Contrast-enhanced ultrasound (CEUS) in the evaluation of bladder pathologies: Review

Contrast-enhanced Ultrasound (CEUS) is an advanced ultrasound (US) technique that utilizes specific US contrast agents (UCAs) to provide a more detailed evaluation of anatomic structures and parenchymal vasculature. Although the use of CEUS has been well-established in echocardiography and imaging of focal liver lesions, the updated guidelines by WFUMB-EFSUMB from 2018 also talk about the use of CEUS in the urinary bladder under non-hepatic applications of CEUS. The most common application of CEUS in the urinary bladder is the differentiation between bladder cancer and benign lesions such as a hematoma in patients presenting with hematuria. CEUS is also a promising imaging modality that can be used to detect and stage bladder urothelial cancers. CEUS greatly improves the diagnostic accuracy of conventional US techniques in the detection of bladder cancer. It has been shown previously that low- and high-grade bladder cancers tend to behave differently on the time-intensity curves (TIC) of CEUS. Low-grade bladder cancers tend to show a TIC with an early peak enhancement with a slow plateau and a longer time taken for contrast disappearance, whereas high-grade bladder cancers tend to show a rapid and high peak enhancement with rapid contrast disappearance (fast wash-out phase). In patients presenting with hematuria, CEUS accurately differentiates the etiology as either malignant or benign (i.e., hematoma) as hematomas are non-vascular lesions and do not show any enhancement as opposed to bladder cancers which tend to be highly vascular. CEUS holds several advantages such as being widely available, quick, and cost-efficient. CEUS is also suitable for patients who have contraindications to undergo CT, MRI, and/or conventional cystoscopy. Additionally, CEUS can be safely performed in patients with renal failure as UCAs are not nephrotoxic and not deposited in tissues as they are blood pool agents and are metabolized and excreted via pulmonary breathing.