Colon (tumor & nontumor)
Polyps
Adenoma overview
Author: Enoch Kuo, M.D.
Editorial Board Member: Raul S. Gonzalez, M.D.
Topic Completed: 1 November 2017
Minor changes: 31 July 2020
Copyright: 2002-2019, PathologyOutlines.com, Inc.
PubMed Search: Adenoma[TI] colon general
Table of Contents
Definition / general | Essential features | ICD coding | Epidemiology | Sites | Pathophysiology | Etiology | Clinical features | Diagnosis | Laboratory | Radiology description | Prognostic factors | Treatment | Clinical images | Gross description | Gross images | Microscopic (histologic) description | Microscopic (histologic) images | Additional references | Board review style question #1 | Board review answer #1Cite this page: Kuo E. Adenoma overview. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/colontumoradenoma.html. Accessed August 6th, 2020.
Definition / general
- Adenoma is a general term for a premalignant lesion - includes conventional adenoma (tubular, tubulovillous or villous), sessile serrated adenoma and traditional serrated adenoma
Essential features
- Neoplastic, premalignant polyp of the colorectum
- Most are tubular adenoma
ICD coding
- K63.5 Colon polyp
Epidemiology
- In the U.S., adenomas are present in 20 - 40% of screening colonoscopies in patients over age 50
- Conventional tubular adenoma is the most common subtype (65 - 85% of all polyps removed), followed by sessile serrated adenoma and then traditional serrated adenoma (< 1%)
- Men have higher risk for adenoma than women (Gastrointest Endosc 2011;74:135)
Sites
- Conventional adenoma is more common in the left hemicolon
- Sessile serrated adenoma is more common in the proximal colon
- Traditional serrated adenoma is more common in the rectosigmoid colon
Pathophysiology
- Conventional adenoma has a neoplastic progression (adenoma - carcinoma sequence) that includes APC, beta catenin, KRAS and TP53 mutations (J Gastroenterol Hepatol 2012;27:1423)
- About 5% of conventional adenomas are also MSI-H (PLoS One 2017;12:e0172381)
- Traditional serrated adenoma is associated with BRAF or KRAS mutations and progress with beta catenin mutation or CpG island methylation
- Sessile serrated adenoma is associated with BRAF mutation and progress with high levels of microsatellite instability through MLH1 hypermethylation
Etiology
- Conventional adenoma is associated with smoking, high BMI and a diet of red meat
- Sessile serrated adenoma is associated with a high fat and meat diet, smoking, alcohol and high BMI (Gastroenterology 2017;152:92)
- Decreased risk of conventional adenoma is associated with dietary fiber intake (Lancet 2003;361:1491), fruit consumption in women (Cancer Res 2006;66:3942) and folate intake (J Nutr 2005;135:2468)
- Only a weak association between fiber and adenoma recurrence (Am J Gastroenterol 2005;100:2789)
Clinical features
- Time to progression from an adenoma to carcinoma ranges from 5 to more than 20 years
- Some adenomas stabilize and regress
- 30% of patients develop new polyps after mean 26 month follow up; higher risk if 3 or more adenomas and at least 1 in proximal colon (Dis Colon Rectum 2004;47:323)
- Risk of finding invasive colorectal adenocarcinoma in the adenoma depends on size: < 1% if < 1 cm vs. 10% if > 2 cm; the risk is increased with villous component present
- Risk of subsequent carcinoma is related to 3 or more polyps, polyp location at transverse or proximal colon or presence of monotonous population of elongated cells (Am J Surg Pathol 2006;30:1120)
- "Advanced adenomas" receive more aggressive clinical management (i.e. repeat colonoscopy in 3 years instead of 5 years) and include:
- > 3 adenomas
- Any adenoma > 1 cm with villous architecture
- Any adenoma with high grade dysplasia
Diagnosis
- Colonoscopy is the gold standard for detecting adenoma
- Capsule endoscopy is less effective at detecting adenoma compared to colonoscopy
Laboratory
- Clinical tests for adenoma include fecal occult blood testing (FOBT) and fecal immunochemical testing (FIT or iFOBT)
- Fecal DNA and antigen testing have better sensitivity and specificity in detecting carcinoma than adenoma
Radiology description
- CT colonography is a screening modality (N Engl J Med 2003;349:2191) that may be used for patients with increased sedation associated risks
Prognostic factors
- 3% annual risk of progression from adenoma to carcinoma if the size of the adenoma is at least 1 cm
- 17% annual risk of progression from adenoma to carcinoma if there is villous architecture
- 37% annual risk of progression from adenoma to carcinoma if there is high grade dysplasia
Treatment
- Excision of a pedunculated adenoma, even with invasive carcinoma, is considered adequate treatment if the margin is negative, there is no vascular or lymphatic invasion and the carcinoma is moderately or well differentiated
- Invasive adenocarcinoma in a sessile polyp requires more than polypectomy
- 1 - 2 conventional adenomas should be monitored every 5 - 10 years after removal (Gastroenterology 2012;143:844)
- 3 - 10 conventional adenomas, adenomas > 1 cm, villous adenomas and adenomas with high grade dysplasia should be monitored every 3 years after removal
- > 10 conventional adenomas should be monitored every < 3 years
- Sessile serrated adenoma < 1 cm should be monitored every 5 years after removal
- Sessile serrated adenoma > 1 cm, with dysplasia or any traditional serrated adenoma should be monitored every 3 years after removal
Clinical images
Images hosted on other servers:
Colonoscopic images of several adenomas
Gross description
- Pedunculated (with stalk), sessile or flat
- Tubular are red (darker than surrounding mucosa)
- Villous are shaggy with papillary fronds
- True margin of resection should be inked when grossing or can be determined by diathermy artifact
- Sessile serrated adenoma is usually flat and covered by a mucous cap
Gross images
Images hosted on other servers:
Polypoid tumor with gyrated surface sitting on a short stalk
Polypoid tumor
Microscopic (histologic) description
- Adenoma is classified into conventional, serrated, traditional serrated, flat (with conventional dysplasia) or mixed adenoma (sessile serrated adenoma with conventional dysplasia)
- Architectural patterns of conventional adenoma:
- Villous (1%): > 75% villous component
- Tubulovillous (5%): 25 - 75% villous component
- Tubular: < 25% villous component
- Degree of villous differentiation increases with size of the adenoma
- Sessile serrated adenoma:
- Epithelial serrations with abundant mucin
- Basal crypt dilation
- Lateral spread of crypt bases (commonly described as boot shaped or anchor shaped crypts)
- Traditional serrated adenoma:
- Eosinophilic cytoplasm with varying mucin
- Thin, hyperchromatic, pencillate nuclei at the base
- Mild villous architecture (villiform)
- Conventional dysplasia can be classified as low grade or high grade, although some GI pathologists recommend not using high grade dysplasia terminology unless clinicians want to know
- Low grade: pseudostratification or stratification of nuclei that do not reach the luminal cell surface; apical mucin is present; nuclei are elongated and dysplastic; mitotic activity, atypical mitosis and loss of polarity are minimal
- High grade: nuclei are enlarged, hyperchromatic or vesicular with prominent nucleoli; nuclei are stratified and reach luminal border; architectural changes include back to back glands, cribriform glands or irregular budding / branching of crypts; mitotic figures are prominent; reduced mucin; necrosis may be present
- By definition, adenoma has no invasion through muscularis mucosae into submucosa
- Intramucosal carcinoma: invasion of mucosa or muscularis mucosa (but not beyond) with desmoplastic response; no biologic potential for metastases
Microscopic (histologic) images
Contributed by Dr. Enoch Kuo
Traditional serrated adenoma
Tubular adenoma
Contributed by Dr. Raul S. Gonzalez
Sessile serrated adenoma
Additional references
Board review style question #1
Which of the following findings has the highest risk for carcinoma?
- 1 cm tubular adenoma with high grade dysplasia
- 1 cm villous adenoma without high grade features
- 4 tubular adenomas each less than 1 cm in size and without high grade features
- Tubular adenoma with a size of 2 cm without high grade features
Board review answer #1
A. 1 cm tubular adenoma with high grade dysplasia; high grade dysplasia has the highest risk for carcinoma, followed by villous architecture and then size of the adenoma (> 1 cm).
Reference: Colon tumor - Adenoma - general
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Reference: Colon tumor - Adenoma - general
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