Anatomy and Histology of the Cervix

Abstract

Although the cervix was recognized as an organ entity as early as 4500 B.C. during the third Egyptian Dynasty, it was Soranus, in the first century A.D., who gave the first accurate description of the cervix uteri as a separate portion of the uterus.⁴⁸ The cervix (term taken from the Latin, meaning “neck”) is the most inferior portion of the uterus protruding into the upper vagina. The vagina is fused circumferentially and obliquely around the distal part of the cervix, dividing it into an upper, supravaginal and lower, vaginal portion.²⁶ The cervix is generally cylindrical in shape, measures in the adult nulligravida 2.5 to 3.0 cm in length, and its normal position is slightly angulated downward and backward. The vaginal portion (portio vaginalis) of the cervix, also referred to as the exocervix, is delimited by the anterior and posterior fornices and has a convex elliptical surface. It is covered by a smooth, shiny squamous mucous membrane and centered by the external os, a circular (in the nulligravida) or slitlike (in the parous woman) opening (Figure 5.1). The portio may be divided into anterior and posterior lips, of which the anterior is shorter and projects lower than its posterior counterpart. The external os is interconnected with the isthmus (internal os) by the cervical canal. The canal is an elliptical, fusiform cavity, measuring in its greatest width 8 mm, and contains longitudinal mucosal ridges, the plicae palmatae (Figure 5.2). These, when hypertrophied or fused because of inflammation, may render the introduction of a uterine curette or dilator difficult because they form blind passages in the canal. The area between the endocervical and endometrial cavity is called the isthmus or lower uterine segment. The latter term is used principally for descriptive purposes during gestation and labor. The use of the terms anatomic and histologic “internal os” seems arbitrary as no convincing morphologic evidence is offered to support such a geographic subdivision of the uterus and the uterus may be divided into corpus, isthmus, and cervix. The muscular layer in the region of the isthmus is less developed than in the corpus, a feature that facilitates effacement and dilatation during labor. The blood supply of the cervix is provided by the descending branches of the uterine arteries, reaching the lateral walls along the upper margin of the paracervical ligaments (cardinal ligaments of Mackenrodt). These ligaments are the main source of fixation, support, and suspension of the organ. Another means of fixation is provided by the uterosacral ligaments, which attach the supravaginal portion of the cervix to the second through fourth sacral vertebrae. Excision of nerve fibers (denervation) within these ligaments is used to relieve intractable dysmenorrhea. The venous drainage parallels the arterial system, with communication between the cervical plexus and neck of the urinary bladder. The lymphatics of the cervix have a dual origin:³⁶ beneath the mucosa and deep in the fibrous stroma. Both systems collect into two lateral plexuses in the region of the isthmus and give origin to four efferent channels running toward: (1) the external iliac and obturator nodes, (2) the hypogastric and common iliac nodes, (3) the sacral nodes, and (4) the nodes of the posterior wall of the urinary bladder. The innervation of the cervix is chiefly limited to the endocervix and peripheral deep portion of the exocervix.²⁶ This distribution is responsible for the relative insensitivity to pain of the portio vaginalis. The cervical nerves derive from the pelvic autonomic system, the superior, middle, and inferior hypogastric plexuses.