What is the most sensitive and specific test for diagnosing perforated viscus?

A CT scan is indeed the most sensitive and specific test for diagnosing a perforated viscus. This imaging modality allows for detailed visualization of the abdominal and thoracic cavities, enabling the identification of free air, which indicates perforation in the gastrointestinal tract. The cross-sectional images produced by a CT scan provide clear information about the location and extent of any perforations, as well as associated complications such as abscess formation or peritonitis, which are crucial for guiding management.

In contrast, while X-rays can show free air under the diaphragm, they are less sensitive and specific compared to CT scans, potentially missing smaller perforations. Ultrasound can detect fluid and can be useful in certain clinical scenarios, but it may not provide the same level of detail as a CT scan and can be operator-dependent. MRI is generally not used in the acute setting for diagnosing perforated viscus due to time constraints and its limited availability in emergency departments. Therefore, the superior diagnostic capability of CT scans makes them the preferred choice for this clinical scenario.