Figure. DR. JASON ROSENBERG RESPONDS
Q A lesion was found at the base of my skull four years ago, and my last MRI revealed a blockage consistent with Arnold Chiari Malformation Type 1. Can you tell me something about this disease?
A Arnold Chiari Malformation Type 1 (CIM) is a developmental malformation of the area toward the back of the skull. When this part of the skull is undersized, the cerebellum can be pushed downward, out of the skull and into the upper neck. This may block the normal flow of cerebrospinal fluid between the neck and skull and cause such common CIM symptoms as headaches, dizziness, and visual problems. Less common symptoms include fainting spells, clumsiness, and difficulty swallowing. Typically, CIM symptoms worsen gradually over time, but they sometimes occur suddenly.
A fluid-filled cavity called a syrinx may also form in the spinal cord itself, resulting in scoliosis, progressive numbness of the arms, or spasticity (stiffnes) and weakness in the legs.
Mild CIM typically has no symptoms and is often discovered during a brain scan being done for another reason. MRI scanning can detect CIM, associated syrinx, and any resulting blockage of cerebrospinal fluid.
A common treatment for CIM is surgery, which involves widening the opening at the base of the skull, expanding the covering membrane, and opening the bony ring of the upper spinal vertebra. Without clear symptoms, there is no real reason for concern or follow-up scans, provided that there is no associated syrinx. In your case it would be important to see a neurologist to determine whether the CIM was present on prior scans, and whether it could have been caused by downward pressure on the cerebellum from your lesion.