Prospective comparison of use of contrast-enhanced ultrasound and contrast-enhanced computed tomography in the Bosniak classification of complex renal cysts

Abstract

Aim: To compare contrast-enhanced ultrasound and contrast-enhanced computed tomography in the evaluation of complex renal cysts using the Bosniak classification.

Methods: Forty-six patients with 51 complex renal cysts were prospectively examined using contrast-enhanced ultrasound and contrast-enhanced computed tomography and images analysed by two observers using the Bosniak classification. Adverse effects and patients' preference were assessed for both modalities.

Results: There was complete agreement in Bosniak classification between both modalities and both observers in six cysts (11.8%). There was agreement of Bosniak classification on both modalities in 21 of 51 cysts (41.2%) for observer 1 and in 17 of 51 cysts (33.3%) for observer 2. Contrast-enhanced ultrasound gave a higher Bosniak classification than corresponding contrast-enhanced computed tomography in 31 % of cysts by both observers. Histological correlation was available in three lesions, all of which were malignant and classified as such simultaneously on both modalities by at least one observer, with remaining patients followed up with US or CT for 6-24 months. No adverse or side effects were reported following the use of US contrast, whilst 63.6% of patients suffered minor side effects following the use of CT contrast. 81.8% of the surveyed patients preferred contrast-enhanced ultrasound to contrast-enhanced computed tomography.

Conclusion: Contrast-enhanced ultrasound is a feasible tool in the evaluation of complex renal cysts in a non-specialist setting. Increased contrast-enhanced ultrasound sensitivity to enhancement compared to contrast-enhanced computed tomography, resulting in upgrading the Bosniak classification on contrast-enhanced ultrasound, has played a role in at best moderate agreement recorded by the observers with limited experience, but this would be overcome as the experience grows. To this end, we propose a standardised proforma for the contrast-enhanced ultrasound report. The benefits of contrast-enhanced ultrasound over contrast-enhanced computed tomography include patients' preference and avoidance of ionising radiation or nephrotoxicity, as well as lower cost.

Keywords: Bosniak classification; Complex renal cyst; contrast enhanced computed tomography; contrast-enhanced ultrasound; renal cell carcinoma.

Figure 1.

CT scan of a cyst indicated by red arrows: unenhanced axial scan (a), enhanced axial scan (b) and enhanced coronal scan (c). Dual screen CEUS scan of the same cyst (d) with unenhanced greyscale image on the right and contrast-enhanced image on the left. Green arrows indicate septation seen within the cyst on US, but not CECT, demonstrating the superior spatial resolution of US. The cyst was classified as Bosniak I on CECT and Bosniak II on CEUS.

Figure 2.

CT scan of a cyst indicated by red arrows: unenhanced axial scan (a) and enhanced axial scan (b). CEUS scan of the same cyst (images (c) and (d)). Septation indicated by green arrows. Postcontrast enhancement of intracystic septa on CEUS is difficult to appreciate on CECT. The cyst was classified as Bosniak II on CECT and Bosniak IIF on CEUS.

Figure 3.

Unenhanced axial CT scan of a cyst (a). Enhanced axial scan of cyst (b) showing some enhancement within cyst. CEUS images show a feeding vessel in the left lower quadrant of cyst (green arrow) in image (c) with gradual filling of the cyst with contrast ((d) and (e)) allowing dynamic assessment of enhancement as opposed to a ‘snapshot’ assessment on CECT. The cyst was classified as Bosniak III on both CECT and CEUS.

Figure 4.

Unenhanced axial CT scan (a) showing a cystic lesion, indicated by red arrows. Enhanced axial CT scan (b). Enhanced coronal CT scan (c). Unenhanced US showing increased peripheral vascularity of the lesion on Doppler imaging (d), but no blood flow within cyst. CEUS images of the lesion ((e) and (f)) showing considerable intracystic enhancement with conspicuous septa. This was classified as Bosniak IV cyst both on CECT and CEUS.

Figure 5.

Axial (A) and coronal (B) unenhanced CT scans demonstrating a large complex cyst (between red arrows). Corresponding enhanced CT axial (C), coronal (D) and sagittal (E) sections through the cyst demonstrate some enhancement within the cyst (green arrows). CEUS of the same cyst (F) with grey-scale image on the right showing internal echoes, and simultaneous contrast-enhanced image on the left showing enhancement of a thickened and trabeculated cyst wall (green arrows) taken at 1 min 3 s following SonoVue injection. Image (G) taken at 1 min 40 s shows enhancement of the thickened wall on CEUS. Image (H) shows measurement of the cyst wall thickness (between green arrows; 15 mm); note further gradual enhancement throughout the contents of the cyst. Image (I) taken in a very late phase shows inhomogenous enhancement throughout the whole of the cyst with the wall (green arrows) being less prominent, and areas of non-enhancement possibly due to necrosis within the cyst shown by the blue arrow. This was classified by observer 1 as Bosniak III on CECT, and Bosniak IV on CEUS. The other observer classified it as Bosniak IV on both modalities. Histology of the lesion demonstrated a clear cell carcinoma.