Complicated appendiceal diverticulosis versus low‐grade appendiceal mucinous neoplasms: a major diagnostic dilemma

Abstract

Aims To research and identify how often complicated diverticular disease of the appendix [appendiceal diverticular disease (ADD)] shows histological mimicry of low‐grade appendiceal mucinous neoplasms (LAMNs) and to provide guidance on the useful histopathological features that allow the appropriate diagnosis to be made. Methods and results Seventy‐four cases of complicated appendiceal diverticular disease were identified from two specialist centres. Of the second opinion/consultation cases, 71% of the ADD cases had been diagnosed by referring pathologists as LAMNs. Salient pathological features were identified and agreed upon to reach the applicable diagnosis. For a diagnosis of complicated diverticulosis, particularly when associated with mucus cysts, the following morphological features were regarded as important: relative retention of the normal mucosal architecture with lamina propria and a maintained crypt architecture, crypts arranged in regular array, epithelial hyperplasia and a lack of nuclear abnormalities extending the length of the crypts. In a formal case–control study undertaken on 30 cases with each diagnosis, ADD and LAMN, loss of lamina propria, a filiform architecture and hypermucinosis were significantly associated with low‐grade appendiceal mucinous neoplasms. Mucosal neuromas were significantly associated with diverticular disease of the appendix. Conclusions To our knowledge, this study represents the largest series in the world literature and serves to highlight the important pathological features to distinguish complicated diverticular disease of the appendix from LAMNs, and emphasises the difficulties experienced by diagnostic pathologists in diagnosing complicated appendiceal diverticulosis. This is important, as LAMNs have a significant risk of transcoelomic spread, while complicated appendiceal diverticulosis has no such risk.

Significance of the Entire Appendiceal Evaluation in the Diagnosis of Serrated Lesions, Low-Grade Appendiceal Mucinous Neoplasm, and Appendiceal Diverticulosis Disease

“…Residual flattened surface epithelium of the atrophy mucosa may also raise concerns about flattened dysplastic epithelium of LAMN. Two cases of ruptured appendiceal diverticula in group 1 were initially misdiagnosed as appendiceal mucinous neoplasms, and similar misdiagnosis also occurred in previous studies ( 18 , 22 ). One misdiagnosed case was completely submitted due to suspicious macroscopic observations, and the other was resampled due to microscopic findings.…”

“…Appendiceal diverticula are classically divided into acquired and congenital types. The majority of diverticula are acquired, with herniation of appendiceal mucosa and submucosa through microanatomical defects in the muscularis propria ( 18 ). The incidence ranged between 0.004% and 2.1% from appendicectomy studies ( 19 ), but the actual incidence may be higher, because it may be overlooked in macroscopic examination for almost two-thirds of the cases without grossly visible changes.…”

Intraoperative Evaluation of the Gastrointestinal Tract

“…The differential diagnosis of mucinous neoplasia includes benign mucin extrusion as a result of perforated appendicitis or ruptured diverticular disease, both of which may produce an inflammatory mass accompanied by extra-appendiceal mucin. However, post-inflammatory changes rarely cause as much luminal dilatation as that a b seen in association with mucinous neoplasms, and they lack the thick, tenacious mucin of mucinous neoplasms [60,61]. Inflammatory changes include mixed inflammation with macrophages and eosinophils as well as goblet cell hyperplasia and reactive changes of the overlying epithelium (Fig.…”

“…3.26a, b). Lamina propria and normal crypts are usually associated with the atypical epithelium; neither of which are features of mucinous neoplasms [60]. The preoperative clinical and radiologic impression can also be quite helpful, as mucinous neoplasms rarely present with findings typical of classic acute appendicitis.…”

LAMN as a differential diagnosis for abdominal pain: a case report from Syria

“…One of the most common types of specimens received in laboratory is vermiform appendices. In juvenile population, most specimens show standard features of acute pyogenic and necrotizing appendicitis, whereas in older population, low-grade appendiceal mucinous neoplasms (LAMNs) should be considered as a differential diagnosis, even they are found in <0.3% of appendectomy specimens, since they can be easily misdiagnosed due to unspecific symptoms like abdominal pain, nausea, vomiting and palpable mass in the right iliac fossa [ 1–4 ]. LAMNs account nearly 1% of gastrointestinal neoplasms and are characterized by villous or flat proliferation of mucinous epithelium with low-grade cytologic atypia and absence of destructive invasion leading to diverticulum-like structures [ 1 , 4–6 ].…”