Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Case Reports
. 2025 Dec 24;13(1):e01947.
doi: 10.14309/crj.0000000000001947. eCollection 2026 Jan.

Heterotopic Ossification in an Appendiceal Sessile Serrated Lesion With Synchronous Neuroendocrine Tumor

Paul J Wurtz  1 , Douglas Walton  2 , Calen Gist  3 , Devin Moore  1 , Serena Murphy  3 , Carl Kay  4
Affiliations
Case Reports

Heterotopic Ossification in an Appendiceal Sessile Serrated Lesion With Synchronous Neuroendocrine Tumor

Paul J Wurtz et al. ACG Case Rep J. .

Abstract

Heterotopic ossification (HO) in colorectal polyps is rare and scarcely reported in serrated lesions. We report an appendiceal sessile serrated lesion (SSL) with mature bone and a contiguous well-differentiated neuroendocrine tumor. A 64-year-old woman had a firm appendiceal-orifice polyp biopsied in 2012 showing calcification; SSL was identified in 2019. In 2024, an 8-mm lesion was removed en bloc by underwater cold snare; histology showed SSL with HO. Laparoscopic appendectomy confirmed residual SSL with HO and an adjacent 4.5-mm grade-1 neuroendocrine tumor (INSM1+, Ki-67 <3%) with negative margins. HO recognition should prompt en bloc excision and attentive pathology.

Keywords: appendiceal orifice; colorectal polyp; heterotopic ossification; neuroendocrine tumor; osseous metaplasia; sessile serrated lesion; underwater cold snare.

PubMed Disclaimer

Figures

Figure 1.
Figure 1.
(A) Colonoscopy in 2012 showing a 4-mm firm lesion at the appendiceal orifice; forceps biopsy revealed dystrophic calcification. (B) Underwater cold-snare polypectomy in 2024 with en bloc removal of an 8-mm recurrent appendiceal-orifice lesion.
Figure 2.
Figure 2.
(A) Hematoxylin and eosin stain, 100×. Sessile serrated lesion overlying osseous metaplasia (heterotopic ossification) at the appendiceal orifice. (B) Hematoxylin and eosin stain, 400×. High-power view of osseous metaplasia showing osteocytes (black arrows) and osteoblast rimming (blue arrows).
Figure 3.
Figure 3.
Hematoxylin and eosin stain, 100×. Appendectomy specimen confirming residual sessile serrated lesion with associated osseous metaplasia.
Figure 4.
Figure 4.
Hematoxylin and eosin stain, 100×. Well-differentiated neuroendocrine tumor (upper right) adjacent to residual sessile serrated lesion (lower left); INSM1 positive, Ki-67 <3%.
See this image and copyright information in PMC

References

    1. Vos AM, Pijnenborg L, van Vliet S, et al. Biological background of colorectal polyps and carcinomas with heterotopic ossification: A national study and literature review. Hum Pathol. 2024;145:34–41. - PubMed
    1. Janež J. Bone metaplasia of the appendix presented with clinical and computed tomography signs of acute appendicitis managed with laparoscopic appendectomy. J Minim Access Surg. 2023;19(2):305–6. - PMC - PubMed
    1. Haque S, Eisen RN, West AB. Heterotopic bone formation in the gastrointestinal tract. Arch Pathol Lab Med. 1996;120(7):666–70. - PubMed
    1. Prados B, Del Toro R, MacGrogan D, et al. Heterotopic ossification in mice overexpressing Bmp2 in Tie2+ lineages. Cell Death Dis. 2021;12(8):729. - PMC - PubMed
    1. Montalvo NF, Beltrán JN, Redrobán LA. Traditional serrated adenoma of the sigmoid colon with osseous metaplasia: A case report. J Med Case Rep. 2012;6:133. - PMC - PubMed

Publication types