Diffusion‐weighted magnetic resonance imaging in follow‐up of superficial urinary bladder carcinoma after transurethral resection: initial experience

Abstract

What's known on the subject? and What does the study add? Diffusion-weighted (DW) MRI is a non-invasive technique measuring the microscopic mobility of water molecules in the tissues without contrast administration. It provides information on perfusion and diffusion simultaneously in any organ, so it can be used to differentiate normal and abnormal tissue structure, and it might help in the characterization of various abnormalities. In recent years, DW-MRI has been applied in the evaluation of urinary tract lesions, such as malignant renal, prostatic and bladder tumours; however, it has not previously been tested on its ability to distinguish residual cancer from fibrotic and inflammatory changes secondary to transurethral resection (TUR) and intravesical chemotherapy, both of which manifest as bladder-wall thickening on T2-weighted MRI. This is the first study to show the feasibility of DW-MRI in follow-up of patients with superficial bladder tumours after TUR. DW-MRI was highly reliable in differentiating post-TUR inflammatory changes from bladder tumours, with results similar to those of conventional cystoscopy. This non-invasive method could be used efficiently in future for follow-up of this patient group and may obviate the need for routine cystoscopy. • To study the feasibility of using diffusion-weighted (DW) magnetic resonance imaging (MRI) in bladder cancer follow-up after transurethral resection (TUR). • Included in the study were 47 patients with a history of TUR of superficial bladder carcinoma, who were admitted to our centre between January and December 2011 for follow-up cystoscopy. • Before cystoscopy, DW-MRI was performed and the apparent diffusion coefficient (ADC) value was measured in a circular region of interest within the carcinoma and normal bladder wall. • Two radiologists, blinded to the results of cystoscopy, independently interpreted the DW images. • A comparison of imaging findings with those of cystoscopy was performed using the McNemar test. • In our 47 patients, cystoscopy identified 34 bladder lesions in 24 patients and in the remaining 23 the bladder looked normal. • In the 24 patients with malignant bladders, DW-MRI detected 32/34 tumours with two false-negative findings of lesions in two patients. • In 23 patients with non-malignant bladders, the DW-MRI data were accurate for 21 patients, as two patients were misdiagnosed as malignant. • The sensitivity, specificity, accuracy, positive and negative predictive values of DW-MRI for identifying bladder tumours were 91.6% (22/24), 91.3% (21/23), 91.5% (43/47), 91.6 (22/24) and 91.3 (21/23), respectively. • Using the McNemar test there was no significant difference between DW-MRI and cystoscopy. • DW-MRI has a high reliability in differentiating post-TUR inflammatory changes from bladder tumours, which is similar to that of cystoscopy. • DW-MRI could be a first-line diagnostic test in follow-up of patients after TUR.