Structure and Epithelial Features
The interior of the cervical canal is lined by a simple columnar epithelium. The epithelial cells secrete mucopolysaccharides, forming a mucus plug in the cervical canal.
The junction between the columnar and stratified squamous epithelia (the transformation zone) is of great clinical significance: 90% of cervical diseases originate here. The topography of this junction varies depending on the woman's age and physiological state:
- In girls, adolescents, and pregnant women, the border is located on the vaginal portion of the cervix, which is considered a physiological variant.
- In reproductive-age women, the junction is located at the level of the external os.
- In postmenopause, the epithelial border shifts into the cervical canal at varying depths.
Contents Passing Through the Cervical Canal
The cervical canal facilitates communication between the uterine tube, uterine cavity, and vagina during certain pathological processes. In primary fallopian tube cancer, blood and tumor breakdown products drain through the uterus and cervical canal into the vagina. This causes early clinical manifestations—pathological vaginal discharge, most commonly serosanguineous, though serous, seropurulent, or watery («meat-water») discharge can also occur.
- During an inevitable or incomplete abortion, a completely detached conceptus descends into the lower parts of the uterus, including the cervical canal.
Clinical Significance and Pathologies
- Cervical ectopy (pseudoerosion): displacement of the columnar epithelium onto the vaginal portion of the cervix. In areas of ectopy, cervical glands are identified instead of stratified squamous epithelium.
- Cervical canal carcinoma: initial stages present with scant clinical manifestations. Diagnosis is challenging because the cervical canal is inaccessible to standard colposcopy. In advanced cases, the cervix acquires a barrel-like shape and a firm consistency.
- Cervical incompetence: when a complete intrauterine septum extends into the cervical canal, it is recommended to preserve the cervical part of the septum to prevent secondary cervical incompetence.
- Criminal (unsafe) abortion: may be performed by introducing foreign bodies or chemical solutions into the cervical canal or uterine cavity; it is life-threatening due to a high risk of infection and hemorrhage.
Instrumental Procedures
The cervical canal is involved in various diagnostic and therapeutic gynecological procedures:
- Prior to inserting an intrauterine device (IUD), bacterioscopic examination of smears from the vagina, cervical canal, and urethra is mandatory; insertion is only permitted with clean smears (grade I–II).
- During fractional diagnostic curettage of the uterine mucosa with hysteroscopy in pediatric patients, Hegar dilators up to No. 8–9 are introduced into the cervical canal, after which the endometrial scrapings are retrieved using a small curette (No. 2 or 4).
- If the retrieval strings of an IUD are missing or broken, the procedure must be performed strictly in a hospital setting: IUD localization is verified by ultrasound, and removal is performed after cervical canal dilation under hysteroscopic guidance.
- When cytological changes are detected in the cervical canal or ultrasound signs of pathology are present, advanced evaluation is indicated: hysterocervicoscopy, curettage of the cervical canal with histological examination of the scrapings, and cone biopsy of the cervix.