A homogeneous, water-attenuation, non-enhancing, hairline-thin walled renal lesion is Bosniak:
I; II; IIF; III
Answer: I. That is the definition of a Bosniak I simple cyst — malignancy risk effectively zero, no follow-up. Say benign and stop.
Malignancy risk of a Bosniak III lesion is approximately:
20%; 50%; 90%; 5%
Answer: 50%. Class III runs about 50% malignant — the coin-flip class, managed with urology referral (resection, ablation, or in some patients active surveillance). Class IV runs ~90%.
Which feature makes a cystic mass Bosniak IV rather than III?
More than four septa; Calcification; Thick enhancing septa; An enhancing soft-tissue nodule
Answer: An enhancing soft-tissue nodule. IV = III plus an enhancing NODULE (focal soft tissue with an obtuse or acute margin against the wall/septum). Thick or irregular enhancing septa/wall alone is III. Calcification, notably, no longer drives class at all.
A cyst has many (≥4) smooth, minimally thickened (3 mm) enhancing septa. Bosniak 2019 class:
IIF; III; IV; II
Answer: IIF. IIF in 2019 is explicit: minimally thickened (3 mm) smooth enhancing septa/wall, OR many (≥4) smooth thin septa. The F means follow — typically US/CT/MRI at 6 months, then annually to 5 years.
A 2 cm homogeneous 75-HU renal lesion on NONCONTRAST CT:
Cannot classify anything without contrast; Bosniak IIF; Bosniak I; Bosniak II — benign, likely hemorrhagic/proteinaceous cyst
Answer: Bosniak II — benign, likely hemorrhagic/proteinaceous cyst. 2019 added explicit noncontrast rules: a homogeneous lesion ≥70 HU on noncontrast CT is a benign class II hyperattenuating cyst. One of the few confident single-phase calls.
Portal-venous-only CT shows a complex septated renal cyst. The report should:
Recommend biopsy; Assign Bosniak III from this study; Call it 'incompletely characterized' and route to renal-mass protocol CT or MRI; Assign IIF to be conservative
Answer: Call it 'incompletely characterized' and route to renal-mass protocol CT or MRI. The classification is DEFINED on dedicated pre+post contrast imaging. A confident class from one phase is a wrong class waiting to happen; the correct verb is 'route', and MRI is often preferred for complex lesions.
Bosniak IIF surveillance typically runs:
6 months, then annually for 5 years; Every 2 years for 10 years; No imaging — IIF is benign; One scan at 12 months, then stop
Answer: 6 months, then annually for 5 years. IIF follows at ~6 months then annually to 5 years; class progression or new enhancing tissue upgrades it. Most IIF lesions (~75–90%) prove benign — the follow-up exists to catch the rest.
Which 2019 change most reduced over-grading?
Thin-septa number threshold and millimeter definitions for thickness; All hyperdense cysts are IIF; III and IV merged; Septa now count only if calcified
Answer: Thin-septa number threshold and millimeter definitions for thickness. 2019 replaced adjectives with numbers: 'few' = 1–3 septa, 'many' = 4+, 'minimally thickened' = 3 mm, 'thick' = ≥4 mm. Shared vocabulary is the point — two readers should land on one class.
Calcification within a renal cyst, per Bosniak 2019:
Excludes the lesion from classification; Automatically IIF; Automatically III; Does not by itself change the class
Answer: Does not by itself change the class. 2019 demoted calcification: it is the enhancing soft tissue that matters. Thick calcification may obscure enhancement on CT — which is an argument for MRI, not for a higher class.
Best next test for a cystic lesion whose septa are equivocally enhancing on CT:
PET-CT; Ultrasound alone; Repeat the same CT; Renal mass protocol MRI
Answer: Renal mass protocol MRI. MRI's contrast resolution makes it the problem-solver for equivocal enhancement and for lesions downgraded or upgraded by subtraction imaging. Bosniak 2019 formally incorporates MRI for exactly this.