Hello and welcome to HCM, An arachnoid cyst is a cyst formed from the layers of arachnoid mater. Arachnoid mater is one of the coverings of the brain. As you have mentioned that it lies at a strategic location near the optic tract and the pineal gland, neurological deficits associated with these structures is expected. But since his vision is normal, it seems that the cyst is not compressing or touching upon these structures. Loss of control over bowel movements and unawareness regarding bowel fullness suggests that the nerves controlling the bowel movements are non-functional. In simple words, the nerves from the brain which control the movement of the bowel are compressed, or damaged by the cystic mass. For treatment of this problem, a complete neurological evaluation is needed to acertain that the bowel abnormality is due to the cyst or some other cause. Surgical removal of the cyst is the treatment of choice. The feasibility of surgical procedure, age at which surgery can be performed, etc can be decided by a pediatric surgeon. So, you need to consult both apediatric neurologist and pediatric surgeon for the problem. Thanks and take care Dr Shailja P Wahal