E. vermicularis is a common helminth infection, especially in the pediatric population. It is transmitted via close contact with the ingestion and inhalation of eggs [17]. While the most common manifestation of helminth infection is anal pruritus, infection of the appendix is well described with initial report of appendiceal Enterobiasis by Stills in 1899 [7]. A recent systematic review of the global literature estimates its overall incidence in appendicitis specimens estimated at 4%, ranging from 2% in the Americas to 8% in Africa [5]. In our population, this incidence was slightly above 1%. Clinical presentation of appendiceal Enterobiasis varies, and pathologic findings range from normal appendix to limited mucosal inflammation to ruptured appendicitis [6–12].
The US data on appendiceal E. vermicularis infection is limited to case reports and series, the largest being a series of 21 patients by Arca et al. with appendiceal helminth identified post-operatively [7]. These patients demonstrated a range of pathologic findings from early appendicitis to ruptured appendicitis with almost all patients some evidence of associated appendiceal inflammation [7]. In contrast other global studies describe a rarity of acute appendiceal inflammation, ranging from 11–23% [9–10, 12]. Given this lack of inflammation, the pathophysiology of the helminth as a cause of acute appendicitis remains controversial [10–12]. One hypothesis is that the helminth creates a luminal obstruction with much lower incidence associated inflammatory changes, as reported by Sondergen et. al. In this cohort, only 2 of 18 appendices showed evidence of inflammation [12]. Symptoms were then attributed to “appendiceal colic” secondary to luminal obstruction. Ultimately, our data is consistent with lower severity inflammation when compared to “true appendicitis,” with majority of our patients demonstrating mucosal inflammation only.
Decreased appendiceal inflammation may influence the differences in clinical presentation of appendiceal helminth infection. Sondergen et. al found this group to have a lower WBC, lower Alvarado score, and more likely to have recurrent right iliac fossa pain and repeat hospitalizations than those with typical appendicitis [12]. Furthermore, both Akkapulu et al. and Fleming et al. demonstrated decreased WBC when compared to controls, which our data does not corroborate [9, 11]. Arca et al. described E. vermicularis of the appendix in 6 asymptomatic patients who underwent routine appendectomy at the time of another abdominal operation.
No case series focusing on the radiographic findings of E. vermicularis of the appendix were identified. After identifying E. vermicularis intraoperatively, Sosin et al. retroactively identified a helminth on pre-operative ultrasound [8]. Our data demonstrates overall smaller appendix on imaging and increased likelihood of equivocal ultrasound findings for acute appendicitis. These finding suggest that in patients with limited physical exam findings and equivocal US findings, we need to consider other possible diagnoses such as pinworm infection.
Limitations of this study include its retrospective nature with data from a single institution. Additionally, only patients who underwent appendectomy were evaluated. Given that diagnosis was made on pathologic examination, our sample is not inclusive of patients treated non-operatively for abdominal pain who may have had Enterobius colonization of the appendix without overt signs of appendicitis, though this is less common in our appendicitis pathway. Our study location was a large academic children’s hospital in the United States and these results may not be generalizable to worldwide populations were enterobiasis rates differ.
Our study has pointed towards differences in presentation of appendiceal Enterobiasis, with lower incidence of discrete right lower quadrant pain, smaller appendix diameter on US, and higher likelihood to need for further diagnostic imaging. These findings suggest a different pathologic process than typical appendicitis, but ultimately management has remained the same and the diagnosis is made on intraoperative identification of worms and pathologic review. The ultimate question is whether patients with appendiceal Enterobiasis may benefit from alternatives to appendectomy such as anti-helminth treatment. However, that question cannot be studied without diagnosis or high clinical suspicion of Enterobius infection in the pre-operative setting. Further studies in larger, multi-center setting, may ultimately provide the ability to consistently make this diagnosis, in the pre-operative setting and determine whether surgical or medical management is optimal.