What can an ultrasound of a feline gallbladder tell me?

Familiarity with the normal feline gallbladder is essential before subtle or early change can be recognised. Without a clear baseline, normal anatomical variation can be mistaken for pathology, or early disease can be overlooked. In cats, the gallbladder is typically located between the quadrate and right medial liver lobes and appears narrow and elongated, with a thin, smooth wall and an anechoic lumen when bile is normal.

Consistency in measurement technique is critical when assessing the biliary tree, particularly the common bile duct. Measurements taken at the porta hepatis will provide the most reliable reference point, as this region is less affected by transient changes in duodenal filling or patient positioning. Using the same anatomical landmarks across serial scans allows subtle progression or resolution of ductal changes to be identified with greater confidence.

Gallbladder imaging is often affected by gas, rib shadowing or poor acoustic windows, particularly in cats with gastrointestinal disease. Small adjustments in positioning and scanning planes can improve visualisation and reduce the risk of artefact being misinterpreted as true intraluminal or wall pathology.

Clinically, not all echogenic material within the gallbladder is abnormal. Fine sludge often layers dependently and shifts position when the patient is moved, reflecting thickened bile rather than structural disease. In contrast, organised mucus forms more structured patterns that remain fixed within the lumen and may create stellate or striated appearances. These non-mobile patterns suggest abnormal bile composition and early mucocele type change, even without complete obstruction.

Features originating from the gallbladder wall rather than its contents suggest a different disease process. For example, wall thickening, layering or a hypoechoic halo is more consistent with inflammation or compromised perfusion than simple bile stasis. When these findings are present, particularly alongside reduced appetite, vomiting, abdominal discomfort or systemic illness, they are more likely linked to inflammatory biliary disease than incidental sludge.

Occasionally, highly echogenic foci with acoustic shadowing may be identified within the gallbladder lumen or wall. Although these findings can indicate mineralisation or cholelith formation, they are uncommon in cats and are not always clinically significant. Without supporting evidence such as ductal obstruction, pain or biochemical disturbance, isolated shadowing structures should be interpreted cautiously to avoid unnecessary escalation.

Ideally, gallbladder ultrasound findings should guide clinical decisions around management, further investigation and urgency. In practice, this includes:

• Context matters with sludge
  Gallbladder sludge is a common ultrasound finding and, on its own, does not always indicate infection or justify antimicrobial therapy without supporting clinical or biochemical evidence.
• Using ultrasound to inform further investigation
  Imaging helps determine whether diagnostics such as bile sampling or liver aspirates are likely to change management, rather than adding unnecessary intervention.
• Urgency depends on the whole picture
  The clinical significance of ultrasound findings increases when paired with systemic illness or changes such as ductal obstruction, gallbladder wall thickening or peritoneal fluid.

Essentially, a feline gallbladder ultrasound can reveal a great deal for veterinarians, from highlighting obstruction risk to characterising intraluminal material and guiding next steps. Interpretation, however, will always rely on context.

At Cat Specialist Services, our internal medicine team works closely with referring vets to support complex biliary cases, whether that involves image review, outpatient ultrasound, recommendations for further investigation or ongoing case management. Referrals and discussions are always welcome.

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