Pituitary macroadenoma in a dog with Cushing's: signs and radiotherapy
9-year-old Boxer with pituitary-dependent hyperadrenocorticism on trilostane for 6 months, with good control of signs. Over recent weeks he has become dull, eats little, paces aimlessly and sometimes stares at the wall. Electrolytes are normal and cortisol is within the target range.
What is the most appropriate next step?
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A. Perform brain MRI (or CT) and, if a macroadenoma is confirmed, consider radiotherapy
Correct. The signs are typical of a pituitary macroadenoma compressing the hypothalamus and thalamus. Radiotherapy shrinks the tumour and improves neurological signs, with a better prognosis for smaller tumours and milder signs; hypophysectomy is another option in specialist centres.
B. Stop trilostane because he has iatrogenic hypoadrenocorticism
With normal electrolytes and cortisol on target, hypocortisolism is unlikely. The signs (pacing, staring at walls) are neurological, of forebrain origin.
C. Increase the trilostane dose to slow tumour growth
Trilostane acts on the adrenal, not the pituitary: it controls hypercortisolism but has no effect on pituitary tumour size.
D. Switch to mitotane, which shrinks pituitary tumours
Mitotane destroys the adrenal cortex and does not act on the pituitary either; it does not treat a macroadenoma.
lightbulb Key takeaway
A dog with pituitary-dependent Cushing's that develops neurological signs (dullness, anorexia, pacing, behavioural change) may have a macroadenoma. Trilostane and mitotane do not halt the tumour; radiotherapy does, especially if given early.
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Updated: October 31, 2026 · Educational content for veterinary professionals. It does not replace current clinical guidelines or the judgement of the attending veterinarian.