Spina bifida

• Cutaneous defect at the level of the sacrococcygeal junction with underlying midline defect in the dorsal lamina of the sacral vertebrae

• Large fluid filled sac herniating through this defect that communicates with the subarachnoid space

• Spinal cord extends caudally and passes through the previously described laminar defect, individual nerve roots of the cauda equine are not visualized

• Syringohydromyelia in the spinal cord just cranial to the defect

• Markedly distended urinary bladder

Spina bifida at the sacrococcygeal junction with meningomyelocele.

• Marked caudal transtentorial herniation with bilaterally symmetric caudal extension of the occipital lobes and lateral ventricles

• Moderate to marked herniation of the cerebellum through the foramen magnum with secondary ventral deviation of the brainstem at this level

• Thinned and flattened occipital bone with a poorly defined osseous tentorium

Chiari malformation with transtentorial and foramen magnum herniation.

The myelomeningocele was open and visible as a wound on the dorsal surface of the tail area. On dissection, the defect was elongated and extended to the spinal canal. The cauda equina was absent and the spinal cord appeared tethered. The spinal processes of the caudal vertebrae and sacral vertebrae 3 and 4 were absent.

The brain was deformed and caudally elongated secondary to the herniation through the foramen magnum. The tentorium cerebelli was absent, causing the severe subtentorial herniaton. Chiari type II malformation has been associated with spina bifida.