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.