What is the most likely diagnosis?
Pituitary macroadenoma is statistically by far the most likely diagnosis when a soft tissue attenuating mass is seen expanding the pituitary fossa.
What other solid tumours are seen in this region?
Meningioma and craniopharyngioma (papillary type) would be the more common entities encountered.
What uncommon differential should always be considered, even if only to immediately dismiss it, on account of how important it is and how devastating the consequences of missing it are?
An aneurysm can mimic a pituitary region mass, especially on CT, and can even expand the fossa. In this case it is especially important to consider as the mass is very sharply demarcated, abuts the left supraclinoid internal carotid artery and has a similar density to the artery after contrast administration.
The mildly hyperdense smoothly lobulated sellar/suprasellar mass measures 25 x 22 x 14 mm and demonstrates vivid contrast enhancement. Paranasal sinuses and ostiomeatal units are clear, with accessory anterior (Agger nasi) ethmoid air cells, left concha bullosa, relatively large septate sphenoid sinus and rightward nasal septal deviation noted.
Sagittal midline bone window image demonstrates smooth enlargement of the pituitary fossa.