Management of Unusual Colonic Polyps
John Heine, MD, FRCSC, FACS
Clinical Associate Professor of Surgery
University of Calgary
Calgary , AB Canada
INTRODUCTION
A polyp is defined as a protrusion above the surrounding normal mucosa1. Pathology giving rise to such protrusions can arise from the mucosa, submucosa or extraluminally. This discussion will review less common colonic polyps. Evolving diagnostic modalities which may aid in the management of these lesions will also be reviewed.
DIAGNOSTIC MODALITIES
MAGNIFICATION CHROMOENDOSCOPY
Combining mucosal magnification and the use of a vital dye, typically 2% indigo carmine, can increase the diagnostic yield of small, flat subtle polyps and more clearly delineate the borders of such lesions. Five distinct mucosal ?pit patterns? have been described, allowing accurate differentiation of lesions into non-neoplastic (Types I and II) and neoplastic (Types III, IV and V). One centre?s experience with 210 colonic lesions reported 100% and 99.8% accuracy in diagnosing non-neoplastic and neoplastic polyps2. Endoscopists trained at this centre were reportedly proficient in this technique in 3 months. Another report demonstrated diagnostic accuracies of 95% with magnification chromoendoscopy and 76% with conventional endoscopy for lesions <5 mm.3 This technique may reduce the time, cost and risk associated with biopsy or polypectomy, although application of the dye is time consuming.
Another magnification technique which may prove useful in the identification and differentiation of polyps is high resolution endoscopy employing a narrow banded imaging system based on the wavelength of blue light.4
ENDOSCOPIC ULTRASOUND (EUS)
Endoscopic ultrasound has proven utility in accurately determining the depth of invasion of malignant lesions arising from the colonic mucosa. EUS has also been employed to assess submucosal lesions. As the mucosa overlying these lesions is usually normal, biopsy is generally ineffective in histologically characterizing such lesions. EUS reliably demonstrates the layers of the intestinal wall and can therefore identify the origin of submucosal lesions, narrowing the differential diagnosis.
Echocharacteristics may also be helpful in determining the likelihood of malignancy. Features which may suggest malignancy include size > 3-4 cm., rapid rate of growth on serial EUS, lymphadenopathy, and irregular margins. Hypoechoic lesions arising from the second and fourth layers (muscularis mucosa and propria) are suggestive of gastrointestinal stromal tumours (GIST). A hyperechoic lesion confined to the submucosa (3rd layer) is most likely a lipoma whereas a hypoechoic lesion in the same layer is most likely a carcinoid.5
EUS may also be helpful in determining the suitability of a lesion for endoscopic mucosal resection (EMR). Lesions amenable to EMR are superficial to the muscularis propria.6
UNUSUAL COLONIC POLYPS
SERRATED ADENOMA (SA)
This lesion is being reported more frequently by pathologists. An element of glandular dysplasia in addition to the typical serrated morphology seen in hyperplastic polyps suggests that they may have malignant potential. SA may represent an intermediate lesion between hyperplastic polyp and CRC. Residual SA has been reported in up to 6% of colorectal cancer (CRC) and foci of high grade dysplasia have been noted in up to 16% of SA?s. These lesions, found in 7% of patients undergoing colonoscopy in one study, will likely become even more prevalent with increasing awareness by pathologists. Follow-up surveillance should likely be the same as for adenomas.7
BENIGN SUBMUCOSAL LESIONS
Such lesions may arise from normal or ectopic tissue within the colonic wall-fat, smooth muscle, blood or lymphatic vessels, neural or neuroendocrine elements (Table 1). Not surprisingly, 60% of these submucosal lesions are reported to arise in the rectum likely reflecting the fact that small lesions may not be visible and are found incidentally on DRE.6
TABLE 16
BENIGN SUBMUCOSAL LESIONS
N=30, < 20 mm
Carcinoid 9 (30%)
Leiomyoma 8 (27%)
Lipoma 6 (20%)
Lymphangioma 5 (16%)
Fibrovascular 2 (6%)
Solitary rectal ulcer can present as an exophytic, polypoid lesion mimicking carcinoma. Clues to the diagnosis include long duration of symptoms, and a history of dysfunctional defecation. Bleeding is the most common presenting symptom followed by mucous discharge, straining and pain. Biopsies show fibromuscular lamina propria, hypertrophied muscularis mucosa, and displaced glands in the submucosa without dysplasia or stromal invasion.15,16
MALIGNANT OR POTENTIALLY MALIGNANT LESIONS
A recent SEER review of 169,073 colorectal malignancies showed that 2.6% were non-adenocarcinoma (Table 2).8 The distribution of malignancies by histologic type varies according to location: 93% and 74% of squamous cell carcinomas and carcinoids, respectively, were found in the rectum, compared to 29% and 21% of neuroendocrine tumours and lymphomas. This study does not report the incidence of GIST.
TABLE 2
NON-ADENOCARCINOMA CRC MALIGNANCY
N=4,435
CARCINOID 1.5%
LYMPHOMA 0.6%
NEUROENDOCRINE 0.3%
SQUAMOUS 0.3%
SARCOMA 0.1%
A study of 150 patients with colorectal carcinoids showed that 40% were discovered incidentally and 10% were multicentric9. Thirteen percent of these patients had an associated colorectal neoplasm (5% adenocarcinoma, 8% adenomas). A review of 880 colorectal carcinoids found that 17% had a second primary malignancy with approximately 50% arising from the GI tract10. Size is predictive of biologic behaviour: none of 57 carcinoids <10 mm had invasion of the muscularis propria or metastatic disease and 10 had evidence of lymphovascular invasion; of 9 carcinoids > 10 mm, 5 had invasion of the muscularis propria, 6 had lymphovascular invasion and 4 had metastatic disease11.
Gastrointestinal stromal tumour (GIST) is the result of a mutation of the Kit proto-oncogene. The majority of these lesions are found incidentally in asymptomatic patients or in the course of investigations for symptoms that were likely not related to the GIST12. Diagnostic accuracy is increased from 78% using EUS alone, to 91% if FNAB is added13. Biologic behaviour can be predicted based on NIH Consensus Criteria (Table 3).14.
A small series of 18 colorectal GIST?s demonstrated that all 6 patients with low or intermediate risk lesions were alive without disease at median follow-up of 65 (15-266) months compared to only 3 of 12 patients alive and NED with high risk lesions12.
TABLE 3
| RISK | SIZE (cm) | MITOSES/50 HPF |
| Low | <5 | <5 |
| Intermediate | <5 | 6-10 |
| 5-10 | <5 | |
| High | >5 | >5 |
| >10 | Any | |
| Any | >10 |
MANAGEMENT OF UNUSUAL COLORECTAL LESIONS
A full discussion of management is beyond the scope of this summary but the approach is similar to that taken for more common lesions: available diagnostic tests are utilized and patient and tumour factors taken into account. These include suitability for endoscopic excision (EUS may be helpful); location of tumour (rectal lesions may be amenable to transanal approach); nature of symptoms; presence/absence of metastatic disease; and patient?s perioperative risk stratification.
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