Colon tumor
Polyps
Adenoma - general

Author: Enoch Kuo, M.D. (see Authors page)
Editor: Raul S. Gonzalez, M.D.

Revised: 7 December 2017, last major update November 2017

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Adenoma[TI] colon general
Cite this page: Kuo, E. Adenoma - general. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/colontumoradenoma.html. Accessed April 21st, 2018.
Definition / general
Essential features
  • Neoplastic, premalignant polyp of the colorectum
  • Most are tubular adenoma
ICD-10 coding
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
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

Images hosted on PathOut server:

Images contributed by Dr. Enoch Kuo:

Traditional serrated adenoma


Tubular adenoma



Images contributed by Dr. Raul S. Gonzalez:

Sessile serrated adenoma

Board review question #1
Which of the following findings has the highest risk for carcinoma?

  1. 1 cm tubular adenoma with high grade dysplasia
  2. 1 cm villous adenoma without high grade features
  3. 4 tubular adenomas each less than 1 cm in size and without high grade features
  4. 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).