On renal ultrasound, the finding of a renal cortical cyst with internal echoes, septations, and a mural nodule corresponds to which Bosniak category, requiring surgical excision?

• A Bosniak I
• B Bosniak IV ✓
• C Bosniak II
• D Bosniak IIF

Explanation

The Bosniak classification categorises renal cysts by imaging features to predict malignancy risk. Bosniak IV lesions have solid enhancing components (mural nodules or solid areas) and are considered malignant until proven otherwise — they require surgical excision (partial or radical nephrectomy). Bosniak I (simple cyst) and II (minimally complex) are benign. Bosniak IIF requires follow-up imaging. Bosniak III (thick irregular septa, no definite enhancement) requires surgery or close follow-up depending on the guideline used.

Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.

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