VAGINA—CYTOLOGY
The superficial cells of the vaginal epithelium are under the influence of ovarian hormones, changing in character over the course of a woman’s lifetime and the phases of the reproductive cycle. These variations are largely dependent upon the amount of circulating estrogen.
In the newborn, the vaginal epithelium is lush as a result of the
transfer of maternal estrogen transmitted across the placenta. The precornified
and cornified cells shed from this epithelium are scattered but occasionally
form loose clusters. A few polymorphonuclear leukocytes but few, if any,
lactobacilli (Döderlein bacilli) are present. After delivery, circulating
estrogen levels fall rapidly and the vaginal epithelium quickly transitions to
that of childhood.
In childhood, when the circulating estrogen is at a low level, the
vaginal epithelium is thin, fragile, and at risk for infection. The cytologic
smear is composed chiefly of basal cells, with a background of mucus and
polymorphonuclear leukocytes. The basal cells are round or oval, with vesicular
nuclei and a large nuclear– cytoplasmic ratio. The cytoplasm is, with only a
few exceptions, basophilic. This smear is typical of an atrophic condition and
similar to that seen after menopause.
During the reproductive years, the vaginal epithelium thickens and
undergoes cyclic change in response to the varying hormone levels of the
menstrual cycle. In the past, these changes from more immature, basaloid cells
early in the cycle to a predominance of mature precornified cells late in the
cycle were used to help assess hormone levels and to provide indirect evidence
of ovulation. Lactobacilli help to maintain an acidic environment, stabilizing
the vaginal flora and promoting cornification. A few white blood cells are
normally present.
In pregnancy, as a result of the high levels of both estrogen and
progesterone, the epithelium becomes a thick layer of superficial cells with
marked keratinization. Desquamation of superficial precornified cells is
associated with marked clumping and folding of the cells, which have elongated
or oval vesicular nuclei. A few cornified cells with pyknotic nuclei,
polymorpho- nuclear leukocytes, lactobacilli, and free nuclei are present in
varying numbers. Near the 12th week of pregnancy, a change in the vaginal smear
occurs; fewer cells are shed, clumping and folding have lessened, pre- cornified
cells predominate, and the overall appearance is similar to that of a normal
early proliferative phase. As pregnancy advances, the increased progesterone
produces progressively smaller precornified cells, which are referred to as
“navicular cells.”
In the puerperium, following the sudden drop of steroid hormones prior to
recurrence of normal menstrual cycles, the vaginal epithelium is thin. The
puerperal vaginal smear is characterized by the presence of a large number of
basal cells, a few precornified and cornified cells, and some inflammatory debris
in the background, but not to the
same extent as in smears from atrophic epithelium. With the return of normal
ovarian cycling, the epithelium will again rebound to its normal prepregnancy
thickness and character.
In the postmenopausal years, the vaginal epithelium is very thin, smooth,
and relatively pale as a result of the cessation of ovarian function and the
significant decrease in estrogen levels. The absence of this protection leads to
bacterial invasion and a resulting inflammatory
reaction in the supporting layers, with a thin layer of edema beneath the
basement membrane. The atrophic smear is characterized by almost 100% basal
cells dispersed in a thick background of mucus. Numerous polymorphonuclear
leukocytes and some lymphocytes are present, but when these occur in excessive
numbers, they usually indicate the presence of clinical infection. Most of the
cells are basophilic, but a few pink acidophils are
found.
