Anus and perianal area
Normal histology

Author: Nat Pernick, M.D. (see Authors page)

Revised: 26 January 2016, last major update April 2005

Copyright: (c) 2002-2016,, Inc.

Cite this page: Normal histology. website. Accessed October 21st, 2016.
Definition / General
  • 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 Hirschsprungs 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
Images hosted on other servers:
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Various images of anal canal

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Anal / rectal junction and sphincter

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Anal transitional zone; rectal adenocarcinoma