Equine Endometrial Biopsy
Management of the infertile broodmare requires
the performance of a breeding soundness examination (BSE).
The BSE consists of transrectal palpation and ultrasonography,
evaluation of vulvar conformation, vaginoscopy and digital
vaginal examination, endometrial culture and cytology and
endometrial biopsy. The three uterine techniques are interpreted
in light of each other and should be performed at the same
time to provide an accurate diagnosis.
Indications for breeding soundness examination
include: repeat breeders, barren mares, prepurchase examinations,
habitual aborters, vaginal discharge, urine poolers, cervical
lacerations, rectovaginal tears and fistulas (prior to surgical
repair), suspected luteal insufficiency, irregular cycles,
physiological anestrous, chronic uterine infection, pyometra,
hydometra, mucometra, multiple endometrial cysts, palpable
uterine abnormalities (neoplasia), and mares over 12 years
of age who have not had a foal within the last year.
Breeding soundness examinations can be performed
during any stage of the estrous cycle, however, it is easiest
during estrus when the cervix is relaxed and immune function
is highest. In this way, should any contamination of the uterus
occur due to a break in technique, the mare is more able to
clear the infection. After the mare's perineum has been prepped
(tail wrapped and tied to the side), the operator uses sterile
technique to obtain the biopsy specimen (performed following
culture and cytology). An alligator type biopsy rod is used
to obtain the specimen which should be at least 5 x 12 mm
in diameter. If inadequate tissue is obtained, a second biopsy
is taken. A single biopsy is representative of the entire
endometrium if no palpable abnormalities are noted. A repeat
biopsy is often taken following uterine therapy to evaluate
the response to treatment. The specimens are placed in 10%
formalin or Bouin's fixative before processing. Samples placed
in Bouin's fixative should be transferred to 70% ethanol or
10% formalin after 3-4 hours of fixation to prevent hardening
of the tissue, which results in poor staining. The biopsy
specimen is processed routinely and stained with hematoxylin
and eosin.
Kenney established a grading system for endometrial
biopsies in 1978. The system was revised in 1986 by both Kenney
and Doig. This system takes into consideration inflammation
and fibrosis of the endometrium and then provides an estimation
of the mare's ability to conceive and maintain a pregnancy
until term. The uterus is graded in the following manner:
Grade I: normal endometrium or mild, focal
inflammation or fibrosis = > 80% chance of conceiving and
maintaining until term.
Grade IIA: mild - moderate inflammation and/or
multifocal fibrosis with 1-3 layers of fibroblasts surrounding
glands or < 2 fibrotic nests per 5 mm linear field = 50-80%
chance of conceiving and maintaining until term.
Grade IIB: moderate inflammation and/or multifocal
- diffuse fibrosis with 4 or more layers of fibroblasts surrounding
glands or 2-4 fibrotic nests per 5 mm linear field = 10-50%
of conceiving and maintaining until term.
Grade III: severe inflammation and/or diffuse
fibrosis with 5 or more fibrotic nests per 5 mm linear field
= < 10% chance of conceiving and maintaining until term.
The biopsy is evaluated for the nature and
severity of the inflammation. Neutrophils are seen during
the acute inflammatory stages of infection; being replaced
by lymphocytes, plasma cells and macrophages as the process
becomes more chronic. Eosinophils are seen associated with
fungal infections, pneumovagina and urine pooling. Stromal
cells produce collagen in response to chronic inflammation
or as a result of normal aging processes. Fibrosis is seen
initially along the vasculature and endometrial glands and
then spreads to the stratum compactum and spongiosum as the
disease process progresses. As the level of fibrosis increases,
the glands form nests. Fibrosis of the basement membrane is
indicative of severe disease. Dilated lymphatics (lacunae)
are often noted with moderate to severe fibrosis when drainage
from these vessels becomes diminished.
The luminal epithelium is assessed for the
presence of a continuous layer of cells and for the height
of the epithelium. In estrus the cells are tall cuboidal to
low columnar; these cells progress to high columnar during
diestrus. The endometrial glands are straight during estrus
and highly convoluted during diestrus. During winter anestrus,
the epithelium is low cuboidal with minimal convolution of
the glands. Endometrial atrophy occurs during winter anestrus
as a normal finding. When this occurs during the physiologic
breeding season, it is indicative of severe pathology and
is most commonly seen in aged mares with diminished ovarian
activity.
The endometrial biopsy is an integral part
of the BSE. Not only does the biopsy allow assessment of pathologic
changes of the endometrium, it provides the clinician with
an accurate prognosis as to the mare's future reproductive
potential. It is important to remember however, that the biopsy
is only one part of the BSE and must be interpreted in light
of the other diagnostic findings during the infertility examination.
- by Cheryl Lopate, MS, DVM
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