Teaching Case

A 45-year-old male patient with history of HIV presented with lower respiratory infection symptoms. The diagnosis of pulmonary pneumocystis jiroveci infection was established but symptoms persisted albeit of treatment and thus full-body imaging was performed to exclude abscess formation.

A chest and abdomen contrast-enhanced CT excluded abscess formation. Nevertheless, a focal cortical mass of the left kidney was detected, appearing enhancing, hyperdense to the adjacent cortex, raising suspicion of neoplasm (Fig. 1). The patient was further referred for US-CEUS for further characterization. This area appeared hypoechoic, showed peripheral vascularity and mild internal blood flow signals on Doppler technique, in keeping with a solid lesion (Fig. 2). CEUS with 2.4 ml of SonoVue^TM (Bracco SpA, Milan) was performed to characterize the lesion’s vascularity, showing early intense arterial enhancement, prior to adjacent cortex, remaining hyper-enhancing on venous and delayed phase, with no wash-out (Fig. 3). A centripetal pattern of enhancement was noted on parametric imaging, while the hyper-vascular enhancement was also confirmed on time-intensity-curve analysis (Fig. 4). The infection’s symptoms improved with conservative treatment but the renal lesion was resected and diagnosed as clear cell renal cell carcinoma (RCC) on histology.

RCC demonstrates on CEUS cortical phase hyper- or isoenhancement, late washout and overall inhomogeneous and perilesional rim-like enhancement.[1] Enhancement homogeneity and tumour-to-cortex intensity ratio may differentiate hypoechoic tumour histotypes, with clear cell RCC (ccRCC) exhibiting more commonly heterogeneity and higher intensity.[2] The typical clear cell (ccRCC) demonstrates on CEUS higher enhancement than the adjacent renal cortex, earlier peak but variable wash-out. On quantitative analysis, ccRCC shows early hyperenhancement, shorter rise time and time to peak, steeper wash-in slope and greater peak intensity, than normal cortex and greater intensity than cortex at the delayed phase. Compared to lipid-poor angiomyolipoma, ccRCC enhances higher and more heterogeneously due to necrosis. Papillary (pRCC) is hypo-enhancing, with different wash-in, enhancing less than cortex and with a later peak, while chRCC shows an intermediate pattern, between hypo-enhancing pRCCs and hyper-enhancing ccRCCs.[3]

Solid renal lesions (SRL) are commonly incidentally detected on CT protocolled for different indications, thus requiring further analysis, in order to establish the solid, cystic or mixed and hyper- or hypo-vascular nature. The differential diagnosis of a solid renal lesion (SRL) includes various types of RCC, angiomyolipoma and oncocytoma. Proteinaecous or haemorrhagic cysts should also be considered, as sometimes mimicking solid lesions on sub-optimally protocolled imaging. CEUS uses an exclusively intravascular contrast agent, thus readily visualising a lesion’s enhancement and establishing the solid or cystic nature. CEUS negates the use of nephrotoxic contrast, feature particularly advantageous for chronic renal failure. Based on EFSUMB guidelines, CEUS is more sensitive than CT for detecting blood flow in hypovascular lesions and can differentiate complex cysts from solid lesions, distinguish pseudotumors from RCC and characterize indeterminate renal lesions by showing a hyper- or hypo-vascular enhancement, although there is overlap between different types.[4]

SRL indeterminate on CT can be further characterized on CEUS, with 95.2% accuracy.[5] Both CEUS and CECT are effective for the differential diagnosis of benign and malignant SRMs but CEUS may be more effective for qualitatively diagnosing small pRCC.[6] CEUS successfully classifies 95.7% of indeterminate lesions on CT. In detail, CEUS was definitive for 94.4% of cases with equivocal CT enhancement, 100% of those with non-contrast CT, and 100% of those with only venous-phase CT. Considering indeterminate lesions on MRI, CEUS classified 100% of lesions.[7] CEUS good diagnostic accuracy was also confirmed on meta-analysis, reporting 96% sensitivity and 82% specificity in detecting renal cancer.[8]

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