Arnold-Chiari malformation and associated anomalies in a dicephalic newborn calf.

A full-term female newborn calf of the Japanese black short-horn breed which was two-headed (dicephalus) and had two incomplete necks was carefully dissected. The calf was one of twins, the other being a normal male. There was no record of reproductive problems with the cow. The left and right heads were of almost the same size and shape. Each head had a nose, mouth, eyeballs, and ears. The brains were very congested. That is to say, in both the left and right brains, the longitudinal fissure was unclear, and these was narrower pattern in the cerebral gyri. The surfaces of the two brains displayed poly- or microgyria-like features. The cerebellar gyri ran longitudinally among the occipital lobes of the cerebral hemispheres. The caudal half of the cerebrum, the cerebellum and the brain stem were distorted ventrally at an angle of approximately 80 degrees. Twisting of the brain stem was observed in the right brain. The end of the medulla oblongata and a tongue-like process of the cerebellum extended through the foramen magnum of the skull into each enlarged vertebral canal (Arnold-Chiari malformation). They extended under the arch of the each 2nd cervical vertebra. The 4th ventricle was also displaced and irregularly dilated. The two necks were conjoined in the single 3rd cervical vertebra at an angle of approximately 45 degrees to each other. The one trunk was slightly distorted. The ribs revealed the presence of a left 14th extra tib. In the lumbar region, spina bifida was apparent. The pelvis was distorted asymmetrically. The tail was short. The viscera appeared as one set, but the rectum and anus were duplicated. Although the calf displayed female features, the vagina was undeveloped. The four limbs appeared normal and the joints moved freely.