Colorectal Serrated Polyp With Stromal Changes: An Interobserver Agreement Study

BACKGROUND: Prolapse-related changes have been shown to be a confounding factor leading to misdiagnosis of serrated polyps in the rectum. Recent data on perineurial-like stromal proliferation in some sessile serrated polyps (SSPs) also highlights this issue. METHODS: Fifty-four consecutive serrated polyps with stromal changes from 42 patients were collected by one pathologist during a 2-month period (July and August of 2014). In addition, 20 cases of serrated polyps with perineurial-like stromal proliferation from 20 patients were retrieved from our pathology database from 2003 to 2010. The polyps were re-reviewed by three gastrointestinal pathologists for stromal changes, basal crypt distortion, and final classification into hyperplastic polyp (HP) or SSP. Final interpretation was correlated to clinicopathologic features and the presence of synchronous SSP and adenoma. In addition, the interobserver agreement on the stromal changes and basal crypt distortion in these polyps was determined. RESULTS: Upon histology review, all polyps showed stromal changes evident by at least one pathologist. Among the 74 polyps evaluated, a consensus diagnosis of HP and consensus diagnosis of SSP were reached in 39 and 11 polyps respectively. The overall interobserver agreement among three pathologists was moderate (kappa value 0.49, 95% confidence interval (CI) 0.32 - 0.66). A consensus diagnosis could not be reached in the remaining 24 polyps (32.4%). The SSPs were larger, were more often located in the right colon, and occurred more frequently in women when compared to HPs (7.3 ± 5.3 vs. 4.5 ± 2.7 mm, P = 0.019; 72.7% vs. 7.7%, P = 0.000014; and 77.7% vs. 30.7%, P = 0.019) but with comparable patient age (54.7 ± 10.6 years vs. 60.7 ± 11.4, P = 0.12). The SSPs were associated with higher risk of concurrent SSP in other parts of the colon (27.3% vs. 0%, P = 0.008) but not with the presence of concurrent adenoma (45.4% vs. 69.6%, P = 1). Among the 24 unclassifiable serrated polyps, 11 were interpreted by two reviewers as SSP and 13 interpreted by two reviewers as HP; the former group were more likely right-sided (45.4% vs. 15.4%, P = 0.046), but size of the polyps and age of the patients were comparable. Stromal changes (prolapse and perineurial-like) were agreed upon by all three pathologists in 33 (44.6%, of 74) polyps and these included 15 with prolapse changes and 18 perineurial-like stromal changes. Among those 15 with prolapse changes, 14 (93.3%) were agreed upon by three pathologists to be HP; in contrast, only four (22.2%, of 18) with perineurial-like stromal changes were diagnosed as HP by all three pathologists (P = 0.00008). Of 74 polyps, 16 were found to have basal crypt distortion involving more than one crypt and eight of them (50%) carried a final interpretation of SSP by all three pathologists and two (12.5%) HP. CONCLUSIONS: Even though serrated polyps with stromal changes can be challenging, up to 67.7% of them could be readily classified as SSP or HP. The remaining unclassifiable serrated polyps with stromal changes may represent a heterogeneous group. Prolapse changes support the diagnosis of HP while basal crypt distortion in more than one crypt supports the diagnosis of SSP.