ACR Guidelines for Incidentalomas

Appearance Recommendation
Bosniak Category Imaging Features General Population Comorbidities or Limited Life Expectancy
I Hairline-thin wall; no septa, calcifications, or solid components; water attenuation; no enhancement Ignore Ignore
II Few hairline-thin septa with or without perceived (not measurable) enhancement; fine calcification or short segment of slightly thickened calcification in the wall or septa; homogeneously high-attenuating masses (≤3 cm) that are sharply marginated and do not enhance Ignore Ignore
IIF Multiple hairline-thin septa with or without perceived (not measurable) enhancement, minimal smooth thickening of wall or septa that may show perceived (not measureable) enhancement, calcification may be thick and nodular but no measurable enhancement present; no enhancing soft tissue components; intrarenal nonenhancing high-attenuation renal masses (>3 cm) Observe Observe or ignore
III Thickened irregular or smooth walls or septa, with measurable enhancement Surgery Surgery or observe
IV Criteria of category III, but also containing enhancing soft tissue components adjacent to or separate from the wall or septa Surgery Surgery or observe
General Population
Mass Size Probable Diagnosis Recommendation Comment
Large (>3 cm) Renal cell carcinoma Surgery Angiomyolipoma with minimal fat, oncocytoma, other benign neoplasms may be found at surgery
Small (1-3 cm) Renal cell carcinoma Surgery If hyperattenuating, and homogenously enhancing, consider MRI and percutaneous biopsy to diagnose angiomyolipoma with minimal fat
Very small (<1 cm) Renal cell carcinoma, oncocytoma, angiomyolipoma⁎ Observe until 1 cm Thin (≤3 mm) sections help confirm enhancement
Limited Life Expectancy or High Risk Comorbidities
Mass Size Probable Diagnosis Recommendation Comment
Large (>3 cm) Renal cell carcinoma Surgery or observe Angiomyolipoma with minimal fat, oncocytoma, other benign neoplasms may be found at surgery; biopsy can be used preoperatively to confirm renal cell carcinoma
Small (1-3 cm) Renal cell carcinoma Surgery or observe If hyperattenuating, and homogenously enhancing, consider MRI and percutaneous biopsy to diagnose angiomyolipoma with minimal fat
Very small (<1 cm) Renal cell carcinoma, oncocytoma, angiomyolipoma⁎ Observe until 1.5 cm Thin (≤3 mm) sections help confirm enhancement