CT, ultrasound and endoscopy: why might different tests be needed?

A simple way to think about it

Imagine trying to understand a problem in a town. A CT scan is like a detailed 3D map: it shows where everything is and how it fits together. Ultrasound is like a live view from a drone: you can watch things move and look closely at particular buildings. Endoscopy is like walking down the street: you see the surfaces right in front of you in fine detail, and can pick things up.

Each view is useful. None tells the whole story on its own.

Ultrasound

Ultrasound uses sound waves to create a moving picture of soft tissues. A probe is placed on the skin, usually after clipping a small patch of fur.

• Good for: organs in the abdomen such as the liver, kidneys, bladder and intestines; measuring the thickness of the gut wall; looking at the heart; guiding needle samples
• Limited by: air and bone, which block sound waves — so it's less useful for the lungs, nose and skull
• Usually: done with your pet awake or lightly sedated

CT (computed tomography)

CT uses X-rays taken from many angles, combined by a computer into detailed cross-sectional and 3D images. A contrast agent may be injected to highlight blood vessels and certain tissues.

• Good for: the nose and sinuses, skull, chest and lungs, bones and joints; seeing the extent of a problem; planning surgery
• Limited by: it shows structure, not the surface of a lining; it can't always tell what a change is without samples
• Usually: needs your pet to be completely still, so is done under general anaesthetic or heavy sedation

Endoscopy

Endoscopy uses a camera to look inside hollow organs such as the gut, airways, nose or bladder.

• Good for: seeing the lining directly; taking targeted samples; removing some foreign objects
• Limited by: it can't see through walls or into solid organs, and some areas are out of reach
• Usually: performed under general anaesthetic

At a glance

Why more than one test may be needed

Tests are often used in a sequence, with each result shaping the next step. For example, a CT scan of the nose might show where an abnormal area is; rhinoscopy can then be used to look at it and take samples. In the abdomen, ultrasound may show a thickened area of gut, and endoscopy or surgery may be used to sample it.

Sometimes tests are combined in one anaesthetic to reduce the number of anaesthetics your pet needs.

Making decisions together

It's reasonable to ask how each test would change the plan for your pet. Factors that are often worth discussing include your pet's general health, the need for anaesthesia, cost and insurance, travel and how much information is likely to be gained.