Mri (14yo, good student, depressive/calm) showed unilateral 1cm lesion in the hippocampal region. observation was advised. what more may he do?

Radiology report: Should give an opinion about what this "lesion" is. If not, please get a second opinion (preferably from a neuroradiologist). A neurosurgical consult may be needed as well depending on the possibilities.

Not much. : Not much else can be done. Just regular follow ups and follow the direction of your doctor.

Likely benign: Impossible to say exactly what this lesion is, and at the age of 14, with good academic fnctn, most likely this is a congenital malformation of no consequence. Rather unusual for an pediatric tumor to be focal over the temporal area. So, my view is a benign coincidental finding of no significance. Prudent to re-image in future, but do not worry.