A standard abdominal ultrasound in dogs can show the size, shape, and internal structure of nearly every organ in the belly, from the liver and kidneys to the bladder, spleen, pancreas, adrenal glands, and the entire gastrointestinal tract. It also picks up free fluid, enlarged lymph nodes, masses, and blood flow through major vessels like the aorta and vena cava. For many conditions, it gives your vet a real-time, detailed look at what’s happening inside your dog without surgery.
Organs and Structures That Are Visible
The ultrasound probe moves systematically through the abdomen, and a full scan covers a long list of anatomy. On the right side, the vet can evaluate the right kidney, right adrenal gland, the right portion of the liver, and the gallbladder. On the left, the left kidney, left adrenal gland, and spleen come into view. The pancreas is examined in two parts: its left lobe near the spleen and its right lobe along the duodenum.
The entire gastrointestinal tract is assessed, including the stomach, duodenum, jejunum, ileum, cecum, and colon. The urinary bladder is checked for stones, wall thickening, or masses. In intact female dogs, the uterus is visible. In intact males, the testicles can also be evaluated. Major lymph node groups, including mesenteric and medial iliac nodes, are scanned for enlargement that could signal infection or cancer. Blood vessels like the portal vein, cranial mesenteric artery, and iliac arteries are visible too, giving information about blood flow to and from the organs.
Liver and Spleen Abnormalities
Ultrasound is one of the primary tools for spotting masses, nodules, and texture changes in the liver and spleen. One of its strengths is helping distinguish between benign and malignant liver lesions based on their appearance. Benign growths typically look uniform in texture and darker than the surrounding liver tissue. Malignant lesions tend to have a mixed, uneven texture, sometimes with a characteristic “target sign” pattern. In one study, heterogeneous (uneven) texture identified malignant liver disease with 93% accuracy, 91% sensitivity, and 94% specificity.
Splenic masses are common in older dogs, and ultrasound can reveal their size, location, and internal characteristics, though a biopsy is often still needed to confirm whether a mass is cancerous. The scan also shows whether the liver or spleen is enlarged, which can point to systemic illness, infection, or infiltrative disease.
Gastrointestinal Problems
If your dog has been vomiting, losing weight, or refusing food, an abdominal ultrasound can reveal what’s going on in the stomach and intestines. The vet looks at the thickness of the gut wall and whether its normal layered structure is intact. A stomach wall thicker than about 6 to 7 mm is considered abnormal and can indicate conditions ranging from inflammation to cancer. Gastric tumors often show up as asymmetrical thickening with a disrupted wall pattern.
Intestinal tumors, particularly lymphoma, tend to appear as focal areas of thickening where the normal wall layers are lost, often accompanied by enlarged nearby lymph nodes. Ultrasound can also detect foreign body obstructions. The classic signs include a section of dilated, fluid-filled intestine upstream of the blockage, with noticeably smaller bowel downstream. Linear foreign bodies like string or fabric create a distinctive pleated or bunched appearance called “plication,” and the foreign material itself is sometimes directly visible on the image.
Kidney and Urinary Tract Findings
Both kidneys are evaluated for size, shape, and internal architecture. Ultrasound can reveal kidney stones, cysts, tumors, signs of chronic kidney disease (where the kidneys appear smaller and brighter than normal), and hydronephrosis, a condition where urine backs up and swells the kidney. The ureters, which carry urine from the kidneys to the bladder, can sometimes be traced if they’re abnormally dilated.
The urinary bladder is one of the easiest organs to image. Bladder stones show up clearly, as do polyps, masses, and wall thickening from chronic infection or inflammation. The trigone region at the base of the bladder, where the ureters connect, gets special attention because tumors in dogs commonly develop there.
Pancreatitis Detection
Pancreatitis is one of the more challenging diagnoses, and ultrasound plays an important but imperfect role. The vet looks for three main signs: an enlarged pancreas, changes in the pancreas’s brightness on the image, and inflammation in the surrounding fat. When any one of those signs is present, ultrasound picks up pancreatitis about 89% of the time, but it also flags some dogs who don’t actually have it (specificity drops to 43%). When all three signs must be present together, the test becomes much more specific (92%) but misses more true cases (sensitivity falls to 43%). This is why vets often combine ultrasound with blood tests to confirm pancreatitis.
Pregnancy Confirmation
Ultrasound is the earliest way to confirm pregnancy in dogs. The gestational sac can be detected as early as day 17 to 19 after ovulation. A heartbeat becomes visible around day 23 to 24, and fetal movement appears by about day 32. Over the following weeks, individual fetal structures develop: the stomach is visible around day 31, the bladder by day 33, and the skeleton by day 35. Ultrasound is excellent for confirming pregnancy and checking fetal viability (heartbeats), but it’s not reliable for counting the exact number of puppies. X-rays taken later in pregnancy, once the skeletons have mineralized, are more accurate for that.
Free Fluid and Lymph Node Changes
One of the first things an ultrasound reveals is whether there’s free fluid in the abdomen. Even small amounts show up clearly. Free fluid can indicate heart failure, liver disease, internal bleeding, ruptured organs, or cancer that has spread within the abdomen. The fluid can also be sampled with a needle during the ultrasound for testing.
Lymph nodes throughout the abdomen are checked for size and appearance. Enlarged nodes near the intestines may suggest lymphoma or inflammatory bowel disease. Enlarged iliac lymph nodes in the pelvic area can point to cancer in the urinary or reproductive tract. The ability to map lymph node changes across the abdomen is one of ultrasound’s advantages over X-rays, which can’t distinguish soft tissue structures as well.
What to Expect During the Procedure
Most dogs don’t need sedation for an abdominal ultrasound. They’re placed on their back or side on a padded table, and the fur over the belly is typically clipped to allow good contact between the probe and skin. A water-based gel is applied, and the scan is painless. Sedation is generally only used if a dog is very anxious or if the vet plans to take a biopsy or fluid sample during the procedure.
Interestingly, fasting before the scan may not be as important as commonly believed. A study of 150 dogs found that intraluminal gas, which can obscure some organs, accumulated regardless of whether the dog had fasted. The assessment of abdominal organs was not significantly affected by fasting status. That said, many clinics still recommend withholding food for 8 to 12 hours beforehand as a precaution, so follow whatever instructions your vet provides.
What Ultrasound Cannot Show
Ultrasound has real limitations. It cannot see through bone or air-filled structures well, so the lungs and the inside of bones are off-limits. Gas in the stomach or intestines can block the view of deeper organs like the pancreas or adrenal glands. While ultrasound can identify a mass and describe its characteristics, it usually cannot give a definitive diagnosis of cancer on its own. A biopsy or fine-needle aspirate, often performed during the same ultrasound session, is typically needed to confirm what a suspicious lesion actually is.