8th Baltic Congress of Radiology

08.10.2022  Tallinn, Estonia

Presentation

Black Box

Synopsis: Contrast-enhanced ultrasound (CEUS) after kidney transplantation is able to diagnose main vascular, urological, and parenchymal complications, improving the diagnostic performance of grayscale ultrasound and color Doppler examination. US contrast agents - second-generation compounds, consisting of a phospholipidic or albumin shell containing microbubbles of an inert lipophilic gas, such as sulfur hexafluoride (SonoVue), perfluorocarbons (Definity or Optison), are administered intravenously and show blood-pool pharmacokinetics: they last in the intravascular compartment for some minutes before dissolving (the gas is excreted through the lungs, while the bio-compatible shell is metabolized by the liver). CEUS is performed with a bolus injection of contrast (1,8 - 2,5mL of Sonovue) through a ≥ 20 Gauge catheter inserted in the antecubital vein of the arm, followed by a 5-10 mL saline flush. CEUS requires a specific contrast imaging mode to avoid microbubbles being destroyed by excessive acoustic power, e.g., by setting a low mechanical index . The following post-contrast phases can be observed : (1) Corticomedullary phase, characterized by an increased contrast between enhancing cortex and still hypoperfused medulla, lasting between 15 and 30 s after injection; (2) Nephrographic phase, showing an homogeneous enhancement across the cortex and medulla, lasting between 30 and 70 s after injection. Imaging performed after > 70 s from contrast injection is referred to as delayed phase. There is no urographic phase, since UCAs are not excreted by the kidney. Transplant renal artery stenosis using CEUS achieves a 87.5% sensitivity and a 95.7% specificity. Transplant renal artery thrombosis: CEUS can confirm arterial occlusion by showing the absence of contrast enhancement, and by reliably defining the site and extent of endoluminal defects, hypoperfused or infarcted parenchymal areas. Transplant renal vein thrombosis: CEUS can depict non-enhancing vein defects and hypoperfused parenchymal areas. Acute cortical necrosis: the peripheral rim sign manifests with prompt filling of the main arteries followed by enhancement of medullary pyramids and absent cortical enhancement. The renal cortex appears as a hypovascular hypoechoic band persisting from the corticomedullary phase up to about 5 min after contrast injection. Arteriovenous fistula: on CEUS, AVF appears as an intraparenchymal pseudo-nodule with intense contrast-enhancement of vascular type, associated to early enhancement of the efferent vein. Urological complications - perirenal collections according to Grzelak et al, the use of CEUS allowed to detect 17,6% more cases of perirenal hematomas than with US alone, and allowed to visualize collection with a thickness lower than 10 mm, values that were undetectable by grayscale US. Parenchymal complications - rejection: the main capability of CEUS in this setting is that of adding time-intensity curve (TIC)-derived perfusion analysis under the form of various quantitative indexes, a feature that showed promising potential for diagnosing rejection. In conclusion: CEUS allows an accurate assessment of renal graft status. CEUS allows the evaluation of both macro- and micro-circulation, as well as perirenal collections or parenchymal abnormalities such as those related to rejection, acute tubular necrosis (ATN), impaired perfusion, and focal lesions.

This agenda item is presented in the following session: S6-1 Urogenital Radiology

Plenary session

08.10.2022 11:00 - 12:30