Vaginal adenosis
Vaginal adenosis is a benign  abnormality in the vagina, commonly thought to be caused by intrauterine and neonatal exposure of diethylstilbestrol and other progestogens and nonsteroidal estrogens, however it has also been observed in otherwise healthy women and has been considered at times idiopathic or congenital. Postpubertal lesions have also been observed to grow de novo. It has a rather common incidence, of about 10% of adult women.

Causes
Vaginal adenosis is characterised by the presence of metaplastic cervical or endometrial epithelium within the vaginal wall, considered as derived from Müllerian epithelium islets in later life. In women who were exposed to certain chemicals, vaginal adenosis may arise in up to 90%. Since these contraceptives were discontinued, incidence has dropped dramatically. Risk is however still present in subsequent generations due to recent exposure.It is thought steroid hormones play a stimulatory growth in adenosis formation. Vaginal adenosis is also often observed in adenocarcinoma patients.

Diagnosis
Colposcopically, it presents itself similarly to columnar epithelium on the cervix, assisted with lugols solution application for diagnosis. It can be discovered as nodules or cysts on the vaginal tube, with biopsy needed for further diagnosis. As seen cytologically, epithelial and stromal cells in vaginal adenosis show characteristic fusion through the basal lamina or with stromal fibroblasts. Adenosal cells can be distinguished as mucinous, tuboendometrial, and embryonic. Its mucinous cells resemble the normal cervical lining, while its tuboendometrial cells resemble the lining of normal fallopian tubes or endometrium.It is sometimes considered a precancerous lesion, given clear-cell adenocarcinoma patients present these lesions in close proximity to atypical tuboendometrial glands, and microglandular hyperplasia has been seen to arise from these lesions.

References
Further reading
OBrien, P. C.; Noller, K. L.; Robboy, S. J.; Barnes, A. B.; Kaufman, R. H.; Tilley, B. C.; Townsend, D. E. (March 1979). "Vaginal epithelial changes in young women enrolled in the National Cooperative Diethylstilbestrol Adenosis (DESAD) project". Obstetrics & Gynecology. 53 (3): 300–308. PMID 424101.
Laronda, Monica M.; Unno, Kenji; Butler, Lindsey M.; Kurita, Takeshi (2012). "The development of cervical and vaginal adenosis as a result of diethylstilbestrol exposure in utero". Differentiation. 84 (3): 252–260. doi:10.1016/j.diff.2012.05.004. ISSN 0301-4681. PMC 3443265. PMID 22682699. PMID 22682699.
Ganesan, R.; Ferryman, S. R.; Waddell, C. A. (1999). "Vaginal adenosis in a patient on Tamoxifen therapy: a case report". Cytopathology. 10 (2): 127–130. doi:10.1046/j.1365-2303.1999.00162.x. ISSN 0956-5507. PMID 10211619. S2CID 33999959.
Laronda, M. M.; Unno, K.; Ishi, K.; Serna, V. A.; Butler, L. M; Mills, A. A.; Orvis, G. D.; Behringer, R. R.; Deng, C.; Sinha, S.; Kurita, T. (2013). "Diethylstilbestrol induces vaginal adenosis by disrupting SMAD/RUNX1-mediated cell fate decision in the Müllerian duct epithelium". Developmental Biology 381(1): 5-16. doi: 10.1016/j.ydbio.2013.06.024. PMID 23830984.