Colposcopy of the Vagina

The squamous mucosa lining the vagina is similar to the original squamous epithelium of the cervix. Embryologically, the epithelium of the distal vagina appears to be derived from the epithelium of the urogenital sinus epithelium, which is itself of endodermal origin, whereas the epithelium of the upper vagina is of mesodermal müllerian origin. The vaginal stroma is composed of a mixture of elastic fibers and can contain mesonephric or wolffian remnants. The persistence of glands arising from müllerian epithelium (so-called vaginal adenosis) is uncommon, and the vagina usually does not contain glands.

The large majority of malignant vaginal neoplasms are squamous cell carcinomas that develop via squamous intraepithelial lesions (SILs; formerly vaginal intraepithelial neoplasia, or VAIN) associated with human papillomavirus (HPV) infection. Patients with risk factors for persisting HPV infection (e.g., smoking, immunosuppression, HIV infection) have an increased risk for vaginal precancer and cancer. Occasional squamous cell carcinomas of the vagina may develop in a background of lichen planus independently of HPV infection. The mechanism of HPV-independent carcinogenesis of the vagina seems to parallel that of the vulva.

SIL of the vagina accounts for less than 1% of lower genital tract intraepithelial neoplasia. Women with vaginal SIL are usually asymptomatic. The first report of SIL is credited to Graham and Meigs in patients years after treatment for carcinoma in situ of the cervix. Vaginal SIL can occur alone or as synchronously or metachronously with cervical or vulvar HPV-related precancer and cancer. Up to 65% of patients with vaginal SIL have been reported to have SIL of the cervix or vulva.

Lesions are often multifocal and occur predominantly in the upper one-third of the vagina, whereas the middle and lower thirds are involved in less than 10%. This is probably due to the dual origin of vaginal epithelium during prenatal development.

Most lower-grade SILs probably regress spontaneously. In contrast, untreated higher-grade SILs progress to invasive cancer in 5 to 8% of cases.

A history of SIL of the cervix is a major risk factor for the development of vaginal SIL. About 0.9 to 7.4% of patients with hysterectomy for cervical SIL later develop vaginal SIL. Vaginal SIL can develop as an independent lesion or close to the cervix (or vaginal apex after hysterectomy). Patients with residual SIL at the vaginal apex after hysterectomy appear at risk of developing invasive vaginal cancer.

As for other HPV-related neoplasias, smoking is a risk factor for vaginal carcinoma. Vaginal SIL is also known to occur more frequently in patients with a history of pelvic radiation for other malignancies such as cervical or endometrial cancer. This increased incidence of vaginal SIL may take some 10 to 15 years to manifest itself. Possible mechanisms of postradiation cellular dysplasia include radiation-induced expression of HPV oncoproteins and radiation-induced changes in the cellular response to HPV infection.

Vaginal adenosis is any condition in which columnar epithelium exists within the vagina. Metaplasia can convert this glandular epithelium to squamous epithelium. It is unclear whether high-risk HPV-infected women with vaginal adenosis are at greater risk for vaginal high-grade squamous intraepithelial lesion (HSIL). Vaginal adenosis may be the origin of the rare entities of vaginal adenoma and adenocarcinoma.

In many cases, vaginal SIL cannot be identified by gross inspection only; colposcopy of the vagina is essential. Particularly, women who have positive cytology after treatment for cervical SIL should be examined carefully for vaginal SIL. At the examination, it is important to rotate the open duckbill speculum through 360 degrees, paying particular attention to the upper vagina. In the posthysterectomy patient, vaginal vault angles can be dimpled, precluding complete colposcopic assessment.

Persisting abnormal cervical cytology in a patient with a colposcopically normal cervix should prompt exact inspection of the vagina. Although patients with the cytologic changes of low-grade squamous intraepithelial lesion (LSIL) may not have an identifiable lesion, cytologic findings of HSIL generally are associated with a corresponding colposcopic and histologic lesion.