Parasitological and histopathological features of appendectomy specimens in Fars Province, southern Iran: a retrospective study

Background:

Although the appendix is the most commonly resected and examined intra-abdominal organ, the pathogenesis and etiology of acute nonspecific appendicitis remain enigmatic. This retrospective study aimed to assess the prevalence of parasitic infection in surgically removed appendices and to evaluate the probable associations between the presence of parasites and the occurrence of appendicitis through parasitological and histopathological examinations of the appendectomy specimens.

Materials and methods:

This retrospective study was carried out from April 2016 to March 2021 among all patients referred to hospitals affiliated with Shiraz University of Medical Sciences, Fars Province, Iran, for appendectomy. Patient information, including age, sex, year of appendectomy, and type of appendicitis, was collected from the available data in the hospital information system database. In positive cases, all pathology reports were retrospectively evaluated for the presence of the parasite and its type, and analytical and descriptive statistics were carried out using SPSS software version 22.

Results:

A total of 7628 appendectomy materials were evaluated in the present study. Of the total participants, 4528 (59.4%, 95% CI: 58.2–60.5) were males, and 3100 (40.6%, 95% CI: 39.5–41.8) were females. The mean age of participants was 23.87±14.28 years. Overall, Enterobius vermicularis was observed in 20 appendectomy specimens. Fourteen of these patients (70%) were less than 20 years old.

Conclusion:

This study indicated that E. vermicularis is one of the common infectious agents that could be found in the appendix and may increase the risk of appendicitis. Therefore, in terms of appendicitis, clinicians, and pathologists must be aware of the possible presence of parasitic agents, especially E. vermicularis, to treat and manage the patients sufficiently.

Highlights

• Although the appendix is the most commonly resected and examined intra-abdominal organ, the pathogenesis and etiology of acute nonspecific appendicitis remain enigmatic.

• This retrospective study aimed to evaluate the probable associations between the presence of parasites and the occurrence of appendicitis through parasitological and histopathological examinations of the appendectomy specimens.

• The present findings indicated that Enterobius vermicularis is one of the common infectious agents that could be found in the appendix and may increase the risk of appendicitis.

Acute appendicitis (AA) is one of the most common causes of abdominal pain and emergency gastrointestinal surgery1,2. Based on Global Burden of Disease studies, ~50 000 annual deaths occur among 11.6 million cases of appendicitis3,4. The incidence of AA is 8.6 and 6.7% for males and females in their lifetime, respectively5, which usually occurs between the ages of 10 and 30 years old6. Clinical manifestations of appendicitis generally include right lower abdominal pain, nausea, and vomiting, as well as anorexia6. Despite recent progress in antibiotic therapy, laparoscopic appendectomy has remained a traditional treatment for AA7,8. Various theories explain the reasons for the appendicitis. However, as many factors have a hand in the occurrence of appendicitis, the underlying cause is still puzzling9. The most important causes of appendicitis include fecal stasis, fecaliths, and lymphoid hyperplasia. Intestinal helminths, tumors, barium swallows, and undigested food residues have rarely been identified as the etiology of appendicitis. Among helminths, Enterobius vermicularis, Ascaris lumbricoides, Trichuris trichiura, Taenia spp., and Schistosoma spp. have been most frequently reported as the possible parasitic agents of appendicitis9–11. The obstruction of the lumen by helminths can lead to appendicitis with or without an acute inflammatory reaction12.

E. vermicularis, commonly known as pinworm, is the most notorious parasitic agent found in the appendix, particularly in children and young adults13. Pinworms mostly reside in the lumen of the ileum, colon, cecum, and appendix13. The most common symptoms of E. vermicularis infection are perianal irritation and restlessness. However, it can be accompanied by serious complications such as vulvovaginitis, salpingitis, and appendicitis14. Among numerous theories explaining the possible relations between pinworms and appendicitis, ectopic migration of the parasite stands out as the foremost hypothesis15,16. Occasionally, erratic migration of eggs, juveniles and adults can provoke granuloma formation in the appendix16, kidney17, peritoneal cavity18, male urinary tract19, and female genital tract20 which may mislead clinicians in the diagnosis and treatment of patients. To date, several studies have been carried out on the prevalence and correlation of parasites and appendicitis worldwide13. However, the role of parasites in the etiology of AA has not yet been discovered clearly21–23. The present study aimed to assess the prevalence of parasitic infections in surgically removed appendices at Namazi and Shahid Faghihi (Sa’adi) hospitals in Shiraz, Fars Province, southern Iran, and to evaluate the prevalence of parasitic agents in the removed appendices as well as the probable associations between the presence of parasites and the occurrence of appendicitis through parasitological and histopathological examinations of the surgically removed appendices.

Materials and methods

Study design

This retrospective study included 7628 surgically removed appendices from clinically diagnosed patients with AA. All the surgical operations were performed at Namazi and Shahid Faghihi hospitals (Sa’adi hospital), the two main teaching hospitals affiliated with Shiraz University of Medical Sciences, from April 2016 to March 2021 (a 5-year period). All appendectomy specimens were routinely submitted for pathological assessment. They were fixed in 10% formalin and cut into one longitudinal and two transverse samples. The sections were stained by the hematoxylin and eosin technique and examined under a light microscope. All pathology reports and recorded demographic data of patients were retrospectively reviewed from the available data in the hospital information system database for the patient’s age and sex, as well as the presence of parasites and the histopathological findings. This work has been reported in line with the PROCESS criteria24.

Statistical analysis

Analytical and descriptive statistics were carried out using Statistical Package for the Social Sciences (SPSS Inc.) version 22 software. Data were described using frequencies (%) and 95% CI, or mean and median, as appropriate. χ ²-test was used for testing the association between demographic variables and histopathological features among the studied population. A P value of less than 0.05 was considered to be statistically significant.

Results

Sociodemographic characteristics of study participants

A total of 7628 appendectomy materials were evaluated in the present study. The results of the sociodemographic characteristics of study participants are shown in Table 1. Of the total participants, 4528 (59.4%, 95% CI: 58.2–60.5) were males, and 3100 (40.6%, 95% CI: 39.5–41.8) were females. The median [interquartile range (IQR] of age was 21 years old13–31. Participants were divided into seven major age groups of less than or equal to 10, 11–20, 21–30, 31–40, 41–50, 51–60, and greater than 60. The largest age group was 11–20 age range (33.7%, 95% CI: 32.6–34.7). The smallest number of cases was in the greater than 60 group. The majority of the specimens (1779/7628) were taken from April 2016 to March 2017 (23.3%, 95% CI: 22.4–24.3).

Table 1.

Demographic features of the cases (n=7628)

Characteristics	Categories	Frequency	% (95% CI)
Sex	Female	3100	40.6 (39.5–41.8)
	Male	4528	59.4 (58.2–60.5)
Age (years)	≤10	1131	14.8 (14.0–15.6)
	11–20	2568	33.7 (32.6–34.7)
	21–30	1862	24.4 (23.4–25.4)
	31–40	1220	16.0 (15.2–16.8)
	41–50	437	5.7 (5.2–6.3)
	51–60	216	2.9 (2.5–3.2)
	>60	194	2.5 (2.2–2.9)
Year	2016–2017	1779	23.3 (22.4–24.3)
	2017–2018	1630	21.4 (20.4–22.3)
	2018–2019	1544	20.2 (19.3–21.2)
	2019–2020	1618	21.2 (20.3–22.1)
	2020–2021	1057	13.9 (13.1–14.7)

Histopathological findings of appendicitis

The distribution of various histopathological findings of appendicitis is shown in Table 2. When our cases were evaluated in terms of histopathological diagnoses, 5813 (76.2%), 65 (0.9%), and 1750 (22.9%) were diagnosed as inflamed appendix, neoplasm of the appendix, and others, respectively (Table 2).

Table 2.

Distribution of various histopathological findings of appendicitis (n=7628)

Groups	Type of histopathological features	Frequency	% (95% CI)
Inflamed appendix
	Acute appendicitis	4683	80.6 (79.5–81.6)
	Gangrenous appendicitis	801	13.8 (12.9–14.7)
	Perforated appendicitis	55	0.9 (0.7–1.2)
	Suppurative appendicitis	134	2.3 (1.9–2.7)
	Periappendicitis	109	1.9 (1.5–2.3)
	Chronic appendicitis	13	0.2 (0.1–0.4)
	Phlegmon	13	0.2 (0.1–0.4)
	Granulomatous appendicitis	5	0.1 (0.03–0.2)
Neoplasm of appendix
	Mucinous neoplasm	38	58.6 (45.6–70.6)
	Neuroendocrine tumor	22	33.8 (22.6–46.6)
	Sessile serrated adenoma	3	4.6 (0.96–12.9)
	Adenocarcinoma	1	1.5 (0.04–8.3)
	Myeloid sarcoma	1	1.5 (0.04–8.3)
Others
	Follicular hyperplasia	670	38.3 (36.0–40.6)
	Normal-structured appendix	508	29.0 (26.9–31.2)
	Fecalith	330	18.9 (17.0–20.8)
	Fibrotic appendix	238	13.6 (12.0–15.3)
	Endometriosis	4	0.2 (0.1–0.6)

Histopathological features based on the demographic characteristics

The distribution of patients according to histopathological features in appendicitis based on demographic features including sex, age, and year is shown in Table 3. The inflamed appendix was higher in males (64%), while other histopathological features were higher in females (55.5%). There was a statistically significant difference between histopathological findings and sex (P<0.001). Inflamed appendix and other histopathological features were most prevalent among participants aged 11–20 years old (32.3 and 39.1%, respectively), and the difference between the age and histopathological features was significant (P<0.001). In contrast, most cases of neoplasm of the appendix were greater than 30 (70.8%).

Table 3.

Distribution of histopathological features in appendicitis based on the demographic features (n=7628)

		Histopathological features
Characteristics	Categories	Number. inflamed appendix (%)	Number. neoplasm of appendix (%)	Number of others (%)	χ 2-test result
Sex					P<0.001
	Female	2095 (36.0)	33 (50.8)	972 (55.5)
	Male	3718 (64.0)	32 (49.2)	778 (44.5)
Age (years)					P<0.001
	≤10	761 (13.1)	1 (1.5)	369 (21.1)
	11–20	1876 (32.3)	7 (10.8)	685 (39.1)
	21–30	1513 (26.0)	11 (16.9)	338 (19.3)
	31–40	988 (17.0)	14 (21.5)	218 (12.5)
	41–50	351 (6.0)	12 (18.5)	74 (4.2)
	51–60	172 (3.0)	5 (7.7)	39 (2.2)
	>60	152 (2.6)	15 (23.1)	27 (1.6)
Year					P<0.001
	2016–2017	1299 (22.4)	17 (26.2)	463 (26.5)
	2017–2018	1269 (21.8)	14 (21.5)	347 (19.8)
	2018–2019	1154 (19.9)	4 (6.2)	386 (22.0)
	2019–2020	1240 (21.3)	16 (24.6)	362 (20.7)
	2020–2021	851 (14.6)	14 (21.5)	192 (11.0)

Parasitological features of appendectomy specimens

Overall, E. vermicularis was only the parasite identified in 20 appendectomy specimens (Fig. 1). The mean and median ages of patients with E. vermicularis infection was 18.1±12.8 and 13.5 (IQR=14.5) years old, respectively; 65% (95% CI: 40.8–84.6) of them were female and 35% (95% CI: 15.4–59.2) male. However, this difference was not statistically significant between the sexes of patients with E. vermicularis infection (P=0.18). Out of 20 cases with E. vermicularis infection, 14 cases (70%, 95% CI: 45.7–88.1) were younger than 20 years old (Table 4). However, this difference was not statistically significant (P=0.074). Pathologic analysis of the appendectomy specimens with E. vermicularis indicated follicular hyperplasia in 11 (55%), AA in six (30%), normal-structured appendix in two (10%), and gangrenous appendicitis in one (5%) (Table 4). In all cases of parasitic infection, either the parasite or its eggs were identified in the lumen of the appendix.

Figure 1.

(A) Enterobius vermicularis worms in the appendix. (B) Triangular alae of E. vermicularis. (C) Section of female worm of E. vermicularis containing eggs in uterus, hematoxylin and eosin staining.

Table 4.

Demographic data and histopathological findings of the patients with Enterobius vermicularis infection of the appendix

No	Sex	Age (years)	Year	Histopathological findings
1	Male	24	2020–2021	Acute
2	Female	15	2020–2021	Follicular hyperplasia
3	Male	14	2020–2021	Follicular hyperplasia
4	Female	6	2020–2021	Follicular hyperplasia
5	Female	40	2020–2021	Follicular hyperplasia
6	Female	39	2019–2020	Acute
7	Female	39	2019–2020	Acute
8	Male	6	2019–2020	Follicular hyperplasia
9	Female	11	2019–2020	Gangrenous
10	Male	4	2019–2020	Acute
11	Female	13	2019–2020	Acute
12	Male	46	2018–2019	Follicular hyperplasia
13	Female	12	2018–2019	Follicular hyperplasia
14	Female	13	2017–2018	Follicular hyperplasia
15	Female	16	2017–2018	Normal-structured appendix
16	Female	6	2017–2018	Follicular hyperplasia
17	Female	16	2016–2017	Normal-structured appendix
18	Female	8	2016–2017	Follicular hyperplasia
19	Male	13	2016–2017	Acute
20	Male	21	2016–2017	Follicular hyperplasia

Discussion

Appendicitis is the most common surgical emergency globally, occurring among people of different ages and sexes25. Although the primary causes of appendicitis are questionable, the role of gastrointestinal parasites must not be overlooked26. Pinworms are the most common parasitic worms capable of resulting in appendicitis, which first was recovered from the appendix by Fabrius in 163427,28. Based on the results of the current study, E. vermicularis was the only reported parasite in the patient’s undergone appendectomy and was reported in 20 of 7628 appendectomy specimens (0.26%) in a 5-year period. The findings of our study are identical to those of a similar study conducted in Qom Province, Iran, with 0.22% appendicitis associated with pinworm infection29. The results of a study conducted in Greece showed that E. vermicularis was identified in only in 0.65% of patients with clinical appendicitis30. In another study by Lala and Upadhyay on 2923 resected appendices in children aged 3–15 years old in New Zealand over a 10-year period, E. vermicularis was present histologically in 4% of cases31. In one study by da Silva et al.32, the helminthes were seen in 24 cases out of 1600 appendectomies (1.5%) during a 10-year period, and E. vermicularis was found in 23 of 24 (95.8%) appendectomy cases, while Taenia spp. was detected in only one (4.2%) case. On the other hand, a study conducted in Kerman province, Iran33 as well as a recent study conducted in Saudi Arabia34, reported the incidence of E. vermicularis in appendectomy specimens ~10 folds more than our results of 2.9 and 2.7%, respectively. This variation in different studies could be a results of geographic areas, lifestyle, sanitary and hygiene level, culture, and sociodemographic features, as well as the techniques followed by the pathologists13. The prevalence of helminthiasis has been significantly decreased in recent decades globally due to screening programs and public health improvement. However, some helminths, particularly those with direct fecal-oral transmission, such as Enterobius and Hymenolepis, are still common35–37.

The invasion of E. vermicularis and the presence of eggs inside the tissue of the appendix change the histology of appendix tissue and could generate various histopathological manifestations with different appendiceal symptoms14. Follicular hyperplasia is the initial pathologic reaction to the presence of E. vermicularis, causing noninflammatory clinical symptoms in the tissue. Numerous studies indicate that the symptoms of appendicitis could merely stem from E. vermicularis infection without any evidence of acute inflammation in histologic observations of the appendix. In other words, E. vermicularis is more commonly associated with noninflamed appendices, and in the current study, noninflamed histological marks were observed in 65% of patients, which is consistent with the results by Lala and Upadhyay in 200431. However, the invasion of pinworms into the tissue could generate inflammatory reactions with hallmarks such as eosinophilic infiltrate and neutrophilic infiltrate, and in our study, 35% of cases indicated acute inflammation with a significant case of gangrenous appendicitis.

In the present study, although the majority of patients who had undergone appendicectomy were male, 65% of the appendices containing E. vermicularis belonged to the female sex. This finding is consistent with the previous studies conducted in Iran and other countries globally31,33,34. The results of a recently published systematic review and meta-analysis study by Taghipour et al.13 on 59 studies involving 103 195 appendix tissue samples showed that the prevalence of E. vermicularis in females was significantly higher than males (odds ratio: 0.47; 95% CI: 0.38–0.59). Moreover, it is noteworthy that a female predominance of pinworm infection is tangible in those between the ages of 5 and 14 years, and sex-based differences and behavioral patterns might be associated with higher infection rates in females13.

In the current study, the mean and median ages of patients with E. vermicularis infection were 18.1±12.8 and 13.5 (IQR=14.5) years, respectively, and of 20 cases of E. vermicularis infection, 14 cases (70%, 95% CI: 45.7–88.1) were less than 20 years old. These findings are consistent with a study by Hamdona et al.38 in Palestine, which showed the highest incidence of patients with E. vermicularis in appendices occurred in the less than 18-year-old age group. Another study carried out on 2267 appendices in Copenhagen revealed that the highest incidence of pinworms in appendectomy specimens occurred in the age group of 6–15 years39. A survey by Gialamas and colleagues revealed that the ages of the patients with histologically proven E. vermicularis in appendices ranged from 15 to 33 years, with a mean age of 25 years18. Moreover, studies revealed that patients with E. vermicularis were younger than patients with Taenia spp.40,41. Age is considered a risk factor for AA, and its association with Enterobius infection in both sexes has been documented13,33.

In the present study, the inflamed appendix was most prevalent among participants aged 11–30 years (58.3%), and the difference between the age and histopathological features was statistically significant (P<0.001). In contrast, most cases (70.8%) of neoplasms of the appendix were greater than 30. Appendiceal neoplasms are regarded as rare gastrointestinal cancers manifesting the symptoms of appendicitis, with the majority of cases categorized as epithelial appendiceal and neuroendocrine tumors42. Although this type of neoplasm may occur at any age, it is more common at ages greater than 50, regardless of sex, and this is congruous with the results of our study43.

It should be noted that the appendectomy must not merely be considered a therapeutic intervention for the patients suffering appendicitis associated with E. vermicularis, as the adult parasites might be present in the lumen of the colon, usually in the cecum. Therefore, clinicians should be vigilant in treating patients after surgery as well as their households with adequate anthelminthic medications such as benzimidazole derivatives or pyrantel pamoate, followed by a repeat dose in 2 weeks to halt the occurrence of reinfection or autoinfection44. In this regard, mebendazole and albendazole are considered promising anthelmintic drugs for the precise treatment of enterobiasis, as they both have adulticidal and ovicidal effects45,46. The existing results should be regarded in the context of their strengths and limitations. In this study, the patient’s data were collected retrospectively during a certain 5-year period. Due to the significant role of our results in the prevention of negative appendectomy and definitive treatment of infections, prospective, longer-duration, and multicenter studies on this topic are thus affirmed. The main strength of this study is its novelty. In addition, the large sample size and coverage of two main hospitals in Shiraz County are the other strengths of this study.

Conclusion

In conclusion, the current study indicated that E. vermicularis is one of the most common infectious agents that could be found in the appendix and may increase the risk of appendicitis. Although sanitation and health infrastructures have diminished the risk of human parasitic infections in several countries, the risk of parasite-associated complications is lurking. Therefore, in terms of appendicitis, clinicians and pathologists must be aware of the possibility of the parasitic agents, especially, E. vermicularis to treat and manage the patients sufficiently. Moreover, it seems that an early diagnosis and precise treatment of E. vermicularis infection are conducive to preventing the occurrence of appendicitis, recurrences, and other ectopic infections.

Ethical approval

This study was approved by the research ethics committee of Shiraz University of Medical Sciences with the ethical code: IR.SUMS.MED.REC.1400.194.

Consent

The patient’s data included in our study were fully anonymized by the medical report section of the hospitals before our accession to them, and information collected from the study participants was kept confidential. Informed written consents was obtained from all subjects and/or their legal guardian(s).

Sources of funding

This research was financially supported by the office of the Vice-chancellor for research at Shiraz University of Medical Sciences with grant No: 23510.

Author contribution

S.M.: conceived, analyzed and interpreted the data and prepared the original draft paper. M.S.: collected the data from the hospital information system database and pathologic analysis of the appendectomy specimens. P.V.: collected the data from the hospital information system database. F.M., M.J.A.A.: conceived, analyzed, and interpreted the data. R.A., F.G.: analyzed and interpreted data. A.T.: conceived and designed the study, review, and editing of the manuscript.

Conflicts of interest disclosure

The authors declared no potential conflicts of interests.

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Guarantor

Dr Aref Teimouri, Department of Parasitology and Mycology, School of Medicine, Shiraz University of Medical Sciences, Shiraz, Iran. E-mail: aref_teimouri@yahoo.com

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Not commissioned, externally peer reviewed.