Ultrasonographic prevalence and proposed morphologic classification of bilobed gallbladder in cats

Morphologic anomalies of the feline gallbladder (GB) have been previously reported in the literature. These morphologic variants are frequently encountered on routine abdominal ultrasound examination. The aim of this study was to provide an ultrasonographic classification system of these variants and document the overall incidence in the feline population.

A prospective, descriptive study was undertaken; cats that had an abdominal ultrasound examination that included at least one sagittal and transverse plane image of the GB were included. GB shape was evaluated and categorized based on a classification scheme of morphologic variants modified from the human literature. Septated (S), bilobed (B1, B2, B3), duplex (D) and complex (C) categories were described.

Of 516 cats included in the study, 389 had normal GB morphology, while 127 had anomalous GB morphology. The overall incidence rate of anomalous GB morphology was 24.61%. When examined by morphologic type, the septated (S) morphology had an incidence of 9.69%. A bilobed (B) morphology was the most commonly observed classification; incidence was 14.35% within our population; incidence of B1, B2 and B3 subtypes were 2.91%, 6.98% and 4.46%, respectively. Duplex GBs only made up 0.39% of the total population. The incidence of complex (C) morphologies was 0.19%.

The incidence of GB morphologic anomalies was higher in our population than previously reported. Identification of these anomalies on routine ultrasound evaluation is common; numerous different morphologies can be identified and a standardized classification scheme is proposed. Complete evaluation of morphology can be challenging, particularly with regard to cystic duct anatomy. Clinical significance is uncertain and future studies are warranted to determine the relationship between morphologic variants and hepatobiliary disease.