The cerebellum sits at the back of the brain just where the spinal cord connects. Often in cases of Spina Bifida, the spinal cord is pulling downward on the cerebellum and the bottom portion of the cerebellum is elongated which is why they call it the "Banana Sign". This condition is called Arnold Chiari. In cases of SB it is often more specifically Arnold Chiari II.
Similar to the "Lemon Sign", the "Banana Sign" goes hand-in-hand with a diagnosis of SB and so it serves as another confirmation that SB is likely present.
Many children with ACII do not show any symptoms and so there is no need to address the condition. In some cases, ACII can interfere with eating, swallowing and breathing and in those cases decompression surgery is the most common approach. De-tethering of the spinal cord is also another approach.
So to unpack this a little more: Due to the defect in the spinal column caused by SB, the spinal cord can become attached (or tethered) to the spinal column. Once a spinal cord becomes tethered, it can begin to pull the cerebellum downward (BS). The cerebellum then gets squeezed in the opening from the skull into the spinal column.
This often prevents cerebral spinal fluid from properly draining from the skull (where it is produced by the ventricles) into the spinal column. Additionally, the increased pressure on the cerebellum can cause problems with eating, drinking and breathing. When that happens, doctors will commonly go into the neck / base of the skull area and try to widen that passageway by removing some bone. This is called decompression. Another approach is to go into the spinal column and de-tether the spinal cord.
Again, many children with SB do not have any symptoms due to ACII and so there is no need to address it.
Parents Note: When we were pregnant, we were told that ACII would prevent our daughter from ever eating or breathing on her own. Annie is now 3 years old and we have never had her show any symptoms concerning ACII