Cervical Pole Necrosis of the Equine Placenta

Mare with her foal in a meadow in provence in France

Cervical pole necrosis (CPN), also known as placental necrosis or placental infarction, is a poorly understood disease of the allantochorion and an infrequent cause of non-infectious abortion in horses. The pathogenesis of this unique lesion is not definitively known, but the necrosis (dead tissue) has been theorized to occur either secondarily to placental detachment at the cervical star or by ischemic insult (lack of blood flow) related to hemodynamic abnormalities associated with long umbilical cords and vascular thrombosis. The University of Kentucky Veterinary Diagnostic Laboratory database was searched for cases of CPN to better characterize this distinctive entity.

Diagnosed CPN Cases

Fifty-seven cases of CPN were diagnosed at the UKVDL from 2013 to 2022 (figure 1). Thoroughbreds were overrepresented (52 cases), but cases were also identified in Standardbreds (two cases), a Warmblood (one case) and in unidentified breeds (two cases).Clinical histories associated with the mares ranged from no signs of impending abortion or no history (33 cases), treated for placentitis (10 cases), premature udder development (nine cases), vaginal discharge (seven cases), placental separation identified by ultrasonography (two cases), a fluid filled fetal abdomen identified by ultrasonography (one case) and hydrops amnion (one case).

Figure 1. Cases of cervical pole necrosis diagnosed by the UKVDL by year (2013- 2022).
Figure 1. Cases of cervical pole necrosis diagnosed by the UKVDL by year (2013-2022).

CPN resulted in abortion (44 cases), premature birth with subsequent neonatal death or euthanasia (seven cases), birth of a viable term foal (three cases) and premature birth of a weak viable foal (one case). Two cases, which included only the placental membranes for examination, didn’t note the foal’s outcome.

Necropsy Findings

Gross necropsy findings, in all cases, consisted of a well demarcated, paper-thin region of tan to green placental necrosis associated with the cervical pole in close proximity to the cervical star (figure 2). Necrotic regions were bordered by a red and raised border that was distinctly evident on the allantoic surface. In addition to the cervical pole lesion, rare cases also exhibited similar regions of necrosis in the gravid and non-gravid allantochorionic horns. Size was not always noted, but when recorded, the necrotic regions ranged in size from 16 to 800 cm2. Umbilical cord lengths averaged 89.4 cm (case study range 37-160 cm; normal range 32-90 cm), and placental weights averaged 6.2 kg (range 1.8-12.7 kg). Fetuses were estimated to range from 180 days of gestation to term (average= 272), averaged 82 cm (range 47-109) from crown to rump and weighed 25.6 kg (range 5.5-69.1 kg) on average.

Figure 2. Allantoic surface of the allantochorion. A locally extensive and well demarcated region of the allantochorion is tannish-green and necrotic. A red, raised line (black arrow) separates the dead region of the placenta from the pink viable tissue.
Figure 2. Allantoic surface of the allantochorion. A locally extensive and well demarcated region of the allantochorion is tannish-green and necrotic. A red, raised line (black arrow) separates the dead region of the placenta from the pink viable tissue.

Additional diagnoses with CPN included fetal septicemia without significant inflammation (seven cases), bacterial placentitis (five cases), various fetal malformations (three cases), bacterial placentitis with fetal septicemia (one case), fetal bacterial pneumonia (one case), in utero meconium passage with aspiration (one case), premature placental separation (one case), umbilical cord torsion (one case) and one combined case of leptospirosis and hydrops amnion.

Final Thoughts

Based on UKVDL data, cervical pole necrosis is an idiopathic, non-infectious, placental disease that can result in abortion, premature birth, delivery of a weak foal or delivery of a viable foal. CPN routinely results in less than 2% of submitted abortions to the UKVDL. Cases in this retrospective study indicate that CPN occurs in both male and female fetuses, most commonly in mid to late gestation and in fetuses with both normal length and long umbilical cords. Cases of CPN were occasionally associated with secondary bacterial infections, which likely developed due to bacterial invasion through the devitalized allantochorion. Future studies are needed to better understand this unique cause of equine abortion.

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