From the Guidelines
The recommended second-line imaging modality for suspected cholecystitis with a negative ultrasound is a hepatobiliary iminodiacetic acid (HIDA) scan, also known as cholescintigraphy, if clinical suspicion for acute cholecystitis is high and other diagnostic possibilities are not being considered, however, if other diagnostic possibilities are being considered for right upper quadrant (RUQ) abdominal pain, or if complications of acute cholecystitis are suspected, a contrast-enhanced CT scan is the preferred subsequent imaging modality. When clinical suspicion for cholecystitis remains high despite normal ultrasound findings, a HIDA scan is particularly valuable [ 1 ]. This nuclear medicine study involves intravenous injection of a radiotracer that is taken up by hepatocytes and excreted into the biliary system. In normal gallbladder function, the radiotracer will fill the gallbladder within 60 minutes. Non-visualization of the gallbladder after 4 hours suggests cystic duct obstruction, which is highly sensitive for acute cholecystitis. Some key points to consider when choosing a second-line imaging modality include:
- The sensitivity of HIDA scan for acute cholecystitis ranges from 90-97%, making it superior to ultrasound in cases where ultrasound results are equivocal or negative [ 1 ].
- Alternative second-line options include contrast-enhanced CT or MRI, but these are generally less sensitive than HIDA scan for this specific indication, however, CT is preferable when complications of acute cholecystitis or acute cholangitis are suspected [ 1 ].
- HIDA scan is particularly useful because it provides functional information about gallbladder contractility and bile flow, rather than just anatomical details, allowing for better assessment of gallbladder pathology.
- CT with IV contrast is preferable and usually appropriate when CT is obtained for subsequent imaging [ 1 ].
From the Research
Second-Line Imaging for Cholecystitis with Negative Ultrasound
When ultrasound results are negative for suspected cholecystitis, the following second-line imaging modalities can be considered:
- Hepatobiliary iminodiacetic acid (HIDA) scan: This modality is often used when the diagnosis of cholecystitis remains questionable after ultrasound 2, 3, 4, 5, 6.
- Fluorodeoxyglucose positron emission tomography-computed tomography (18FDG PET-CT): This test has shown promise in detecting gallbladder inflammation and could potentially replace HIDA scan in cases that remain equivocal after ultrasound 2.
- Computed Tomography (CT) scan: Although CT scan is not typically used as a second-line imaging modality for cholecystitis, it can be useful in certain cases, such as when ultrasound is negative and clinical suspicion remains high 4.
Advantages and Limitations of Each Modality
The advantages and limitations of each modality are:
- HIDA scan: High sensitivity and specificity for diagnosing acute cholecystitis, but may have false-positive results and is not always available 3, 4, 5, 6.
- 18FDG PET-CT: High sensitivity and specificity for detecting gallbladder inflammation, but may not be widely available and is a more expensive test 2.
- CT scan: High sensitivity for detecting acute acalculous cholecystitis, but may not be specific for cholecystitis and exposes patients to radiation 4.
Clinical Considerations
When choosing a second-line imaging modality for suspected cholecystitis with negative ultrasound, clinical considerations include: