Osseous Metaplasia in a Rectal Inflammatory Polyp in an Adolescent Patient: A Case Report and Review of the Literature

Abstract

Osseous metaplasia/heterotopic bone formation is a well-known phenomenon encountered in various neoplastic and non-neoplastic conditions. Osseous metaplasia in colorectal polyps is extremely rare. We report a case of osseous metaplasia in a rectal inflammatory polyp in a 17-year-old man with a longstanding history of painless rectal bleeding. The patient was referred to our facility for evaluation of a four-month history of painless rectal bleeding, as well as rectal prolapse and episodes of fecal urgency. A total colonoscopy revealed an approximately 1.0 cm tan-red sessile and pedunculated polyp in the rectum. No other abnormalities were identified in the colon. The polyp was removed via snare polypectomy. On gross examination, the polyp measured 1.2 x 1.1 x 0.8 cm and was quadrisected and submitted entirely for histologic examination. Sections of the polyp showed fragments of denuded polypoid colonic mucosa with inflammatory granulation tissue formation and overlying purulent debris. The inflammatory granulation tissue was composed of abundant dilated small blood vessels, a marked mixed acute and chronic inflammatory infiltrate, and active fibroblast proliferation. At the junction of the intact colonic mucosa and the adjacent inflammatory granulation tissue, multiple foci of woven bone formation without bone marrow were identified. Osseous metaplasia most likely occurs by osteoblasts differentiating from fibroblasts secondary to inflammation, tissue damage, or substances such as bone morphogenetic proteins released from neoplastic cells.Osseous metaplasia could also be caused by dystrophic calcification in necrotic tissue. To our knowledge, this is the eighth reported case of osseous metaplasia in a rectal inflammatory polyp.

A Benign Rectal Polyp With Osseous Metaplasia: A Pediatric Case Report and Literature Review

“…Around 21 previous cases have reported osseous metaplasia. The patients present clinically with a history of painless rectal bleeding with or without prolapsed rectal mass [1][2][3][4][5][6]. Further, the age variation of osseous metaplasia cases is between nine and 39 years, with a few elderly cases above 70 years old [5].…”

“…The patients present clinically with a history of painless rectal bleeding with or without prolapsed rectal mass [1][2][3][4][5][6]. Further, the age variation of osseous metaplasia cases is between nine and 39 years, with a few elderly cases above 70 years old [5]. Moreover, the size of rectal polyps varies between 8 and 12 mm, with a male predominance [1][2][3][4][5][6][7].…”

“…Metaplasia is defined as the replacement of a typical differentiated cell type with another one that presents outside its tissue [1]. Although more than 20 previous cases have reported osseous metaplasia, only seven are in inflammatory rectal polyps [3][4][5]. The exact pathogenesis is not fully understood; however, several mechanisms and theories of the chronic inflammatory process and metaplastic changes have been investigated [1][2][3].…”

Kemik Metaplazisinin Eşlik Ettiği İnflamatuar Rektal Polip: Ayrı Bir Antite mi?

“…In their study published in 2003; Kawai et al (25) transferred the human BMP-2 gene to the skeletal muscle of rats by cutaneous electroporation and observed the formation of ectopic bone consisting of active osteoblasts and osteoclasts in all rats. Wood et al (5) presented a case of inflammatory rectal polyp with osseous metaplasia in a 17-year-old patient in their recent article and suggested that this may be a distinctive disease entity. We share the same perspective with them.…”

“…Very few cases have been reported, especially in the pediatric population. Although its pathophysiology is not known clearly, there are several theories suggested (5). In this case report, we presented a case of bone formation in a rectal inflammatory polyp presenting with rectal bleeding in a 7-year-old girl.…”