Acute cholecystitis is inflammation of the gallbladder, the small organ beneath the liver responsible for storing and releasing bile. Most cases (90% to 95%) are caused by gallstones blocking the cystic duct, known as calculous cholecystitis. Acalculous cholecystitis (ACC) is a distinct and less common form, accounting for only 5% to 10% of all acute cases. This inflammation occurs without the presence of gallstones, making it a more challenging and often more severe diagnosis than the calculous form.
Understanding the Difference
Cholecystitis is categorized based on the presence or absence of gallstones. In calculous cholecystitis, a gallstone physically obstructs the cystic duct, causing bile to back up and increase pressure inside the gallbladder. This obstruction leads to physical distension and chemical irritation, resulting in inflammation and often a secondary bacterial infection.
The inflammation in acalculous cholecystitis occurs despite the absence of a mechanical blockage. The gallbladder’s typical function involves contracting to release bile into the small intestine, a process that is impaired in both forms of the disease.
Instead of an anatomical obstruction, the mechanism behind acalculous cholecystitis involves a physiological failure of the gallbladder. The inflammation arises from a combination of bile stasis (stagnant bile) and hypoperfusion, which is a significant reduction in blood flow to the gallbladder wall. This lack of proper emptying and blood supply causes injury to the inner lining, leading to severe inflammation.
Primary Risk Factors and Causes
Acalculous cholecystitis is strongly associated with severe, underlying systemic illness and is often considered a complication rather than a primary disease. The condition predominantly affects patients who are already hospitalized and critically ill, as they are subjected to conditions that stress the body.
Major trauma, extensive burns, and recent complex surgery are significant risk factors because they induce a powerful systemic stress response. Severe sepsis or a state of shock also greatly increases the risk, causing widespread reduced blood pressure and poor circulation. This state of low blood flow, or ischemia, is particularly damaging to the gallbladder wall.
Prolonged periods without eating, such as due to critical illness or reliance on total parenteral nutrition (TPN), contribute to the problem. When a person does not eat orally, the gallbladder lacks the hormonal stimulation needed to contract and empty bile, leading to stasis. Stagnant bile can become highly concentrated, causing chemical irritation and increasing pressure within the organ. The combination of bile stasis and gallbladder wall ischemia rapidly progresses to severe inflammation and potential tissue death.
Recognizing the Signs
Recognizing acalculous cholecystitis is often difficult because the patients who develop it are typically critically ill, which can mask the usual symptoms. Many of these patients are sedated, intubated, or unable to communicate. Therefore, the classic signs of gallbladder inflammation, such as pain in the upper right abdomen, may not be present or cannot be elicited.
A persistent and unexplained fever may be one of the only initial signs pointing toward acalculous cholecystitis. Laboratory tests may show an elevated white blood cell count (leukocytosis) or abnormal liver function tests, including elevated bilirubin levels. If the patient is conscious, they may exhibit subtle abdominal distention or tenderness in the upper right quadrant.
Mild jaundice (yellowing of the skin and eyes) can be observed more frequently in acalculous cholecystitis than in the calculous form. The clinical presentation is often nonspecific, meaning the signs could be attributed to many other complications associated with critical illness. This ambiguity necessitates a high degree of suspicion from the medical team to pursue specific diagnostic imaging.
Diagnosis and Treatment Approach
The diagnosis of acalculous cholecystitis relies heavily on combining clinical suspicion with specific imaging studies, as laboratory findings alone are not definitive. An abdominal ultrasound is typically the first imaging test performed because it is non-invasive and can be done quickly at the patient’s bedside. Findings suggestive of the condition include a thickened gallbladder wall (greater than 3.5 millimeters) and the presence of fluid surrounding the gallbladder.
If ultrasound results are inconclusive, a computed tomography (CT) scan may be used to further evaluate the gallbladder and rule out other abdominal issues. In some stable patients, a hepatobiliary iminodiacetic acid (HIDA) scan may be performed to assess the gallbladder’s function. This nuclear medicine scan can reveal a non-visualizing gallbladder, suggesting an inability to fill or empty bile, which supports the diagnosis.
The treatment of acalculous cholecystitis is considered an urgent matter due to the high risk of gangrene and perforation. Initial management includes starting broad-spectrum antibiotics to cover potential bacterial infection, although antibiotics alone are usually insufficient. A common and often lifesaving first intervention is percutaneous cholecystostomy, where a drainage tube is inserted through the skin and into the gallbladder.
This procedure relieves pressure and drains the stagnant, infected bile, which helps to stabilize the critically ill patient. Once the patient’s overall condition improves, the definitive treatment is usually a cholecystectomy (surgical removal of the gallbladder). For patients who remain poor surgical candidates due to severe underlying illness, the drainage tube may be left in place until they recover, with surgery postponed or avoided entirely.