Ultrasound of the Canine and Feline Liver and Biliary System: Normal and Abnormal Findings

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

Key Takeaways

• Ultrasonography is the primary imaging modality for evaluating canine and feline hepatic and biliary systems, assessing parenchymal echotexture, vascular architecture, and biliary distension in real-time without ionizing radiation. Normal hepatic echogenicity is typically isoechoic or slightly hyperechoic to the renal cortex in dogs, and hypoechoic to the spleen.
• Diffuse hepatic hyperechogenicity, often seen with lipidosis, steroid hepatopathy, or fibrosis, is a common abnormality. In cats, hepatic lipidosis is characterized by a diffusely hyperechoic liver, hepatomegaly, rounded margins, and attenuated vascular walls, often requiring further investigation with biochemistry and cytology.
• Biliary obstruction is identified by dilation of intrahepatic bile ducts (the "double-barrel" sign) and extrahepatic bile ducts, with normal diameters generally not exceeding 3 mm in dogs and 4 mm in cats at the porta hepatis. Causes include pancreatic masses, duodenal neoplasia, and cholangitis.
• Focal hepatic lesions, such as cysts and nodules, require characterization by echogenicity, margins, and vascularity. Ultrasound-guided fine-needle aspiration has limited accuracy (30.3% cytologic-histologic agreement in dogs, 51.2% in cats), often necessitating core biopsy or surgical wedge biopsy for definitive diagnosis, particularly for suspected neoplasia or when cytology is non-diagnostic.
• In cats, cholangitis frequently coexists with pancreatitis, and while hepatic parenchyma may be normal, findings like hyperechoic liver parenchyma, hyperechoic gallbladder contents, and pancreatic enlargement are statistically significant indicators. A normal ultrasound does not exclude feline cholangitis, and bile aspiration for culture and cytology is diagnostically valuable.
• Complications of ultrasound-guided sampling include hemorrhage, bile peritonitis, and pneumothorax. Early detection involves immediate post-procedure scanning with Doppler interrogation for hemorrhage, observation for bile tracking for peritonitis, and thoracic scanning for pneumothorax if respiratory distress occurs.

Ultrasonography is the first-line imaging modality for evaluating hepatic and biliary disease in dogs and cats. It provides real-time assessment of parenchymal echotexture, vascular architecture, biliary distension, and focal lesions without ionizing radiation. This article serves the practicing veterinarian who needs a structured approach to the hepatic ultrasound examination, from normal variants through diffuse disease, nodular lesions, and biliary obstruction. It addresses the diagnostic reasoning that connects sonographic patterns to differential diagnoses and guides decisions about sampling and advanced imaging.

The liver is the largest solid organ in the abdomen, and its sonographic appearance overlaps substantially between health and disease. In cats, the biliary tree is affected by disease more often than the hepatic parenchyma itself, which is frequently involved secondarily to systemic illness, as described in the feline biliary tree and gallbladder disease review. This species difference shapes the examination priorities and the interpretation framework presented here. The article assumes familiarity with basic ultrasound physics, transducer selection, and image optimization.

At a Glance

Physics and Technique Principles

Ultrasound image quality in the cranial abdomen depends on transducer frequency, focal zone placement, and patient preparation. A microconvex or phased-array transducer in the 5 to 8 MHz range suits most dogs, cats and small dogs benefit from 8 to 12 MHz probes. Fasting for 8 to 12 hours reduces gastric gas and gallbladder contraction, although the gallbladder may still appear partially collapsed in some individuals. The liver is examined from the right and left subcostal windows, with the patient in dorsal and lateral recumbency. Intercostal approaches are often necessary in deep-chested dogs.

Depth and gain settings should be adjusted so that the diaphragm appears as a thin, curved hyperechoic line and the liver parenchyma displays a homogeneous, medium-level echogenicity. The near field of the left liver lobes is prone to reverberation artifact from overlying stomach gas. Changing the patient's position or using a standoff pad can reduce this artifact. Color Doppler interrogation of the portal vein, hepatic veins, and caudal vena cava should be part of every hepatic examination, because vascular patency and flow direction carry diagnostic weight in portal hypertension and congenital shunts.

Normal Sonographic Anatomy

The liver occupies the cranial abdomen, caudal to the diaphragm and surrounding the caudal vena cava and portal vein. The left lateral and left medial lobes lie to the left of midline, the quadrate and right medial lobes near the gallbladder, and the caudate lobe adjacent to the right kidney. The gallbladder sits in a fossa between the quadrate and right medial lobes, appearing as an anechoic, pear-shaped structure with a thin, barely perceptible wall. Bile is normally anechoic, although echogenic, dependent sludge is common in both species and may be clinically insignificant.

The portal vein branches are identified by their hyperechoic, echogenic walls, which result from the fibrous tissue in the portal triads. Hepatic veins have thin walls and course toward the caudal vena cava. This distinction is fundamental: portal veins carry blood from the gastrointestinal tract to the liver, while hepatic veins drain the liver into the systemic circulation. The main portal vein is measured at its entry into the liver, just caudal to the porta hepatis, and normally does not exceed approximately 10 mm in dogs. The hepatic artery is usually not visible in normal dogs but may become prominent in inflammatory or neoplastic conditions.

Normal hepatic parenchyma is homogeneous and of medium echogenicity. In dogs, the liver is typically isoechoic to the renal cortex and hypoechoic to the spleen. In cats, the liver is often slightly hyperechoic to the renal cortex. The echogenicity comparison to the spleen is less reliable in cats because the normal feline spleen is more variable in appearance. The liver margins are sharp, and the diaphragmatic surface is smooth. The caudate lobe is visible dorsal and lateral to the right kidney, and its size and shape vary with body condition.

Diffuse Parenchymal Disease

Diffuse hepatic disease produces changes in echogenicity, size, and texture that are often subtle and nonspecific. Hyperechoic parenchyma is the most common abnormality and occurs when fat, fibrosis, or both replace normal hepatocytes. In cats, diffuse hyperechogenicity is a hallmark of hepatic lipidosis, in which the liver is also enlarged with rounded margins and attenuated vascular walls. The ultrasonographic findings of feline cholangitis study found that most cats with histologically confirmed cholangitis had normal liver size and echogenicity, but those with hyperechoic parenchyma, echogenic gallbladder contents, and pancreatic enlargement were more likely to have the disease. This combination of findings should prompt evaluation of the pancreas and biliary tree in any cat with suspected cholangitis.

Hypoechoic parenchyma is less common and may reflect acute hepatitis, congestion, or infiltration with neoplastic cells. A mottled or heterogeneous appearance suggests multifocal disease, which may be inflammatory, neoplastic, or vascular in origin. The liver size should be assessed subjectively and, when possible, objectively. Hepatomegaly is present when the liver extends beyond the costal arch, the caudal margins are rounded, and the stomach is displaced caudodorsally. Microhepatica is more difficult to confirm sonographically but is suggested by a small liver with an enlarged, hyperechoic spleen and ascites, findings that accompany cirrhosis.

In cats with feline infectious peritonitis, hepatic changes are common. The abdominal ultrasonographic findings of cats with feline infectious peritonitis study reported hepatic abnormalities in 80% of affected cats, most frequently hepatomegaly and a hypoechoic liver. These findings are nonspecific, but when combined with effusion, lymphadenopathy, and intestinal wall changes, they support a clinical diagnosis of FIP. The same study emphasized that no single sonographic finding is diagnostic, and confirmation requires molecular testing or histopathology.

Focal and Nodular Lesions

Focal hepatic lesions are categorized by echogenicity, margin definition, internal architecture, and vascularity. Simple cysts are anechoic, thin-walled, and show distal acoustic enhancement. They are common in older cats and are usually incidental. The feline biliary tree and gallbladder disease review notes that ultrasound identifies liver cysts and dilated bile ducts reliably, but it does not distinguish cyst types or predict malignant potential. Polycystic liver disease, associated with concurrent renal cysts, occurs in both species and carries a guarded prognosis.

Nodules are more challenging. Benign nodular hyperplasia produces hypoechoic or isoechoic nodules with smooth margins, and it is common in older dogs. Primary or metastatic neoplasia may appear as hypoechoic, hyperechoic, or target lesions, and the appearance overlaps with abscesses, granulomas, and hematomas. Contrast-enhanced ultrasound improves characterization of focal lesions by assessing perfusion patterns, but it is not widely available in general practice. The decision to sample a nodule should be based on size, number, clinical context, and the owner's willingness to pursue treatment. Ultrasound-guided fine-needle aspiration is a rapid, low-morbidity procedure, but its accuracy is limited. The accuracy of ultrasound-guided fine-needle aspiration of the liver study reported overall cytologic-histologic agreement in only 30.3% of canine and 51.2% of feline cases, with inflammatory disease correctly identified in fewer than half of affected animals. Core biopsy or surgical wedge biopsy remains the standard for definitive diagnosis when the cytologic result does not match the clinical picture.

Biliary System and Obstruction

The gallbladder and biliary tree are examined for wall thickness, luminal contents, and duct diameter. Gallbladder wall thickening in cats is associated with cholangitis, cholecystitis, and neoplasia, but it also occurs with hypoalbuminemia and right-sided heart failure. Echogenic bile, or sludge, is common and usually benign, but it can precede cholelith formation. Choleliths appear as hyperechoic foci with distal shadowing and may be incidental or associated with obstruction.

Extrahepatic bile duct obstruction produces dilation of the intrahepatic bile ducts, which appear as parallel, branching anechoic tubes adjacent to portal veins, the so-called "double-barrel" or "shotgun" sign. The common bile duct is measured at the porta hepatis, and dilation beyond 3 mm in dogs or 4 mm in cats is abnormal. Causes include pancreatic masses, duodenal neoplasia, choleliths, and stricture. In cats, cholangitis and pancreatitis frequently coexist, and the magnetic resonance imaging and cholangiopancreatography findings in cats with cholangitis and pancreatitis study demonstrated that MRI detects pancreatic duct dilation and parenchymal signal changes more sensitively than ultrasound. When sonographic findings are equivocal and clinical suspicion remains high, advanced imaging or exploratory surgery is warranted.

Structured Assessment Protocol for Hepatic and Biliary Ultrasound

A consistent scanning sequence reduces the risk of overlooking clinically significant findings. Begin with the liver in its entirety using a microconvex or curvilinear transducer in dogs and a high-frequency linear or microconvex transducer in cats. Sweep from the diaphragmatic surface to the caudal margin in both sagittal and transverse planes. Record the following in every examination: overall echogenicity relative to the falciform fat and renal cortex, parenchymal texture, hepatic margins, vascular conspicuity, and the appearance of the gallbladder and extrahepatic bile ducts.

Assess the gallbladder for wall thickness, luminal content, and distension. The normal feline gallbladder wall measures less than 1 mm when imaged perpendicular to the ultrasound beam. Wall thickening in cats is a non-specific finding that accompanies cholangitis, pancreatitis, and feline infectious peritonitis. In the retrospective series of cats with confirmed or presumed FIP, hepatic changes were present in 80% of cases, most commonly hepatomegaly and a hypoechoic liver, and these findings were frequently accompanied by abdominal effusion and lymphadenopathy. Gallbladder wall thickening alone does not distinguish inflammatory from neoplastic or infectious causes, and the finding must be interpreted alongside the complete abdominal examination.

Evaluate the intrahepatic biliary tree by tracing the portal branches. Normal intrahepatic bile ducts are not visible as discrete structures. When visible, they appear as tubular anechoic structures running parallel to portal veins, and their presence indicates dilation. The extrahepatic bile duct in dogs normally measures up to 5 mm, and in cats up to 4 mm. Measurements should be taken at the porta hepatis with the transducer aligned along the long axis of the duct. A duct that exceeds these dimensions, or that fails to decrease in size after a meal, warrants investigation for obstruction.

Decision Points in Diffuse Parenchymal Disease

Diffuse parenchymal changes are common and often non-specific. The sonographic pattern must be integrated with biochemical findings, signalment, and the presence of extrahepatic disease.

A diffusely hyperechoic liver with normal or increased size and attenuated visualization of the portal vessel walls is typical of vacuolar hepatopathy, steroid hepatopathy, or hepatic lipidosis. In cats, hepatic lipidosis is a diagnostic priority when the liver is hyperechoic relative to the falciform fat and the patient is anorexic and icteric. However, the retrospective study of feline cholangitis found that most affected cats had sonographically normal liver size, echogenicity, and biliary systems. Statistically significant changes in that cohort included hyperechoic liver parenchyma, hyperechoic gallbladder contents, and increased pancreatic size. The authors noted that cats with this combination of findings may have cholangitis, but the absence of sonographic abnormalities does not exclude the diagnosis. A normal ultrasound examination does not rule out inflammatory biliary disease, and biopsy or bile culture remains necessary when clinical suspicion is high.

A diffusely hypoechoic liver is less common. In cats, this pattern has been associated with FIP, as described above, and with lymphoma. In dogs, a hypoechoic liver may accompany acute hepatitis, sepsis, or infiltrative neoplasia. The finding is non-specific and should prompt cytologic or histologic sampling.

The normal feline liver is homogeneous and slightly hypoechoic or isoechoic to the spleen. Ultrasound elastography has been investigated as a non-invasive tool to characterize feline liver tissue, but strain values did not differ significantly between the liver, spleen, and kidneys in healthy cats, and the body wall was the only structure with a significantly different value. Elastography therefore does not currently replace tissue sampling for diagnosis of feline hepatic disease.

Nodular Lesions and Sampling Strategy

Focal and nodular lesions require a systematic approach to characterization and sampling. Benign nodular hyperplasia is common in older dogs and appears as well-defined, isoechoic or mildly hyperechoic nodules that do not distort the hepatic capsule. Nodular regeneration in cirrhosis produces similar appearances but is accompanied by parenchymal architectural distortion, irregular margins, and ascites. Metastatic disease typically presents as multiple hypoechoic nodules of variable size, although hyperechoic or target lesions occur. Primary hepatic neoplasia, including hepatocellular carcinoma and biliary carcinoma, may be solitary or multifocal and often shows heterogeneous echogenicity with central necrosis.

Ultrasound-guided fine-needle aspiration is a rapid and minimally invasive technique, but its accuracy is limited. In a retrospective series of 97 dogs and cats, overall agreement between cytologic and histopathologic diagnoses was 30.3% in dogs and 51.2% in cats. Vacuolar hepatopathy was the category with the highest agreement, yet it was also the most commonly misdiagnosed category cytologically. Inflammatory disease was accurately identified in only 5 of 20 dogs and 3 of 11 cats. These figures support a policy of obtaining histologic samples whenever the cytologic result would change management, when the lesion is suspected to be neoplastic, or when the cytologic findings are non-diagnostic.

Core biopsy under ultrasound guidance is preferred for nodular lesions and for diffuse disease when architectural information is required. Use a 16 to 18 gauge automated biopsy needle, sample the periphery of a nodule to avoid central necrosis, and obtain at least two cores from different sites. Coagulation status should be assessed before biopsy, and the patient monitored for 6 to 12 hours afterward for hemorrhage. In cats, the smaller liver volume and thinner capsule increase the risk of hemorrhage, and a transhepatic approach through a margin of normal parenchyma is recommended.

Biliary Obstruction and Extrahepatic Bile Duct Assessment

Extrahepatic biliary obstruction produces a characteriztic pattern of dilated intrahepatic bile ducts, a distended gallbladder, and a visible extrahepatic bile duct. The most common causes in dogs are pancreatic masses, duodenal masses, and cholangitis. In cats, cholangitis, pancreatitis, and biliary neoplasia predominate. The feline biliary tree is the primary target for infectious and non-infectious disease, and parenchymal changes are often secondary to systemic illness.

When obstruction is suspected, measure the extrahepatic bile duct at its widest point and document the level of obstruction. A dilated duct that terminates abruptly at a mass or thickened pancreatic region localizes the lesion. The gallbladder should be assessed for distension, wall thickening, and the presence of sediment or choleliths. Hyperechoic gallbladder contents were a statistically significant finding in cats with cholangitis, and the presence of biliary sludge does not by itself indicate obstruction.

Percutaneous bile aspiration under ultrasound guidance is a valuable diagnostic step in cats with suspected cholangitis. The technique carries a risk of bile peritonitis if the gallbladder wall is not apposed to the liver, and the aspirate should be submitted for cytology and aerobic culture. Antibiotic therapy should not be delayed pending culture results, and the choice of agent should follow current formulary and label references. In cats, the frequent association between cholangitis and pancreatitis means that the pancreas must be examined carefully in every biliary case. Magnetic resonance cholangiopancreatography has demonstrated advantages over sonography in detecting pancreatic parenchymal changes and pancreatic duct dilation in cats with suspected cholangitis and pancreatitis, and it should be considered when sonographic findings are equivocal and advanced imaging is available.

Documentation and Reporting

The ultrasound report should record the transducer frequency, patient positioning, and the specific findings for each hepatic and biliary parameter. Include measurements of the extrahepatic bile duct and gallbladder wall, a description of parenchymal echogenicity relative to the renal cortex and falciform fat, and the number, size, and echogenicity of any nodules. State whether the intrahepatic bile ducts are visible and whether the gallbladder contains sludge, sediment, or choleliths. Describe the pancreas and the regional lymph nodes, because concurrent pancreatic disease changes the differential list and the sampling plan.

Images should be labelled with the patient identifier, date, and transducer orientation. Cine loops are useful for documenting vascular patency and bile duct continuity. The report should distinguish between findings that are diagnostic, findings that are suggestive but require confirmation, and findings that are incidental. This distinction guides the referring clinician and prevents over-interpretation of non-specific changes. Where the evidence base is limited, as with elastography and the sonographic differentiation of cholangitis subtypes, the report should acknowledge the uncertainty and recommend the appropriate confirmatory test.

Recognized Complications and Early Detection

Ultrasound-guided sampling of the liver and biliary system carries specific risks. Hemorrhage is the most common complication after fine-needle aspiration or biopsy, particularly in patients with coagulopathy, thrombocytopenia, or vascular neoplasia such as haemangiosarcoma. Detect hemorrhage early by scanning the sampling site immediately after needle withdrawal and again 5 to 10 minutes later. Free fluid accumulating around the liver, a new anechoic pocket at the biopsy site, or a progressively distending gallbladder fossa all indicate active bleeding. Doppler interrogation before sampling identifies large vessels along the needle path, and color Doppler after sampling can confirm ongoing extravasation.

Bile peritonitis follows inadvertent puncture of the gallbladder or a distended extrahepatic bile duct. The risk rises when the gallbladder is markedly distended, the wall is thickened or necrotic, or the patient has cholangitis with a friable biliary tree. Detect this complication by observing bile tracking along the needle tract during aspiration, by noting new peritoneal fluid after the procedure, or by re-scanning the gallbladder for collapse or wall disruption. Clinical deterioration with progressive abdominal pain, vomiting, or fever within 24 to 48 hours warrants immediate surgical evaluation.

Pneumothorax occurs when a cranial intercostal approach is used and the needle crosses the pleural space. The right cranial liver lobes lie close to the diaphragm, and the costophrenic recess can be entered with a steeply angled needle. Detect this early by visualizing the needle tip in real time throughout the pass, by watching for the pleural line moving away from the chest wall, and by scanning the thorax after sampling if the patient shows respiratory distress. A shallow angle, a subcostal approach where feasible, and breath-holding during the pass reduce this risk.

Common Errors and Corrective Actions

Less experienced operators frequently mistake the right kidney or the pancreatic body for a liver lobe when the hepatic echogenicity is markedly reduced. The kidney has a distinct capsule and corticomedullary junction, while the pancreas lies caudal to the portal vein and is more oval in cross-section. Confirm the liver by identifying the portal vein branches with their echogenic walls and the hepatic veins with their thin walls converging on the caudal vena cava.

Another frequent error is diagnosing biliary obstruction from a single dilated bile duct without confirming the level and cause. A dilated common bile duct with a normal gallbladder does not confirm extrahepatic obstruction, because cholestasis from sepsis, hemolysis, or fasting can also distend the duct. Trace the duct to its termination at the duodenal papilla, assess the gallbladder for concurrent distension, and correlate with serum bilirubin and liver enzyme activity before concluding obstruction.

Misinterpreting the gallbladder wall as thickened when the patient is not fasted is common. The normal gallbladder wall can appear artificially thick when the lumen is contracted or when the transducer is angled obliquely through the wall. Measure the wall perpendicular to the lumen and repeat after a 12-hour fast. Similarly, echogenic gallbladder contents are often dismissed as sludge, but in cats this finding is statistically associated with cholangitis and warrants further investigation.

A third error is sampling a single nodule and concluding that the entire liver is benign or malignant. Cytology from one site frequently misses inflammation or neoplasia elsewhere, and the agreement between cytologic and histopathologic diagnoses is limited in both dogs and cats. Sample multiple lobes, include parenchyma away from visible nodules, and submit tissue for histopathology when the cytologic result does not match the clinical picture.

Troubleshooting Table

Evidence Limitations and Referral Criteria

The evidence base for hepatic and biliary ultrasound in small animals has notable gaps. Most studies are retrospective, use small sample sizes, and lack standardized histopathologic correlation. The sonographic features of feline cholangitis overlap substantially with those of hepatic lipidosis and lymphoma, and no single B-mode finding reliably distinguishes these conditions. Ultrasound elastography has been investigated in healthy cats, but strain values did not differ between organs, and the technique has not yet been validated for distinguishing diffuse hepatic disease in clinical patients. Advanced imaging such as MRI and MR cholangiopancreatography can identify pancreatic and biliary abnormalities that sonography misses, but these modalities are not widely available and their routine use is not established.

Expert opinion still differs on several points. Some clinicians recommend routine fine-needle aspiration of the gallbladder for bile culture in cats with suspected cholangitis, while others reserve this for cases with sonographic biliary abnormalities. The role of hepatosupportive drugs in liquefying thick bile is described in the literature, but controlled efficacy data are lacking. The threshold for surgical intervention in cats with extrahepatic biliary obstruction remains debated, particularly when the obstruction is partial or when concurrent pancreatitis is present.

Referral to a specialist is warranted when the sonographic findings are equivocal, when the suspected disease is beyond the operator's experience, or when advanced imaging or interventional procedures such as endoscopic retrograde cholangiopancreatography are considered. Laboratory involvement is indicated when cytologic findings are non-diagnostic, when infectious disease such as feline infectious peritonitis is suspected, or when histopathology is required for definitive diagnosis. In cats with suspected FIP, hepatic changes such as hepatomegaly and hypoechogenicity are common but non-specific, and diagnosis relies on molecular testing or histopathology instead of ultrasound alone. Regulatory reporting is rarely triggered by hepatic ultrasound findings, but clinicians should be aware of reportable diseases in their jurisdiction through resources such as the WOAH terrestrial animal health standards and local professional guidance from bodies such as the AVMA practice resources.

Frequently Asked Questions

How should I proceed when only basic B-mode ultrasound equipment is available?

Basic B-mode equipment remains adequate for most hepatic and biliary assessments. High-frequency linear transducers improve near-field detail but are not essential for identifying hepatomegaly, diffuse echogenicity changes, large nodules, biliary distension, or gallbladder disease. Use a microconvex or curvilinear probe at 5 to 8 MHz for deep-chested dogs and a higher frequency for cats. When elastography or Doppler is unavailable, rely on B-mode findings combined with ultrasound-guided sampling. The American College of Veterinary Radiology resources provide guidance on minimum imaging standards. Document limitations in the report and refer cases where diagnostic confidence is compromised by equipment constraints.

When is cytology alone sufficient, and when should I recommend histopathology?

Cytology from ultrasound-guided fine-needle aspiration agrees with histopathology in roughly 30% of canine and 51% of feline cases, with vacuolar hepatopathy showing the highest agreement and inflammatory disease frequently misclassified. Use cytology when diffuse metabolic disease such as lipidosis or steroid hepatopathy is suspected, or when sampling is high risk. Recommend histopathology when cytology is non-diagnostic, when nodular lesions require architectural assessment, when cirrhosis is suspected, or when the clinical picture suggests neoplasia. Histopathology also remains necessary when cytologic findings conflict with biochemical and ultrasonographic data. Discuss the diagnostic gap with owners before sampling so expectations align with the limitations of each technique.

How does the diagnostic approach differ between cats and dogs with suspected biliary disease?

Feline biliary disease is more common than primary hepatic parenchymal disease, and cholangitis frequently coexists with pancreatitis. Cats with cholangitis often have sonographically normal liver size and biliary systems, so a normal ultrasound does not exclude the disease. Hyperechoic liver parenchyma, hyperechoic gallbladder contents, and pancreatic enlargement are the most consistent findings. In dogs, biliary obstruction from pancreatitis, neoplasia, or cholelithiasis is more readily identified by extrahepatic bile duct dilation. Cats also develop biliary mucoceles less commonly than dogs. The feline biliary tree and gallbladder disease review emphasizes that bile aspirates for culture and cytology are diagnostically valuable in cats, and ultrasound guidance facilitates this sampling.

What should I include in the ultrasound report to support clinical decision-making?

Record liver size, echogenicity relative to the spleen and falciform fat, parenchymal texture, and the presence of nodules with their size, number, and echogenicity. Describe the gallbladder wall thickness, luminal contents, and bile duct diameter. Note whether the extrahepatic bile duct is visible and measure it when dilated. Include Doppler findings if vascular assessment was performed. State whether sampling was attempted and which technique was used. The MSD Veterinary Manual provides reference ranges for normal biliary dimensions. Report limitations such as poor acoustic windows or gas artefact, and state a clear conclusion with differential diagnoses ranked by likelihood. This structure allows the clinician to act without repeating the examination.

How do I manage a cat with suspected feline infectious peritonitis and hepatic changes?

Hepatic changes occur in approximately 80% of cats with confirmed or presumed FIP, with hepatomegaly and hypoechoic parenchyma being the most common findings. These changes are non-specific, so the diagnosis relies on integrating abdominal ultrasound with effusion analysis, serum globulins, and molecular testing. The abdominal ultrasonographic findings in cats with FIP also report lymphadenopathy in 80% and intestinal wall changes in over half of cases. When FIP is suspected, sample effusion for coronavirus RT-PCR and perform histopathology or immunohistochemistry on affected tissues if feasible. Hepatic changes alone do not confirm FIP, and concurrent cholangitis or neoplasia must remain on the differential list.

How should I explain sampling recommendations to an owner when ultrasound findings are equivocal?

Frame the discussion around diagnostic certainty. Explain that ultrasound identifies structural changes but often cannot distinguish inflammation from neoplasia or fibrosis. Describe the difference between cytology, which examines individual cells, and histopathology, which evaluates tissue architecture. The accuracy of ultrasound-guided fine-needle aspiration of the liver demonstrates that cytology can miss inflammatory disease in a substantial proportion of cases. Use this evidence to justify why histopathology may be recommended despite additional cost and risk. Present the sampling plan, the complications that can occur, and the expected turnaround time for results. This approach respects the owner's need for transparent reasoning while supporting the diagnostic pathway.

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

• Feline biliary tree and gallbladder disease: Aetiology, diagnosis and treatment. 2017.
• Abdominal ultrasonographic findings of cats with feline infectious peritonitis: an update.. 2023.
• Ultrasonographic findings of feline cholangitis.. 2012.
• Magnetic resonance (MR) imaging and MR cholangiopancreatography findings in cats with cholangitis and pancreatitis.. 2013.
• Ultrasound elastography of the liver, spleen, and kidneys in clinically normal cats.. 2014.
• Accuracy of ultrasound-guided fine-needle aspiration of the liver and cytologic findings in dogs and cats: 97 cases (1990-2000).. 2004.
• 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.

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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.