Unusual histopathologic findings of appendectomy specimens: A retrospective study of cases at Jordan University Hospital over the last decade (2015-2024)

The study included patients of all age groups and both genders who underwent appendectomy at Jordan University Hospital, Amman, Jordan between January 2015 and December 2024, either as a primary procedure or incidentally, provided that histopathological reports and slides stained with hematoxylin and eosin (H&E) and relevant immunohistochemical markers were available. Patients were excluded if they lacked complete pathological reports and slides, or had missing demographic or clinical information. Of the 2,345 individuals who underwent appendectomy, 2,275 had complete pathological reports and corresponding histological slides. The study was conducted in accordance with Institutional Review Board (IRB) approval from Jordan University Hospital (approval date: 17/04/2025, number 10/2025/9202). The study outcomes included the prevalence of unusual histopathological findings in appendectomy specimens and their distribution by patient age and gender. This retrospective study involved retrieving histopathological reports from hospital records, along with slides of appendectomy specimens that exhibited unusual histological features, from the archives of the pathology department at Jordan University Hospital. An experienced pathologist re-evaluated the slides of appendices with unexpected findings and amended the diagnoses where necessary. Statistical analysis Statistical analysis was performed using the Statistical Package for the Social Sciences (SPSS, version 26.0; IBM Corp., Armonk, NY, USA), including descriptive statistics such as mean, standard deviation, and frequency distribution. The chi-square test was applied to evaluate associations between categorical variables, with a p -value of <0.05 considered statistically significant. Microsoft Excel was used for data entry, preliminary data cleaning, and visualization, including generating tables and graphs to present the findings.

Among the included patients, 53.9% were male (n=1,226) and 46.1% were female (n = 1,049), with ages ranging from 1 day to 87 years (mean age: 27.5 ± 18.6 years). Patients were stratified into age groups, with the most common group being 10–19 years, accounting for 665 (29.2%) cases. This was followed by the 20–29-year age group, which included 527 (23.2%) cases. The least represented age group comprised individuals aged ≥70 years. The annual frequency of appendectomy cases is illustrated in Figure 1 . - The annual frequency of appendectomy cases. The primary indication for appendectomy was suspected acute appendicitis, which was also the most frequent pathological finding, reported in 1,634 cases (72.3%). A total of 470 appendices (20.7%) were histologically normal. Other unusual histopathological findings are detailed in Table 1 . - Unusual histopathological findings in appendectomy specimens. Patients who were preoperatively diagnosed with acute appendicitis and underwent appendectomy (n=1,937) were subsequently analyzed. These patients were divided into 2 groups: negative and positive appendectomy groups. The 10-year negative appendectomy rate between 2015–2024 was 12.4% (n=240), with a female predominance (57.1%). The mean age was 21.5 years in the negative appendectomy group and 25.4 years in the positive appendectomy group. The negative appendectomy rate fluctuated over the 10-year period, with some years showing higher percentage than others. In 2015, the rate was relatively low at 7.1%; however, it increased in subsequent years, peaking at 18.5% in 2017. Subsequently, the negative appendectomy rate gradually declined, reaching 8.1% in 2021, before slightly rising again to 13.6% in 2024. The Chi-square test revealed a significant association between gender and appendectomy outcomes ( p <0.001), indicating that females were more likely to undergo negative appendectomy than males. Additionally, a p -value of 0.014 indicated a significant association between age group and appendectomy outcome, with patients aged ≤40 years more likely to undergo negative appendectomy. However, patients aged >40 years also exhibited a substantial number of positive appendectomy outcomes. A total of 46 cases showed fibrous obliteration of the appendiceal lumen, with 52% presenting with symptoms of acute appendicitis. This condition was observed across all age groups. Moreover, appendiceal serositis was identified in 27 patients, while fecalith impaction was identified in 26 patients. Among these, 48.1% of patients with serositis and 78.57% of patients with fecalith impaction exhibited symptoms suggestive of acute appendicitis. Neither condition was observed among patients aged ≥70 years. Furthermore, 23 appendectomies specimens exhibited low-grade appendiceal mucinous neoplasms (LAMNs), of which 17 were pure LAMNs not associated with other tumors. The clinicopathological characteristics of the pure LAMNs are summarized in Table 2 . - Clinicopathological Features of Low-grade appendiceal tumors including age, gender, stage, grade and year of appendectomy (n=17). While 17 of the 23 cases of LAMN involved pure tumors, the remaining 6 were associated with other neoplasms: one with a borderline mucinous tumor of the ovary, one with ovarian metastasis, and 4 with colonic mucinous adenocarcinoma. Seven patients were diagnosed with well-differentiated neuroendocrine tumors, 6 of whom presented with symptoms of acute appendicitis. The clinicopathological characteristics of neuroendocrine tumors are summarized in Table 3 . - Clinicopathological features of appendiceal neuroendocrine tumors including age, gender, grade and stage (n=7). Additionally, 6 cases of mucosal hyperplasia were identified, 4 of which were associated with symptoms of acute appendicitis. Another 6 patients were diagnosed with appendiceal endometriosis, 5 of whom had suspected acute appendicitis. Three cases demonstrated ischemic changes in the appendix. One case involved a 6-month-old male infant with intussusception and transmural hemorrhagic infarction. Another case involved a 64-year-old woman with an obstructed incisional hernia, and the appendix showed mucosal infarction. The third case was a 43-year-old man with a history of appendiceal phlegmon who presented with hemorrhagic infarction. Two cases of high-grade appendiceal mucinous neoplasms (HAMNs) were identified. Additionally, 2 cases of appendiceal diverticulosis were reported. One case involved a 58-year-old patient who, one year earlier, had presented with symptoms of acute appendicitis complicated by phlegmon. Persistent symptoms and follow-up CT imaging demonstrated ongoing phlegmon, while re-evaluation of the prior appendectomy slides revealed appendiceal diverticula. The second case involved a 43-year-old man with recurrent lower abdominal pain. One case of appendiceal involvement in Hirschsprung disease was reported, along with a single case of a sessile serrated polyp with low-grade dysplasia.

Anatomically, the appendix is a narrow, hollow organ of the gastrointestinal tract. It is a blind-ended organ with an average length of 9 cm and is located between the cecum and ileum. The appendix is associated with various inflammatory and neoplastic diseases. Appendiceal diseases are classified into inflammatory conditions and neoplastic types. The most common inflammatory condition is acute appendicitis, which may present as simple, suppurative, perforated, or gangrenous. The appendix can also develop various neoplasms, including mucinous neoplasms, neuroendocrine tumors, lymphoma, and others. 3 In our study, appendiceal serositis was identified in 1.2% (n=27) patients, This condition refers to inflammation of the appendiceal serosa and may be caused by acute appendicitis. However, its presence should alert clinicians to possible inflammation in adjacent structures such as the female genital or urinary tracts. In some cases, no identifiable cause is found. 1 Fibrous obliteration of the appendiceal lumen was identified in 2% (n=46) of our patients, while previous studies report a prevalence ranging from 1% to 30%. This condition results from recurrent inflammation leading to proliferation of spindle cells separated by fibrous tissue, forming a neural-like lesion that obstructs the appendiceal lumen and induces hyperplasia of neuroendocrine cells in the lamina propria and submucosa. This pathological process ultimately results in progressive fibrosis of the appendiceal wall. 4 , 5 Fecalith impaction was observed in 1.1% (n=26) of patients, compared to a reported prevalence range of 1.4–67% in the literature. A well-established association exists between fecalith impaction and the development of non-perforated appendicitis in adults. Additionally, abnormal appendices may be detected in individuals without symptomatic fecaliths. Notably, the presence of gangrenous and perforated appendicitis is not associated with fecalith impaction. 6 Appendiceal diverticulosis was observed in approximately 0.1% of cases (n=2), which is lower than the 1.74% reported by Lim et al. 7 The mean age of our patients with diverticulosis was 52 years, which is older than the average age reported in their study. Diagnosing appendiceal diverticulosis is difficult because it is uncommon and its tendency to mimic acute appendicitis, particularly when complicated by diverticulitis. Several studies have indicated up to a 70% risk of perforation in cases of appendiceal diverticulitis. A well-established correlation exists between appendiceal diverticulosis and tumors, particularly mucinous neoplasms and neuroendocrine tumors. 8 Additionally, Enterobius vermicularis (E. vermicularis) infection was identified in 0.4% of cases (n=8). According to a study by Pogorelic et al, 9 E. vermicularis can cause acute appendicitis, particularly in young females. The parasite is a common infection worldwide, with higher incidence in children and individuals living in crowded environments. Enterobius vermicularis usually diagnosed by histopathologic examination and has been reported in 0.96% of appendectomy specimens. This type of infection should be considered by pediatric surgeons, with helpful diagnostic clues including young age, prolonged symptoms, and a small appendiceal diameter. Finally, we identified 6 cases of appendiceal endometriosis (0.3%), consistent with previous studies. Additionally, some studies have reported a prevalence of 2.8% of endometriosis of the appendix in females with history of endometriosis. 10 Endometriosis can affect any segment of the gastrointestinal tract, including the appendix. It may be asymptomatic or may mimic acute appendicitis. Other recognized symptoms include cyclic right lower quadrant pain, melena, and intestinal perforation. 11 Microscopic examination typically shows unremarkable mucosa with the presence of endometrial glands, stroma, and hemorrhage within the muscular and seromuscular layers. Appendiceal mucinous neoplasms, are rare tumors with variable malignant potential, representing <1% of all appendiceal neoplasms. These neoplasms are heterogeneous and are increasingly diagnosed, particularly low-grade appendiceal mucinous neoplasms (LAMNs). The incidence of LAMNs appears to be rising in Jordan, a trend also reported in Saudi Arabia by AlAli et al. 12 Early-stage LAMNs are typically discovered incidentally in appendectomy specimens from patients with symptoms of acute appendicitis. Advanced cases often present with increased abdominal girth due to mucin accumulation in the peritoneal cavity. LAMNs and appendiceal carcinomas are the main subtypes of appendiceal mucinous neoplasms. In our study, LAMNs (n=23) outnumbered adenocarcinomas (n=8), consistent with the findings of El-Essawi et al 13 in Saudi Arabia. Appendiceal carcinomas include mucinous, colonic‐type, and crypt cell adenocarcinomas. Due to the heterogeneity of appendiceal mucinous neoplasms, treatment strategies vary depending on tumor stage and grade. Standard therapy for low grade tumors involves early surgical resection of the primary site. In advanced stages, treatment includes peritoneal debulking combined with hyperthermic intraperitoneal chemotherapy (HIPEC). Treatment options for high-grade tumors include surgical debulking and HIPEC, with some patients also receiving neoadjuvant chemotherapy. 14 , 15 In our study, LAMNs accounted for 1.0% of all cases, a rate similar to that reported by Guner et al 16 and higher than that observed by Köhler et al 17 in Germany. Unlike the LAMN cases reported by Köhler et al, 17 which were mostly diagnosed in 2018, our cases were evenly distributed across the study period. Moreover, the age range of patients with LAMN (16-86 years) was similar to that reported by Köhler Et al. 17 LAMNs may be asymptomatic or present with various symptoms, such as vomiting, abdominal distension, or a palpable abdominal mass. Although LAMNs typically have a favorable prognosis, they may rupture and lead to peritoneal seeding by mucin and tumor cells—a condition known as pseudomyxoma peritonei, which carries a poor prognosis. These tumors may spread via lymphatic or hematogenous routes. Histopathological examination of LAMN typically shows loss of mucosal architecture, including decreased lymphoid follicles. The mucosal architecture is disorganized, showing patterns such as villous or papillary formations, or appearing flattened. The epithelial lining is typically monolayered and exhibits cytologic atypia. Glands are arranged back-to-back with a pushing pattern of invasion. The lamina propria is often thinned, and the muscularis mucosa may be obliterated as shown in Figure 2 . 18 , 19 - A histopathological section of Low-grade mucinous appendiceal neoplasm. Haematoxylin and eosin stain.20X Low-grade appendiceal mucinous neoplasms were staged according to the eighth edition of the AJCC Staging Manual, which defines 5 stages: pTis, pT3, pT4a, pTxM1a, and pTxM1b. Stage pTis includes LAMNs confined to the appendix and extending into, but not through, the muscularis propria. Stage pT3 indicates LAMN penetration by neoplastic epithelium or acellular mucin through the muscularis propria into peri-appendiceal tissues without serosal involvement. Stage pT4a includes LAMNs with localized involvement of the visceral peritoneum, with or without neoplastic cells in the mucin. Stages pTxM1a and pTxM1b represent LAMNs with mucinous peritoneal deposits lacking and containing neoplastic cells, respectively. 20 , 21 Certain pathological features, both macroscopic and microscopic of LAMN-affected appendices are associated with the risk of pseudomyxoma peritonei or tumor recurrence. Macroscopically, the risk of pseudomyxoma peritonei is elevated in cases where the appendiceal lumen is narrow (<1–2 cm) and contains a large amount of mucin along with a thickened wall. Microscopic features include serosal involvement by acellular mucin, rupture of the appendiceal wall, and dissection of neoplastic epithelium beyond the mucosal surface. 22 , 23 Synchronous appendiceal and ovarian tumors may originate from a single primary site if peritoneal mucin deposits are present. In contrast, the absence of peritoneal mucin deposits suggests independent appendiceal and ovarian primaries. Currently, no convincing evidence exists for a genetic anomaly that increases the risk of mucinous tumors. Determining the origin of mucinous tumors, ovarian or appendiceal, requires comprehensive histopathological and immunohistochemical analysis, because surgical management differs accordingly. 24 We identified one case of synchronous LAMN and borderline ovarian mucinous tumor in a 50-year-old patient, similar to a case reported by Muramoto et al 25 in a 41-year-old patient. We also observed 4 cases of synchronous LAMN with colonic mucinous carcinoma. 26 and one case of LAMN metastasis to the ovary. Ovarian metastasis of LAMN should be suspected when the primary presentation includes massive ascites, biopsy reveals acellular mucin, and imaging shows an abnormal appendix with a normal-appearing ovary. 27 Additionally, our study identified 2 cases of high-grade appendiceal mucinous neoplasms (HAMNs), with a prevalence of 0.1%, which is lower than that of LAMNs. High-grade appendiceal mucinous neoplasms exhibit pushing invasion and mucin dissection into the appendiceal wall. They demonstrate various growth patterns, including villous, undulating, and flat architectures. The lining epithelial cells exhibit prominent nuclear and cytological atypia. Clinically, patients may present with abdominal pain, distension or a palpable mass. If these tumors spread to the peritoneum, they may result in grade 2 pseudomyxoma peritonei. The average age of patients with HAMN in our study was 58 years, which is comparable to the 57 years reported by Gonzalez et al. 28 We identified approximately 0.4% (n=8) of cases with appendiceal mucinous adenocarcinoma, which is similar to the rate reported by Vyas et al. 29 It exhibits a highly variable clinical course. Patient survival is influenced by several factors, including tumor biology, extent of invasion, and potential to develop pseudomyxoma peritonei. Treatment typically involves both surgical and systemic approaches. Life-prolonging interventions, such as cytoreductive surgery and HIPEC, may be considered in selected cases. 30 Mucinous adenocarcinomas account for approximately 58% of malignant appendiceal tumors and can penetrate the appendiceal wall, resulting in peritoneal dissemination. Due to their indolent nature, they are often diagnosed at an advanced stage. Histopathological examination reveals jagged glands arranged irregularly, either invading the appendiceal wall or surrounded by extracellular mucin occupying >50% of the lesion. Malignant cells may be present individually, arranged in linear or clustered patterns, or form complex glandular structures. The epithelial lining displays prominent, high-grade cytologic atypia. Approximately 0.3% (n=7) of cases involved well-differentiated neuroendocrine tumors, a lower proportion than that of LAMNs (1.0%). This finding aligns with AlAli Et al 12 but contrasts with Kangaspunta Et al 31 who reported a predominance of neuroendocrine tumors. A study conducted in Croatia by Pogorelić et al 32 indicated a 0.49% incidence of neuroendocrine tumors in children, consistent with findings from other studies. Neuroendocrine tumors represent the most common malignant appendiceal neoplasms in children. In our study, well-differentiated neuroendocrine tumors were more common in females, primarily among those aged 21–60 years, consistent with findings by Andrini Et al. 33 These tumors are often identified incidentally and are generally non-aggressive, although a few cases may demonstrate more aggressive behavior. They are typically located in the distal third of the appendiceal tip. Although often asymptomatic, when present, symptoms depend on tumor size and the presence of distant metastases. 34 Among gastrointestinal sites, the appendix ranks as the fifth most common location for neuroendocrine tumors. These tumors may originate from mucosal crypts or submucosal neuroendocrine cells. The recommended grossing method involves bivalving the tip and submitting both halves for microscopic examination. Histological examination reveals uniform round cells with speckled chromatin, granular amphophilic cytoplasm, inconspicuous nucleoli, and an arrangement in nests and cords. 35 , 36 as shown in Figure 3 - A histopathological section of a neuroendocrine tumor. Haematoxylin and eosin stain.10X. Similar to the LAMN staging system, appendiceal neuroendocrine tumors were staged according to the AJCC/UICC/WHO criteria, based on tumor size and depth of invasion. The stages are as follows: T1 tumors measure ≤2 cm; T2 tumors measure >2 cm and ≤4 cm; T3 tumors are >4 cm or show infiltration into subserosal fat or the mesoappendix regardless of size; T4 tumors cause serosal perforation or direct invasion into adjacent organs. Management of well-differentiated neuroendocrine tumors depends on tumor size and location. Neuroendocrine tumors 2 cm or arising at the appendiceal base often require right hemicolectomy. 37 Globally, only 2 cases of synchronous well-differentiated synchronous appendiceal neuroendocrine tumors with mucinous neoplasms have been reported. 38 In our study, 4 cases of colon cancer involving the appendix were identified. Appendiceal metastases from colon cancer are rare and may occur via direct invasion, peritoneal seeding, or lymphatic and hematogenous spread. Biological behavior and histopathological features differ among adenocarcinoma of appendiceal origin, primary colonic adenocarcinoma, and metastatic carcinoma involving the appendix. 39 One case of an appendiceal sessile serrated polyp was also identified in the present study. These polyps primarily occur in the right colon but may rarely arise in the appendix. 40 Histologically, they are characterized by dysplastic epithelium involving 50% of the basal crypts with saw-toothed appearance. Study limitations There may be some limitations to the results of the present study, and the first one was that it was single centered implying small size of the patients, therefore it was difficult to find significant relationships from the collected data, since the statistical analysis required a larger sample. In addition, the results may not accurately represent the findings of the whole population of the country. The second limitation was the lack of reliable clinical data to some patients because the attending clinicians did not prove them on the request forms. The third limitation was absence of some slides representing unusual appendiceal findings from archives of the pathology lab because some patients took the slides to other centers for revision and not returned them back. The second and third limitations led to exclusion of some cases from this study limiting the sample size. The Fourth limitation was that the slides of unusual histopathological findings were reviewed by only one experienced pathologist and this lack of peer review hindered seeking feedback and help from departmental colleages who might provide valuable information. In conclusion, this study provides valuable insights into the spectrum of histopathological findings in appendectomy specimens, reinforcing the importance of routine histopathological examination of resected appendices. Although acute appendicitis remains the most common diagnosis, a substantial number of specimens demonstrated unusual histopathological findings. These findings included neoplasms, infections, and various benign lesions. Notably, mucinous neoplasms were more prevalent than well-differentiated neuroendocrine tumors. Increased awareness of these findings among histopathologists may enhance diagnostic accuracy and improve patient outcomes.