel segments; the inner prolapsing and returning limbs of the bowel are terminal ileum (called as intussusceptum) and attached mesentery and lymph nodes is dragged between these limbs [3, 39]. Outermost bowel receiving intussusceptum is the colon (called as intussuscipiens). Due to the compromised vascular supply, the thickest ileal segment is the returning limb of the ileum [3].

The diagnostic accuracy of US have verified with the several studies with a sensitivity of 97–100% and a specificity of 88–100% [24]. Thus, US has become as the primary modality of choice, replacing the contrast enema, in patients with suspected intussusception. Transverse section of intussusception appears as an oval or round mass with concentric rings and hypoechoic rim, described as 'doughnut' or 'target' configuration on US [1]. The crescentic shaped, hyperechoic, mesenteric fat can be seen in the center of the mass (called as 'the crescent in doughnut sign') (**Figure 3A** and **B**). The longitudinal appearance of intussusception is called as 'pseudo-kidney' or 'sandwich' sign (**Figure 3C**). On color Doppler US, double rings sign between the layers can be seen (**Figure 3B**) and absence of blood flow may indicate ischemia or irreducibility [22]. US can also be performed safely and accurately to monitor the hydrostatic reduction. Successful hydrostatic reduction rates are approximately 80% with a very few complication rates (2.7%to 4.26%) [24]. Some findings on US are useful to predict the success of enema or hydrostatic reduction such as; reduced vascular flow, thickened outer wall (>10 mm), trapped fluid and/or large (>1 cm short axis) lymph nodes within the intussusceptum [1, 3]. The appearance of intramural or subserosal air,

### **Figure 3.**

*A 5-month-old boy with intussusception. (A) Transverse section demonstrates "target sign" composed of intussusceptum (thin arrow), intussuscipiens (thick arrow) and a lymph node (dashed arrow) within the trapped mesenteric fat tissue. (B) Doppler shows swirling of arteries and veins within intussusception. (C) Longitudinal section shows typical "sandwich" or "pseudokidney" sign (arrows).*

manifested as echogenic foci, indicates the risk of necrosis and perforation, for those enema/hydrostatic reduction is contraindicated [1].

The US can identify pathologic lead points in approximately two third of cases, particularly in older age group [43]. Similarly pathologic lead points may occur in younger than expected age group as < 3 months of age [24]. Common lead points are; Meckel's diverticulum, duplication cyst, lymphoma or polyp. Cystic fibrosis, Henoch-Schonlein purpura, or polyposis syndrome may cause recurrent intussusceptions. Lead points or underlying disease should be searched elaborately in a patient with unusual age, abnormal localization of intussusception, recurrent disease and long duration of symptoms [3].

Small bowel intussusception comprises 10% of cases and is usually transient and asymptomatic. Common locations are the periumbilical area, left upper or lower quadrant of the abdomen. Most cases are due to small bowel hyperperistalsis. They are usually smaller than ileocecal intussusception (<1 cm diameter) and involve shorter bowel segment. If small bowel intussusception is persistent and symptomatic or involving longer segment (>3.5 cm), the patient should be scrutinized carefully to identify pathological lead point [3].

### **9. Intestinal malrotation and volvulus**

Intestinal malrotaton is not an infrequent phenomenon with a prevalence of 0,2– 0,5% of live births. While the most patients are asymptomatic, 3–8% of malrotated bowel is symptomatic in the first year of life with bilious vomiting, pain and malabsorption [1]. The normal midgut rotates 2700 counterclockwise in utero around the axis of superior mesenteric artery (SMA). Incomplete rotation of bowel during fetal period results in short mesenteric root, abnormal positioning of duodeno-jejunal junction and ileocecal valve and close proximity of duodenum and cecum [3]. Twisting of malrotated small bowel around its mesentery may cause obstruction and volvulus, an emergent situation that requires prompt surgical intervention [44].

The well-known sonographic finding of intestinal malrotation is the inversion of the SMA and superior mesenteric vein (SMV). Patients should be lay supine while US evaluation and transducer applied at the upper midline to recognize SMA at its point of origin on the abdominal aorta [1]. SMV can also be identified tracing from the main portal vein to the midline after giving branch of splenic vein. Normally, the SMV is found on the right side or anterior to the SMA. If SMV located ventrally or left to the SMA, it is an abnormal location, which raises suspicion but do not always indicate malrotation [3]. For evaluating duodenum and to see the passage or beak sign of acute volvulus, oral water instillation may be useful. In suspected malrotation patients, when US findings are abnormal or inconclusive, an upper GI study should be performed, as a gold standard, to confirm the diagnosis [45].

Midgut volvulus is a fatal complication of malrotation, and 90% of cases occur in the first year of life, even %75 of cases occur in the first month. The typical sonographic feature of volvulus is the 'whirlpool sign', which is the swirling of SMV and its tributaries around the SMA in clockwise direction, best appreciated on color Doppler. Associated US findings of malrotation are proximal duodenal dilatation with distal tapering, duodenal wall thickening (> 2 mm), fixed midline bowel, intraabdominal free fluid, dilatation of the distal SMV and increased resistive index on SMA [3, 39].

Off-midline scanning due to inappropriate position of the transducer may demonstrate SMV and SMA as an abnormal relation which is the most common cause of the false-positive diagnosis of malrotation. Another reason for falsepositive diagnosis is the 'whirlpool' sign occurs due to normal counterclockwise rotation. False-negative diagnosis may also be observed due to severe abdominal distension, abdominal guarding, abundant bowel gas, and/or an inexperienced operator. If there is strong clinical suspicion, an emergency upper GI study should be performed to clarify the diagnosis [3].
