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Anatomy of the Cervix
- Introduction
- Epithelium
- Squamocolumnar junction (SCJ)
- Transformation zone (TZ)
Introduction
The anatomy of the cervix is of premier importance in understanding cervical
disease processes. The various epithelia, the
squamocolumnar junction, and the transformation
zone are highlighted in the discussion below.
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Click on the image to enlarge. The normal cervix, seen with everted columnar
epithelium as well as squamous metaplasia. From Giuntoli RL et al:
Textbook and atlas: Atkinson's correlative atlas of colposcopy,
cytology, and histopathology , Philadelphia, 1987, Lippincott-Raven.
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The cervix represents the distal portion of the uterus and is about 30
mm long and 25 mm wide, projecting into the posterior vagina. The endocervical
canal extends through the central portion of the os. It is limited proximally
by the internal os (opening into the fundus) and distally by the external
os. The part of the cervix viewed during gross examination is called the
ectocervix or portio vaginalis.
Epithelium
The cervix can be divided into three separate areas, based on the type
of epithelium covering each specific region.
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Three types of epithelium on the cervix. From Wright VC et al: Basic
and advanced colposcopy: a practical handbook for diagnosis and
treatment, ed 2, Komoka, Ont, Canada, 1995, Biomedical Communications.
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The three types are:
The different types of epithelium convey varied risks for the development
of cervical neoplasia, with immature metaplasia being at greatest risk
for such changes.
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Click on the image to enlarge. Original squamous epithelium of reproductive
period. From Burghardt E et al: Text and atlas: colposcopy—cervical
pathology, New York, 1991, Thieme.
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Click on the image to enlarge. Lugol’s staining of squamous
epithelium, with positive Schiller test in the 11 0’clock position.
From Burghardt E et al: Text and atlas: colposcopy—cervical
pathology, New York, 1991, Thieme.
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Ectocervix
The squamous epithelium extends from the embryologic junction of the vagina
and vulva to the location of the SCJ on the cervix at birth. It appears
flat, pink, uniform, and featureless. It is not modified by acetic acid
and remains pink, but because it does contain glycogen, it stains mahogany-brown
with Lugol’s iodine. Vascular atterns are visually inconspicuous. Histologically
it is well-differentiated, stratified squamous epithelium.
Endocervix
The columnar epithelium extends proximally from the SCJ to the endocervical
canal and internal os. It is made up of a single layer of tall, mucus-secreting
cells with a pebbled or villous appearance. In the natural state it seems
dark red because of the underlying stromal vessels. It blushes white and
looks grapelike in structure with acetic acid application but remains
unaltered by Lugol’s iodine.
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Click to enlarge. Ectopy before acetic acid application. From
Burghardt E et al: Text and atlas: colposcopy—cervical
pathology, New York, 1991, Thieme.
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Click to enlarge. Columnar epithelium unaltered by iodine application.
From Burghardt E et al: Text and atlas: colposcopy—cervical
pathology, New York, 1991, Thieme.
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Click to enlarge. Ectopy with grapelike appearance following
acetic acid application. From Burghardt E et al: Text and atlas:
colposcopy—cervical pathology, New York, 1991, Thieme.
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Squamocolumnar Junction
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Click to enlarge. The normal squamocolumnar junction. From Giuntoli
RL et al: Textbook and atlas: Atkinson's correlative atlas of
colposcopy, cytology, and histopathology, Philadelphia, 1987,
Lippincott-Raven.
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Click to enlarge. Steplike border between ectopy and squamous
epithelium. From Burghardt E et al: Text and atlas: colposcopy—cervical
pathology, New York, 1991, Thieme.
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The SCJ of the cervix is the line along which the stratified squamous
epithelium meets the mucus-secreting columnar epithelium of the endocervix.
Morphogenetically there are two SCJs.
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Click to enlarge. Diagram of the anatomic squamocolumnar junction.
From Burke L et al: Text and atlas: colposcopy, Norwalk,
Conn, 1991, Appleton & Lange.
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The original SCJ, or site of the SCJ at birth, is where the squamous
covering of the portio vaginalis joins the columnar epithelium. The union
or border between these two epithelia is sharp and distinct. The SCJ noted
at the time of colposcopy is called the new or functional
SCJ (or simply SCJ). The functional SCJ is established between
the newly formed squamous epithelium of the TZ and the endocervical columnar
cells. This transition may be gradual and less abrupt. The new
SCJ is more proximally positioned, i.e., closer to the external cervical
os. The SCJ is easily identified as a transient white line after acetic
acid application. It is positioned between the distal smooth, pink epithelium,
and the proximal red papillary epithelium.
Transformation zone
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Diagram showing the location of the transformation zone and the
physiologic squamocolumnar junction. From Burke L et al: Text
and atlas: colposcopy, Norwalk, Conn, 1991, Appleton & Lange.
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Click to enlarge. Active transformation in periphery and separate
area on anterior lip. From Burghardt E et al: Text and atlas:
colposcopy—cervical pathology, New York, 1991, Thieme.
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The TZ represents the area of epithelium between the original
SCJ and the new SCJ. The precise identification of the TZ is of
utmost importance because virtually all cervical squamous neoplasia begins
in this area and because the extension and the limits of cervical neoplasia
coincide with the distribution of the TZ. The TZ is composed of immature
metaplasia adjacent to the new SCJ and mature metaplasia between the former
and the original SCJ. These two epithelial types and potential pathologic
alterations are further described in the section on pathophysiology.
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Click to enlarge. Eight months later: the focus on the anterior
lip has enlarged. From Burghardt E et al: Text and atlas: colposcopy—cervical
pathology, New York, 1991, Thieme.
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Click to enlarge. Another 8 months later: the periphery and
area on the anterior lip have established a connection. From Burghardt
E et al: Text and atlas: colposcopy—cervical pathology,
New York, 1991, Thieme.
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Normal and abnormal anatomic variants are further discussed in the section
on the New Colposcopic Terminology.
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