CANINE MEDICINE
sheepdogs.12 While extrahepatic biliary duct obstruction is a recognized cause of mucocele formation in
people, prospective studies in dogs do not support
this finding.13 Conversely, it appears that extrahepatic
biliary duct obstruction is secondary to mucocele formation.14
Other suggested causes of canine mucocele formation include progestational therapy or progestational
compounds, cholecystitis, and glucocorticoid excess.4,15,16 To date, none of these theories has been
widely supported.
displays a distinctive striated or stellate (kiwi fruit or
starfish) pattern (Figures 3 & 4).17
If differentiation is difficult, a second ultrasonographic
examination after the administration of a cholagogue
(an agent that promotes increased bile flow from the
gallbladder, such as cholecystokinin octapeptide given intravenously over one minute at a dose of 0.04
µg/kg23 ) may be helpful. If a patient has biliary sludge,
gallbladder contraction occurs within 10 minutes, and
It has been proposed that mucocele formation is the
result of progressive biliary sludging.17 As biliary sludge
forms and progresses, gallbladder motility may be decreased, resulting in biliary stasis and increased water
absorption. As the gallbladder continues to absorb
water, its contents become more solid and immobile.
The most widely supported theory of canine mucocele formation implicates mucus-secreting cell
proliferation and dysfunction.18 In this condition, cystic mucinous hyperplasia of the gallbladder epithelium
occurs, and the gallbladder epithelial cells secrete excessive mucus into the gallbladder lumen. This condition may be a primary defect (an inherent disorder of
the mucous cells) or a secondary defect (exposure to
excessive bile salts).19
Diagnosing Gallbladder Mucocoeles
History and signalment
Most patients with mucocoeles are older (average
age of 9 years), and no sex predilection has been established.11 Mucocoeles are usually reported in small
or medium-sized dogs, and Shetland Sheepdogs and
Cocker Spaniels are overrepresented.20 In one study,
66% of Shetland Sheepdogs with gallbladder disease
had confirmed mucocoeles.12
Figure 3. A transverse ultrasonogram of a canine gallbladder
containing normal biliary sludge. The echogenic material within
the gallbladder has fallen dorsally, and the supernatant of more
normal bile can be appreciated ventrally as an anechoic area.
(Image courtesy of Dr. Benjamin D. Young, Texas A&M University's Large Animal Clinical Sciences Department of Radiology.)
Clinical Signs
About 77% of patients with mucocoeles are clinically ill, often with an acute onset of signs.21 Vomiting,
anorexia, lethargy, polyuria, polydipsia, and diarrhea
are most often reported.21 Cumulatively, studies have
shown that almost one-quarter of patients with mucocoeles were asymptomatic.10,14,17,18,22
Physical Examination Findings
The most common physical examination findings in
patients with mucocoeles are abdominal pain and icterus. A small percentage of patients may be febrile or
have abdominal distention.18
Diagnostic Test Results
Laboratory evaluation and radiographic findings may
vary, but common results are listed in Table 1. It may
be difficult to appreciate the differences between biliary sludge and a true mucocele on ultrasonographic
examination. Biliary sludge is movable and gravitydependent, whereas a mucocele is immobile and
Figure 4. A transverse ultrasonogram of a canine gallbladder
containing a mucocele. This image demonstrates the classic
stellate pattern and nongravity-dependent gallbladder contents
pathognomonic for mucoceles. (Image courtesy of Dr. Benjamin D. Young, Texas A&M University's Large Animal Clinical Sciences Department of Radiology.)
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