Physiological changes in the cervix

ECTOPY OR ECTROPION

In the prepubertal girl, the squamocolumnar junction lies around the external os or on the ectocervix. At the time of puberty, in pregnancy (particularly the first pregnancy) and in many steroid contraceptive users, changes in the hormonal milieu result in an alteration in the shape and an increase in the bulk of the cervix. These changes result in eversion of the endocervical epithelium with the squamocolumnar junction being carried passively further out on to the anatomical ectocervix. This rim of endocervical tissue forms an ectopy or ectropion exposed around the external os. The ectopy appears red through the thin covering epithelium and the surface is villous (Figure 3.1).

The exposure of the delicate endocervical epithelium to the acid environment of the vagina leads to squamous metaplasia with the squamous epithelial cells differentiating from pluripotential uncommitted cells, through an intermediate stage referred to as reserve cell hyperplasia. Squamous metaplasia is a protective mechanism in which relatively fragile endocervical columnar epithelium is replaced by a more robust squamous epithelium.

The metaplastic squamous epithelium may occlude the mouths of the endocervical crypts with the resultant formation of retention cysts or Nabothian follicles (Figure 3.2). This process also restores the position of the squamocolumnar junction to the external os. The area of squamous metaplasia is termed the transformation zone. This is the site at which the majority of cervical neoplasms arise.