To briefly summarize the embryology of the normal appendix, during the fifth foetal week, a bud at the junction of the small and large bowel develops and undergoes rapid growth into a pouch. The proximal end of this pouch starts growing differentially to give rise to the caecum. The appendix first appears at the eighth week of gestation as an outpouching of the caecum. Then, it gradually rotates to a more medial location following the respective rotation of the gut, which results in the fixation of the caecum in the right lower quadrant [9]. The normal embryogenesis of the appendix is well-known. However, there are no data regarding the causes of its duplication, and malrotation does not seem to be responsible for the pathophysiology of the condition. Cave [4] tried to explain the pathogenesis of duplication. To achieve this, he concluded with two theories: a) the persistence of a transient embryological structure and b) incidental appendiceal duplicity to a more general affection of the primitive midgut. However, even though Cave’s theories may explain some types of duplication, they are inadequate to explain all types reported.

It is difficult to diagnose double appendixes using routine imaging examinations. Abdominal ultrasound and computed tomography (CT) are the main methods available. However, these image examinations – mainly the CT scan – are usually not included in the routine workup of otherwise healthy patients with pain in the right iliac fossa. In cases where the patient is a child, the situation is even more challenging since a CT is avoided as the initial imaging choice due to the risk of radiation exposure. The CT has been reported to identify duplication of the appendix, especially in cases where both appendixes are significantly inflamed [10].