Mucocele of the gallbladder is a condition caused by the prolonged blockage of the cystic duct, usually by an impacted gallstone. Another name for this condition is hydrops of the gallbladder. It is most often not identified before surgery but is an incidental finding at the time of either laparoscopic or open cholecystectomy. This diagnosis is made when the gallbladder is surgically decompressed, and clear mucous-like fluid has replaced the green or brown bile. Patients present with signs and symptoms of acute or chronic cholecystitis.
A malfunctioning gallbladder causes cholecystitis. The liver makes bile which travels down the bile duct, to be stored in the gallbladder. After eating certain foods, especially spicy or greasy foods, the gallbladder is stimulated to empty the bile out of the gallbladder, through the cystic duct, down the bile duct into the duodenum. This process aids in food digestion. If the gallbladder is improperly functioning, the bile may not empty completely which may lead to stone formation. Gallstones can cause mechanical blockage of the cystic duct. The gallbladder also serves to concentrate bile and reabsorb water from the bile. The gallbladder can store up to 1500 mL of bile and can distend if there is an outlet obstruction. If this outlet obstruction is complete, usually from an impacted gallstone in the cystic duct, the bile salts will get reabsorbed by the gallbladder mucosa over time and be replaced by clear, watery mucus. Other etiologies of gallbladder mucocele include anything that causes a blockage of the cystic duct or distal biliary tree. Neoplasms including gallbladder polyps and tumors can result in hydrops. Congenital strictures, gallbladder parasites, and external compression from liver disease or tumors can also cause gallbladder mucoceles. Other factors that can lead to hydrops include anything that increases the risk of cholecystitis such as drastic weight reduction, prolonged TPN, gastric surgeries with disruption of the vegas nerves, critical illness, diabetes, hyperlipidemia, hypercalcemia, and biliary conditions such as Carole disease. Patients with acute acalculous cholecystitis can also form gallbladder mucoceles. The mechanism is the same as that of mechanical cystic duct obstructions. However, this is a functional condition resulting in a non-emptying, distended gallbladder where biliary mucus replaces bile salts. 
Mucoceles can occur in any patient with acute calculous or acalculous cholecystitis. Gallbladder disease occurs in men and women. Certain populations are more prone to gallbladder disease. The risk of gallbladder disease increases in women, obese patients, pregnant women, and patients in their 40s. Drastic weight loss or acute illnesses may also increase the risk, as well as a family propensity for this condition and the formation of gallstones. Other conditions that cause breakdown of blood cells, for example, Sickle Cell disease, also increase the incidence of gallstones. Most gallstones are asymptomatic. In the United States, approximately 14 million men and 6 million women between the ages of 20 to 74 have gallstones. The prevalence increases as a person ages. Obesity increases the likelihood of gallstones, especially in women due to increases in biliary secretion of cholesterol. On the other hand, patients with drastic weight loss or fasting have a higher chance of gallstones secondary to biliary stasis. Gallstones also have a hormonal association. Estrogen has been shown to increase bile cholesterol as well as decrease gallbladder contractility. Women of reproductive age or on birth control medication containing estrogen have a two-fold increase in gallstone formation compared to men. People with chronic illness such as diabetes also have an increase in gallstone formation as well as reduced gallbladder wall contractility due to neuropathy. 
Stasis of the gallbladder results in the buildup of intraluminal pressure which eventually results in ischemia of the gallbladder wall and inflammation. This stasis can also lead to the colonization of bacteria which contributes to the inflammatory response. If the pressure is not relieved, the gallbladder wall will become progressively ischemic and eventually result in gangrenous changes and perforation leading to sepsis and shock. These findings are referred to as acute cholecystitis. Chronic acalculous cholecystitis is less insidious. Symptoms are more prolonged and less severe. The mechanism is the same, but it has not progressed to the findings associated with acute acalculous cholecystitis. Symptoms can also be more intermittent and vague, although often patients can present with signs of acute biliary cholic. Patients with hydrops of the gallbladder usually present with signs of more acute cholecystitis.
The gallbladder will distend to varying degrees. Clear, watery mucus replaces the normally colored bile, and a distended gallbladder can contain over 1500 mL of this mucus. There will be varying degrees of acute inflammation of the gallbladder wall with possible microabscesses present. Various species of bacteria are present in 11% to 30% of the cases. Rokitansky-Aschoff sinuses are present 90% of the time in cholecystitis specimens. These are a herniation of intraluminal sinuses from increased pressures possibly associated with ducts of Luschka. Most often, an impacted gallstone is located in the cystic duct or Hartmann pouch. This stone is usually singular, but multiple stones can also be present. Cases caused by other etiologies such as polyps, tumors, or parasites exhibit these findings in pathology. Extreme or prolonged cases can lead to actual perforation of the gallbladder. 
Cases of chronic cholecystitis present with progressing right upper abdominal pain with bloating, food intolerances (especially greasy and spicy foods), increased gas, nausea, and vomiting. Pain in the midback or shoulder may also occur. This pain could be present for years until diagnosis. Cases of acute cholecystitis have similar but more severe symptoms. Often these symptoms are mistaken for cardiac issues. The finding of right upper abdominal pain with deep palpation, or Murphy sign, is classic for this disease. The gallbladder can often be palpated at the right costal margin especially in the thin patient. It can sometimes be felt as low as the umbilicus due to extreme distension. Often, a specific dietary event such as, "I ate pork chops and gravy last night," leads to the acute attack. Patients usually present with a history including several days of progressive symptoms.
A physical exam with a comprehensive history is paramount in making the diagnosis of cholecystitis. A complete blood count and a comprehensive metabolic panel are also important. In cases of chronic cholecystitis, these results may be within the reference range. In acute cholecystitis or severe disease, white blood cell count may be elevated. Liver enzymes may also be elevated. If the bilirubin level is above 2, then consider a possible common bile duct stone. Even in the presence of severe gallbladder disease, lab values may be within the reference range. Amylase and lipase must also be checked to rule out pancreatitis. Often a CT scan is ordered in the emergency department as the first test in the work up. This imaging often shows findings of cholecystitis and gallstones. A gallbladder ultrasound is the best test to evaluate gallbladder disease initially. A distended and edematous gallbladder with gallstones or an impacted nonmobile stone in the cystic duct or Hartman pouch is a common finding with this condition. In cases of acute cholecystitis, a HIDA scan is recommended. This scan will diagnose gallbladder function or cystic duct obstruction. The addition of cholecystokinin in cases of no gallstones may also diagnose acalculous cholecystitis. This is indicated by an ejection fracture less than 35% but results in hydrops are most often 0%. 
A recommended treatment for cholecystitis with hydrops is laparoscopic cholecystectomy because of its low morbidity and mortality rates with quick recovery. This procedure can also be done with an open technique in cases where the patient is not a good laparoscopic candidate. If the patient is acutely ill and considered a poor surgical candidate, consider treating with temporizing percutaneous drainage of the gallbladder.
Many other conditions can mimic gallbladder disease. Patients who present with acute biliary colic are often worked up for cardiac issues. Other common conditions with similar presenting symptoms are peptic ulcer disease, irritable bowel disease, inflammatory bowel disease, gastroesophageal reflux disease, pulmonary embolism, and musculoskeletal disorders. The diagnosis of acute cholecystitis with possible hydrops in patients with a palpable gallbladder, Murphy sign, and a positive gallbladder ultrasound should not be confused with any other diagnosis. 
A mucocele of the gallbladder must be differentiated from other gallbladder conditions. Acute percutaneous drainage vs cholecystectomy is usually the first line of treatment. This diagnosis must be suspected both by the surgeon and the radiologist. Suspicion for gallbladder cancer must also be considered by all treating personnel and the appropriate treatment course must be taken using an interprofessional team to obtain the best results.
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