Mare's Cervix Anatomy PDF

Anatomy The mare's cervix has a cylindrical shape that is formed by an inner circular smooth muscle layer rich in elastic fibers and an outer longitudinal smooth muscle layer. These muscle layers are continuous with the muscle layers of the vagina and uterus. A thickened circular muscle layer forms...

Anatomy The mare's cervix has a cylindrical shape that is formed by an inner circular smooth muscle layer rich in elastic fibers and an outer longitudinal smooth muscle layer. These muscle layers are continuous with the muscle layers of the vagina and uterus. A thickened circular muscle layer forms the body of the portio vaginalis, which is the caudal portion of the cervix that protrudes into the anterior vagina. The cervical inner circular muscle is surrounded by submucosa and a highly folded, fern-like mucosa. A simple columnar epithelium lines the lumen of the cervix and contains many mucigenous cells including goblet cells. There are longitudinal folds lining the cervical lumen that are continuous with the endometrial folds of the uterus. Each dorsal and ventral longitudinal fold may extend into the vagina as the dorsal and ventral frenulum.1 Inexperienced examiners often incorrectly identify the dorsal or ventral frenulum as an adhesion. The vaginal epithelium is stratified squamous epithelium. Etiology The epithelium is frequently exposed to trauma and must be renewed. The renewal is accomplished by cell regeneration. A basic principle of epithelial healing is that if cells are not inhibited by contact with like cells or with their normal underlying or overlying connective tissue they tend to migrate and proliferate.2 There is a tendency for traumatized cervical epithelium to adhere transluminally or to the vagina when healing. Stage II labor in the mare is rapid, and if the fetus passes through the birth canal before the cervix has fully dilated there is potential for the cervix to tear. Lacerations can be partial, affecting only the muscular layer, or full thickness, affecting all three layers. Both types result in a defect in the cervix and loss of proper cervical function. When the traumatized tissue heals spontaneously there is rarely reconnection of a damaged muscular layer. The overlying epithelium can form transluminal adhesions which can prevent the cervix from properly relaxing and allowing uterine secretions to drain normally. A lacerated edge of the portio vaginalis can also adhere to the vaginal epithelium, resulting in a cervix that cannot fully close. If there has been a prolonged dystocia and the cervical tissue experiences pressure necrosis there is a possibility that the portio vaginalis or a portion of the portio vaginalis will slough and or adhere to the anterior vaginal wall. When cervical adhesions attach to the vaginal wall the cervix may not be able to close adequately during early pregnancy, resulting in loss of the early embryo. If there is some degree of initial cervical closure the competency of the cervix may become inadequate after 3 months of gestation when the gravid uterus moves cranially out of the pelvic canal into the abdomen, resulting in the cervix being pulled cranially. If these vaginal cervical adhesions prevent adequate cervical closure the pregnant mare is at risk for developing an ascending placentitis in late gestation. Some substances infused into a uterus for therapeutic resolution of endometritis can be caustic to the cervix and vagina. Uterine infusions containing chlorhexidine, iodine, acriflavin, and tetracyclines have been associated with severe endometrial inflammation (Figure 284.1).3 If the cervical epithelium becomes necrotic and sloughs, transluminal adhesions can form and completely prevent anything from entering (semen) or leaving (uterine secretions and post-breeding debris) the uterus (Figure 284.2). Diagnosis Although severe cervical adhesions may be apparent on a visual (speculum) vaginal examination, Equine Reproduction, Second Edition. Edited by Angus O. McKinnon, Edward L. Squires, Wendy E. Vaala and Dickson D. Varner c 2011 Blackwell Publishing Ltd. P1: SFK/UKS P2: SFK Color: 1C c284 BLBK232-McKinnon February 2, 2011 15:44 Trim: 279mm X 216mm Printer Name: Yet to Come 2722 Mare: Problems of the Cervix Figure 284.1 Severe inflammation of the cervix subsequent to administration of sulfa urea uterine boluses that also contained acriflavin into a mare's uterus. thorough evaluation of the cervix must be made by a manual (digital) examination per vaginum. While many theriogenologists prefer to perform vaginal and uterine procedures on mares during estrus it may be prudent that cervical evaluations be performed during diestrus when the cervix is closed, has good shape and tone, and its competency can be determined. Mares in general tolerate this procedure well and can be restrained in hand or placed in a stock. The mare should be prepared for examination by wrapping the tail to contain the tail hairs and prevent hair from being carried into the vagina. The genital tract should be examined by palpation per rectum to ascertain that the mare is not pregnant. If the examiner can feel the endometrial folds of the uterus one can assume that the mare is not more than 2--3 weeks pregnant. It is contraindicated to perform a vaginal cervical examination in a pregnant mare as the intrusion to the genital tract may lead to an ascending placentitis. Feces should also be removed from the rectum at this time to decrease the chance of defecaFigure 284.2 Transluminal adhesion after severe cervicitis subsequent to administration of sulfa urea uterine boluses containing acriflavin. tion during the vaginal examination. The perineum should be cleansed thoroughly with povidine scrub or gentle soap and water prior to vaginal examination. After a thorough rinse with clean water the excess rinse water can be removed with a clean dry towel. The examiner should then don a sterile plastic examination sleeve and sterile surgical glove. Nonirritating water-soluble sterile lubricant should be applied to the examination hand and arm to facilitate passage through the caudal genital tract. The forefinger should be placed in the lumen of the cervix and the entire wall (muscle layer and both mucosal layers) of the cervix should be palpated between the thumb and forefinger. All 360◦ of the portio vaginalis should be present and not attached to the vaginal mucosa. The cranial cervical canal should be patent and free of adhesions. Management Complete resolution of cervical adhesions is rarely accomplished regardless of the treatment. If only a few filamentous web-like transluminal adhesions are present and the mare is not having problems with chronic endometritis and fluid accumulation, the web-like adhesions can simply be manually disrupted prior to natural cover or artificial insemination. The mare should be carefully monitored ultrasonographically for evidence of uterine fluid accumulations and treated appropriately should fluid accumulate. A uterine lavage tube that contains an inflated cuff may be positioned just cranial to the cervix to help drain uterine fluid. Traction can be placed on the lavage tube while the uterus is being lifted and massaged to help evacuate uterine contents. Oxytocin (5--10 IU) can be administered during this procedure to contract the uterus. Long-term placement of an indwelling catheter to aid uterine drainage generally is not effective in resolving uterine fluid accumulations or preventing the reformation of transluminal adhesions. These filamentous web-like adhesions will recur, but if the mare becomes pregnant these thin adhesions will not interfere with parturition. Mares may have a cervical laceration with an adhesion of the lacerated flap of portio vaginalis to the anterior vagina. If the laceration involves more than 40--50% of the length of the cervix, the cervix should probably be surgically repaired. The portio vaginalis adhesion must be carefully dissected from the vaginal wall before suturing the debrided laceration edges. One should avoid excising the anterior vaginal artery that courses along the ventral aspect of the cervix and caudal uterine body. This artery will tend to retract into the tissue and be difficult to P1: SFK/UKS P2: SFK Color: 1C c284 BLBK232-McKinnon February 2, 2011 15:44 Trim: 279mm X 216mm Printer Name: Yet to Come Cervix Adhesions 2723 ligate successfully. Local chemical or electrical cautery may be required to achieve hemostasis. One surgical cervical laceration correction technique is to place a tension suture on the caudal aspect of the cervix and attach the tension suture to the hymen or vulva to keep the cervix suspended until the laceration incision has healed.4 Alternatively after a threelayer closure of the cervical laceration one may also consider leaving a long loop of a retraction suture on each side of the incision line so that the retraction suture loop extends out of the vulva. These two retraction sutures can then be used to pull and lift the portio vaginalis off the vaginal floor two to three times a day to attempt to reduce the amount of adhesions that form post-operatively between the portio vaginalis and the anterior vagina. After several days one strand of each loop can be excised and the suture removed. One may apply a soothing ointment that contains corticosteroids between the cervix and vaginal wall to help reduce the formation of adhesions. If the cervix does not appear to be lacerated but the portio vaginalis is adhered to the vaginal floor, one may carefully dissect the portio vaginalis from the vaginal floor and place two retraction sutures in the caudal aspect of the portio vaginalis to allow twice daily manipulation to discourage adhesions from reforming. Although daily manipulation of the portio vaginalis and application of a steroid-containing ointment may prevent the immediate formation of adhesions, some degree of adhesions will regrow within several days after the manipulations are discontinued. There is no effective treatment to resolve severe transluminal adhesions that are present along the entire length of the cervix. Many of these cases have a concurrent chronic pyometra since the uterus cannot drain. If a pyometra is not present initially, one is likely to develop if the severe transluminal adhesions are disrupted as there is a great risk that bacteria will be trapped cranial to the adhesions. These mares would not be able to carry a pregnancy on their own or even produce an embryo for embryo transfer but they would be candidates for donation of oocytes for transfer into recipients. Mares with severe transluminal adhesions and a concurrent pyometra may be clinically stable for years, but some mares occasionally may exhibit colic if the uterus gets severely distended.5 Such a case may be managed by intermittent drainage and lavage of the uterus. One may even consider hysterectomy to eliminate the pyometra and colic in some cases. Once formed cervical adhesions are difficult to eliminate. One should always keep the long-term function of the cervix in mind whenever a mare's cervix is being invaded, be it for a routine examination, uterine therapy, or dystocia resolution.