Duplex appendix is a rare anomaly of the appendix and is usually discovered incidentally during surgery for appendicitis.

Epidemiology

Duplication of the vermiform appendix is extremely rare. It is found in only 1 in 25,000 patients (incidence ~0.004%) operated on for acute appendicitis. Although duplication anomalies are uncommon, they have clinical and medicolegal significance.

A case is also reported in which a child had two appendicectomies performed in a 5 month period.

Associations

When anomalies of the appendix are detected in childhood they are nearly always associated with severe intestinal, genitourinary or bony malformations, seen most often in conjunction with type B1 and C duplications.

Pathology

Classification

This classification was proposed by Wallbridge in 1963, and at the time of writing (July 2016) remains the most widely accepted classification.

The Cave-Wallbridge classification divides appendix duplications into three types:

• type A: single caecum with one normally localised appendix exhibiting partial duplication

• type B: single caecum with two completely separate appendices and divided into two further subgroups

  • type B1 (‘bird-like type’): two appendices located symmetrically on either side of the ileocaecal valve, resembling the normal arrangement in birds

  • type B2 (‘taenia coli’ type): one appendix arises from the caecum at the usual site, and the second branches at varying distances along the lines of the taenia from the first

• type C: double caecum, each bearing its own appendix

Some authors have since described further types of complex multiplicity of the appendix. For example, "horseshoe appendix", "duplicated appendix and caecum"⁶, and "triple appendix" but these are often only diagnosed at surgery and not with imaging.

Differential diagnosis

Possibilities to consider include:

• caecal diverticulum

• appendiceal diverticulosis

• triple appendix