Although described in various organs, heterotopic bone formation known as osseous metaplasia (OM) is a rare phenomenon in the gastrointestinal tract.1–11 OM in the stomach is even less common than that in other parts of the gastrointestinal tract, with less than 10 cases reported in the English literature to date.6–11 Thus far, 4 hyperplastic polyps and 2 adenomatous polyps were reported in the literature.6–11 Ohtsuki et al reported the first case of OM in a hyperplastic polyp of the stomach in 1987.11 We present a rare case of a 65-year-old man with a history of pernicious anemia and hypothyroidism.
We present a 65-year-old man with a medical history of gastric adenoma, obesity, pernicious anemia, and hypothyroidism. The patient was evaluated for melana where severe anemia was discovered on a routine blood evaluation. He was admitted to the emergency department where he received 2 units of packed red blood cells. A computed tomography scan was ordered, revealing a 2.1 × 1.4-cm soft-tissue polypoid lesion arising from the lesser curvature of the stomach. There was a central high-attenuating focus measuring 4 mm (Figure 1). The patient was evaluated with initial endoscopy, which revealed a large polyp. He was referred for endoscopic polypectomy and endoscopic ultrasound. Examination highlighted a single pedunculated 2-cm polyp with stigmata of recent bleeding in the stomach. A single-piece polypectomy was performed using a hot snare in the stomach body (Figure 2). Surrounding this lesion, a flat carpet-like polypoid area was noted, measuring at least 3 cm in diameter. No associated mass was identified on the endoscopic ultrasound. Jumbo forceps biopsies were obtained from this area after resection of the pedunculated polyp. Additional endoscopic findings included normal esophageal and duodenal mucosa.
The stomach body's polypectomy specimen demonstrated a gastric adenomatous polyp with a mostly tubular pattern and multiple areas of high-grade dysplasia (Figure 3). There was surface ulceration with granulation tissue noted. The polyp stroma contained multiple areas of OM. The additional biopsies from the surrounding flat carpet-like polypoid area revealed the same histologic findings with the gastric adenomatous polyp with high-grade dysplasia. A different focus of OM was also noted in one of the tissue fragments from this area. No evidence of intestinal metaplasia or malignancy was found in either specimen. In addition, Helicobacter pylori organisms were not identified on immunostained sections. A subsequent robotic-assisted local wedge gastrectomy was performed 6 weeks later to excise the dysplastic flat carpet-like polypoid area revealing the same histologic findings without evidence of malignancy.
OM, defined as ectopic bone formation within soft tissues, has been described in a variety of neoplastic and nonneoplastic conditions in many organs throughout the body, including breast, prostate, uterus, lungs, and skin appendages. Bone formation outside the skeletal system is more often seen in pathological conditions, such as burns, prolonged bedridden states secondary to extensive injuries, myositis ossificans, certain orthopaedic surgeries, or as an incidental finding. OM in the gastrointestinal tract is quite rare.1–7 It was first described in colonic adenocarcinomas by Duke in 1939.12 Adenocarcinoma of the rectum seems to be the tumor most frequently found to contain the bone with a prevalence of 0.4%.13–17
OM in the stomach is rarer than other parts of the gastrointestinal tract, with less than 10 cases reported in the English literature to date.6–11 Thus far, 4 hyperplastic polyps and 2 adenomatous polyps were reported in the literature.6–11 It was Ohtsuki et al who reported the first case of OM in a hyperplastic polyp of the stomach in 1987.11 OM has also been seen in a carcinoma of the stomach. Ishizuka et al reported such findings in a gastric carcinoma in 1983.18 Although OM has been previously associated with dysplastic and malignant conditions, the impact of its identification as pathologic findings on clinical management is still unknown. Our patient has undergone a wedge gastrectomy because of the background of high-grade dysplasia and to rule out malignancy. Further studies to assess the clinical significance of OM in the stomach and other sites in the gastrointestinal tract are needed. To the best of our knowledge, this is the first reported case of identifiable OM in a gastric polyp radiologically. This finding could alert radiologists and gastroenterologists for the presence of an associated aggressive lesion.
Several theories have been proposed regarding OM in soft-tissue organs. The most widely accepted theory is that the osteogenic factors, such as osteonectin and nestin, released by the neoplastic or inflammatory tissue stimulate undifferentiated stromal mesenchymal cells or fibroblasts to undergo transformation to osteoblasts.1,7,19–21 Bone morphogenic proteins have also been believed to be associated with osteogenic activities since 1988.3,4,22,23
Author contributions: O. Tawfik wrote, edited, and revised the article for intellectual content and is the article guarantor. S. Jonnalagadda edited the article, reviewed the literature, and provided the endoscopic images. R. Downing edited the article and provided radiologic images. G. Siddiqui wrote, edited, and revised the article for intellectual content. M. McNally edited the article and provided the surgical findings in the report.
Financial disclosure: None to report.
Informed consent was obtained for this case report.
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