Ectopic Pregnancy in an Apparently Healthy Bitch

Introduction

Ectopic pregnancy refers to the abnormal location of an embryo or fetus outside of the uterus. The condition is relatively common in humans, with an incidence of 20.7 cases reported per 1,000 pregnancies in one large hospital.¹ Ectopic pregnancies, however, are considered rare in dogs.² The most common site for the development of an ectopic pregnancy in humans is the fallopian tube, which is not recognized as a clinical entity in either dogs or other domestic animals.² To the author's knowledge, the only reported site of ectopic pregnancy in dogs is the abdominal cavity. A case of canine abdominal ectopic pregnancy is described below, following which previous reports of canine ectopic pregnancy in the veterinary literature are reviewed.

Case Report

A 5 yr old intact female Lagotto Romagnolo weighing 16 kg was referred to the author's hospital following palpation of an abdominal mass during a routine veterinary examination. On presentation to the referring veterinarian, the owner reported no signs of illness at home. An apparently normal whelping had taken place 5 mo previously, and two healthy pups had been delivered. The bitch had neither subsequently demonstrated signs of estrus nor had she been bred. There were no abnormalities on physical examination apart from a midabdominal mass measuring approximately 15 cm in diameter. Thoracic radiography was within normal limits, whereas abdominal radiography demonstrated a fetal skeleton in the ventral midabdominal region (Figure 1). A tentative diagnosis of uterine fetal mummification was made, and the owner elected to perform an ovariohysterectomy to remove the mummified fetus within the uterus.

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The patient was premedicated with intramuscular buprenorphine^a (0.01 mg/kg) and subcutaneous acepromazine^b (0.014 mg/kg) and meloxicam^c (0.16 mg/kg). General anesthesia was induced with IV propofol^d (10 mg/kg) administered slowly to effect. Anesthesia was maintained with isoflurane^e in oxygen. Following routine surgical preparation and sterile draping, a ventral midline incision was created from the umbilicus to the pubis. The uterus was exteriorized and found to be nongravid. An adhesion between the uterus and jejunum was noted on the medial surface of the caudal right uterine horn, adjacent to the bifurcation of the uterus. Incorporated within the adhesion was a small amount of dark brown tissue.

The initial surgical incision was extended cranially to the xiphoid process of the sternum to allow a complete exploratory laparotomy. Abdominal exploration revealed a midabdominal mass completely enclosed by adherent jejunum, mesentery, and omentum (Figure 2). Careful blunt and sharp dissection with Metzenbaum scissors allowed the adhesions between the mass and abdominal organs to be broken down. Blood vessels supplying the mass were not encountered, and no significant hemorrhage occurred during dissection. The mass was removed from the abdomen, and small clumps of hair were left behind on the mesenteric, omental, and intestinal surfaces. Clumps of hair were manually removed from these surfaces using thumb forceps.

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The mass contained a preserved near-term fetus compressed into a roughly spherical shape. Approximately half the surface area of the fetus was covered by a dense, fibrous membrane. Figure 3 shows a photograph of the fetus following removal of the fibrous membrane that encased it.

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The uterointestinal adhesion was broken down, and the dark brown tissue was found to be closely associated with a defect in the uterine wall on the medial surface of the caudal right uterine horn (Figure 4).

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No further abnormalities were noted in the abdomen. Ovariohysterectomy was performed, and the abdomen was lavaged with sterile saline before a routine closure. A sample was not collected for bacterial culture and sensitivity, and an abdominal drain was not placed. Recovery from anesthesia was uneventful.

Following surgery, the patient was prescribed meloxicam^c (0.1 mg/kg per os q 24 hr for 10 days) and amoxicillin^f (9.4 mg/kg per os q 12 hr for 10 days). At the time of suture removal (10 days postoperatively), the patient was in good health.

Discussion

Ectopic pregnancy, in which an embryo or fetus is abnormally located outside the uterus, is a well-known phenomenon in people, but is considered rare in animals.^1,2 In humans, the two main classifications for ectopic pregnancy are tubal (when implantation occurs within the oviduct) and abdominal (when the conceptus resides within the abdominal cavity).² Tubal ectopic pregnancy is the most common form in people; however, documented cases of tubal ectopic pregnancies have not been reported in either dogs or other domestic animals.² Abdominal ectopic pregnancies are further classified as either primary or secondary based on the location of initial implantation.³ Primary cases are those in which the conceptus escapes the reproductive tract prior to implantation and forms a placental relationship with either a peritoneal or omental surface, whereas secondary cases initially gestate within the oviduct or uterus and subsequently escape into the abdomen.²

Escape of the conceptus from the uterus leading to the development of secondary abdominal ectopic pregnancy requires rupture of the uterine wall.² This can occur in association with trauma or inappropriate obstetric manipulation, or it may be due to devitalization of the uterine wall secondary to infection, the presence of a dead fetus, or uterine torsion.⁴ It can also result from inappropriate administration of oxytocin.⁵ Except for traumatic cases, most cases of uterine rupture are expected to occur during parturition when uterine contractions result in considerable strain on the uterine wall.⁴

The majority of reported cases of abdominal ectopic pregnancies in dogs are considered likely to be secondary to uterine rupture.^6–12 The authors of two recent cases, however, theorize that the reported ectopic abdominal pregnancies were primary.^13,14 Those two authors classified the cases as primary abdominal ectopic pregnancies due to the lack of gross uterine pathology at the time of ectopic fetus removal. In both of those cases, uterine histopathology was not performed to evaluate if microscopic evidence of uterine pathology was present or not. The length of time that had elapsed since the previous whelping was unknown in one case and was 1 yr in the other, which is adequate time for the strongly regenerative myometrial tissue to heal, leaving little or no gross evidence of previous rupture.^2,8 Without evidence to support the classification of these cases as primary abdominal ectopic pregnancies, they should likely be considered secondary to uterine rupture.

The clinical signs associated with the presence of an abdominal fetus are variable.^6–14 The only consistent clinical finding is the presence of an abdominal mass. Other clinical signs that have been attributed to ectopic abdominal pregnancy in dogs are pyrexia, dyspnea, abdominal distension, inappetance, anorexia, lethargy, vomiting, and diarrhea. In the majority of reported cases, dogs appear healthy at the time of diagnosis. There is one reported case of a bitch carrying a litter of pups to term with two extrauterine fetuses from a previous pregnancy within the abdominal cavity.¹²

The number and location of extrauterine fetuses are also variable. The presence of between one and four extrauterine fetuses at the time of surgery has been reported.^6–14 Many previous case reports describe difficultly removing extrauterine fetuses due to extensive adhesions with abdominal organs. The abdominal organs that have been involved include the intestines, mesentery, broad ligament of the uterus, liver, ovary, and body wall. Despite the extensive dissection that may be required, all reported cases recovered well from surgery and showed no signs of ill health at follow-up examinations (when performed).^6–14

The case described herein was consistent with previously described cases of secondary abdominal ectopic pregnancy. This case was classified as secondary rather than primary because the uterus demonstrated gross pathologic changes consistent with previous rupture and because the ectopic fetus lacked a placental relationship with any abdominal organs.³ Because the fetus grossly appeared close to term and there was no history of trauma during gestation, it is likely that rupture of the fetus through the uterine wall into the abdominal cavity occurred at parturition. Undiagnosed dystocia may have preceded the uterine rupture, and the lack of either periparturient or postparturient signs of illness is consistent with previously reported cases of abdominal ectopic pregnancy.^6,13

During surgery, no gross evidence of a bacterial infection was noted, and a sample was not collected for bacterial culture and sensitivity. Lack of microbiologic investigation may have resulted in a bacterial infection being overlooked; however, the patient was prescribed empiric antibiotic therapy with amoxicillin^f. With a lack of clinical suspicion for an infectious process, an abdominal drain was not considered necessary by the primary surgeon. Because the disease process appeared adequately typified on gross examination, the excised tissue was not submitted for histopathology.

Ectopic abdominal pregnancy should be considered as a differential diagnosis for any intact female dog presenting with an abdominal mass. It should also be considered a differential diagnosis when a bitch that has recently whelped presents with nonspecific clinical signs.¹⁰ A history of trauma during pregnancy should raise the index of suspicion for ectopic abdominal pregnancy secondary to uterine rupture.¹⁰ The condition should not be ruled out when there is no history of mating, as mating may occur without the knowledge of the owners.⁸ Ectopic pregnancy may even be considered in a spayed bitch, as the abdominal ectopic pregnancy may have been overlooked at the time of spay or an embryo that had not yet implanted may have escaped into the abdomen at the time of surgery, leading to the development of a primary abdominal ectopic pregnancy.⁴ Definitive diagnosis is based on radiographic, ultrasonographic, and surgical findings.

Based on the limited case data available, prognosis for this condition following surgical removal of the ectopic fetus is excellent.^6–14 Considering the lack of clinical signs in a number of dogs in which an extrauterine fetus has been chronically present, it may be acceptable to manage apparently healthy cases conservatively. This should not be considered the preferred method of treatment as clinical signs associated with the presence of an extrauterine fetus may become evident after the fetus has been abnormally located after several months or years.

Conclusion

The case of canine ectopic pregnancy described herein is found to be similar to cases of canine ectopic pregnancy described previously in the veterinary literature. Of interest is the fact that an abdominal ectopic pregnancy may exist for an extended period of time without overt evidence of illness being manifested. Ectopic pregnancy should be considered as a differential diagnosis when an abdominal mass is noted in a dog, whether or not signs of systemic illness are present. Surgical removal of the fetus is the treatment of choice, following which prognosis is excellent.