What is the differential now, taking into account MRI appearances?
A cystic / necrotic / haemorrhagic pituitary macroadenoma is the most likely diagnosis. A craniopharyngioma is a possibility. Rathke cleft cysts can have variable signal, as can epidermoids (so-called white epidermoids).
Are there peripheral enhancing components? What effect does this finding have on the differential above?
Yes, in addition to thin septations, there are a number of peripheral nodular components which demonstrate contrast enhancement. They are difficult to identify on the post contrast images as once enhanced they become isointense to the intrinsically hyperintense T1 centers. Presence of solid enhancing components essentially excludes a Rathke's cleft cyst or a white-epidermoid (which was only an unlikely possibility to begin with).
Given the T1 signal hyperintensity, what do you think about the possibility of this representing a craniopharyngioma?
Although still possible, most craniopharyngiomas with prominent T1 hyperintense components are of the adamantinomatous subtype, which are more frequently seen in children and in 90% of cases have peripheral calcification. As such, it is a less likely possibility, and a macroadenoma should be favoured.
Assuming this is a macroadenoma, what do you think the signal intensity of the non-enhancing component is due to?
The two options are blood or necrosis (or both). There is little susceptibility induced signal drop out at the margins or within the lesion, which if this was predominantly haemorrhage, after one month would be a prominent feature. As such this most likely represents necrosis, with coagulative necrosis and a protein rich necrotic soup accounting for the high T1 signal.
Assuming this is a macroadenoma, would you use the term 'pituitary apoplexy'?
Apoplexy usually denotes a sudden onset of symptoms due to very rapid enlargement of the gland / tumour, often with dramatic loss of vision, headache and even loss of consciousness. A one month history would be out of keeping with this. In addition the dominant finding is usually haemorrhage, rather than necrosis.
What incidental finding is present in the white matter and what does it suggest?
Deficiency of white matter in the peri trigonal regions with undulation of the lateral margins of the lateral ventricles is suspicious for changes secondary to neonatal periventricular leukomalacia.
A 19 x 23 x 25mm ovoid mass lesion is seen in the pituitary fossa with suprasellar extension. The mass is not clearly separate from the anterior portion of the pituitary, which cannot be identified. A solid component is located anterolaterally (towards the left) and this component enhances. The optic chiasm is markedly compressed, draped over the superior aspect of the mass lesion. The mass is T1 and T2 hyperintense centrally with no significant enhancement post contrast. There are a few fine internal septations. No restricted diffusion within the mass. No calcifications.
The remaining imaged brain, including posterior fossa structures, are normal.
The white matter in the peri trigonal regions is thinned with undulation of the lateral margins of the lateral ventricles.