Difference between revisions of "Squamous metaplasia of the rectum/anus"

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*Present in the transformation zone between the columnar epithelium of the [[rectum]] and squamous epithelium of the [[anus]] - similar to the transformation zone of the [[uterine cervix]].<ref name=pmid20436833>{{Cite journal  | last1 = Pineda | first1 = CE. | last2 = Welton | first2 = ML. | title = Management of anal squamous intraepithelial lesions. | journal = Clin Colon Rectal Surg | volume = 22 | issue = 2 | pages = 94-101 | month = May | year = 2009 | doi = 10.1055/s-0029-1223840 | PMID = 20436833 }}</ref>
*Present in the transformation zone between the columnar epithelium of the [[rectum]] and squamous epithelium of the [[anus]] - similar to the transformation zone of the [[uterine cervix]].<ref name=pmid20436833>{{Cite journal  | last1 = Pineda | first1 = CE. | last2 = Welton | first2 = ML. | title = Management of anal squamous intraepithelial lesions. | journal = Clin Colon Rectal Surg | volume = 22 | issue = 2 | pages = 94-101 | month = May | year = 2009 | doi = 10.1055/s-0029-1223840 | PMID = 20436833 }}</ref>


Anatomy & histology:
Note:
*Typically, the squamocolumnar junction is just above the dentate line (also ''pectinate line'').
*The anatomy & histology of the anus covered in the ''[[anus]]'' article.
*Squamous epithelium 1 cm proximal to the dentate line is considered abnormal.<ref name=pmid11174313>{{Cite journal  | last1 = Bujanda | first1 = L. | last2 = Iriondo | first2 = C. | last3 = Muñoz | first3 = C. | last4 = Etxezarraga | first4 = C. | last5 = Ramírez | first5 = MM. | last6 = Ramos | first6 = F. | last7 = Sánchez | first7 = A. | title = Squamous metaplasia of the rectum and sigmoid colon. | journal = Gastrointest Endosc | volume = 53 | issue = 2 | pages = 255-6 | month = Feb | year = 2001 | doi =  | PMID = 11174313 }}</ref>
*The dentate line divides the anal canal into upper two thirds and lower third.


==Microscopic==
==Microscopic==

Latest revision as of 02:42, 16 June 2016

Squamous metaplasia of the rectum/anus is a metaplastic change of the columnar epithelium of the rectum.

It can histologically mimic anal intraepithelial neoplasia (AIN), especially. high-grade squamous intraepithelial lesion (HSIL).

General

  • Present in the transformation zone between the columnar epithelium of the rectum and squamous epithelium of the anus - similar to the transformation zone of the uterine cervix.[1]

Note:

  • The anatomy & histology of the anus covered in the anus article.

Microscopic

Features:

  • Uniform cell spacing - no crowding - key feature.
  • Nuclei are uniform size and round.
  • Distinct cell borders
  • +/-Intercellular bridges (due to edema) - common.

Negatives:

  • No mitoses/rare basal mitoses - think cancer/AIN if you see 'em.
  • Usually no hyperchromatism (think cancer/CIN if you see it).

DDx:

Images

  • ISM - very low mag.

  • ISM - low mag.

  • ISM - intermed. mag.

  • ISM - high mag.

IHC

  • p16 -ve
    • Usually weak-to-moderate patchy, not full thickness.
  • Ki-67 - scattered cells positive.

See also

References

  1. ↑ Pineda, CE.; Welton, ML. (May 2009). "Management of anal squamous intraepithelial lesions.". Clin Colon Rectal Surg 22 (2): 94-101. doi:10.1055/s-0029-1223840. PMID 20436833.
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