Acalculous cholecystitis– an imaging and therapeutic update

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Executive Summary

Acalculous cholecystitis (AC) is a significant yet frequently underappreciated cause of morbidity and mortality, particularly within critically ill and elderly populations. Unlike acute calculous cholecystitis (ACC), which is primarily driven by gallstone-induced cystic duct obstruction, acute acalculous cholecystitis (AAC) arises from a multifactorial pathogenesis involving ischemia-reperfusion injury and cholestasis.

Key takeaways from this briefing include:

  • High Risk in Critical Care: AAC is predominantly found in patients with severe trauma, sepsis, burns, or those on mechanical ventilation. In children, AC accounts for 50% to 70% of all cholecystitis cases.

  • Diagnostic Challenges: Clinical signs are often nonspecific or masked by sedation and underlying critical illness, requiring a high index of clinical suspicion and multidisciplinary coordination.

  • Imaging Utility: Ultrasound remains the first-line diagnostic tool due to its bedside availability. However, CT and HIDA scans offer superior sensitivity and specificity for identifying complications such as gangrene or perforation.

  • Interventional Shifts: While surgery is the gold standard for calculous disease, image-guided percutaneous cholecystostomy (PC) is often a definitive treatment for AAC, with lower recurrence rates than ACC once the acute illness resolves.

Pathogenesis and Epidemiology

Acalculous cholecystitis is defined as gallbladder inflammation in the absence of gallstones. It presents in two primary forms: acute (AAC) and chronic (CAC), with the latter defined by symptoms lasting at least three months.

Pathogenic Mechanisms

The exact cause of AAC is not entirely clear but is generally attributed to a combination of:

  • Ischemic-Perfusion Injury: Critical systemic disease leads to mucosal injury.

  • Cholestasis: Bile stasis results in mucosal damage, potentially involving the activation of phospholipase A2 and superoxide dismutase.

  • Bacterial Invasion: Secondary enteric organisms—including E. coli, E. faecalis, Klebsiella spp., Pseudomonas spp., Proteus spp., and B. fragilis—frequently invade the injured mucosa.

  • Mechanical Factors: In pediatric populations, extrinsic compression (e.g., porta hepatis adenopathy) or congenital ductal stenosis may precipitate the condition.

Risk Profiles

  • Demographics: AAC is more common in elderly men and children.

  • Critical Illness: Highly associated with hospitalization for sepsis, major surgery, severe trauma, burns, and total parenteral nutrition (TPN).

  • Outpatient Factors: Patients with chronic disorders like diabetes, hypertension, end-stage renal disease, and heart failure are also susceptible.

  • Immunosuppression: Increased risk in patients with leukemia, AIDS, or bone marrow transplant recipients.

Clinical Presentation and Diagnostic Guidelines

The clinical presentation of AAC often mimics ACC, featuring fever, tachycardia, and right upper quadrant pain. However, in the ICU, patients may be obtunded or intubated, masking these symptoms.

Diagnostic Criteria (Tokyo Guidelines 2018 - TG18)

Diagnosis is established through a triad of findings:

  1. Local signs of inflammation: e.g., Murphy sign or right upper quadrant pain.

  2. Systemic signs of inflammation: e.g., fever, elevated CRP, or leukocytosis.

  3. Imaging findings: Characteristic gallbladder wall changes or fluid.

Severity Grading

Grade

Severity

Characteristics

Grade I

Mild

No associated organ dysfunction.

Grade II

Moderate

Marked local inflammation without organ dysfunction.

Grade III

Severe

Signs of organ system dysfunction (respiratory, neurologic, renal, etc.).

Diagnostic Imaging Modalities

Imaging is critical for diagnosis, severity assessment, and ruling out alternative pathologies.

1. Ultrasound (US)

The preferred first-line modality due to portability and lack of ionizing radiation.

  • Major Criteria: Wall thickening (>3 mm), sonographic Murphy sign (if assessable), intramural gas, or mucosal sloughing.

  • Minor Criteria: Gallbladder distension (>8 cm long, >5 cm transverse), echogenic bile/sludge, or pericholecystic fluid.

2. Hepatobiliary Scintigraphy (HIDA Scan)

Evaluates gallbladder physiology. Non-visualization of the gallbladder after 60 minutes (and potentially after morphine administration) confirms cholecystitis. It is highly specific, though it carries a 25% false-negative rate in AAC cases where the cystic duct remains patent.

3. Computed Tomography (CT)

Used when US is equivocal. CT is highly sensitive (95%) and superior for identifying complications like emphysematous changes or perforation. Findings include pericholecystic fat stranding and mucosal hyperenhancement.

4. Magnetic Resonance Imaging (MRI)

Provides excellent soft tissue contrast but is often limited by the inability of critically ill patients to cooperate with long scan times.

Complications of AAC

AAC carries a higher risk of severe complications compared to calculous cholecystitis:

  • Gangrenous Cholecystitis: Occurs in up to 50% of AAC surgical specimens. The risk is significantly higher in AAC (31.2%) than in ACC (5.6%).

  • Perforation: Observed in 10% to 20% of cases, significantly increasing mortality rates (which can exceed 30%).

  • Emphysematous Cholecystitis: Characterized by gas in the gallbladder wall or lumen; CT is the most sensitive modality for detection.

  • Hemorrhagic Cholecystitis: A rare complication identified by hyperattenuating bile on CT or blood products on MRI.

Therapeutic Interventions

Management is dictated by the severity of the disease and the patient's surgical risk (assessed via CCI and ASA-PS scores).

Percutaneous Cholecystostomy (PC)

PC is an image-guided drainage procedure performed by interventional radiologists.

  • Definitive Treatment: Unlike in ACC, where PC is a bridge to surgery, PC is often definitive for AAC because the absence of stones minimizes the risk of recurrence (typically <10% after tube removal).

  • Approaches:

    • Transhepatic: Lower risk of bile leak and higher catheter stability; higher risk of hemorrhage.

    • Transperitoneal: Lower risk of hemorrhage; higher risk of bowel transgression or tube dislodgement.

  • Success Rate: Technical success is reported at ≥95%.

Endoscopic Drainage

Advanced gastroenterological techniques are utilized when PC is not feasible or if the patient has coagulopathy/ascites.

  • ET-GBD: Transpapillary drainage via plastic stents; preferred if simultaneous ERCP is required.

  • EUS-GBD: Ultrasound-guided drainage into the stomach or duodenum, typically using lumen-opposing metal stents (LAMS). LAMS have shown technical success rates of 93.3% in non-surgical candidates.

Chronic Acalculous Cholecystitis (CAC)

CAC is a diagnosis of exclusion in patients with intermittent biliary colic or nonspecific symptoms like nausea lasting over three months.

  • Imaging: Often shows non-specific wall thickening or enhancement.

  • Functional Testing: HIDA scans with Sincalide (CCK-8) or a fatty meal are necessary to measure the gallbladder ejection fraction. An ejection fraction of <33% is compatible with a diagnosis of chronic cholecystitis.