March 2019 Case

Fellow: Roberto A. Taguibao, MD
Faculty: Kevin Waters, MD, PhD

The patient is a previously healthy young child presenting with abdominal pain. One week prior to admission the patient began to experience vague peri-umbilical abdominal pain with associated nausea. The pain increased in intensity and shifted to the right lower quadrant with associated fever and chills. Six hours prior to admission the abdominal pain became severe, worsened with movement and associated with diarrhea. Physical examination showed a non-distended, moderately tender abdomen that was worse in the right lower quadrant. Imaging was suggestive of acute appendicitis. Laparoscopic appendectomy was performed. Gross examination showed a mildly inflamed, non-perforated appendix. Cut sections show the lumen containing fecal material and purulent exudate.

Enterobius vermicularis infection of the appendix

Enterobius vermicularis, also known as pinworm is a human parasite that causes enterobiasis. It belongs to the phylum Nematoda or roundworms and is the most common parasitic infection in the developed world¹.

Adult worms reside in the right colon (cecum, ascending and appendix). The mature female then migrates to the anal and perianal area to lay her eggs. This is the diagnostic stage where it is visible to the naked eye as a white-yellow worm in the perianal area. The deposited eggs can be seen with the naked eye and can be picked up with a transparent adhesive tape and viewed under a microscope (Scotch tape swab)². Transmission is either autoinfection, directly from anal and perianal area to the mouth, usually by fingernail contamination or from a contaminated environment³. When ingested, the embryonated eggs (infective stage) hatch in the small intestine and migrate to the large intestine where they mature into adult worms³. The highest incidence of infection is in children in late childhood and early adolescents; most of the patients are asymptomatic⁴.

The worms are white-yellow, threadlike, and measure between 2-5 mm in greatest diameter⁵. Microscopically, the worms have a thick eosinophilic outer cuticle where the lateral ala project (figure 3 ←). Internal organs can be visible in the internal aspect of the worm like the intestines, reproductive organs or the eggs. The eggs have a characteristic D-shape in which one side is flat and the other side is curved. The surrounding tissue in most cases have minimal inflammatory response to the worm. The finding of mucosal inflammation has been strongly linked to presence of parasite ova⁶. Rarely, some form of tissue reaction can occur, with increased eosinophils, granulomatous inflammation and ulceration with a marked inflammatory response in cases where the worm invades the tissue⁷.

Centers for Disease Control and Prevention, Parasites-Enterobiasis, Pinworm infection frequently asked questions at www.cdc.gov
Gutiérrez, Yezid (2000). Diagnostic pathology of parasitic infections with clinical correlations (PDF) (Second ed.). Oxford University Press. pp. 354–366. ISBN 0-19-512143-0. Retrieved 21 August 2009.
Jorgensen et. al., Manual of Clinical Microbiology 11th Edition, ASM press Canada, 2015
Cerva L, Schrottenbaum M, Kliment V: Intestinal parasites: a study of human appendices. Folia Parasitol. 38:5-9 1991 PMID: 1916531
Odze R, Goldblum J., Surgical Pathology of the GI Tract, Liver, Biliary Tract, and Pancreas 3rd Edition, Saunders Elsevier 2015
Williams DJ, Dixon MF: Sex, Enterobius vermicularis and the appendix. Br J Surg. 75:1225-1226 1988 PMID: 3233475
Sterba J, Vlcek M: Appendiceal enterobiasis: its incidence and relationships to appendicitis. Folia Parasitol. 31:311-318 1984 PMID: 6510834