E. vermicularis belongs to the group of nematodes, humans are the only known natural hosts of this parasite [5, 6]. Humans get infection by ingesting eggs from contaminated food, water, dust or even by hand contacts from the infected persons [5]. Embryonated eggs measure from 30 to 60 µm, hatch in the stomach of the new infected patients, and transform into larvae that migrate to caecum where they mature into adults pinworms that approximately measure 1 cm in length [6]. The caecal region constitutes the common habitat of adult parasites where they live and mate. At night, the gravid female travel to the anal region to deposit thousands of eggs. These eggs can lead to a new infection if ingested at least 6 h after being laid [3, 6]. The female parasite is very mobile while depositing eggs at night in the anal region, leading to a harsh nocturnal pruritus that can cause insomnia, loss of appetite, loss of weight, especially in children. Eggs are eliminated in the faeces of infected patients, or they stick under finger nails when the patient scratches his anus. A new cycle of infection can resume when another person ingests food or water containing eggs; usually an auto-infestation occurs as the infected patients get the parasite by ingesting eggs from their fingers and hands.
Usually, the pathogenicity of E. vermicularis is mild, ranging from asymptomatic to nocturnal anal pruritus [2]. In fact, our patient did not report any clinical symptoms suggestive of oxyuriasis, such as nocturnal anal itching. However, cases of patients with symptoms of clinical acute appendicitis associated with E. vermicularis have been reported in the literature [7]. The reported incidence of E. vermicularis appendicitis varies widely from 0.2 to 41.8%, and young girls are mostly affected [2, 10]. Our current case is epidemiologically particular as it was an adult male patient. However controversies and speculations still remain in regard to the pathophysiology of appendicitis associated with E. vermicularis [3]. Several studies support the fact that clinical symptoms of appendicitis seem to result from luminal obstruction by adult parasites, rather than a true inflammation of the appendiceal wall [1, 6,7,8, 11]. When located in the appendix lumen, the parasite causes contraction of the appendiceal wall (appendiceal colic) leading to clinical symptoms similar to those of the classic appendicitis [1]. In fact, mostly resected appendiceal specimens from these patients showed no evidence of histological inflammation [7, 8, 11]. In a recent study by Lala and Upadhyay [7], of 2923 resected appendices in pediatric population, only 4% showed E. vermicularis on histology, and only 25% of these parasitic appendicitis showed concurrent histological acute inflammation. The common histological findings in resected appendiceal specimens range from normal to various inflammatory patterns such as lymphoid hyperplasia, eosinophilic infiltrate, or neutrophilic infiltrate [1, 3, 6]. In our case, intense acute inflammatory patterns were observed: mucosal ulceration, suppurative necrosis with numerous neutrophils and plasma cells as well as lymphoid hyperplasia in the appendiceal wall. On macroscopic examination, stercoliths were seen in the appendix wall, but the parasites were not seen. In contrast, some authors have reported macroscopically visible parasites [2]. In our case, what is questionable, is the role of the parasites found in the specimen. Are they the causative agents of the acute suppurative appendicitis or an incidental finding? Perhaps the appendicitis resulted from the luminal obstruction by stercoliths found on macroscopic examination.
Also, aberrant migrations leading to extraintestinal findings of E. vermicularis have been reported, in the liver [12], bladder [13], lungs [14], kidney [15] or in the female genital tract [16, 17]. Thus, this parasite can have a wide range of pathogenicity, implying that pathologists should be familiar to its histological aspects for correct diagnosis. In fact, the histologic identification of E. vermicularis or its eggs on resected specimens is not difficult when the pathologist performs a careful searching for this parasite. In appendiceal specimens, the parasites are mostly evident in the lumen. The cross section shows the characteristic double and lateral “thorn-like” extensions (alae) from the thin eosinophilic wall of the parasite [3]. Within the wall of parasites, annular structures are easily seen, corresponding to the intestine, also numerous oval eggs, with flattened edges can be found in gravid females [3, 18, 19]. Adult male parasites look smaller than adult females, they are recognisable by their characteristic genitals with finely granular and round-shaped appearance [18]. However in solid organs like ovaries, spleen or liver, the histological diagnosis can be tricky as parasites have no sufficient space to develop. Granulomas and other inflammatory changes around oval structures (eggs) can be the main aspects to lead the pathologist to the correct diagnosis.
In summary, histological patterns of acute appendicitis associated with E. vermicularis are a very rare finding. Care should be taken by pathologists to thoroughly examine any appendiceal specimen to search for this parasite for appropriate anti-helminthic treatment of patients and their close family members.
