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Anus and perianal area

General

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.

General
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● 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
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Various images of anal canal


Anal / rectal junction and sphincter


Anal transitional zone; rectal adenocarcinoma

End of Anus and perianal area > General > Normal histology


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