1 CONTACT Amelia Andersson aia30@msstate.edu © 2025 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (http:// creativecommons.org/licenses/by-nc/4.0/), permitting all noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. Citation: Clinical Theriogenology 2025, 17, 11097, http://dx.doi.org/10.58292/CT.v17.11097 Case Report Abdominal ectopic pregnancy in a mixed-breed dog Amelia Andersson,a Kasey Forton,a Tom Campbell,b Jeremy Shapero,b Jacob Shivley,b Brittany Baughmana aDepartment of Pathobiology and Population Medicine, College of Veterinary Medicine, Mississippi State University, Starkville, MS, USA bDepartment of Clinical Sciences, College of Veterinary Medicine, Mississippi State University, Starkville, MS, USA Abstract An intact, ~ 4-6 year female, mixed-breed dog was presented to an academic spay-and-neuter clinic for a routine ovariohysterec- tomy and transitioned to an abdominal exploratory after palpation of 2 intraabdominal, firm masses during surgical preparation. Intraoperatively, the masses appeared to arise from the small intestine with intimate association to the surrounding mesentery. Due to the level of communication between the masses and the small intestine, euthanasia and postmortem examination were elected. At postmortem evaluation, 3 highly vascularized and encapsulated masses were within the small intestinal mesentery; when excised, each contained a well-developed fetus and 2 were in the early stages of mummification. The largest fetus was free within moderate serosanguinous fluid, and had a thick vascular structure wrapped around the left forelimb. Histologically, this structure was composed of 2 vessels, consistent with an umbilical vein and artery. The fetal capsule contained moderate number of multinu- cleated basophilic cells, suspicious for placental trophoblasts. The uterus and ovaries had no gross lesions. Although limited in utility due to the postmortem and ex-vivo nature of image acquisition, computed tomography displayed appropriate late-preg- nancy development of fetal skeletons and faint, mineral attenuating structures within the maxillary and mandibular alveoli consis- tent with developing dentition. Some changes consistent with fetal death were noted in the smallest fetal skeleton. The diagnosis was a full-term abdominal ectopic pregnancy. This case report describes a canine abdominal ectopic pregnancy diagnosed during postmortem examination, with additional characterization using advanced imaging and histopathology. Keywords: Dogs, ectopic pregnancy, histopathology, imaging Introduction The subject of reproduction is dynamic and although less is understood about pregnancy abnormalities in companion animals, knowledge from human medicine can be extrapo- lated and applied to veterinary cases to further our under- standing. The normal pregnancy length in dogs is ~ 61 days.1 Fertilization of 1 or more ova occurs in the uterine tube and ~ 1 week later, the resultant zygote migrates through the uterine horn, with implantation as a blastocyte occurring ~ 2 weeks after fertilization.1 Approximately day 22, the embryo is developed and the fetal phase continues from ~ day 35 to parturition.1 Failure at any point in this process can result in a failed pregnancy. One such abnormality, termed ectopic pregnancy, occurs when pregnancy develops in an abnormal location, with the type of ectopic pregnancy based on the location of fetal development. Although this phenomenon is recognized in veterinary species, it is better described in human medicine where this pathology is more often diag- nosed and studied. In animals and humans, ectopic pregnancies are of 2 types, namely, tubal or abdominal.2-4 The former is described as fer- tilization and fetal development within the uterine tube and the latter is pregnancy in the abdominal cavity.2 Abdominal ectopic pregnancies are further subdivided into a primary form, where the fertilized oocyte adheres to the mesentery or viscera in the abdominal cavity, or a secondary form, when there is rupture somewhere along the reproductive tract, such as the uterine tube or uterus, after fetal implantation, with the fetus within the abdominal cavity.3,4 Various modalities exist to help diagnose pregnancy in small animals. Diagnostic imaging is particularly useful in estimat- ing fetal development as mineralization of the fetal skeleton is apparent radiographically at or beyond 45 days of pregnancy.5 Radiographic alignment of the fetal skeleton can also be help- ful in evaluating viability, as axial or appendicular skeletal malalignment or collapse of the fetal skull bones may suggest fetal death.5 Additionally, overlap or compression of fetal mailto:aia30@msstate.edu http://creativecommons.org/licenses/by-nc/4.0/ http://creativecommons.org/licenses/by-nc/4.0/ http://dx.doi.org/10.58292/CT.v17.11097 2 Citation: Clinical Theriogenology 2025, 17, 11097, http://dx.doi.org/10.58292/CT.v17.11097 structures into smaller than normal dimensions is suggestive of mummification.5 In veterinary and human medicine, histopathology of the female reproductive tract and fetal structures in cases of ecto- pic pregnancies is another diagnostic modality contributing to the working knowledge of abnormalities during pregnancy. Albeit better reported in human literature, location of blasto- coele-lining cells called trophoblasts is a key component in categorizing the type of ectopic pregnancy, as trophoblastic growth and neovascularization are microscopic components of primary abdominal pregnancies.6 Secondary abdominal pregnancies follow rupture of the uterus.2,4 Tubal abdominal pregnancies are the most common type of ectopic pregnancy in humans, given the female anatomy;6 however, this category is considered extremely rare, if not impossible, in companion animals, as the only reported cases in veterinary literature are in nonhuman primates.2 We describe an abdominal ectopic pregnancy in a shelter dog with an emphasis on postmortem diagnostics including advanced imaging, histopathology of the female reproductive tract and fetal tissue, and immunohistochemical staining of the fetal tissue. Case presentation An intact, ~ 4-6 year female mixed-breed dog was presented to the shelter medicine service for a routine ovariohysterec- tomy. During 4 months prior to presentation, the dog was cared for by another shelter. Dog gave birth to a litter of pups 5 months before first adoption. Dog’s reproductive cyclicity or breeding history was not known. As per staff, during the 4 months prior to surgery, the dog was timid but otherwise had a normal mentation, ate and drank normally, and main- tained normal bodily functions. On arrival, spay/neuter clinic performed a cursory physical examination. Dog had a body condition score of 5/9 and weighed 22 kg. Temperature, pulse, and respiratory rates were within normal limits, and auscultation of the heart revealed normal heart sounds, rate, and rhythm. Palpation of the abdomen revealed 2, firm, mid- to cranial-abdominal masses. Due to financial limita- tions of the sheltering organization, preoperative bloodwork and imaging were not performed. The attending clinician, in conjunction with the sheltering organization, decided to proceed with ovariohysterectomy, in addition to an abdomi- nal exploratory, to continue investigation of the abdominal masses. Case management After surgical preparations, ~ 15 cm skin incision was made on ventral midline extending 5 cm cranially to the umbilicus. The subcutaneous tissues were bluntly dissected using Metzenbaum scissors that facilitated entry into the body wall using a stab incision through linea alba and extension with Mayo scissors. Palpation of the internal organs revealed the masses to be unas- sociated with the retroperitoneum and instead were intimately associated with the intestinal tract. Intestines were gently moved for better visualization of the masses. In so doing, a third mass was identified and additionally, large portions of the jejunum and ileum were firmly adhered to the 3 masses. Based on the extent and severity of the adhesions, and particularly the degree of mesenteric vasculature adhesion, resection and anastomosis would be the most effective means to remove the masses, but at great cost to the length of the small intestinal tract. Uterus appeared grossly intact upon cursory evaluation. Outcome Surgical observations were relayed to the shelter coordina- tor and euthanasia was elected. Dog was euthanized intra- operatively using intravenous Euthasol with subsequent closure of the body wall and submitted for postmortem evaluation. Postmortem findings The body condition score was 4/9 (with 5/9 being ideal) and there was mild autolysis. A ventral midline incision (appro- priately opposed) was noted consistent with the aforemen- tioned abdominal surgery with no gross changes. A scant amount of yellow-tinged, clear mucoid material oozed from the vulva. Within the thoracic cavity, the lungs were mottled pink to pur- ple to dark red and were wet and heavy on palpation. On cut surface the lungs oozed a scant to moderate amount of serous fluid. A scant amount of white, stable foam was present at the tracheal bifurcation. Within the lumen of the right atrium and ventricle were ~ 10-15 long, slender, white adult nematodes morphologically consistent with Dirofilaria immitis. Abdominal cavity contained ~ 75-100 ml of serosanguine- ous fluid. Liver was moderately enlarged with rounded mar- gins and had an accentuated reticular pattern in addition to multifocal fluid-filled cysts ranging from 1-4 mm in diame- ter. Stomach contained a scant amount of yellow to white mucoid ingesta and there was a locally extensive area of reddened glandular mucosa. Within the mesentery, there were 3 large masses (Figure 1). The first, and largest mass (Figure 2) was red to brown, round, smoothly marginated, soft on palpation and measured ~ 12 x 10 x 8 cm. The sec- ond mass was red to brown, multilobulated, hard and mea- sured ~ 11 x 6 x 5 cm. The third, and smallest mass was grossly similar to the medium-sized mass and measured ~ 10 x 7 x 5 cm. The largest mass had a thick, tan, fibrous cap- sule containing ~ 40-50 ml serosanguineous fluid and a fully developed, haired fetus with grossly normal external features. The fetus was not adhered to the inner capsular wall but appeared to have an umbilicus with an enlarged and congested umbilical artery and vein tightly wrapping around the left forelimb. Unfortunately, due to how friable the cord was, upon fetal manipulation, the umbilicus sepa- rated from the capsular wall. The second and third masses contained smaller fetuses intimately adhering to the capsu- lar wall and were shrunken and appeared in the early mum- mification stages. No fetal capsules had any appreciable gross vasculature connecting the capsule to the mesentery; however, multiple jejunal arches were dilated and con- gested. On cut surface, the uterine lumen was empty. The uterine mucosa was mildly reddened and on palpation a slight depression between the left uterine horn and the uterine body was appreciable although no gross defects were present. The right uterine horn, ovaries, and uterine tubes were grossly normal. No connection between the reproductive tract and the fetal capsules were identified; remainder necropsy findings were within normal limits. Tissue from the uterine body was submitted for bacterial culture. http://dx.doi.org/10.58292/CT.v17.11097 Citation: Clinical Theriogenology 2025, 17, 11097, http://dx.doi.org/10.58292/CT.v17.11097 3 Bacteriology Histopathology Tissues collected during postmortem examination were fixed in 10% neutral buffered formalin for 24 hours, then sectioned and prepared for histologic evaluation following standard procedures utilizing hematoxylin and eosin stain. On histopathologic evaluation of the largest fetus, the cap- sule was composed of thick, mature dense fibrous connective tissue containing many haphazardly arranged, small-caliber vessels. The capsule was lined by simple squamous epithelial cells containing multifocal loose collagen attachments with Figure 1. Thoracic and abdominal contents (A), note 3 irregularly shaped multilobulated masses (arrows); gastrointestinal tract (B); and jejunal mesentery containing 3 fetal masses (C). A B C Specimen type Culture type Results Uterine stump Aerobic Mild growth of Klebsiella pneumoniae ssp. pneumoniae and Streptococcus bovis Anaerobic Mild growth of Clostridium perfringens http://dx.doi.org/10.58292/CT.v17.11097 4 Citation: Clinical Theriogenology 2025, 17, 11097, http://dx.doi.org/10.58292/CT.v17.11097 scattered lymphocytes, plasma cells, and hemosiderophages, and had scattered hemorrhage. The thin membrane covering the fetus was multifocally hypercellular (Figure 3A). The luminal surface contained moderate numbers of variably sized, deeply basophilic multinucleated cells occasionally having intracytoplasmic tan material (Figure 3B). These mul- tinucleated cells lined the luminal surface of multiple vessels and were suspected to be placental trophoblasts (Figure 3C). Evaluation of the vascular structure wrapped around the fetal forelimb (Figure 2B) was histologically hindered by severe autolysis but appeared to be composed of 2 tortuous lumi- nal structures. One vascular structure had a thick smooth muscle wall and the other was lined by endothelium, and thus these structures were interpreted to be the umbilical artery and vein, respectively. In multiple longitudinal and cross sections of the uterine body, the endometrial intersti- tium was expanded by moderate fibrous connective tissue and clusters of lymphocytes, plasma cells, and hemosid- erophages. Endometrial glands contained intraluminal eosinophilic material with cellular debris and chronic hem- orrhage. Occasional clusters of amorphous basophilic mate- rial were also present at the luminal surface. No gross lesions were associated with the depression in the uterine body pal- pated during postmortem evaluation and there were no appreciable lesions consistent with a site of implantation or placentation. Immunohistochemical staining on tissue from the fetal cap- sule was performed to better characterize the cell origin of the multinucleated cells suspected to be trophoblasts. Majority of the multinucleated cells had intracytoplasmic immunoreac- tivity for histiocytic markers Iba-1 and CD18. Multinucleated cells were not immunoreactive for cytokeratin, an epithelial cell marker. Figure 2. Largest and most developed ectopic fetus (A) and is exposed (B); note thick vascular structure (arrow) is tightly wrapped around left forelimb; fetus after opened capsule (C); note fetus is covered by thin, friable, tan membrane (asterisk). A B C http://dx.doi.org/10.58292/CT.v17.11097 Citation: Clinical Theriogenology 2025, 17, 11097, http://dx.doi.org/10.58292/CT.v17.11097 5 Figure 3. Light microscopic images of largest ectopic fetus stained with hematoxylin and eosin: (A) thick fetal capsule and multi- focal hypercellular (caret) luminal surface with moderate numbers of variably shaped multinucleated cell (4 x); (B) multinucle- ated, deeply basophilic cells (asterisk) lining the luminal surface of the fetal capsule (40 x); (C) cross section of a vessel from the fetal membrane with intraluminal multinucleated cells (10 x); (D) locally extensive region of jejunal serosa (outlined in brackets) with numerous naked hair shafts situated within a collagenous stroma (4 x); and (E) hair shafts surrounded by low numbers of multinucleated cells (arrows [20 x]). ^ ^ ^ ^ ^ ** A B D E C http://dx.doi.org/10.58292/CT.v17.11097 6 Citation: Clinical Theriogenology 2025, 17, 11097, http://dx.doi.org/10.58292/CT.v17.11097 Within the serosa of the segment of jejunum intimately asso- ciated with the largest fetal capsule, was a small focus contain- ing multiple naked hair shafts (Figure 3D) surrounded by multinucleated cells and fibroblasts (Figure 3E). Lamina pro- pria was expanded by lymphocytes and plasma cells and con- tained dilated and congested vessels. Few crypts were expanded by scant cellular debris. One locally extensive focus contained large, prominent lymphoid follicles expanding and distorting overlying mucosa. Other notable findings in other nonreproductive organs included neutrophilic and histiocytic bronchopneumonia with numerous intravascular and intraalveolar microfilaria, in addition to severe pulmonary edema and congestion. Pulmonary vessels were severely dilated and 1 focal, severely dilated artery was bisected by smooth muscle forming 2 ves- sels containing intravascular erythrocytes and degenerate neu- trophils (neovascularization). Microfilaria were also present in multiple vessels, within the interstitium of the heart, and within multifocal renal glomeruli. The spleen had moderate lymphocytolysis and lymphoid depletion, possibly related to stress and chronic antigenic stimulation associated with heart- worm disease. Diagnostic imaging Computed tomography (CT) was performed on the gastroin- testinal tract after it was removed during postmortem evalua- tion. There were 3 fetal skeletons, each partially encircled by a thick, soft tissue to soft tissue-hyperattenuating capsule were noted amongst the small intestines (Figure 4). There was moderate amount of gas within the capsules and surrounding the fetuses (might have been entirely secondary to postmor- tem change and examination). Numerous small intestinal loops were closely associated and border effaced with the cap- sules, consistent with the adhesions noted during laparotomy. The 2 larger fetal skeletons displayed appropriate osseous development for a pregnancy of 42-45 days and all fetuses contained several, small, smoothly marginated, mineral atten- uating structures within the maxillary and mandibular alveoli, consistent with developing dentition (Figure 5). The smallest fetal skeleton had mild cranial collapse with a step defect between the developing parietal bones and dorsoventral nar- rowing of the cranial cavity (Figure 6). This fetus also had an abnormal, mixed kyphotic and lordotic conformation of its vertebral column. These changes may suggest earlier fetal death than the other, larger fetuses or secondary to mummifi- cation. Additional information regarding blood supply to the fetuses and capsules could not be obtained due to the post- mortem and ex-vivo acquisition of the images, in addition to the limitations in spatial resolution and contrast resolution in noncontract enhanced CT. Figure 4. Maximum intensity projection computed tomographic image (bone window) of the gastrointestinal tract and ectopic fetuses. The fetuses are surrounded by soft tissue to soft tissue-hyper attenuating (30-90 Hounsfield Unit) capsules and gas. Multiple loops of small intestine approximate and efface with these capsules. Figure 5. Maximum intensity projection computed tomo- graphic image (bone window) of the largest fetal skeleton. Small, smoothly marginated, mineral attenuating structures are noted within the mandibular and maxillary alveoli (yel- low arrows) consistent with developing teeth. The cranial structures and vertebral column (not entirely in plane) are normal. http://dx.doi.org/10.58292/CT.v17.11097 Citation: Clinical Theriogenology 2025, 17, 11097, http://dx.doi.org/10.58292/CT.v17.11097 7 Discussion There is limited information in veterinary literature outlining etiology and mechanism for canine ectopic pregnancies, with even fewer details characterizing prevalence, histopathology, and advanced imaging. There are no official criteria to classify ectopic pregnancies in animals; however, basic categories based on location of fetal implantation and mechanism of extrusion from the uterus have been developed for research and educa- tional purposes. Despite differences in female reproductive anatomy between humans and domestic animals, the literature from both fields of medicine subcategorize ectopic pregnancies into 4 categories: cervical, ovarian, tubal, and abdominal or peritoneal,3,7 with the former 2 predominantly reported in human literature. In humans and veterinary species, tubal ecto- pic pregnancy refers to pregnancies in which the zygote adheres more cranially to the uterine body, usually in the uterine tube, thus hindering it from descending into the uterine body or implanting in the uterine horns, respectively.3,4,7 Abdominal ectopic pregnancies are significantly more uncommon in humans compared to domestic species and occur when the zygote implants outside of the reproductive tract, most com- monly as a result of internal trauma, such as a uterine rupture, resulting in pregnancy occurring within the peritoneal cavity.7 Depending on the mechanism and location of implantation, abdominal pregnancies are further divided into primary and secondary abdominal ectopic pregnancies. When implantation occurs within the mesentery or abdomi- nal viscera by either a fertilized or unfertilized ovum (later fertilizes in the abdominal cavity), the pregnancy is catego- rized as a primary abdominal ectopic pregnancy. A true pri- mary abdominal ectopic pregnancy is further characterized with histopathology by trophoblasts and neovascularization between the fetal capsule and supporting tissue structures.6 Secondary abdominal ectopic pregnancies occur after implan- tation when there is rupture of either the uterine tube or uter- ine body and expulsion of the fetus within the mesentery of peritoneal viscera of the abdomen.3 Various outcomes may occur depending on whether the fetal placenta is retained or detached, or if the conceptus is able to maintain a viable blood supply from the tissue in which it is implanted. Failure to maintain a viable vascular network for blood flow and fetal nutrient supply can result in mummifica- tion or fetal death. Studies on ectopic pregnancies in compan- ion animals are limited, likely due to underdiagnosis. In many cases, especially in cases of adoptions, companion animals are obtained already spayed or if intact, have limited to no history regarding the animal’s reproductive history. This is especially important as a history of having had previous litters or a his- tory of trauma increases the likelihood and suspicion for ecto- pic pregnancy. In the present case, prior to adoption, the dog was on the street with no history other than the information of having 1 previous litter. Due to this we speculate this case as a secondary abdominal ectopic pregnancy; however, there was no gross or histological evidence of a uterine horn or uterine body rupture. Histopathology of the uterus had signs of chronicity, albeit minimal, based on lymphoplasmacytic inflammation, few hemosiderophages, and fibrosis throughout the endometrial interstitium. Although there was no evidence of rupture or trauma within the reproductive tract, previous trauma cannot be ruled out as the regions of fibrosis may indicate a site of past repair. Additionally, no infectious agents or neoplastic features were present histologically. Bacterial culture of the uterine stump was performed out of caution; however, given the degree of autolysis and low growth of mixed gram positive and nega- tive bacteria, these findings were considered insignificant. A limitation is the largest, most well-developed fetus was the only fetal specimen examined histologically and neither the uterine tube nor the ovaries were evaluated histologically. To authors’ knowledge there are limited current literature reports detailing histopathology of ectopic pregnancies in dogs. Dogs have a zonary and endotheliochorial type placentation and the normal histologic layers consist of the placental laby- rinth, the junctional zone, and the glandular zone.8 The junc- tional zone is where trophoblasts reside and, early in pregnancy, they invade the maternal endothelium and endo- metrial glands.8 In human medicine, a histopathologic diag- nosis of tubal ectopic pregnancy had villi, trophoblasts and embryos were within fallopian tubes.3 Abdominal ectopic Figure 6. Transverse computed tomographic image (bone window) of the skull of the smallest fetus (left) and sagittal maximum intensity projection of the same fetus’s vertebral column (right). There is a small step defect between the developing parietal bones (yellow arrow) and dorso-ventral collapse of the cranium (yellow bracket). There is moderate lordosis of the lumbar spine and kyphosis of the thoracic spine (blue arrows). These changes coupled with its smaller size may indicate earlier demise of this fetus. http://dx.doi.org/10.58292/CT.v17.11097 8 Citation: Clinical Theriogenology 2025, 17, 11097, http://dx.doi.org/10.58292/CT.v17.11097 pregnancies are difficult to diagnose as there has to be placen- tation and/or a mummified fetus with a ruptured uterine tube or uterus.2 This is especially difficult given the rapidly regener- ative nature of the myometrium and the reason why rupture sites are not usually identifiable.2 In this case, villi were not appreciable; however, within the fetal membrane there were multifocal clusters of large, multi- nucleated, deeply basophilic cells.9 Differentials for multinu- cleated cells within fetal tissue included trophoblasts, with syncytiotrophoblasts favored over cytotrophoblasts given the large number of nuclei present within individual cells, versus a multinucleated histiocytic cell. Cytotrophoblasts are mono- nucleated giant cells whereas syncytiotrophoblasts are multi- nucleated giant cells; they serve as a connection between dam and fetus, based on their location within or around maternal vessels.8,10 Immunohistochemical (IHC) staining of the multinucleated cells in this case was largely immunoreactive for Iba-1 and CD18 and negative for cytokeratin. The IHC results identified the multinucleated cells to be of histiocytic rather than epithe- lial cell (i.e. trophoblast) origin, as initially suspected. However, the timeframe and degree of fetal development fits more closely with the cells being syncytiotrophoblasts. Other immunohistochemistry stains (positive identifiers of placen- tal trophoblasts), CD31, CK7, CK8/18, and CKAE1/AE3 were not performed, thus these cells being true placental tropho- blasts cannot be ruled out.10,11 Multinucleated histiocytes likely represent an inflammatory response to free fluid, kera- tin, or squamous epithelium, as similar histologic features were described in a case study involving a pregnant woman who underwent multiple intrauterine procedures during her third trimester, resulting in leakage of amniotic fluid.11 This is less likely in the current case since the degree of inflammation in the fetal tissue was minimal and there was no evidence of fluid leakage. The histiocytic infiltration in combination with the hair shaft granuloma was most likely a response to irrita- tion from fetal hair, keratin, or amniotic fluid, thus, multinu- cleated cells can be speculated to be a secondary reaction to migration of fetal hair from the ectopic fetus.11 The former was more likely in this case as multifocal cells predominantly con- tained intracytoplasmic tan material, likely consistent with amniotic fluid, although this pigment can also be a feature of syncytiotrophoblasts.11 No apparent phagocytosis of keratin or squamous epithelial cells was appreciable in this case. Trophoblasts may have an indirect role in vascular remodeling in the dam, as a study in mice reported evidence of vascular remodeling leading to spiral artery dilation.12 Although the source did not indicate remodeling as a direct result of tropho- blast cell invasion into the uterus, the authors did not rule out an indirect association between trophoblasts and changes in the spiral arteries.12 This emphasizes the need to understand the role of vascular remodeling in association with the viability of small animal ectopic pregnancies, and the role of trophoblasts in the growth and development of an ectopic fetus. This dog had vascular remodeling of the pulmonary artery secondary to chronic heartworm disease but there was no evidence connect- ing these lesions to the ectopic pregnancy. The normal CT features of canine fetuses are poorly described in literature. This is likely because CT incurs a higher dose of ionizing radiation than radiography and is generally contrain- dicated in pregnant dogs without cause to justify the risk to the developing fetuses.5 In pregnant human patients, CT is generally avoided when other modalities can be used to make  a diagnosis and is considered inappropriate in the diagnosis of ectopic pregnancy.6 However, the dose of ionizing radiation for CT studies of the thorax and head are considered low risk to the developing fetus and guidelines for cross sectional imaging of pregnant people have been developed.2 Additionally, CT of human fetuses is used for diagnosis of certain conditions and has been documented to improve outcomes when indicated.1 Cross-sectional imaging in ectopic pregnancies have been described in humans; however, there is little published infor- mation on advanced imaging in canine ectopic pregnancy.6 A single case report of a presumed secondary abdominal ectopic pregnancy in a dog diagnosed via CT has been published.6 In this report, a heterogeneous rounded mass containing discon- tinuous, mineral attenuating structures and a discernable ver- tebral column was noted within the abdomen of an intact female Maltese dog. The mass was devoid of any connection or origin of any of the abdominal organs and was associated with the omentum and mesentery when surgically excised. Due to the more organized vertebral column, an abdominal ectopic pregnancy was diagnosed.6 In the current case, the ectopic fetuses were also closely associ- ated with the mesentery, yet were far more organized and developed with respect to their skeletal structures. Additionally, only 2 had gross signs of mummification, with the largest being free within the capsule and surrounded by fluid. Small, developing teeth were noted on CT. When fetal teeth are observed radiographically in the pregnant dog, parturition can be expected within 8 days.5 However, with CT having superior contrast resolution and eliminating superimposition of structures compared to radiography, it is difficult to extrap- olate the significance of observable, developing teeth; it may support the diagnosis of a full-term ectopic pregnancy in the current case. Additionally, a history of recent pregnancy with or without known trauma during pregnancy, may heighten the index of suspicion for ectopic pregnancy, especially when the mating history is unknown.4 In many human cases, patients diagnosed with abdominal ectopic pregnancies have a good prognosis as long as the mass  or masses do not cause secondary complications such as torsion, altered peristalsis, or inflammation secondary to necrosis from fetal infection or fetal vascular occlusion.3 Complications are often accompanied by clinical signs such as  anorexia, abdominal distention, diarrhea, or vomiting, although clinical presentations can vary depending on where the zygote implants and how much viscera is secondarily affected. As a result, surgical removal of the ectopic fetus(es) is considered the treatment of choice. In this case, euthanasia was elected based on financial limita- tion and the extensive need for resection and anastomosis (might have resulted in prolonged time under anesthesia and postsurgical complications). Coinfection with Dirofilaria immitis in this dog might also have contributed to the decision to euthanize as higher worm burdens are cost- and time-inten- sive to treat and often associated with an overall compromised health status. Although clinical signs associated with heart- worm infection were not reported in this dog, the number of microfilaria present histologically in the lung, heart, and kid- neys would likely have resulted in further anesthetic and life- long complications, such as cardiopulmonary or vascular compromise, if left untreated. http://dx.doi.org/10.58292/CT.v17.11097 Citation: Clinical Theriogenology 2025, 17, 11097, http://dx.doi.org/10.58292/CT.v17.11097 9 This case report characterized diagnostic findings associated with an ectopic pregnancy in a dog through the examination of advanced imaging, postmortem and histopathological evalua- tion with the goal to further understand this phenomenon and better develop management techniques when diagnosed. Taking into account the history and signalment, an abdominal ectopic pregnancy is a valid, albeit rare, differential diagnosis to consider in any intact female dog presenting with an abdominal mass. Learning points • Histologic criteria for primary abdominal ectopic pregnan- cies include trophoblasts and neovascularization  • Secondary abdominal ectopic pregnancies follow injury or trauma to the reproductive tract • Diagnostic imaging is an incredibly useful modality to diag- nose ectopic pregnancies • Ectopic pregnancy is a valid differential for a veterinary patient presenting with abdominal masses and an unknown reproductive history Acknowledgement Authors thank the radiology, necropsy, histology, and micro- biology laboratory technicians and support staff at Mississippi State University College of Veterinary Medicine for their contributions. Conflict of interest Authors have no conflict of interest to declare. References 1. Pretzer SD: Canine embryonic and fetal development: a review. Theriogenology 2008;70:300-303. doi: 10.1016/j.theriogenology. 2008.04.029 2. Corpa, JM: Ectopic pregnancy in animals and humans. Reproduction 2006;131:631-640. doi: 10.1530/rep.1.00606 3. 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