Dynamic contrast MRI of the sella: a microadenoma enhances LATER than the normal gland; a macroadenoma is measured and its reach is named — optic chiasm, cavernous sinus (Knosp grade), sphenoid sinus — because that decides surgery.
Orient first
- A microadenoma is under 10 mm and a macroadenoma 10 mm or more; hormone-secreting microadenomas are small and may be seen only on dynamic sequences.
- The normal gland enhances early and brightly; an adenoma enhances more slowly and appears as a relatively low-signal focus on early dynamic images.
- Cavernous sinus invasion is graded by the tumour's relation to lines drawn across the internal carotid artery (Knosp) — verify the grading used locally.
Acquire the study
- Pituitary MRI: thin-section coronal and sagittal T1 and T2, dynamic coronal post-contrast T1, and delayed coronal and sagittal post-contrast T1.
The manoeuvre
- Coronal T2 and T1: gland height, stalk position, a focal low-signal lesion and the floor of the sella.
- Dynamic coronal post-contrast T1: a focus that enhances later than the surrounding gland.
- Macroadenoma: measure three orthogonal diameters in mm; the "snowman" waist at the diaphragma sellae.
- Optic chiasm on coronal T2: elevation, compression and distance from the tumour.
- Cavernous sinus on coronal post-contrast T1: encasement of the internal carotid artery and the Knosp grade.
- Haemorrhage on T1 (apoplexy) and sphenoid sinus invasion.
What confirms it
- A focal, relatively hypoenhancing lesion on dynamic imaging (micro) or a sellar mass with the features above (macro).
What licenses you to exclude it
- A normal dynamic pituitary MRI does not exclude a very small secreting adenoma — say so when the endocrine picture is strong.
The classic misread
- Calling a Rathke cleft cyst (non-enhancing, T1 variable, midline) an adenoma.
- Missing a craniopharyngioma or meningioma — calcification and a dural tail point away from adenoma.