Microscopic description and IHC:
A parasite is seen in the lumen of the appendix. The characteristic feature of Enterobius vermicularis infection histologically is the lateral ala, or triangular horns, that are situation 180 degrees opposite one another. The parasite also contains a thick cuticle with easily visible internal organs. The appendix otherwise appears unremarkable with no significant inflammatory reaction to the parasite.
Discussion:
Enterobius vermicularis, commonly known as a pinworm, is most common in children between the ages of 5-10 years old; between 4-28% of children worldwide are affected. Most children are asymptomatic; however, the most common symptom is anal itching (pruritus ani).
The parasite is spread via fecal-oral transmission. Eggs are ingested and hatch in the duodenum and migrate to the terminal ileum, cecum, or appendix to mate. After mating, the males die and the females migrate to outside the anus to lay eggs. These eggs are what are thought to cause the pruritus ani. The eggs can then be passed to another human host or the infected can become auto-infected. Humans are the only natural host.
Cellophane tape (the Scotch tape test) can be applied to the anus of a symptomatic patient and then applied to a glass slide and viewed under a microscope. The eggs from the perianal region will stick to the tape and the infection can be diagnosed. Patients are treated with antiparasitics such as albendazole.