Squamous metaplasia of the rectum/anus
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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.
- +/-Nucleoli present.
- 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
- ↑ 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.