Infectious and Inflammatory Diseases of the Urinary Tract

Imaging Manifestations of Acute and Chronic Renal Infection That Mimics Malignancy: How to Make the Diagnosis Using Computed Tomography and Magnetic Resonance Imaging

“…On MRI, mature abscesses typically show heterogeneous, predominantly low signal intensity on T1-weighted (T1W) and predominantly high signal intensity on T2W depending on the amount of fluid, cellular debris and protein [17]. After contrast administration, abscesses often show peripheral rim enhancement with progressive enhancement [18].…”

“…Delayed phase post-contrast scanning is particularly important for the differentiation of abscesses from non-abscessed infectious foci and infarctions or scars, with the latter having viable tissue that enhances on delayed imaging [19]. Restricted diffusion on DWI is a typical feature of organized abscesses due the accumulation of white blood cells with intact cell membranes, which leads to high cellularity and viscosity [17]. As described above, this finding can also be seen in RCC, UCC, and lymphoma; however, usually within tumours only the solid enhancing components (indicating viable tumour) will show restricted diffusion (ie, in areas of viable tumour) unlike in abscesses where liquid components also show restricted diffusion (Figure 4).…”

“…The diagnosis on MRI could be challenging but patients are usually ill and therefore preferentially imaged with CT. The presence of susceptibility artifact on gradient recalled echo sequences may suggest the diagnosis [17]. Contrast administration could be useful for assessment of renal parenchyma involvement and viability [26].…”

Virtual measurements of paracellular permeability and chronic inflammation via color coded pixel-wise T1 mapping

“…It is generally agreed that inflammation is a central player in the pathogenesis of these inflammatory urological diseases, but the role of inflammation is typically presumed from patient symptomatology or the presence of bacteria or white blood cells in urine but rarely directly detected for the current standard of care. Detection of inflammation in the upper urinary tract by direct or indirect imaging methods is recommended for recurrent UTI to rule out renal obstruction or the factors that increase the risk for relapsing infection (10). Suspicion of pyelonephritis or incomplete bladder emptying in a patient with recurrent UTIs prompts ultrasound, a first-line imaging method for complicated upper UTI diagnosis.…”

“…Although useful, these imaging methods have a limited role in current clinical management of diseases presumed to be driven by inflammation in lower urinary tract such as IC (31,41) and RC (59,60). Narrow field of view (FOV) limits cystoscopy of bladder and the use of ultrasound and CT is limited by poor soft tissue contrast (10). Although MRI offers good soft tissue contrast in multiplanar images for well-defined, fixed anatomical location of upper urinary tract, the variable shape of a distensible bladder wall and its variable location within the pelvic region continues to challenge MRI use for imaging inflammation, hemorrhage, edema, or fibrosismediated mural thickening (53).…”