The inverted appendix – a potentially problematic diagnosis: clinicopathologic analysis of 21 cases

Abstract

Aims: Inverted appendices are rare, but have the potential to cause diagnostic confusion among endoscopists and pathologists. The aim of this study was to describe the clinicopathological features of inverted appendices seen at our institution over the last 30 years. Methods and results: Twenty-one inverted appendices were identified and the clinical and pathological features reviewed. Patients were predominantly middleaged women. Most cases were detected incidentally on colonoscopy. Endoscopically, inverted appendices appeared polypoid in the proximal caecum. All resections featured associated pathological processes, including endometriosis (n = 3), inflammatory mucocoele (n = 1), low-grade appendiceal mucinous neoplasm (n = 2), traditional serrated adenoma (n = 1) and inflammatory fibroid polyp (n = 1). Five cases were endoscopically mischaracterised as caecal polyps and removed via polypectomy; initial pathological impressions were erroneous in most cases. All polypectomies featured a dome-like configuration covered by mucosa on the convex surface; the majority had aggregates of ganglion cells and neural plexi embedded in muscularis propria. The vast majority of cases, regardless of the procedure, showed lymphoid aggregates. Among post-polypectomy patients with follow-up, none experienced perforation-associated morbidity despite the histological presence of muscularis propria. Conclusions: The diagnosis of an inverted appendix should be considered in polypectomy specimens from the caecum or appendiceal orifice with (i) dome-like tissue configuration covered by mucosa on the convex surface, (ii) a deep, robust smooth muscle component with ganglion cells (muscularis propria) and (iii) associated lymphoid aggregates. Prompt recognition on H&E will avoid unnecessary time and resource investment.

Multiple intestinal hemangioma concurrent with low-grade appendiceal mucinous neoplasm presenting as intussusception—a case report and literature review

“…The patient was finally diagnosed with mixed hemangioma of the appendix combined with low-grade mucinous tumor. Based on the literature search using the term “appendiceal mucinous tumor” and “intussusception” from the articles in the PubMed database between January 2000 and February 2021, 29 articles [ 19 – 47 ] were obtained, among which 20 [ 19 – 21 , 23 , 24 , 26 – 40 ] were eligible after excluding 9 articles including 2 [ 22 , 47 ] in Japanese language and 1[ 25 ] in Dutch, 2 [ 41 , 42 ] involved the cases with no appendiceal mucinous tumor, 2 [ 44 , 46 ] with appendiceal mucinous tumor with no intussusception, 1 [ 45 ] with sigmoidorectal intussusception caused by a mucinous adenocarcinoma of the sigmoid colon, as well as 1 study [ 43 ] focused on the histological and imaging features. Among the remaining 20 articles, one article [ 26 ] mentioned 3 related cases in the literature review including 1 with LAMNs induced intussusception, 1 with intussusception caused by appendiceal mucocele [ 48 ], and 1 with intussusception caused by appendiceal mucocele combined with schistosomiasis [ 49 ].…”

“…Mucocele was non-neoplastic mucinous lesion characterized by markedly thinned or denuded mucosa combined with luminal dilatation, without atypia and hyperplasia. In addition, one article concerning the clinicopathologic features of 21 cases of inverted appendix reporting 3 cases met the demands of the literature search [ 40 ]. Finally, 25 cases were included (Table 3 ).…”

“…One case was diagnosed LAMNs pTis associated with ovarian cyst of the follicular-luteinic type [ 27 ]. One case (4.0%) was diagnosed with simple retention cysts [ 49 ], one (4.0%) with simple retention cysts and Schistosomiasis [ 50 ], one (4.0%) with serrated dysplasia of low grade [ 40 ], one (4.0%) with LAMNs pT3 [ 23 ], two (8.0%) with LAMNs pT4a [ 32 , 38 ], as well as one (4.0%) with HAMNs of the appendix and well-differentiated neuroendocrine carcinoma [ 33 ]. For the classification of intussusception, 8 cases (36.2%) were appendix intussuscepting into the caecum, and 15 cases (60.0%) were colonic intussusception.…”

Neuroendocrine tumours in patients operated for acute appendicitis: a retrospective clinical study

“…More rare, these tumours may be located outside the gastrointestinal tract, such as bronchi, ovary, and thymus 2 . Appendiceal NETs developed from neuroendocrine cells of the appendix 1,3 are benign tumours that metastasize very rarely, and are the most common appendiceal tumours 4 . Such tumours can be seen in about 0.33% of appendectomy specimens 5 .…”

Appendix intussusception: a challenging differential diagnosis

“…In the histopathology laboratory, the majority of appendix specimens are inaccurately diagnosed: polyps or nodules of the caecum . The macroscopic evaluation can point in the direction of appendiceal intussusception, but the microscopic examination gives the diagnosis certainty, based on the dome‐like appearance of the supposed caecal polyp, covered with mucosa on the convex surface, with muscularis propria and numerous lymphoid aggregates.…”