A 63-year-old man presented to the hospital accident and emergency department with an episode of syncope. He also gave a history describing several weeks of left-sided facial pain, which was initially thought to be secondary to a tooth abscess. On systemic enquiry the patient also reported having intermittent episodes of night sweats and mild anorexia, but he was otherwise well. Physical examination revealed the patient to have significant postural hypotension, allodynia affecting all three divisions of the trigeminal nerve and a palpable liver edge. Laboratory biochemistry investigations revealed profound panhypopituitarism. An MRI with gadolinium contrast of the brain subsequently revealed a hypothalamic mass sitting posterior to the optic chiasm and wrapping around the floor of the third ventricle with extension into the infundibulum. A second mass was also observed within Meckel's cave extending towards the foramen ovale. The masses appeared radiologically similar but anatomically separate (Figures 1 and and22). Figure 1 Coronal T1 weighted MRI of the brain (a) pre- and (b) post-gadolinium contrast enhancement. The white arrows highlight the two distinct enhancing masses. There is a 15×12 mm hypothalamic mass that wraps around the floor of the third ventricle. ... Figure 2 Sagital T2 weighted MRI scan with a white arrow highlighting the hypothalamic mass lesion, which exhibits some extension into the infundibulum. The panhypopituitarism that resulted led to a clinical presentation of Addison's disease. What is the differential diagnosis? What further investigations are indicated?