Ultrasonographic Evaluation of the Canine and Feline Abdomen: A Systematic Approach

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-11

Key Takeaways

• A systematic, organ-by-organ scanning protocol is crucial for reproducible abdominal ultrasound examinations in dogs and cats, minimizing the risk of overlooking lesions and ensuring comparability of serial studies.
• Proper transducer selection (7.5-12 MHz for small animals, 3.5-7.5 MHz for large dogs) and patient preparation (12-18 hour fast) are essential to overcome challenges like bowel gas and achieve optimal image resolution and penetration.
• Recognizing common artifacts such as acoustic shadowing (from gas or mineral), enhancement (deep to fluid), and reverberation is vital to differentiate them from true pathological findings.
• The pancreas, often difficult to visualize, is typically isoechoic to slightly hyperechoic to the liver, and hyperechoic peripancreatic fat is a sensitive marker for pancreatitis in cats, though diagnosis requires integration with clinical signs and laboratory data.
• Splenic echogenicity should be fine and homogeneous, slightly coarser than the liver; hypoechoic nodules or mottling warrant cytologic or histologic sampling, particularly when mast cell disease is suspected.
• Gallbladder assessment includes wall thickness (normal <2 mm in dogs, <1 mm in cats) and bile echogenicity; dependent sludge is common and often incidental, but wall thickening suggests cholecystitis.

Abdominal ultrasonography in dogs and cats is a real-time, noninvasive imaging method that provides structural and, to a limited degree, functional information about the solid organs, gastrointestinal tract, and peritoneal cavity. This article presents a systematic scanning protocol for the small animal abdomen, with organ-by-organ evaluation, normal sonographic anatomy, and recognition of common artifacts. It is written for the practicing veterinarian who performs or interprets abdominal ultrasound and who needs a reproducible framework for image acquisition and interpretation. The clinical questions addressed include how to distinguish normal from abnormal parenchymal texture, how to avoid common interpretive errors, and how to integrate ultrasound findings with laboratory data when the imaging result is equivocal.

The value of a systematic approach is most evident when the target organ is difficult to image. The pancreas, for example, is anatomically inaccessible, frequently obscured by bowel gas, and inconsistently visualized even in healthy animals. Adherence to a structured scanning method, proper transducer selection, and patient preparation overcome these obstacles Ultrasonography of the pancreas. The same principle applies to the entire abdomen: a fixed sequence of transducer positions and imaging planes reduces the likelihood of overlooking a lesion and ensures that each examination is comparable across time points in the same patient.

At a Glance

Physics and Image Formation Principles

Ultrasound images are constructed from reflected sound waves at tissue interfaces. The amplitude of the returning echo determines brightness, while the time delay determines depth. Spatial resolution improves with higher transducer frequency, but penetration decreases. A 10 MHz transducer provides excellent near-field detail for superficial structures in cats and small dogs, whereas a 5 MHz transducer is required to image the deep abdomen of a large-breed dog. Modern machines allow frequency adjustment within a single transducer, and the operator should select the highest frequency that adequately penetrates the region of interest.

Gain settings, time-gain compensation, and dynamic range determine the display of returning echoes. Incorrect gain produces a falsely hypoechoic or hyperechoic parenchyma. The operator should calibrate gain on a known normal structure, such as the liver or the urinary bladder lumen, before interpreting the image. Depth and focus should be adjusted so that the region of interest occupies the full image width and the focal zone sits at the level of the structure being examined.

Artifacts and Their Interpretation

Acoustic shadowing occurs when sound is completely reflected or absorbed, as at gas interfaces or mineralized structures. It appears as an anechoic band deep to the reflector. Shadowing from bowel gas is common and can obscure the pancreas and retroperitoneal structures Ultrasonography of the pancreas. Shadowing from a small, curvilinear reflector within a solid organ suggests a calculus or mineralized focus. Acoustic enhancement appears as increased echogenicity deep to a fluid-filled structure, such as the gallbladder or urinary bladder, and is a normal finding that should not be mistaken for a parenchymal lesion.

Reverberation artifacts arise when sound bounces between two highly reflective interfaces, producing parallel equidistant lines. These are frequently seen at the body wall or within the lumen of the gastrointestinal tract. Side-lobe artifacts create spurious echoes within anechoic structures, such as the bladder lumen, and can mimic sediment or a mass. Changing the transducer angle or frequency usually eliminates these artifacts. The operator must document whether an apparent lesion persists in two orthogonal planes before recording it as a real finding.

Patient Preparation and Positioning

Fasting for 12 to 18 hours reduces gastric contents and intestinal gas, improving visualization of the pancreas, liver, and retroperitoneal structures. Water should be withheld for a shorter period to avoid gastric distension. Hair over the ventral abdomen is clipped from the xiphoid to the pubis and laterally to the flank. Acoustic coupling gel is applied directly to the skin. Sedation is rarely required for abdominal ultrasound, but fractious cats may need chemical restraint to allow a complete examination. The patient is positioned in dorsal recumbency for most of the examination, with lateral recumbency used for the spleen and left kidney.

The Systematic Scanning Sequence

A fixed sequence begins with the liver and gallbladder in the cranial abdomen, then moves to the spleen on the left, the stomach and pancreas, the right kidney and adrenal gland, the left kidney and adrenal gland, the small intestine, the urinary bladder, and the prostate or uterus. The mesenteric lymph nodes are assessed throughout. Each organ is examined in both longitudinal and transverse planes, and measurements are taken in a consistent orientation. The entire abdomen is scanned in a grid pattern to avoid missing peripheral lesions. This sequence is repeated at each examination so that serial studies are directly comparable.

The liver is evaluated from a subcostal or intercostal approach. The normal liver is homogeneous, with echogenicity similar to or slightly greater than the renal cortex and less than the spleen. The hepatic veins are visible as anechoic tubular structures converging on the caudal vena cava, whereas the portal veins have echogenic walls. The gallbladder is anechoic with a thin wall. Biliary sludge appears as dependent echogenic material and is often incidental, but it can be associated with cholestasis. The common bile duct is not consistently visible in normal dogs and cats.

The spleen is examined from the left cranial abdomen. It is homogeneous with a fine echotexture, and its echogenicity is slightly greater than that of the liver. The splenic vein is visible at the hilus. The normal spleen is not markedly enlarged, and the margins are smooth. Hypoechoic nodules, a mottled parenchyma, or subjective enlargement are abnormal findings that require cytologic or histologic sampling, particularly when mast cell disease is suspected Ultrasonographic findings in abdominal mast cell disease.

Organ-by-Organ Evaluation: Liver and Biliary System

Begin the hepatic evaluation in the right cranial abdomen, using the diaphragm as a cranial landmark. The liver is best imaged from a subcostal or intercostal approach with the transducer angled cranially. Assess the left lateral and left medial lobes from the ventral midline, the quadrate and right medial lobes from the right ventral body wall, and the caudate lobe from the right flank.

Normal hepatic parenchyma is homogeneous, moderately echogenic, and coarser than the spleen but finer than the pancreas. The echogenicity of the normal liver is similar to or slightly less than that of the renal cortex and slightly greater than that of the splenic parenchyma in dogs. In cats, the liver is typically isoechoic to or slightly more echogenic than the spleen. Compare hepatic echogenicity to the falciform fat, renal cortex, and spleen in every patient, as the reference organ that best matches the liver varies with body condition and species.

Measure the caudal vena cava and portal vein diameters at the porta hepatis. The portal vein to aortic diameter ratio is normally less than 0.8 in dogs. The hepatic veins are thin walled and drain into the caudal vena cava, while the portal veins have echogenic walls and branch within the parenchyma. Color Doppler confirms venous flow direction and patency.

The gallbladder is anechoic with a thin, smooth wall. Wall thickness should not exceed 2 mm in dogs and 1 mm in cats. Bile is normally anechoic, dependent echogenic debris or sediment may be physiologic in fasted animals, particularly cats. Evaluate the common bile duct as it courses from the porta hepatis to the duodenal papilla. The normal duct is less than 3 mm in dogs and less than 4 mm in cats, though mild dilation can occur postprandially.

Percutaneous ultrasound-guided cholecystocentesis is a minimally invasive technique for bile collection, and an experimental study in healthy cats demonstrated that a right-sided transhepatic approach or direct fundic aspiration with a 22-gauge needle was not associated with ultrasonographic complications in 11 of 12 cats, although transient decreased appetite and mild abdominal pain occurred in 4 cats percutaneous ultrasound-guided cholecystocentesis in healthy cats. Reserve this procedure for cases where bile cytology or culture will change management, and confirm normal coagulation status beforehand.

Spleen and Lymph Nodes

Image the spleen from the left cranial abdomen, following the organ from its rounded head near the gastric fundus along the left body wall to the tail. The splenic parenchyma is homogeneous and finely textured. Normal splenic thickness varies with body size, but the head rarely exceeds 2 cm in dogs and 1.5 cm in cats. The marginal veins are visible as thin anechoic lines on the capsular surface.

Evaluate the splenic lymph node at the hilus, though it is inconsistently identified in normal animals. The medial iliac lymph nodes are located at the aortic bifurcation, caudal to the renal vessels. Normal lymph nodes are hypoechoic, oval, and measure less than 5 mm in short axis in most dogs and cats. Rounding of the short axis to long axis ratio beyond 0.5, loss of the echogenic hilus, or short axis greater than 8 mm warrants cytologic sampling.

In abdominal mast cell disease, the affected spleen in cats may be subjectively enlarged, mottled, irregular, or contain nodules, while affected lymph nodes in both dogs and cats are hypoechoic or inhomogeneous, enlarged, and rounded ultrasonographic findings in abdominal mast cell disease. These changes are not specific to mast cell disease, and cytology or histopathology is required for a definitive diagnosis.

Pancreas and Peripancreatic Assessment

The pancreas is the most technically demanding organ to evaluate consistently. Bowel gas, patient discomfort, and the small size of the normal gland all contribute to imaging difficulty, and these obstacles are overcome by adhering to a systematic scanning method, proper transducer selection, and proper patient preparation ultrasonography of the pancreas. Use a high frequency linear transducer (7.5 to 12 MHz) in most cats and small dogs, and a microconvex or curvilinear transducer in larger dogs.

Identify the right limb of the pancreas between the descending duodenum and the right kidney. The body lies ventral to the portal vein, caudal to the pylorus. The left limb extends from the body toward the splenic hilus, dorsal to the stomach. The normal pancreas is isoechoic to slightly hyperechoic compared to the liver, with a smooth margin and a fine, homogeneous texture. Normal thickness is less than 6 mm in dogs and less than 5 mm in cats, measured at the thickest point of each limb.

Pancreatic assessment must include the peripancreatic fat. Hyperechoic peripancreatic fat had the highest sensitivity (68%) for feline pancreatitis among individual ultrasound characteriztics, while increased pancreatic thickness, abnormal pancreatic margin, and hyperechoic peripancreatic fat each had specificity above 90% ultrasonographic findings of the pancreas in cats with elevated serum pancreatic lipase immunoreactivity. In dogs, abdominal ultrasound is weakly correlated with the specific canine pancreatic lipase assay and only moderately correlated with a clinical diagnosis of pancreatitis, and ultrasound severity is a poor indicator of clinical severity association between abdominal ultrasound findings, the specific canine pancreatic lipase assay, clinical severity indices, and clinical diagnosis in dogs with pancreatitis. Interpret pancreatic ultrasound findings in the context of serum lipase, clinical signs, and other laboratory data instead of in isolation.

Kidneys and Adrenal Glands

Evaluate each kidney in both sagittal and transverse planes. The right kidney sits in the renal fossa of the caudate liver lobe, and the left kidney lies caudal to the spleen. Normal renal length varies with body weight: approximately 6 to 9 cm in dogs and 3.5 to 4.5 cm in cats. The cortex is hypoechoic relative to the liver and spleen, the medulla is more hypoechoic, and the renal pelvis is a thin hyperechoic line. Corticomedullary distinction should be crisp.

Measure the adrenal glands in the transverse plane. The left adrenal lies craniomedial to the left kidney, lateral to the aorta. The right adrenal sits between the caudal vena cava and the right kidney. Normal adrenal thickness is less than 7.5 mm in dogs and less than 5 mm in cats. The glands are bilobed or peanut shaped, with a hypoechoic cortex and hyperechoic medulla.

Gastrointestinal Tract

The stomach is evaluated from the left cranial abdomen, with the transducer oriented along the long axis of the fundus and body. Normal wall thickness is 3 to 5 mm in dogs and 1.5 to 3 mm in cats. The wall has five distinct layers: the hyperechoic luminal interface, hypoechoic mucosa, hyperechoic submucosa, hypoechoic muscularis, and hyperechoic serosa. Loss of this layering is an abnormal finding that requires cytologic or histologic characterization.

The duodenum is identified to the right of the body wall, coursing caudally from the pylorus. The jejunum occupies the mid abdomen, and the ileum is identified by its thickened muscularis layer, located medial to the cecum. Normal duodenal wall thickness is 3 to 5 mm in dogs and 2 to 3.5 mm in cats. The ileum is normally thicker than the duodenum in cats, up to 3.5 mm. Measure wall thickness from the luminal surface to the serosal surface, excluding the contents.

Documentation and Reporting

Record images in at least two orthogonal planes for each organ. Label each image with the patient identification, date, transducer frequency, and anatomic location. Store cine loops for the pancreas and any region where motion or peristalsis complicates static image interpretation. Document the following for each organ: size, echogenicity relative to a named reference organ, margination, wall thickness where applicable, and any focal lesions with their location, dimensions, echogenicity, and vascularity.

Write the report in a structured format that separates findings from interpretation. List normal findings first, then abnormalities in order of clinical importance. State the limitations of the examination, including poor acoustic windows, patient motion, or gas interference. Provide a differential diagnosis for each significant abnormality and recommend the next diagnostic step, whether that is cytology, biopsy, advanced imaging, or serial recheck. The American College of Veterinary Radiology resources provide additional guidance on imaging standards and reporting expectations.

Adjust the examination to the patient. In cats and small dogs, use the highest frequency transducer that provides adequate penetration. In large or obese dogs, lower frequencies and harmonic imaging improve depth penetration at the cost of resolution. If the patient is painful, as is common with pancreatitis, perform the examination in stages and consider analgesia before imaging ultrasonography of the pancreas.

Recognized Complications and Early Detection

Ultrasound-guided procedures and prolonged scanning carry specific risks. Percutaneous ultrasound-guided cholecystocentesis can cause bile peritonitis, hemorrhage, or transient post-procedural pain. In healthy cats, a right-sided transhepatic approach into the gallbladder fundus produced no ultrasonographic complications, whereas direct fundic puncture through a right ventral approach was associated with mild abdominal effusion in one subject and transient decreased appetite in four of twelve cats (Percutaneous ultrasound-guided cholecystocentesis in healthy cats). Detect bile leakage early by scanning the gallbladder fossa and right cranial abdomen immediately after needle withdrawal and again at 24 to 48 hours. Free anechoic fluid with echogenic strands, peritoneal thickening, or progressive distension warrants immediate surgical assessment.

Pancreatic scanning can induce or worsen clinical signs. Probe pressure over an inflamed pancreas aggravates pain, and excessive transducer force can obscure the very structures being examined. Monitor the patient for vocalisation, flinching, or tachycardia during compression. Reduce pressure, use a standoff pad, or switch to a higher frequency linear transducer to improve contact without force.

Hemorrhage after fine-needle aspiration of the spleen, liver, or kidney is usually self-limiting but can be significant in coagulopathic patients. Scan the puncture site continuously during withdrawal and for two minutes afterward. A developing subcapsular hematoma appears as a hypoechoic or anechoic crescent beneath the organ capsule. If the patient is unstable, obtain a coagulation panel before any interventional procedure.

Common Errors and Corrective Actions

Less experienced operators frequently mistake the splenic head or a renal crest for the pancreas, or they interpret a normal hypoechoic pancreas as a mass. The pancreas lies between the duodenum and the transverse colon on the right and between the spleen and stomach on the left. Trace the splenic vein to the portal vein, the left limb of the pancreas runs alongside it. When in doubt, identify the duodenal papilla as the termination point of the pancreatic duct.

Another frequent error is over-calling pancreatitis based on a single finding. Ultrasonographic changes correlate only weakly with the specific canine pancreatic lipase assay and moderately with a composite clinical diagnosis, and ultrasound severity does not mirror clinical severity indices (Association between abdominal ultrasound findings, the specific canine pancreatic lipase assay, clinical severity indices, and clinical diagnosis in dogs with pancreatitis). In cats, hyperechoic peripancreatic fat carries the highest sensitivity for pancreatitis at 68 percent, while increased pancreatic thickness, abnormal margination, and hyperechoic peripancreatic fat each exceed 90 percent specificity (Ultrasonographic findings of the pancreas in cats with elevated serum pancreatic lipase immunoreactivity). Use a combination of findings, not a single sign, before committing to a diagnosis.

A third error is failing to adjust gain and depth when moving between organs. The liver and spleen require different time-gain compensation than the bladder or kidney. Recheck settings whenever the target organ changes depth or echogenicity.

Limitations of the Evidence and Divergent Expert Opinion

The evidence base for abdominal ultrasound in small animals is uneven. Pancreatic ultrasonography is operator dependent, and the normal pancreas cannot be imaged consistently even with optimal technique (Ultrasonography of the pancreas). Studies of feline pancreatitis use serum feline pancreatic lipase immunoreactivity as the reference standard, but this assay itself has imperfect sensitivity, so ultrasound specificity may be underestimated or overestimated depending on the population (Ultrasonographic findings of the pancreas in cats with elevated serum pancreatic lipase immunoreactivity). Expert opinion differs on whether a normal ultrasound excludes significant pancreatic disease. Most specialists agree it does not, but some advocate repeated imaging at 48 to 72 hours when clinical suspicion remains high.

Mast cell disease illustrates another limitation. Ultrasonographically unremarkable livers and spleens can still contain mast cell infiltrates, so a normal study does not rule out systemic disease (Ultrasonographic findings in abdominal mast cell disease). Findings such as hypoechoic nodules, organomegaly, and rounded lymph nodes are suggestive but not pathognomonic. Cytology or histopathology remains necessary for confirmation.

Referral, Consultation, and Reporting Thresholds

Refer to a board-certified radiologist or internist when findings are equivocal, when the pancreas cannot be adequately assessed despite optimal technique, or when an interventional procedure carries high hemorrhagic risk. Specialist consultation is also warranted when ultrasound findings conflict with laboratory results or clinical progression. The American College of Veterinary Radiology maintains directories of diplomates and practice standards for diagnostic imaging (American College of Veterinary Radiology resources).

Laboratory involvement is indicated before any biopsy or aspiration. A minimum database of platelet count, coagulation times, and buccal mucosal bleeding time should be reviewed. If the patient is anemic or thrombocytopenic, delay elective sampling until the coagulopathy is addressed.

Regulatory reporting applies when zoonotic disease is suspected, such as larval cestode infection or leptospirosis, or when a notifiable disease is identified. The World Organization for Animal Health maintains the terrestrial animal health code that defines reportable diseases and surveillance expectations (WOAH terrestrial animal health standards). Local requirements vary, so confirm the current list with the relevant national authority before proceeding.

Frequently Asked Questions

How should I adapt the systematic abdominal scan when only a low-frequency curvilinear transducer is available?

A 5 to 8 MHz curvilinear probe remains serviceable for most abdominal surveys in dogs and cats, but resolution of superficial structures such as the adrenal glands, pancreas, and intestinal wall layers will be reduced. Increase the scanning depth and use the focal zone to target the region of interest. Apply gentle transducer pressure to displace bowel gas, and reposition the patient to bring deeper organs closer to the probe. For fine detail, consider a standoff pad or acoustic coupling gel to improve near-field resolution. If a high-frequency linear probe is unavailable, document the limitations in the report and note that subtle lesions may have been missed.

What is the minimum number of images required for a defensible abdominal ultrasound report?

There is no published standard mandating a specific image count, but a complete study should include at least one longitudinal and one transverse clip or still image of each solid organ, plus representative images of the urinary bladder, prostate or uterus, and gastrointestinal segments. Capture the pancreas only when visible, and record peripancreatic fat in both right and left cranial quadrants. Include cine loops for the liver, spleen, and kidneys to document vascular flow with Doppler. A minimum of 12 to 16 images is typical for a full survey. The American College of Veterinary Radiology resources provide guidance on study completeness and image labeling expectations.

How do I distinguish a true pancreatic lesion from a loop of small intestine on ultrasound?

The pancreas is isoechoic to surrounding fat in many cats and some dogs, making it difficult to identify consistently. A normal pancreas is often invisible, and the institutional description of pancreatic ultrasonography notes that inability to image the normal pancreas is a recognized limitation. To differentiate pancreas from bowel, trace the structure in two planes. Intestine shows peristalsis, a five-layer wall pattern, and continuity with adjacent loops. The pancreas does not peristalse and lies dorsal to the stomach and duodenum on the right and dorsal to the spleen on the left. The splenic vein courses along the left limb of the pancreas and serves as a reliable landmark.

Should I recommend abdominal ultrasound in a cat with suspected pancreatitis but normal pancreatic lipase immunoreactivity?

Ultrasound can still contribute to the diagnostic workup. In a retrospective study of cats with elevated serum feline pancreatic lipase immunoreactivity, the ultrasonographic findings of the pancreas in cats showed that hyperechoic peripancreatic fat had the highest sensitivity at 68 percent, while increased pancreatic thickness, abnormal margins, and hyperechoic fat each had specificity above 90 percent. A normal ultrasound does not exclude pancreatitis, and an abnormal ultrasound does not confirm it. Use ultrasound to identify concurrent disease such as cholangitis, inflammatory bowel disease, or neoplasia, and to guide sampling. The test is best interpreted alongside clinical signs and laboratory data instead of in isolation.

How should I explain the limitations of abdominal ultrasound to a client who expects a definitive diagnosis?

Frame the discussion around what ultrasound can and cannot show. Explain that ultrasound provides real-time images of organ structure, but it cannot always distinguish inflammation from neoplasia, and some diseases produce no visible changes. For example, the retrospective study of abdominal mast cell disease found that two ultrasonographically unremarkable canine livers and one unremarkable spleen were infiltrated by mast cells. Advise the client that ultrasound is one step in a diagnostic plan, and that cytology or histopathology may be required for a definitive answer. Set expectations about cost, sedation requirements, and the possibility of repeat imaging.

What are the practical considerations for ultrasound-guided cholecystocentesis in a cat?

Percutaneous ultrasound-guided cholecystocentesis is feasible in cats but carries a risk of bile peritonitis. In an experimental study of healthy cats, percutaneous ultrasound-guided cholecystocentesis was performed with a 22-gauge needle via a right-sided transhepatic approach or directly into the gallbladder fundus. Mild abdominal pain and decreased appetite occurred in 4 of 12 cats within 2 days, and one cat developed a small volume of effusion immediately after aspiration. Use a transhepatic approach when possible to seal the puncture tract, aspirate gently to avoid gallbladder collapse, and monitor the patient for 24 to 48 hours. Reserve the procedure for cases where bile analysis will change management.

Related Clinical & Scientific Guides

• MRI Monitoring of Brain Tumor Response to Therapy in Dogs
• Ultrasound-Guided Drainage of Abscesses in Small Animals
• Radiographic Monitoring of Total Hip Replacement in Dogs

References and Further Reading

• Ultrasonography of the pancreas.. 1991.
• Ultrasonographic findings in abdominal mast cell disease: a retrospective study of 19 patients.. 2004.
• Quantification of murine pancreatic tumors by high-resolution ultrasound.. 2013.
• Percutaneous ultrasound-guided cholecystocentesis in healthy cats.. 2003.
• Association between abdominal ultrasound findings, the specific canine pancreatic lipase assay, clinical severity indices, and clinical diagnosis in dogs with pancreatitis.. 2020.
• Ultrasonographic findings of the pancreas in cats with elevated serum pancreatic lipase immunoreactivity.. 2013.
• American College of Veterinary Radiology Resources. American College of Veterinary Radiology.
• MSD Veterinary Manual, Professional Edition. MSD Veterinary Manual.
• American Veterinary Medical Association Practice Resources. American Veterinary Medical Association.

Related Articles

• Radiographic Evaluation of the Canine and Feline Thorax: Cardiac and Pulmonary Assessment
• Imaging the Canine and Feline Spine: Radiography and Advanced Modalities
• Ultrasound of the Canine and Feline Gastrointestinal Tract: Normal and Abnormal Findings
• Thoracic Radiograph Patterns in Dogs: Differential Diagnosis and Clinical Approach
• Ultrasound of the Canine and Feline Liver and Biliary System: Normal and Abnormal Findings

This article is educational professional reference material for veterinary audiences. It is not a substitute for veterinary diagnosis, individual clinical judgment, current product labeling, or applicable regulatory requirements.