Pituitary Macroadenoma in Dogs with Cushing’s Disease
In this article
By Dr Duncan Houston
A dog with well-managed Cushing’s disease can still develop a new problem if a pituitary tumour grows. Changes in alertness, vision or walking should not automatically be attributed to age or the familiar hormonal condition.
Equally, weakness or poor appetite during treatment is not proof of a brain tumour. Medication-related problems and other illnesses can be urgent and need assessment too.
Quick Answer
A pituitary macroadenoma is an enlarged pituitary tumour that may compress nearby brain structures. Hormone-control medicines can manage Cushing’s signs without reliably treating the mass itself. MRI or CT helps assess the tumour, and specialist options may include radiotherapy or, in selected centres and patients, pituitary surgery.
How does the pituitary cause Cushing’s disease?
The pituitary gland signals the adrenal glands to produce cortisol. In pituitary-dependent Cushing’s disease, a pituitary tumour produces inappropriate stimulation. Many tumours are small, but larger masses can create neurological problems as well as hormonal effects.
The MSD Cushing’s disease reference distinguishes medical hormone management from treatments directed at the pituitary tumour. A good response in drinking, appetite or skin does not establish that tumour size is stable.
Which signs raise concern?
New dullness, persistent pacing or circling, altered interaction, apparent vision loss, seizures and difficulty navigating can indicate brain dysfunction. Signs depend on tumour location and surrounding effects, and some enlarged tumours are found before obvious neurological changes.
Size must be interpreted in context. Imaging specialists consider the gland relative to nearby structures and the brain, rather than relying on one internet millimetre cutoff to decide whether treatment is worthwhile.
What should you do when signs change?
| Situation | Action |
|---|---|
| Stable Cushing’s signs, no neurological change | Continue the monitoring plan and discuss whether imaging would alter decisions. |
| New behaviour, vision or walking changes | Arrange prompt assessment and discuss referral. |
| Poor appetite, vomiting or weakness while taking trilostane | Contact the prescribing vet urgently before the next dose. |
| Collapse, seizures, severe disorientation or inability to stand | Seek emergency care immediately. |
What else needs ruling out?
Excessive suppression of adrenal hormone production, electrolyte disturbances, low blood glucose, hypertension, another brain disorder and unrelated systemic illness can resemble parts of the picture. The medicine name, dose, last administration and recent blood results are therefore important history.
Do not increase Cushing’s medication to treat a new neurological sign. Follow existing sick-day instructions and contact the clinic if your dog becomes unwell.
How is a macroadenoma assessed?
The vet performs a physical and neurological examination and reviews endocrine control. Blood pressure, blood and urine testing help assess other causes and anaesthetic suitability. MRI provides detailed brain imaging; CT may be used in some settings.
Imaging defines the mass and its effect on adjacent tissue, but the exact tumour classification may remain presumptive without tissue. Ask what the scan would change: treatment selection, prognosis, monitoring or a decision about comfort-focused care.
When is this an emergency?
Collapse, repeated seizures, a prolonged seizure, severe weakness or rapidly reduced responsiveness needs immediate treatment. Keep the dog away from stairs and hazards, do not put anything in its mouth during a seizure and bring current medicines. Do not wait for a scheduled specialist appointment.
What treatment options exist?
Radiotherapy may be used to control the mass. Protocols differ, and the number of visits, anaesthetic requirements, expected response and adverse effects should be explained by the treating centre. The MSD radiation overview describes several approaches rather than one universal schedule.
Hypophysectomy, removal of the pituitary gland and tumour, is available for selected patients at experienced centres. The Royal Veterinary College’s canine hypophysectomy programme demonstrates that surgery is a real option, although it requires specialist expertise and ongoing hormone replacement.
Some dogs continue to need Cushing’s medication after tumour-directed treatment. Supportive treatment and quality-of-life care may be the most appropriate choice when more intensive intervention is unsuitable.
Your decision plan
- Record specific new signs and obtain safe videos where useful.
- Review current medicines and test results with the treating vet.
- Ask whether imaging and referral would change available choices.
- Discuss treatment goals, practical demands, risks and an individual estimate of costs.
- Agree monitoring and emergency instructions in writing.
Common mistakes and prevention
- Assuming hormone control means tumour control.
- Believing pituitary surgery is impossible in every dog.
- Using tumour diameter alone to predict outcome.
- Dismissing treatment-associated vomiting or weakness.
There is no proven way to prevent a pituitary tumour. Consistent follow-up and early reporting of changes help identify when the plan needs revision.
Frequently asked questions
Does every dog with Cushing’s need an MRI?
Not necessarily. Discuss whether the result would change care, especially if neurological signs appear.
Does trilostane shrink the tumour?
It controls cortisol production and is not a reliable treatment for the pituitary mass itself.
Is a benign tumour harmless?
No. A non-spreading mass can still damage nearby brain structures.
Can treatment cure Cushing’s disease?
Outcomes vary by treatment and patient. Long-term monitoring remains necessary.
Separate the hormonal problem from the mass effect, then choose a plan that fits your dog’s health and comfort.
For help organising care questions and observations, visit ASK A VET™. Urgent medical signs require in-person veterinary assessment.
