Abstract
ContextLow-grade appendiceal mucinous neoplasm (LAMN) and appendiceal adenocarcinoma are known to cause the majority of pseudomyxoma peritonei (PMP, i.e. mucinous ascites); however, recognition and proper classification of these neoplasms can be difficult despite established diagnostic criteria.ObjectiveTo determine the pathological diagnostic concordance for appendix neoplasia and related lesions during patient referral to an academic medical center specialized in treating patients with PMP.DesignThe anatomic pathology laboratory information system was searched to identify cases over a two-year period containing appendix specimens with mucinous neoplasia evaluated by an outside pathology group and by in-house slide review at a single large academic medical center during patient referral.Results161 cases containing appendix specimens were identified over this period. Forty-six of 161 cases (28.6%) contained appendiceal primary neoplasia or lesions. Of these, the originating pathologist diagnosed 23 cases (50%) as adenocarcinoma and 23 cases (50%) as LAMN; however, the reference pathologist diagnosed 29 cases (63.0%) as LAMN, 13 cases (28.3%) as adenocarcinoma, and 4 cases (8.7%) as ruptured simple mucocele. Importantly, for cases in which the originating pathologist rendered a diagnosis of adenocarcinoma, the reference pathologist rendered a diagnosis of adenocarcinoma (56.5%, 13 of 23), LAMN (39.1%, 9 of 23), or simple mucocele (4.3%, 1 of 23). The overall diagnostic concordance rate for these major classifications was 71.7% (33 of 46) with an unweighted observed kappa value of 0.48 (95% CI, 0.27–0.69), consistent with moderate interobserver agreement. All of the observed discordance (28.3%) for major classifications could be attributed to over-interpretation. In addition, the majority of LAMN cases (65.5%) had potential diagnostic deficiencies including over-interpretation as adenocarcinoma and lacking or discordant risk stratification (i.e. documentation of extra-appendiceal neoplastic epithelium).ConclusionsAppendiceal mucinous lesions remain a difficult area for appropriate pathological classification with substantial discordance due to over-interpretation in this study. The findings highlight the critical need for recognition and application of diagnostic criteria regarding these tumors. Recently published consensus guidelines and a checklist provided herein may help facilitate improvement of diagnostic concordance and thereby reduce over-interpretation and potential overtreatment. Further studies are needed to determine the extent of this phenomenon and its potential clinical impact.
Highlights
Mucinous appendiceal neoplasms that may give rise to pseudomyxoma peritonei (PMP) remain a challenging tumor type for pathological classification despite their description dating back to the 19th century when the term PMP was first used by Werth.[1]
For cases in which the originating pathologist rendered a diagnosis of adenocarcinoma, the reference pathologist rendered a diagnosis of adenocarcinoma (56.5%, 13 of 23), Low-grade appendiceal mucinous neoplasm (LAMN)
PMP is clinically defined as mucinous or gelatinous ascites and peritoneal implants associated with the pathological finding of neoplastic mucin-producing cells in the peritoneal cavity. [2,3] It is understood that the vast majority of PMP arise from perforated mucinous neoplasms of the appendix, and represent their peritoneal extension, with a minority of cases being due to mucinous adenocarcinomas arising from other sites.[4]
Summary
Mucinous appendiceal neoplasms that may give rise to pseudomyxoma peritonei (PMP) remain a challenging tumor type for pathological classification despite their description dating back to the 19th century when the term PMP was first used by Werth.[1]. PMP is clinically defined as mucinous or gelatinous ascites and peritoneal implants associated with the pathological finding of neoplastic mucin-producing cells in the peritoneal cavity. [2,3] It is understood that the vast majority of PMP arise from perforated mucinous neoplasms of the appendix, and represent their peritoneal extension, with a minority of cases being due to mucinous adenocarcinomas arising from other sites.[4] Ovarian origin of PMP is rare and generally associated with mucinous adenocarcinoma arising from mature cystic teratoma.[5,6] Most cases of PMP have low-grade histologic features (sometimes termed “lowgrade mucinous carcinoma peritonei” according to the World Health Organization (WHO)), while close to one quarter of cases have high-grade histologic features (sometimes termed “high-grade mucinous carcinoma peritonei” according to the WHO) with a corresponding worse prognosis.[4] In addition, the presence of signet ring cells has emerged as an independent negative prognostic factor, especially if tissue invasion is seen.[7,8]
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