CT attenuation values and mineral distribution can be used to differentiate dogs with and without gallbladder mucoceles

Abstract

Gallbladder mucoceles are potentially fatal in dogs. Multiphase CT angiography was performed to evaluate the canine gallbladder in three conditions: no sludge, sludge occupying ≥25% of the lumen, and mucoceles. Twenty dogs with normal hepatobiliary bloodwork and no‐to‐minimal gallbladder sludge, 13 dogs with normal bloodwork and ≥25% sludge in the gallbladder lumen, and 18 dogs with histologically confirmed gallbladder mucoceles were enrolled in a prospective, observational diagnostic accuracy study. Three regions of interest (ROI) were stratified in the dorsal‐ventral orientation and a single ROI was measured within the hepatic parenchyma. Mean attenuation and presence of mineral were recorded. Average Hounsfield units (HU) were recorded for precontrast, arterial, portovenous, and late venous phases. The overall median HU value for mucoceles was significantly higher than gallbladders without sludge and with sludge; precontrast median overall attenuation was 49.3, 35.8, and 39.7 HU, respectively (P < .000004). Mineral was seen in four (20%) dogs with no sludge, seven (56%) dogs with sludge, and nine (50%) dogs with mucoceles. Mineral in the dogs with mucoceles was located within the central aspect of the gallbladder lumen in 67% of mucoceles; this mineral distribution was not seen in any dog without a mucocele. Computed tomography can differentiate a subset of gallbladder mucoceles from dogs with and without gallbladder sludge, especially in the precontrast series. An HU value of 48.6 is 52% sensitive and 96% specific for a gallbladder mucocele. A hyperattenuating gallbladder on precontrast CT images and centrally distributed mineral can be a gallbladder mucocele.

Computed tomographic features of confirmed gallbladder pathology in 34 dogs

“…As this material was seen predominantly in pathologies that cause mucin production, such as CMH and gallbladder mucoceles, we hypothesize that this hyperattenuating material may be due to mucinous material because of its distribution both in a gravity dependent and suspended locations throughout the gallbladder (Figure 7C,D). Similar hyperattenuating luminal contents were noted in dogs with gallbladder mucoceles 12 . Hyperattenuating material is an unexpected finding in dogs with gallbladder wall edema, bactibilia, and cholecystitis, but may be due to the presence of concurrent pathologies or gallbladder sludge that was undetected on gross pathology or cytology.…”

“…The presence of hyperattenuating material was defined as material that was 35-100 HU as this was expected to be hyperattenuating to the normal HU of bile that has been reported to be 34-35.8 HU. 12,13 Cystic mucosal hyperplasia, gallbladder mucocele, gallbladder wall edema, bactibilia, cholecystitis, and cholelithiasis were the pathologies most commonly associated with hyperattenuating material. As this material was seen predominantly in pathologies that cause mucin production, such as CMH and gallbladder mucoceles, we hypothesize that this hyperattenuating material may be due to mucinous material because of its distribution both in a gravity dependent and suspended locations throughout the gallbladder (Figure 7C,D).…”

“…Between the remainder of the pathologies present, the mean HU of bile remained between 28 and 42 HU, consistent with previous studies. 12,13 The lower HU in dogs with bactibilia suggests a reduced density of bile. Inflammation within the gallbladder has been suggested to alter gallbladder's water absorption ability, 21 and the presence of bacteria may lead to inflammation that could cause a less concentrated bile, lowering the HU.…”

“…Mineral attenuating material was designated as any material >100 HU 12 . Mineral attenuation material was the most common finding of all the various pathologies evaluated.…”

“…13 It was noted that the gallbladder volume and CBD diameter as assessed on ultrasound were not significantly different from CT. 13 In regard to the use of CT for evaluation of gallbladder mucoceles, dogs with mucoceles have higher attenuating gallbladder luminal contents and often have centrally distributed mineral as compared to dogs with gallbladder sludge or no gallbladder sludge. 12 For evaluation of the biliary tract using CT cholangiography, F I G U R E 1 Transverse images, precontrast (B, D) and postcontrast (A, C, E), in soft tissue window (window level: 40, window width: 350); slice thickness: (A) 2.5 mm, (B-E) 5 mm; algorithm: (A) detail, (B-E) soft tissue. A, Normal gallbladder wall thickness in a dog with white bile.…”