My friend's 4 year old son has arachnoid cyst.Ask for advice.

  Dear Sir:
  My friend in China has a son of 4 years old. Five months ago,
  he fell down when he played with other kids. To be safe,
  my friend took him to see a doctor. In CT scan, the doctor found
  that there is fluid in the left, rear part of his brain. The diagnosis
  is arachnoid cyst. The doctor likes to check the boy 6 months later.
  If the situation does not become better then, the doctor wants to give
  him a surgery. Until now, the boy always looks very normal. My friend
  worrys about the possible surgery, and wants to know:
  (1)What are the usual treatments to his son's case?
  (2)If there are other treatments, to avoid the surgery;
  (3)If there are advanced methods in USA to treat such desease. If necessary
  my friend will seek treatment for his son in USA.
  (4) If it is possible that the arachnoid cyst will disappear later without
  any treatment.
  Both my friend and I know nothing about this desease, please give a
  detailed advice. Thank you very much!
  Zhangfei

[CCF neurology MD MM]

_
Unless this cyst is causing problems like creating pressure or causing a focus for seizures
it is not necessary to perform surgery.
If surgery is performed it is usually fairly simple, however it is doubtful
if it is even necessary.
If the boy fell down because of a seizure then surgery might be indicated,
otherwise it might be best left alone.
It is unlikely to disappear without surgery but many people have these
cysts without even realizing they are present and they never cause problems.