Page 982 - Small Animal Internal Medicine, 6th Edition

954 PART VIII Reproductive System Disorders

extended) is a better alternative. Serial vaginal cytologies or estrus. Rare reports of vaginal vascular ectasia causing
documenting the influence of estrogen on vaginal mucosa hemorrhage exist. Excessive exogenous administration of
VetBooks.ir early in the cycle, and progesterone assays performed 1 to 2 estrogen may be encountered when an ovariohysterecto-
mized bitch is treated for urethral sphincter incompetence
weeks later documenting folliculogenesis without ovulation
or luteinization (i.e., serum progesterone [<1.0 ng/mL]),
unwanted pregnancy using diethystilbesterol or estradiol
confirm the diagnosis of a split heat. Occasionally split cycles with estrogenic compounds or from attempts to prevent
occur on a regular basis in a mature bitch. This not only cypionate in the intact bitch. Small dogs can acquire estrogen
makes them difficult to breed but is likely associated with exposure iatrogenically from owners using transdermal or
abnormalities of the hypothalamic-pituitary-ovarian axis. aerosolized topical hormone replacement therapy. Recog-
nized sequelae to chronic estrogen exposure include bone
marrow dyscrasias, predisposition to the cystic endometrial
ABNORMALITIES OF THE CANINE gland hyperplasia/pyometra complex, and development of
ESTROUS CYCLE ovarian cysts. After confirmation of endogenous hyperestro-
genism is obtained through history and vaginal cytologies
Abnormal estrous cycles result in either a prolongation or an (which can be confirmed with serum estrogen measure-
abbreviation of a phase of the cycle, or an alteration in the ment), abdominal ultrasonography is recommended to eval-
normal sequence of events. An owner’s interpretation of a uate ovarian pathology (Fig. 55.1). Normal preovulatory
bitch’s behavior and physical characteristics may not equate follicles measure 4 to 9 mm in diameter, smaller than follicu-
with the actual physiologic events, necessitating prospective lar cysts and most functional ovarian neoplasias. Analysis of
documentation of the cycle through vaginal cytologic evalu- the estrogen and progesterone levels in fluid from abnormal
ation, vaginoscopy, behavioral evaluation, and serum LH cystic ovarian structures obtained via ultrasound guidance
and progesterone levels as described (see Chapter 54). can be contributory to the diagnosis but is not necessary if
serum levels have been obtained. Histologic analysis of
PROLONGED PROESTRUS/ESTRUS tissues obtained surgically confirms the diagnosis and is
Prolonged proestrus or estrus occurs when a bitch displays always indicated.
vulvar bleeding for more than 30 to 35 consecutive days, Because follicular cysts may spontaneously undergo
accompanied by attractiveness to males. Greater than 80% atresia or luteinization, not all bitches experiencing pro-
to 90% superficial cells are present on vaginal cytology. Such longed proestrus or estrus require treatment. Progression of
bitches are variably receptive to breeding. Prolonged proes- the follicular cyst to an atretic follicle or a corpora lutea can
trus and/or estrus results from a persistent production of be monitored ultrasonographically, via vaginal cytologic
estrogens, with or without small elevations in progesterone. analysis, and by serum estrogen and progesterone measure-
If present, progesterone enhances the presence of sexual ments. Therapy aimed at terminating prolonged proestrus or
receptivity. Endogenous sources of prolonged estrogen expo- estrus becomes necessary if spontaneous regression fails to
sure in the bitch, with or without progesterone, include occur, vaginal bleeding is a continuing nuisance, estrus
ovarian follicular cysts and secretory neoplasias. Secretory behavior and the attraction of males is unacceptable, or other
anovulatory follicular ovarian cysts tend to be solitary, lined complications develop (blood loss anemia, marrow dyscra-
with granulosa cells, and exceed normal preovulatory folli- sias, vaginal hyperplasia). Medical and surgical options exist
cles in size when measured ultrasonographically, ranging for treatment of persistent pathologic follicular cysts. Medical
from 1 to 5 cm in diameter. Bilateral follicular cysts may
indicate a problem with the hypothalamic-pituitary-ovarian
axis. Follicular cysts tend to occur in bitches younger than 3
years of age. Ovarian neoplasias capable of producing estro- 0
gen occur and include tumors of epithelial origin (cystade- L HORN
nomas and adenocarcinomas) as well as tumors of 1
gonadal-stromal origin (granulosa-theca cell tumors).
Ovarian neoplasia tends to occur in bitches older than 5 2
years of age. Ovarian tumors can occur unilaterally or, less L K
commonly, bilaterally. Functional cystic ovarian pathology 3
and ovarian neoplasia and can occur simultaneously. Cysts L OVARY
found in the contralateral ovary and endometrial hyperpla- 4
sia accompanying a functional tumor occur most frequently
with gonadal-stromal origin tumors. 5
Other than hyperestrogenism, there are few differential
diagnoses for prolonged vulvar bleeding in the bitch. Vulvar
bleeding secondary to infection, inflammation, or neoplasia FIG 55.1
of the genitourinary tract, a vaginal foreign body, or a coagu- Follicular ovarian cyst (L ovary). LK, Left kidney, L Horn, left
lopathy should be differentiated from prolonged proestrus uterine horn.