CEUS of the Kidneys: Differentiation of Cysts by Bosniak and Solid Lesions (EFSUMB)
The Role of CEUS in Evaluating Renal Lesions
CEUS is indicated for patients with contraindications to contrast-enhanced CT (CECT) or contrast-enhanced MRI (CEMR), or when these cannot be performed (Diagnostic Ultrasound: Abdomen & Pelvis, 2022). The method evaluates the perfusion of cyst walls, septa, and solid components in real-time. Correct imaging classification of cystic lesions is key to management strategy.
B-mode is insufficient for assessing changes in Bosniak III and IV; CEUS often yields unexpected results (EFSUMB Course Book, 2020). CEUS can both upgrade and downgrade categories: for example, a suspected malignant tumor on CECT and CEMR may show no perfusion on CEUS — a simple cyst with hemorrhage (Bosniak 2).
Bosniak Categories and CEUS Findings
| Category | CEUS Features | Management |
|---|---|---|
| Bosniak II | Thin septa; virtually no perfusion | — |
| Bosniak IIF | Multiple septa, slightly thickened or calcified, sometimes thickened or nodular; minimal solid components absent | Dynamic observation: repeat CEUS in 6 months |
| Bosniak III | Thick septa with marked perfusion on CEUS | Surgical excision (partial or radical nephrectomy) or ablation |
| Bosniak IV | Contrast-enhancing solid components | Surgical excision or ablation |
Prognostic Significance
According to the EFSUMB Course Book (2020), 40–60% of such changes (Bosniak III/IV) are malignant. Repeat CEUS for Bosniak IIF in 6 months is performed to not miss malignancy. Analysis of the time-intensity curve (TIC) allows differentiation between the absence of perfusion in a hemorrhagic cyst and perfusion of cortical tissue.
Methodological Basis
The application of CEUS in non-hepatic applications, including the kidneys, is regulated by EFSUMB guidelines — The EFSUMB Guidelines and Recommendations for the Clinical Practice of Contrast-Enhanced Ultrasound (CEUS) in Non-Hepatic Applications: Update 2017 (Ultraschall Med, 2018).
Frequently asked questions
When should CEUS be used instead of CT or MRI for renal cysts?
CEUS is indicated for patients with contraindications to contrast-enhanced CT (CECT) or MRI (CEMR) or when these cannot be performed (Diagnostic Ultrasound, 2022).
What percentage of Bosniak III/IV lesions are malignant?
According to the EFSUMB Course Book (2020), 40–60% of such changes are malignant.
What is the management strategy for Bosniak IIF according to CEUS?
Dynamic observation: CEUS should be repeated in 6 months to not miss malignancy (EFSUMB Course Book, 2020).
Why is B-mode insufficient for Bosniak III and IV?
B-mode does not adequately assess changes; CEUS reveals perfusion of thickened septa and solid components, often changing the classification (EFSUMB Course Book, 2020).
How does CEUS help with a hemorrhagic cyst?
CEUS shows the absence of perfusion in a cyst with hemorrhage (Bosniak 2), confirmed by the time-intensity curve (TIC), even if there is suspicion of a tumor on CECT/CEMR.