Symmetric undivided diplopagus with cardiac malformation in a Japanese wild boar (Sus scrofa leucomystax)

A captured Japanese wild boar (Sus scrofa leucomystax) fetus was dicephalic.The fetus had two heads, but one body from the cranial neck region.Computed tomography imaging revealed that the two crania merged at the occipital bone, and the vertebral bodies between the atlas and the seventh thoracic vertebra were deformed.The fetus was found to have two tongues and laryngopharynges, but its esophagus and trachea were not duplicated.Each head contained a cerebrum and cerebellum, but the brains merged at the obex of the medulla oblongata, and the cervical spinal cord had duplicated ventral clefts.The heart was composed of three atria and four ventricles.This is the first report of a dicephalus with cardiac malformation in a wild boar. KEY WORDS: dicephalus, diplopagus, wild boarDiplopagus (conjoined twins) is a congenital anomaly that arises in monozygotic twins at an early developmental stage [9].Several types of diplopagus have been reported, which are classified according to whether they are separated or attached, and symmetric or asymmetric, and according to their site of attachment [2,3].Dicephalus is an attached and symmetric-type malformation involving duplication of the head [2].In this report, we describe a dicephalic fetus in a captured Japanese wild boar (Sus scrofa leucomystax).A malformed fetus was found in the uterus of a wild boar captured in Tottori Prefecture, Japan, on 9 May, 2018.The wild boar was captured using a binding trap as part of a program for the extirpation of injurious animals in Tottori Prefecture.The dead malformed fetus was taken to the Veterinary Medical Center of Tottori University.The fetus was a symmetric undivided diplopagus with two heads (Fig. 1).It was 18.3 cm long, weighed 346.9 g, and was estimated to be at 50-51 days of gestation (Tsuji et al., Joint Meeting of the Primate Society and the Mammal Society of Japan, Okayama, Japan, Sep 2013, poster presentation, P-170).No littermates were identified.Macroscopically, the fetus had two heads that joined in the cervical region.Each head had one snout, one nasus, a pair of eyes, and a pair of ears.The fetus was subjected to computed tomography (CT) imaging, then immersed in 10% neutral-buffered formalin.Subsequently, it was dissected and the major organs, including the brains and the spinal cord, were fixed in 10% neutral buffered-formalin.The organs were embedded in paraffin and cut into 3-4 µm thick sections, which were stained with hematoxylin and eosin (HE).The CT images showed that each head had separate maxillae and mandibles, but shared a spinal column and axial skeleton.The two skulls were fused at the level of the occipital bone and shared a foramen magnum (Fig. 2).In the cervical spinal column, there were no spinous processes, and the fourth and fifth thoracic spinous processes were fused (Fig. 2).In addition, the spinous processes after the tenth thoracic spine were missing.The vertebral bodies from the atlas to the seventh thoracic vertebra were composed of two nodular tori, but the right side of the fourth thoracic vertebral body was not apparent (Fig. 3).The oral cavity of each head contained a cleft palate, a tongue, and a laryngopharynx, but there was no duplication of the esophagus and trachea.The mucosal surface of the ventral midline of the trachea was slightly raised.Dissection of the skull bones revealed duplication of the encephalon.Each head contained an olfactory bulb, a pituitary gland, a cerebrum, a cerebellum, a mesencephalon, and a pons.The brains merged at the level of the obex of the medulla oblongata.Although the appearance of the spinal cord was unremarkable, the couple of cleft-like structures were observed in the ventral part of the cervical spinal cord on the cross-section.