Intestinal Thickness on Cat Ultrasound: What It Means

Name: Intestinal Thickness on Cat Ultrasound: What It Means
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

An ultrasound measures how thick your cat's intestinal wall is, layer by layer, and that number helps your veterinarian decide whether inflammation or cancer is more likely. Normal feline small intestine walls are thin, and a thickened wall with lost layering raises concern for lymphoma. This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

Intestinal wall thickness is measured in millimeters on ultrasound, and your vet compares each segment (duodenum, jejunum, ileum) against expected normal ranges for cats.
Mild, uniform thickening with preserved wall layers usually points toward inflammatory bowel disease (IBD), while marked thickening with loss of normal layering raises suspicion for lymphoma.
Ultrasound alone cannot confirm either diagnosis. A definitive answer usually requires tissue biopsy, often taken during endoscopy or surgery.
One small study found mean ileal thickness of 0.22 cm in cats with chronic GI signs versus 0.21 cm in healthy cats, a difference too small to be meaningful on its own [1].
Thickening is not always cancer or IBD. Other causes include severe inflammation, scarring, and a rare feline condition called gastrointestinal eosinophilic sclerosing fibroplasia [2].

What Cat Ultrasound Intestinal Thickness Actually Measures

When your veterinarian performs an abdominal ultrasound, they place a probe on your cat's shaved belly and use sound waves to build a picture of the organs inside. For the intestines, they look at each loop in cross section and measure the wall from the outer edge to the inner edge. That measurement is the intestinal wall thickness.

The wall has distinct layers, and your vet evaluates both the total thickness and whether those layers are still visible. Normal feline small intestine walls are thin, typically in the range of about 2 to 3 millimeters depending on the segment and the machine used. The exact reference range varies by equipment, technique, and the individual cat, so your vet interprets the number in context.

The large intestine, also called the colon, absorbs fluid and electrolytes, stores feces, and houses healthy bacteria [3]. It has a slightly different normal thickness than the small intestine, and your vet measures it separately.

Why the measurement matters

A thickened intestinal wall is a signal, not a diagnosis. It tells your vet that something is irritating or infiltrating the tissue. Common explanations include chronic inflammation, lymphoma, and less common conditions. The pattern of thickening, the segments involved, and other findings on the same scan all shape the interpretation.

If you want a broader picture of what a normal scan looks like, see Abdominal Ultrasound in Cats: Normal Findings and Common Abnormalities.

How Ultrasound Helps Distinguish IBD From Lymphoma in Cats

This is the question most owners are really asking. Chronic vomiting, weight loss, and diarrhea in an older cat often come down to two possibilities: inflammatory bowel disease or low-grade intestinal lymphoma. The two can look similar, and they can even coexist in the same cat.

What IBD looks like on ultrasound

Inflammatory bowel disease produces inflammation in the intestinal wall. On ultrasound, this often shows up as mild to moderate, fairly uniform thickening with the normal wall layers still visible. The changes tend to be diffuse, meaning they affect long stretches of intestine instead of one isolated lump.

What lymphoma looks like on ultrasound

Lymphoma is a cancer of lymphocytes, and in the cat intestine it often causes more dramatic changes. Vets look for marked thickening, loss of the normal layered appearance, and sometimes a mass-like region. Lymphoma and adenocarcinoma are two of the more common digestive tumors in cats, and intestinal tumors in cats tend to spread rapidly [3].

A 2025 study of cats with low-grade intestinal T-cell lymphoma and lymphoplasmacytic enteritis found that the jejunum was consistently affected in both conditions, followed by the ileum and duodenum [4]. In other words, the location of the thickening does not cleanly separate the two diseases. The stomach and colon were involved far less often [4].

Why the overlap matters

Because IBD and lymphoma can produce overlapping ultrasound findings, and because both can affect the same segments, ultrasound is a strong screening tool but a weak final answer. Your vet uses it to decide how worried to be and whether to recommend a biopsy.

For a deeper look at how vets read the whole GI tract on ultrasound, see Ultrasound of the Canine and Feline Gastrointestinal Tract: Normal and Abnormal Findings.

Other Causes of a Thickened Intestinal Wall

Cancer is not the only explanation, and it is not even the most common one. Cancer of the digestive system represents less than 10% of all cancers in cats, and when it does occur it most often develops in the small intestine [3]. Older cats are predisposed, with an average age of 10 to 12 years, and Siamese cats have increased risk for some intestinal cancers [3].

Other causes your vet considers include:

Chronic inflammatory disease, including lymphoplasmacytic enteritis
Feline gastrointestinal eosinophilic sclerosing fibroplasia (FGESF), a rare condition that mostly affects young to middle-aged cats, with a median age of 3.5 years, and appears overrepresented in Ragdolls [2]
Infectious causes such as feline enteric coronavirus, which is highly contagious among cats in close contact and causes small intestine inflammation, though it is not usually fatal [3]
Scarring or prior injury to the bowel wall

In the FGESF study, the proximal duodenum was the most commonly involved site, and lesions there grew inward toward the lumen [2]. That is a specific pattern your vet may recognize on the scan.

How to Prepare Your Cat for the Ultrasound

Most abdominal ultrasounds in cats do not require sedation, but some cats need mild sedation to stay still. Your vet will tell you which applies to your cat.

Food is the main variable. Many clinics ask you to withhold food for roughly 8 to 12 hours before the appointment so the stomach and intestines are easier to see. Water is usually allowed. If your cat has diabetes or another condition that makes fasting risky, tell the clinic when you schedule.

You will also want to bring a few things:

A list of current medications and supplements
Any prior lab work or imaging from another clinic
A carrier your cat travels comfortably in

A small patch of fur on the belly is typically clipped so the probe makes good contact. The fur grows back.

What Happens During the Procedure

Your cat lies on a padded table, usually on their side or back. The veterinarian or a technician applies gel to the clipped belly and moves the probe slowly across the abdomen. Most scans take 20 to 40 minutes.

The room is usually dim, and the person scanning may be quiet while concentrating. That is normal. Your cat may be held gently in position, and if they are stressed, the team may pause or adjust.

During the scan, your vet measures wall thickness in multiple segments, checks the layering pattern, and looks at surrounding structures like lymph nodes, the liver, and the pancreas. Enlarged lymph nodes near the intestine can support a suspicion of lymphoma, though they are not proof.

If your vet finds something that needs a sample, they may recommend a fine needle aspirate or a biopsy. Those are separate procedures and are usually scheduled after the scan, not during it.

Recovery Timeline and Home Care

Ultrasound is noninvasive, so recovery is simple. The main cleanup is the gel.

Time After the Scan	What to Expect	What You Should Do
Immediately after	Gel on the belly, possibly a small shaved patch	Wipe off leftover gel with a warm damp cloth
First few hours	Normal behavior in most cats, mild sleepiness if sedated	Offer water first, then a small meal
Same day	Full return to normal activity for most cats	Resume normal feeding and medications unless told otherwise
24 to 48 hours	Any sedation effects should be gone	Call the clinic if your cat is still groggy or not eating
Until results are discussed	Waiting period for the radiologist or vet report	Keep a simple log of appetite, vomiting, and stool

If your cat was sedated, keep them indoors and away from stairs or high furniture until they are fully steady. Do not let them outside unsupervised.

Possible Complications and Warning Signs

Ultrasound itself rarely causes problems. The most common issues are stress, mild skin irritation from the gel or clipping, and sedation-related grogginess. Serious complications are uncommon.

Watch for these after the appointment:

Trouble waking up or staying awake longer than expected
Vomiting that continues or gets worse
Refusing all food for more than 24 hours
Pain when you touch the belly
Trouble breathing

Call your vet if any of these appear. If your cat's belly looks swollen or feels tight, see Why Is My Cat's Belly Swollen? for context on what swelling can mean.

Questions to Ask the Veterinarian

Bring these to your follow-up conversation. The answers shape what happens next.

Which segments of the intestine were thickened, and by how much?
Were the normal wall layers still visible, or were they lost?
Were the lymph nodes enlarged?
Do these findings point more toward inflammation or toward lymphoma?
Is a biopsy recommended, and would it be endoscopy or surgery?
What are the risks of waiting and rechecking in a few weeks?
What does the treatment plan look like for each possible diagnosis?

If your vet recommends a biopsy, ask how the sample will be evaluated. Full-thickness surgical biopsies allow the pathologist to see all layers, while endoscopic samples are smaller. Your vet will explain which fits your cat's situation.

Limitations and When to Contact a Veterinarian

Ultrasound has real limits. It cannot confirm lymphoma or rule it out. A normal-looking wall does not guarantee a normal biopsy, and a thickened wall does not guarantee cancer. One study found that ileal thickness alone was not a reliable predictor of serum cobalamin, a marker of ileal function, which reinforces that a single number rarely tells the whole story [1].

Measurement reliability is also a factor. Even in controlled research settings, repeated measurements of the same intestinal segment can vary between sonographers and between exams [5]. That means small differences between two scans may reflect technique instead of a real change in your cat.

Individual cases always need a veterinarian who can examine your cat, review the full history, and interpret the images in context.

Contact your vet the same day if your cat:

Has vomited more than three times in 24 hours
Has bloody or black stool
Refuses food for more than 24 hours
Seems painful when picked up or when the belly is touched

Go to an emergency clinic now if your cat:

Is struggling to breathe
Has a hard, distended, painful abdomen
Is collapsed, unresponsive, or having seizures
Is straining to defecate with no stool produced and seems in severe pain

Schedule a routine visit if your cat:

Has had soft stool or intermittent vomiting for more than two weeks
Is losing weight despite a normal appetite
Has been diagnosed with IBD and is not improving on treatment

Frequently Asked Questions

Can ultrasound tell the difference between IBD and lymphoma in my cat?

Not with certainty. Ultrasound can show patterns that make one more likely than the other, but the two conditions overlap enough that a biopsy is usually needed for a firm diagnosis. Your vet uses the scan to decide how strongly to recommend that next step.

Does a thickened intestinal wall always mean cancer?

No. Inflammation, scarring, and rare conditions like eosinophilic sclerosing fibroplasia can all thicken the wall. Cancer of the digestive system is uncommon in cats overall, so many thickened walls turn out to be something else.

How thick is a normal cat intestine on ultrasound?

Normal small intestine walls in cats are thin, generally in the low single-digit millimeter range, with visible layers. The exact reference range depends on the ultrasound machine, the segment measured, and the sonographer's technique, so your vet compares your cat's values against their own lab's standards.

Will my cat need to be sedated for the ultrasound?

Many cats do not need sedation for a routine abdominal scan. If your cat is anxious, painful, or wiggly, your vet may recommend mild sedation to get clear images. The decision is made case by case.

What happens if the ultrasound is inconclusive?

Your vet may recommend a recheck scan in a few weeks, additional blood work, or a biopsy. Sometimes the answer comes from watching how your cat responds to a trial of diet change or medication. Your vet will lay out the options based on how sick your cat is.

References

Correlation between ultrasonographic measurements of the ileum and serum cobalamin concentrations in healthy cats and cats with chronic gastrointestinal signs: A pilot study. Brazilian journal of veterinary medicine, 2026.
Computed Tomographic and Ultrasonographic Features of Feline Gastrointestinal Eosinophilic Sclerosing Fibroplasia in Cats. Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association, 2025.
Disorders of the Stomach and Intestines in Cats - Cat Owners. Merck Veterinary Manual.
Lesions Distribution, Nature and Severity Along the Gastrointestinal Tract in Cats With Low-Grade Intestinal T-Cell Lymphoma or Lymphoplasmacytic Enteritis. Journal of veterinary internal medicine, 2025.
Intra-rater and inter-rater reliability of ultrasonographic intestinal wall thickness measurements in healthy horses. Equine veterinary journal, 2026.