Appendiceal diverticulosis mimicking an appendiceal mucocele: A rare cause of adult ileo-colic intussusception

A 22-year-old male presented to the Emergency Department with abdominal pain, nausea and vomiting. Symptoms had started 12 hours before, and were progressively worsening. Physical examination revealed peri-umbilical tenderness and signs of peritoneal irritation. Laboratory studies showed PCR elevation and leucocytosis. An abdominal ultrasound was requested due to suspected appendicitis.

On ultrasound, neither the appendix or indirect ultrasonographic signs of appendicitis were encountered; however, target (Fig.1) and pseudokidney images (Fig.2), compatible with an intestinal intussusception, were seen in the peri-umbilical area. A leading point could not be detected on ultrasound; therefore an abdominopelvic Computed Tomography (CT) was performed. CT confirmed the presence of a 14 cm long ileo-colic intussusception, with the ileum ascending to the level of the hepatic flexure (Fig.3). Extending beyond the intussusception into the transverse colon, a tubular structure with fluid density content was encountered (Fig.4). The imaging findings were suggestive of an appendiceal mucocele, acting as a leading point for the intussusception. Laparoscopic ileo-colic resection was then performed. Histopathological analysis of the surgical specimen (Fig.5) did not reveal any signs of epithelial atypia, instead, several appendiceal diverticula were encountered.

Intussusception is defined as the invagination of a bowel loop – intussusceptum – into the lumen of an adjacent loop – intussuscipiens.[1] The great majority occur in young children, involve the ileo-colic segment and are idiopathic in nature, with leading points being identified in only 5% of cases.^[2]Adult intussusceptions are much rarer, representing less than 5% of all cases, and in contrast to what happens in children, these are generally associated with an underlying organic cause, that can be identified in 70-90% of cases.[1] The most commonly encountered leading point is a malignant tumour. Other causes include benign tumours, Meckel’s diverticulitis, adhesions, and endometriosis.[1,3,4] Appendiceal lesions, such as mucoceles, are rarely associated with ileo-colic intussusceptions, with only a few cases reported in literature.[4,5,6]

The classical clinical triad of intermittent abdominal pain, bloody diarrhoea and palpable mass is usually absent in adult intussusceptions. Adults present with insidious and non-specific symptoms, such as abdominal pain, nausea and alterations in bowel habits.[4] Laboratory studies can show elevation of inflammatory markers, but are otherwise non-specific.

US is useful for the diagnosis not only in children, but also in adults. Classical US signs of intussusception include the target/doughnut sign, and the pseudokidney sign.[3]

CT is the most accurate imaging method for the diagnosis, determining the exact location and extension of the intussusception, which typically presents with a “bowel-within-bowel” appearance. In adults, CT is particularly important because it can detect an underlying organic cause for the intussusception. Intussusception-related complications such as bowel occlusion and ischaemia are also better depicted on CT.[1,3]  

Treatment of ileo-colic intussusception differs between paediatric and adult populations, mainly because adult intussusceptions are frequently associated with malignant lesions.[5] The treatment of choice for mucocele-related intussusception is surgical resection. Endoscopic or surgical decompression should be avoided, due to high risk of peritoneal seeding and pseudomyxoma peritonei.[7] However, in the presented case, histological analysis of the surgical specimen did not confirm the clinico-radiological suspicion of mucocele-related intussusception, instead several appendiceal diverticula were encountered. It has been previously reported that appendiceal diverticulosis may be associated development of retention cysts, which can mimic the imaging presentation of mucoceles, but have a significantly better prognosis.[8]

Teaching Points

• When an ileo-colic intussusception is encountered in an adult, an underlying organic cause must always be excluded;
• Appendiceal diverticulosis can lead to cystic dilatation of the appendix, that mimics the imaging appearance of an appendiceal mucocele, and can rarely act as a leading point for intussusception.