A 17-year-old male presents with 3-month history of headache, weight gain, decreased concentration, polyuria, and polydypsia. His headaches are mostly in morning and involves the frontal region. On examination he was found to have bitemporal visual field defect and no facial hair. MRI scan revealed a suprasellar paially calcified cystic lesion with displacement of optic chiasm. The most likely pathology is: