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 style answer #1Cite this page: Kuo E. Adenoma overview. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/colontumoradenoma.html. Accessed January 25th, 2021.
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
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
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
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 style 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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