Proposing Incidental-Reporting and Data System: A classification system for incidental findings in radiology

Table 2 Indicative example for each Incidental-Reporting and Data System category

I-RADS category	Indicative example
I-RADS 0	A 1.5 cm hypodense liver lesion detected on a non-contrast abdominal CT performed for suspected renal colic; a multiphase abdominal CT has been performed previously on the patient but is not available to the reporting radiologist
I-RADS 1	A simple renal cyst measuring 1.5 cm detected on abdominal CT performed due to suspected acute appendicitis
I-RADS 2	A small (3 mm) incidental pulmonary nodule detected on a cardiac CT, in a low-risk, nonsmoking patient
I-RADS 3	A 2 cm indeterminate adrenal lesion discovered incidentally on trauma CT
I-RADS 4	A 2.5 cm spiculated pulmonary nodule incidentally identified on a CT angiogram of the chest performed for suspected pulmonary embolism; morphology and margins highly concerning for malignancy
I-RADS 5	A 3.5 cm irregular mass in the pancreatic head with upstream biliary ductal dilatation, found incidentally on an abdominal MRI performed to evaluate hepatic steatosis; findings concerning for pancreatic carcinoma
I-RADS 6	Patient with biopsy-proven metastatic colon cancer and multiple known hepatic metastases, incidentally detected in the lower slices (upper abdominal slices) of a chest CT angiogram performed to exclude pulmonary embolism

These examples are illustrative and non-exhaustive and do not define strict category boundaries. Rare incidental findings (including musculoskeletal, spinal, and soft-tissue findings) should be categorized based on perceived clinical significance rather than lesion rarity. I-RADS: Incidental-Reporting and Data System; CT: Computed tomography; MRI: Magnetic resonance imaging.