NQ-053 Answer: (D) Chiari malformation, type II

Pathology of the cases: The cardinal findings are the presence of cerebellar tissue in the cervical spinal cord along the midline (white arrow) and malformation of the brain stem (black arrow). The cerebellar tissue is most consistent with extension of the vermis into the upper cervical cord. The combination of these features is a strong indication of Chiari malformation type II. This patient also had a myelomeningocele which is another feature of Chiari II malformation.

• Chiari type I: Conical elongations of the cerebellar tonsils and neighboring parts of the cerebellar hemispheres that extend into the vertebral canal (i.e., below the foramen of magnum). The protruded cerebellar tissue could be histologically normal, infracted or sclerosed. The medulla is either unaffected or flattened by the cerebellar tongues. Chiari malformation type I is often associated with syringomyelia, hydromyelia, syringomyelia, and less commonly hydrocephalus.

• Chiari type II: Displacement of the cerebellar vermis combined with deformities of the medulla and tectal plate. This type is often associated with syringomyelia, hydromyelia, spinal bifida, meningocele, and hydrocephalus. It can also associate with other malformation of the brain, cranium and meninges, cardiovascular, gastrointestinal and genitourinary systems. Most, if not all, Chiari type II malformations are associated with a neural tube defect.

• Chiari type III: Encephalocele formed by herniation of the structures of the posterior fossa, including the cerebellum, through an occipitocervical or high cervical bony defect. There may also be beaking of the tectum, elongation and kinging of the brain stem and lumbar spina bifida.

Dandy-Walker syndrome: The three essential features of Dandy-Walker syndrome include complete or partial agenesis of the vermis, cystic dilatation of the fourth ventricle and enlargement of the posterior fossa. Malformation of the brainstem, however, is not one of the features of Dandy-Walker syndrome. The vermis is present in this case and is free of hydrocephalic changes. Hydrocephalus is a frequent but inconstant finding. Other CNS findings include elevation of the tentorium cerebelli and lateral, transverse sinuses and torcula (torcular Herophilli), and lack of patency of the foramina of Magendie and Luschka. Other cerebral and visceral anomalies are present. It is the presene or absence of other cerebral and viseral abnormalies that determines the prognosis.

Herniation of cerebellar tonsils: Space occupying lesion in the posterior can lead to herniation of the cerebellar tonsil. In those cases, the tonsils are typically congested and often appear fragile or necrotic on gross examination. In the present case, the cerebellar tissue appears healthy looking. In addition, it is malformed. In contrasted, herniated tonsils came from the side and should not have malformation.