Debating Deposits, Redux: Substantial Interobserver Agreement Exists in Distinguishing Tumor Deposits From Nodal Metastases in Small Bowel Neuroendocrine Tumors.

Context: Recent data suggest mesenteric tumor deposits (MTDs) indicate poor prognosis in small bowel well-differentiated neuroendocrine tumors (SB-NETs), including compared to positive lymph nodes, making their distinction crucial.

Objective: To study interobserver agreement in distinguishing SB-NET MTDs from positive nodes.

Design: Virtual slides from 36 locally metastatic SB-NET foci were shared among 7 gastrointestinal pathologists, who interpreted each as an MTD or a positive node. Observers ranked their 5 preferred choices among a supplied list of potentially useful histologic features, for both options. Diagnostic opinions were compared using Fleiss multirater and Cohen weighted κ analyses.

Results: Preferred criteria for MTD included irregular shape (n = 7, top choice for 5), perineural invasion/nerve entrapment (n = 7, top choice for 2), encased thick-walled vessels (n = 7), and prominent fibrosis (n = 6). Preferred criteria for positive nodes included peripheral lymphoid follicles (n = 6, top choice for 4), round shape (n = 7, top choice for 2), peripheral lymphocyte rim (n = 7, top choice for 1), subcapsular sinuses (n = 7), and a capsule (n = 6). Among 36 foci, 10 (28%) each were unanimously diagnosed as MTD or positive node. For 13 foci (36%), there was a diagnosis favored by most observers (5 or 6 of 7): positive node in 8, MTD in 5. Only 3 cases (8%) had a near-even (4:3) split. Overall agreement was substantial (κ = .64, P < .001).

Conclusions: Substantial interobserver agreement exists for distinguishing SB-NET MTDs from lymph node metastases. Favored histologic criteria in making the distinction include irregular shape and nerve/vessel entrapment for MTD, and peripheral lymphocytes/lymphoid follicles and round shape for positive nodes.