As the authors note, magnetic resonance imaging (MRI) is increasingly being adopted for the preoperative staging of patients with bladder cancer. However, MRI is a costly and time-consuming exam and may be contraindicated in a non-negligible proportion of individuals – due to metal, renal function, etc. Therefore, in this study, they assess high-resolution micro-ultrasound.
This is a technology that was developed by Exact Imaging, a company based in Ontario, Canada. Their ExactVu™system uses an EV29L 29 MHz side-fire transducer (Exact Imaging, Markham, Canada). It is being tested in multiple GU spaces, including in prostate cancer, and holds significant promise in the field of prostate cancer diagnosis and surveillance.
This was an observational prospective investigative study performed from October 2017 (ongoing) in male and female patients, age > 18 years, with a diagnosis of primary or recurrent bladder cancer scheduled for an endoscopic treatment (transurethral resection or TURBT). The end-points of the current study were:
- Feasibility of microUS in bladder cancer patients
- Ability to differentiate between the three layers of a normal bladder wall (urothelium, lamina propria and muscularis propria)
- Test its accuracy in determining the presence/location of bladder lesions
- Compare microUS results and pathological staging
Images were acquired transvaginally in females and transrectally in males. They were all done at the time of TURBT, so under general anesthesia. The bladder was emptied, then refilled with 50 cc sterile fluid. Dr. Saita did note that, due to the structure of the probe and the need to advance further in the rectum to acquire bladder procedures, this is still too uncomfortable for patients to do in a clinic.
The procedure was completed in 23 total patients, of which 11 were female and 12 were male. The authors did note that given to the current shape of the micro-US probe, the transvaginal route allowed a more precise exploration of the cranial portion of the bladder in female patients.
With regards to the layers of the bladder, micro-US was capable of accurately differentiate the three layers of the bladder wall in all individuals. An example of the 3 layers are seen below:
He notes that the 2 physicians doing the ultrasound were both experienced with it in the prostate cancer setting, so it does require some training to read. They cannot yet comment on interobserver variability.
Next, bladder cancers were clearly visualized, appearing as heterogenous structures protruding from the normal bladder wall. In all 14 nonmuscle invasive bladder cancer (NMIBC) cases, lesions were not disrupting or only focally disrupting the hyperintense line representing the lamina propria and this finding was concordant with final pathology, showing 13 pTa and 1 pT1 tumors. See slide below:
In 7 cases that had predicted muscle-invasive bladder cancer (MIBC), 5 had histologically confirmed MIBC. The two incorrect cases were HG pT1 tumors. See below:
In 2 patients, micro-US based staging was not possible due to poor visibility – both had LG pTa tumors.
Conclusions: Preliminary results show that micro-US depicts normal anatomy of the bladder wall well, detects bladder tumors and discriminates NMIBC from MIBC with a strong pathological correlation.
Overall, the pilot study was a success, meeting its primary endpoints, warranting further evaluation in larger cohorts. A manuscript of these results is in the process of being published.
Presented by: Alberto R. Saita, Humanitas Clinical and Research Center, Department of Urology, Rozzano, Italy