Appendiceal intussusception happens when the appendix segment is pulled into itself or into the caecum. This condition can mimic various chronic and acute abdominal conditions. It is an important entity to recognise since it could be mistaken for a caecal mass.
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Terminology
The term inverted appendix, a.k.a. appendiceal inversion, is sometimes used as a synonym for an appendix intussuscepting into the caecum 5-7.
Epidemiology
Appendiceal intussusception is a rare condition, with an estimated incidence of 0.01% of patients who underwent appendicectomy 1,6.
Clinical presentation
Symptoms of appendiceal intussusception have been divided into four groups:
asymptomatic patients
symptoms similar to acute appendicitis
symptoms consistent with intestinal intussusception: abdominal pain and vomiting occur for several days; bowel movements may be normal, or less frequently, there is constipation, diarrhoea or melaena
a prolonged history of intermittent severe attacks of right lower quadrant abdominal pain; vomiting and melaena may be present
The diagnosis is rarely made preoperatively because of its variable presentation and unspecific symptoms.
Pathology
Aetiology
Appendiceal intussusception can occur without any underlying abnormality. Anatomical variations of the appendix and pathological conditions such as tumours or polyps, endometriosis, parasitism, cystic fibrosis, appendicoliths and foreign bodies, have all been described as possible causes.
Classification
The McSwain classification may be used to classify appendiceal intussusception 6.
Radiographic features
Radiograph
In most cases the radiographic findings are normal. When there is associated small bowel obstruction, abdominal radiographs can demonstrate features thereof (i.e. dilated small bowel loops with air-fluid levels).
Fluoroscopy
A concentric ring appearance of the caecal mucosa on a contrast enema may be seen and known as coiled spring sign, which is associated with various conditions, including post appendicectomy stump inversion and appendiceal intussusception 3,4.
Ultrasound
Ultrasonography has a role, especially in children. Longitudinal sonograms may show the inverted appendix protruding into the caecal lumen.
Similar findings to the intestinal intussusception can be seen, which include:
target sign (also known as the doughnut sign)
CT
CT is the most commonly used diagnostic modality. A CT can clearly show the appendix invaginated into the caecal lumen.
The appearance of bowel-within-bowel, which identifies the appendix surrounded by the caecum, can be seen.
Differential diagnosis
On imaging, differential considerations include
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