Anatomy of the Cervix
The cervix uteri (cervix) is the lowest portion of the uterus (Fig. 44–1). The cervix consists of roughly equal supravaginal and vaginal portions. The part of the cervix that protrudes into and can be viewed from the vaginal aspect measures 2 cm (average) in length (Fig. 44–2). The supravaginal portion measures 1.5 cm (average) in length. Overall, the entire cervix in the nonpregnant, menstruating woman measures 3.5 cm in length and 2 cm in diameter. During the postmenopausal period or with prolapse, the relative length of the cervix may increase (Fig. 44–3A, B). Similarly, after cerclage, the relative length of the cervix may appear on ultrasound measurement to substantially increase (Fig. 44–4A, B). This apparent increase is undoubtedly due to the addition of a portion of the isthmus into the suture. As the cervix is viewed via an opened speculum, it is cylindrical in appearance with a central opening, the external os. The latter measures 3 to 5 mm in diameter (nulliparous) and up to 1 cm or more in a multiparous woman (Fig. 44–5). The reflection of the upper portion of the vagina (vault) around the protruding cervix forms recesses or fornices (anterior, posterior, right, and left lateral) (Fig. 44–6).
Most of the cervix is covered with multilayered squamous epithelium and has a pink appearance. The endocervical canal is lined by a single layer of glandular mucus-secreting epithelium and has a red coloration (Fig. 44–7). The endocervical canal is narrow (0.5 cm) and extends from the vaginal end (external os) to the point of entry into the lower portion of the uterine cavity (internal os) (Fig. 44–8A through C). The mucous epithelium is thrown into numerous folds and clefts that extend into the underlying stroma (collagen) for varying depths (Fig. 44–9). The purpose of the folds and clefts is to greatly increase the surface area of the endocervical canal without actually increasing its overall length (Fig. 44–10). Unfortunately, a popular misnomer has ingrained itself irreversibly in gynecologic literature and usage: “endocervical glands.” These are not glands but rather an extension of the single-cell–layered endocervical canal. Several studies have shown that the endocervical mucosa projects 3 mm into the underlying stroma but may plunge as deep as 6 mm (Fig. 44–11A, B).
The cervix is endowed with a copious blood supply via the descending branch of the uterine artery and the vaginal artery. This accounts for its ability to miraculously heal and to survive the worst kind of iatrogenic insults.
