If its cyst in neck it could be Branchial cyst or cystic hygroma
or thyroid lesion or a necrosed enlarged lymph node
or coming from a salivary gland
or anuerysm (this can be easily seen on MRI)
you have written details of MRI so its difficult to comment upon.
if its big get it aspirated and send for examination.
then dont think of aspirating it.
your cousin needs detailed ENT examination and Flexible nasopharyngolaryngoscopy.