This is a case demonstrating Arnold Chiari malformation, type II. The 2-D images reveal:

1. Lemon sign with frontal scalloping.

2. Gross hydrocephalus and a small posterior fossa.

3. Herniating posterior fossa contents into upper cervical canal.

4. A large open neural tube defect seen as diverging neural arches in the lumbar region. This is well documented in 2D and 3D imaging.