Veterinary Medicine - April 2009 - (Page 171)

Gallbladder mucoceles PEER-REVIEWED gallbladder contraction include parasympathetic stimulation by the vagus nerve, sympathetic inhibition of the splanchnic nerve, neurotensin, and substance P.6-8 Gallbladder relaxation 1. A surgically removed canine gallbladder with a mucocele. The cystic duct has been ligated and removed, and the resultant opening allows visualization into the distended gallbladder. (Image courtesy of Dr. Roy R. Pool, Texas A&M University’s Department of Veterinary Pathobiology.) The gallbladder relaxes in response to somatostatin, vasoactive intestinal polypeptide, nitric oxide, and pancreatic polypeptide.3,6,9 The relaxation phase is associated with bile storage and modi cation. During this period, the sphincter of Oddi is closed. GALLBLADDER MUCOCELE PATHOPHYSIOLOGY A gallbladder mucocele is an abnormally distended gallbladder containing a buildup of luminal mucus. Grossly, the gallbladder appears enlarged (unless it is ruptured) and contains gelatinous material that may be congealed mucus, a mucus cast, or inspissated bile (Figures 1 & 2). Before 2000, mucoceles were considered rare.10 In fact, most were noted as incidental necropsy ndings.11 Given the diagnostic tools available at the time, the true clinical impact and incidence of mucoceles before the 1990s are unknown. Predisposition to mucoceles may be associated with dyslipidemias in particular breeds such as Shetland sheepdogs.12 While extrahepatic biliary duct obstruction is a recognized cause of mucocele formation in people, prospective studies in dogs do not support this nding.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. 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 2. A longitudinal cross section of the gallbladder shown in Figure 1. The yellow material is the mucocele, and the black material is bile. The pink area is a hematoma that developed during surgical excision. (Image courtesy of Dr. Roy R. Pool, Texas A&M University’s Department of Veterinary Pathobiology.) in clinically normal geriatric dogs.5 At present, the signi cance of biliary sludge in dogs is unknown. Gallbladder contraction The gallbladder musculature contracts in response to cholecystokinin; this hormone is released from enterocytes after the ingestion of a fatty meal. In particular, proteoses, peptones, and long-chain fatty acids stimulate cholecystokinin release. Cholecystokinin concentrations peak about 20 minutes after a meal and may remain elevated for almost two hours. Once the gallbladder contracts, its contents are emptied into the duodenum within about 60 minutes.3 Cholecystokinin also causes relaxation of the sphincter of Oddi and the release of pancreatic digestive enzymes. Other factors that contribute to VETERINARY MEDICINE April 2009 171 http://www.prnpharmacal.com/proin

Table of Contents Feed for the Digital Edition of Veterinary Medicine - April 2009

Veterinary Medicine - April 2009 Contents Idea Exchange Practical Matters An Update on Gallbladder Mucoceles in Dogs Digital Radiography Equipment Benefits and Considerations How to Perform a Two-portal Laparoscopic Ovariectomy Author Guidelines CE Form/Advertiser Index Marketplace/Classifieds Mind Over Miller

Veterinary Medicine - April 2009

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