Microscopic examination of multiple sections of the uterus revealed multifocally extensive areas of partial- to full-thickness
(transmural, perforating) ulceration of the uterine wall (Figure 2). Ulcerated areas were characterized by defects of the endometrium, myometrium, or epimetrium and were lined by a thick rim
of uterine tissue that displayed lytic (liquefactive) necrosis admixed with moderate numbers of neutrophils and multifocal
colonies of cocci and bacilli. Neighboring veins within the myometrium were dilated with acute fibrin thrombi. The mesothelium
of the epimetrium was prominent and exhibited mesothelial cell hyperplasia and a few neutrophils in the subserosa (indicative
of acute peritonitis).
2. A histologic section of the dog's uterine wall. Note the full-thickness ulceration of the wall, which is lined by a rim
of necrosuppurative material containing mixed bacterial colonies (dots). This ulcer has perforated focally (asterisk). Fibrin thrombi are noted occluding nearby myometrial veins (arrows). Normal adjacent endometrium (e), the inner layer of the myometrium (i.m.), and the outer layer of the myometrium (o.m.) are present (hematoxylin-eosin stain).
Based on the histologic examination results, acute suppurative endometritis (pyometra) with partial to full-thickness, perforating
ulcers and secondary bacterial infection was diagnosed.
Uterine rupture can occur spontaneously during an otherwise normal parturition.1 In another case report, uterine rupture in a cat was discovered when the cat was presented for an elective ovariohysterectomy
eight weeks after parturition. During surgery an irregular mass with bone protruding from it was found encasing the right
ovary, ovarian vessels, and spleen. It was speculated that during parturition a kitten had been liberated into the peritoneal
cavity through the ruptured portion of the right uterus.2
Uterine rupture in general is more common in dogs than in cats and is more commonly seen as a complication secondary to dystocia
or exogenous oxytocin or prostaglandin administration.1 Uterine rupture in a pregnant bitch can also occur after uterine torsion,3 iatrogenic trauma,3 or pyometra4 or can develop as a result of a preexisting injury, such as a scar or perforation.5 In people, the most common cause of uterine rupture is dehiscence of a previous cesarean section scar.6 Women with a history of two previous cesarean deliveries have an almost fivefold greater risk of uterine rupture than those
with only one previous cesarean delivery.7 Complete and incomplete uterine ruptures are distinguished by whether the serous coat of the uterus is involved.5 With incomplete ruptures, the serous coat is intact, and the fetus and placenta are inside the uterine cavity.8
In this case, many possible causes may have led to the uterine ruptures. First, the dog's pyometra and bacterial infection
could have led to uterine wall friability and a complete uterine rupture with secondary peritonitis. However, pyometra commonly
occurs in older, nonbred bitches a few weeks after estrus when the cervix is completely or almost completely closed in response
to luteal hormones.3 The dog in this report did not fit this scenario since the bitch had been successfully bred three times and its cervical
canal was most likely open as the most recent parturition occurred only four days before presentation.
Second, since the bitch had whelped three litters in 12 months, it is possible that incomplete uterine ruptures had previously
occurred, leading to weakened areas within the uterine wall. As noted previously, partial- to full-thickness perforated ulcers
were noted on histologic examination of the dog's uterus. Under the stress of the third litter, incomplete ruptures could
have become complete ruptures, penetrating the uterine serosa.
Third, although the owners reported that the dog showed no signs of distress or pain during whelping, the possibility that
dystocia occurred during the last parturition cannot be ruled out.
In summary, this information could be used to help emphasize to clients the importance of veterinary examinations after whelping
and responsible breeding practices.
This case report was provided by Amy Long, DVM, Pet's Friend Animal Clinic, 158 San Lazaro Ave., Sunnyvale, CA 94086 and C.
Tyler Long, DVM, and Richard Luong, BVSc, DACVP, Department of Comparative Medicine, Stanford University, Stanford, CA 94305.
Dr. Amy Long's current address is Parktown Veterinary Clinic, 1393 South Park Victoria Drive, Milpitas, CA 95035.