Nakamura and colleagues first described IMGP in 1992 as a non-neoplastic colorectal polyp with three main histological features: 1) inflammatory granulation tissue in the lamina propria; 2) proliferation of smooth muscle from the muscolaris mucosae; 3) hyperplastic glands with occasional cystic dilatation [1]. A review of literature on MEDLINE revealed only 60 cases of IMGPs reported from 1992 to 2009 [1–13].
IMGP can be asymptomatic [1, 4, 6, 8, 11], whereas hemorrage is the most common symptom: it can develop as positive fecal occult blood [1, 5, 7, 8, 11], hematochezia [1, 5, 7–10, 12, 13] or anemia [1, 8]. Other non-specific symptoms may be abdominal pain or constipation [1, 8]. In our case the patient was investigated for positive fecal occult blood, although he had signs of chronic anemia for several months before the admission to our hospital.
Large bowel is the only gastrointestinal tract where IMGP has been described, with the exception of the case in the terminal ileum reported by Griffiths et al. [2]. It is mostly located in the left colon: of 60 cases, 9 (15%) were in the rectum, 30 (50%) in the sigma, 6 (10%) in the descending colon, 13 (21,6%) in the transverse colon, 1 (1,7%) in the ascending colon, 1 (1,7%) in the ileum [1–13]. We reported the first case of IMGP of the cecum. According to the literature the endoscopy can show a pedunculated (88,3%) or sessile polyp (11,7%), with a smooth (90%) or lobulated (10%) surface [1–13]. The polyp we found appears to be rare because it is a sessile polyp with a lobulated surface and superficial erosions.
The final diagnosis of IMGP is achieved by histological examination through endoscopic mucosal resection (EMR) or polypectomy, whereas the simple biopsy alone is not enough for a correct diagnosis as in our case. Some authors [8, 12] reported a correlation between the characteristic surface of the polyp under magnifying endoscopy and its histological features. As their experience is limited to 10 patients more cases should be studied.
IMGP must be differentiated from other non-neoplastic polyps such as inflammatory cap polyps (ICP), inflammatory cloacogenic polyps, juvenile polyps (JP), inflammatory fibroid polyps (IFP), polyps secondary to mucosal prolapse syndrome (MPS), polypoid prolapsing mucosal folds of diverticular disease [6]. Bathal et al. [14, 16] consider IMGP and all these lesions as part of a same group with small histological variations and as result of prolapse. However, we agree with others [1, 9–18] who consider IMGP as a distinct entity. In fact, each type of these polyps presents both histological and clinical differences from the IMGP. Inflammatory cap polyps (ICP) are usually multiple, sessile, covered by a fibrin cap and associated with inflammatory bowel diseases or colonic cancer [19]. Moreover the common symptoms of ICPs are mucous diarrhea and tenesmus, and they usually develop in the rectosigma. Inflammatory cloacogenic polyps are solitary, peduncolated, with tubulovillous architecture and localized only at the anorectal transition zone [20]. Juvenile polyps do not show proliferation of the muscolaris mucosae and develop in young age [1]. Inflammatory fibroid polyps (IFP) mostly occur in stomach and small bowel and are histologically characterized by connective tissue with abundant inflammatory cells, in particular plasma cells and eosinophils [15]. IMGP should not be also considered as polyps secondary to mucosal prolapse syndrome or as polypoid prolapsing mucosal folds of diverticular disease. In the former, polypoid lesions are usually villous, granular or cauliflower-like, frequently found in females and in older patients than IMGPs [1]. In the latter, no correlation between IMGP and diverticular disease has been found [21].
Concerning therapy, endoscopic treatment of IMGP is the gold standard because it is clinically and histologically benign as reported in literature [1–9, 11–13], with the exception of Kayhan et al. [10] who performed a left hemicolectomy because of the polyp size (> 6 cm). We also decided for surgical resection because of increased risk of endoscopic polypectomy (bleeding and perforation) related to polyp diameter and the absence of a peduncle. However we agree with authors who consider that the number of surgical resections for colonic IMGP will decrease and endoscopic resection will increase in the future considering the recent advances of the diagnostic and therapeutic endoscopy [12, 13].
The causes of IMGP are still unclear. Nakamura et al. [1] think that chronic trauma from the fecal stream and from peristalsis may have a role in its pathogenesis. This theory came from the observation that IMGP were found only in the left colon where the feces are solid and more able to injure the colonic mucosa [1, 8]. Nevertheless, recent papers described IMGPs in the proximal transverse [7, 11] and ascending colon [12] or in the cecum as we found.
