Home   Chapter Home   Jobs   Conferences   Fellowships   Books


Anus and perianal area


Normal histology

Reviewer: Nat Pernick, M.D. (see Reviewers page)
Revised: 13 April 2013, last major update April 2005
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.


● Lacks a peritoneal covering
● Three histologic types: glandular (proximal), transitional (also called intermediate, cloacogenic) and keratinized or nonkeratinized squamous (distal)
● Anal glands and transitional zone epithelium are CK7+/CK20-, different from colorectal carcinoma (CK7-/CK20+, Arch Pathol Lab Med 2001;125:1074)
● Notes: ganglion cells are normally absent 1-2 cm above dentate line (important for Hirschsprung’s disease biopsies); multinucleated stromal cells are common (may be fibroblasts)

Proximal colorectal zone:
● Top of puborectalis to dentate line
● Glandular and transitional mucosa
● 1-2 cm long
● Similar to rectal mucosa but with shorter more irregular crypts, more smooth muscle fibers in lamina propria

Anal transitional zone (ATZ):
● 0.3 cm to 1.1 cm
● Zone between uninterrupted columnar mucosa above and uninterrupted squamous epithelium below
● Wrinkled glistening appearance
● Transitional epithelium resembles urothelium (small basal cells with nuclei perpendicular to basement membrane, columnar, cuboidal, polygonal or flat) with 4-9 cell layers, minimal mucin production
● Not highly specialized and may incorporate features of both urothelium and squamous epithelium (Hum Pathol 1978;9:579)
● Contains anal glands in submucosa, also endocrine cells, rare melanocytes
● Expresses CK7 and CK19 but not CK20

Lower distal zone:
● Dentate line to squamous mucocutaneous junction: nonkeratinizing squamous epithelium without skin appendages, without glands
● Contains melanocytes
● Anal papillae contain squamous mucosa that joins rectal mucosa
● Squamous mucosa merges with perianal skin (with keratin, hair follicles and apocrine glands) at anal verge / anal margin

Micro images

Various images of anal canal

Anal / rectal junction and sphincter

Anal transitional zone; rectal adenocarcinoma

End of Anus and perianal area > General > Normal histology

This information is intended for physicians and related personnel, who understand that medical information is often imperfect, and must be interpreted in the context of a patient's clinical data using reasonable medical judgment. This website should not be used as a substitute for the advice of a licensed physician.

All information on this website is protected by copyright of PathologyOutlines.com, Inc. Information from third parties may also be protected by copyright. Please contact us at copyrightPathOut@gmail.com with any questions (click here for other contact information).