Adult Arnold-Chiari malformation and intrinsic brain stem neoplasm: a difficult differential diagnosis.

The occurrence of a brain stem neoplasm in three adults previously treated for an adult Arnold-Chiari malformation is reported. The diagnosis of adult Arnold-Chiari malformation had been confirmed by angiography and computed tomographic scanning. All patients were treated with a combination of ventricular shunts and posterior fossa decompression. The diagnosis of brain stem neoplasm was not made until late in the clinical course, and all patients died within 2 years of the onset of symptoms.