Cervical intraepithelial neoplasia (CIN) is a premalignant condition of the uterine cervix . The ectocervix (surface of the cervix that is visualized on vaginal speculum examination) is covered in squamous epithelium, and the endocervix, including the cervical canal, is covered with glandular epithelium. CIN refers to squamous abnormalities. Glandular cervical neoplasia includes adenocarcinoma in situ and adenocarcinoma. (See "Cervical cytology: Evaluation of atypical and malignant glandular cells" and "Cervical adenocarcinoma in situ" and "Invasive cervical adenocarcinoma".)
Screening for cervical cancer includes cervical cytology and testing for oncogenic subtypes of human papillomavirus (HPV). Follow-up of abnormalities in screening tests with colposcopy and cervical biopsy may result in a diagnosis of CIN or cervical cancer .
CIN may be low grade or high grade. Women with low-grade CIN have minimal potential for developing cervical malignancy, while those with high-grade lesions are at high risk of progression to malignancy.
The definition, incidence, and pathogenesis of CIN are reviewed here. The management of CIN and the epidemiology and virology of HPV infection are discussed separately. (See "Cervical intraepithelial neoplasia: Management of low-grade and high-grade lesions" and "Epidemiology of human papillomavirus infections" and "Virology of human papillomavirus infections and the link to cancer".)
Historically, premalignant squamous changes of the cervix were described as mild, moderate, or severe cervical dysplasia. In 1988, a new terminology system was introduced, the Bethesda system, which was then revised in 1991 and 2001. In this system, different terminology was used for cytologic (on Pap test) and histologic (on biopsy) findings [3-5]. Cytologic findings were described with the term "squamous intraepithelial lesion" and histologic changes were described with the term "cervical intraepithelial neoplasia (CIN)". The term CIN has three degrees of severity (figure 1 and picture 1):