What is the most likely diagnosis?
Papillary craniopharyngioma - is most likely. The absence of any sizeable dural tail makes meningioma unlikely. A normal pituitary fossa essentially excludes a macroadenoma. Other rare tumours/lesions are much less likely (e.g. pituicytoma, exophytic hypothalamic astrocytoma, ganglioglioma etc...)
Does the absence of cysts or calcification disuade you from the diagnosis of a craniopharyngioma?
It shouldn't. Papillary craniopharyngiomas, in contrast to adamantinomatous tumours, usually are solid (or only have smaller cysts) and rarely calcify.
Contrast enhanced CT demonstrates a suprasellar mass which vividly enhances. Although contrast does make it harder to assess, there is no convincing evidence of calcification. The pituitary fossa is unremarkable and the anterior cerebral arteries, although contacted, are not encased. There is no cystic component.