Pituitary imaging for hypersomatotropism in cats

Why the pituitary matters in diabetic cats

Hypersomatotropism (HST) is excess growth hormone, almost always from a pituitary adenoma (Scudder and Church, Journal of Feline Medicine and Surgery, 2024). It causes insulin resistance and often difficult diabetes. It is common:

• In a UK study of 1,221 diabetic cats (Niessen et al., PLOS ONE, 2015), 319 (26.1%) had a serum IGF-1 above 1000 ng/ml, and the estimated HST prevalence among diabetic cats was 24.8%.
• In an Australian study of 87 diabetic cats (Kennedy et al., Journal of Feline Medicine and Surgery, 2025), 14 (16%) had an IGF-1 above 1000 ng/ml.

Most cats with HST in the UK study did not show typical acromegalic features, and only 24% of clinicians had a strong suspicion before testing. In the Australian study, clinical features could not separate diabetic cats with and without HST.

Where imaging fits

Imaging follows endocrine testing; it does not replace it.

• An IGF-1 above 1000 ng/ml had a positive predictive value of 95% for HST in diabetic cats.
• Values between 700 and 1000 ng/ml are a grey zone. The authors of a 2024 review recommend either repeating IGF-1 later or intracranial imaging.
• Imaging then confirms a pituitary mass, measures it and supports treatment planning.

flowchart TD
  accTitle: When does a diabetic cat need pituitary imaging?
  accDescr: Based on a UK prevalence study and a 2024 review. An IGF-1 above 1000 ng/ml makes hypersomatotropism very likely, and imaging then confirms and measures a pituitary mass for treatment planning. Between 700 and 1000 ng/ml, either repeat IGF-1 later or image the pituitary.
  igf["Diabetic cat: serum IGF-1"] --> q{{"IGF-1 result?"}}
  q -- "Above 1000 ng/ml" --> img["Pituitary imaging to confirm and plan"]
  q -- "700 to 1000 ng/ml" --> grey["Repeat IGF-1 later, or image"]

CT or MRI

How the result feeds treatment decisions

• Hypophysectomy. In 68 cats, all had contrast-enhanced CT and pituitary height was recorded, though enlargement was not required for the diagnosis. Diabetic remission occurred in 41 cats (71% of the 58 that survived 4 weeks). Pituitary height was not associated with diabetic remission or survival. Of 25 cats imaged before surgery, 24 had an enlarged pituitary (height 4.3 to 13.3 mm), and the larger tumours were not particularly more difficult to remove.
• Medical treatment. In a prospective study of medical treatment in 23 cats (Miceli et al., Journal of Feline Medicine and Surgery, 2022), 12 had pituitary imaging. Cats whose IGF-1 fell had a lower median pituitary height (3.2 mm) than those whose IGF-1 did not (6 mm).

Pituitary imaging protocol at a glance

Pituitary imaging is contrast-enhanced, with CT or MRI. The normal height reference comes from contrast-enhanced CT or MRI, and the hypophysectomy series used contrast-enhanced CT, with 3D reconstruction for surgical planning. Small lesions may need MRI to be identified.

What the radiologist looks at

• Pituitary height. The normal height in cats is below 3.8 mm, and pituitary enlargement or neoplasia affects fewer than 2% of cats. In 62 cats having head CT for other reasons, mean pituitary height was 3.1 ± 0.4 mm and only one cat (1.6%) had an enlarged gland. A CT study of 51 domestic shorthairs (Costanza et al., Animals, 2023) proposed that a height above 4 mm, or a pituitary-to-brain ratio above 0.49, should be considered enlarged.
• Consistent measurement. Because size is used in treatment decisions, the report should give pituitary height and width measured in a consistent plane, and describe any extension beyond the sella.
• Beyond the pituitary. On head CT, cats with HST had thicker frontal and parietal bones (on average 0.8 mm), a wider zygomatic distance (5.4 mm), thicker mandibular rami (1.1 mm) and a smaller nasopharyngeal cross-section than controls. Prognathia inferior and temporomandibular joint changes were more frequent. The differences were small.

What your report will include

Every Veheri case is read by a radiologist or neurologist, and when you order you can choose Diplomate-only reporting or the full specialist panel. Neurology reporting covers CT and MRI. You can chat directly with the specialist assigned to your case, and a simplified pet owner report helps you explain the findings to the owner.

When you take the report forward:

• A normal-sized pituitary does not rule out HST. The 2024 review makes this point, and of 2 cats with no lesion on CT or MRI, the one that had necropsy showed acidophil hyperplasia.
• Imaging shows a mass, not its hormone output. The diagnosis rests on endocrine testing together with imaging.
• Cats without diabetes. In 28 non-diabetic cats with presumed HST (Miceli et al., Journal of Veterinary Internal Medicine, 2026), 3 had neurological signs and 8 of 17 had a hypertrophic cardiomyopathy phenotype. The authors suggest considering HST in cats with signs of growth hormone excess or a pituitary tumour, even without diabetes.

What to include when you request a pituitary imaging report

• signalment: age, breed and sex
• IGF-1 result, date and assay, and how long the cat has received insulin, because insulin treatment itself raises IGF-1
• insulin requirement and glycaemic control
• acromegalic features: prognathia, broad face, respiratory stridor, polyphagia
• neurological signs and cardiac findings
• whether the study is for diagnosis or for surgical or radiotherapy planning

How Veheri can help

Veheri works with veterinary radiologists and neurologists and reports MRI and CT studies remotely for clinics. For dogs, see pituitary MRI in dogs with hypercortisolism, and for other feline neurology, brain MRI in cats.