Page 982 - Small Animal Internal Medicine, 6th Edition
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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.
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