Anatomical observation of six calves affected with segmental aplasia of the spinal cord.

Four male and two female Holstein-Friesian calves with segmental aplasia of the spinal cord were examined macroscopically and radiographically, and in some cases also histologically. External symptoms included inability to stand, deep depression of the body near the middle of the back but without any blemish in the skin, and slight reduction of the body length. Both hind limbs were almost normal. In every case segmental aplasia of the spinal cord was observed between the caudal thoracic and the cranial lumbar region. Owing to this defect, the vertebrae of that limited area consisted only of the body and the ribs fused on both sides. The sternum showed abnormal ossification at its caudal part. Other defects were observed such as kyphoscoliosis (six cases), polycystic kidney (one case), cryptorchidism (one case), and XX/XY chimerism (one case). From these findings it was apparent that this anomaly was uniquely different from the other two main spinal cord anomalies, spina bifida and perosomus elumbis. One conceivable pathogenesis of this rare anomaly, it was conjectured, is as follows: This anomaly results primarily from a segmental disorder of the neural tube, probably due to vascular problems, whereby a part of the spinal cord fails to develop properly from its normal genesis. Anomalous shapes of the vertebral column and ribs are perhaps secondary defects caused by aplasia of the spinal cord.