Non-invasive imaging is of great value in the staging of MIBC . Many investigators have considered 18F-FDG PET is of no value in detecting localized urinary bladder cancers [15, 16]. This limitation has been predominantly attributed to the urinary excretion of 18F-FDG. The concentrated activity in the urinary bladder made the mural lesions evaluation difficult . To overcome these limitations of 18F-FDG PET imaging, washing out the excreted 18F-FDG in the urinary bladder is mandatory. Using diuretics before the acquisition, or post-void imaging, or retrograde irrigation of the urinary bladder with a double-lumen Foley catheter, or other tracers were tried by some investigators to improve the sensitivity of PET imaging. A study conducted by Anjos et al. including 17 patients reported that detection of residual or locally recurrent urinary bladder tumors was dramatically improved using 18F FDG PET/CT with delayed imaging following intravenous injection of furosemide as well as oral rehydration . Another similar study conducted by Kamel et al. evaluating the role of forced diuresis in the improvement of diagnostic accuracy of pelviabdominal 18F FDG PET in 32 patients. Coupling of forced diuresis with parenteral hydration eliminated any significant 18F FDG activity from the lower urinary tract in 31of 32 (97%) patients after voiding the urinary bladder 3 successive times. This study concluded that the furosemide challenge was non-invasively resolved the inherent 18F FDG contrast handicap in the lower urinary tract .
Compared with conventional imaging, several studies found that FDG PET/CT scan has better diagnostic accuracy for the detection of metastatic deposits or other unexpected malignant tumors [18,19,20]. Nayak et al. found that CECT and PET/CT studies had a 44 and 78% sensitivity, respectively in detecting nodal metastasis . Also, a study by Kibel et al. including 43 patients with negative CT as well as, bone scans and PET/CT detected histopathologically proven nodal metastatic infiltrates in 7 out of 9 patients, displaying sensitivity, specificity, positive predictive value, and negative predictive value of 70%, 94%, 78%, and 91%, respectively . Another review study done by Bouchelouche et al. concluded that 18F FDG PET/CT was a useful imaging tool in detecting metastatic disease .
The present study was carried out to evaluate the importance of delayed post-diuretic FDG PET/CT in initial staging and restaging of 35 patients diagnosed with MIBC and how this was reflected on the treatment decisions of these patients.
In group A, we found a significant difference between FDG PET/CT and conventional imaging staging. Stage migration, due to upstaging by FDG PET/CT occurred in 38.9% of patients of group A, with major changes in management occurred as a result, both in the selection of treatment method (from direct cystectomy to neoadjuvant chemotherapy for better systemic control) and in overall treatment intent (from curative measurement to palliation), which means that important changes in the therapeutic management and plan of treatment of these patients was done.
In group B, FDG PET/CT helped in good evaluation of patients pre- and post-therapeutic disease (whether stationary course, upstaging, or downstaging of the disease) which helped in proper decision making accordingly.
Other many previous studies have tried to evaluate the impact of FDG PET/CT imaging on the management of patients. A study by Apolo et al. including 57 patients, presented with bladder malignancy revealed that FDG PET/CT detected more malignant disease in 40% of patients than conventional CE-CT or MRI. Questionnaires on intended patient management were completed by oncologists before and after FDG PET/CT to determine how these findings had an effect on patient management. They reported that planned management in 68% of patients had changed by clinicians based on the FDG PET/CT findings. However, an important limitation of this study was the possibility of disease progression between conventional CECT and FDG PET/CT, since the time interval between them was not determined. Moreover, the method and extent of conventional staging were unclear. Therefore, the results of their analysis may not reflect the true clinical impact of the additional diagnostic data from FDG-PET/CT imaging .
Another study by Laura et al. reported that, in 13.5% of their patients with urinary bladder cancer, the treatment was changed on the basis of FDG PET/CT results (due to FDG PET/CT upstaging), and treatment plan was changed in 4.2% of patients due to detection of second primary tumors by FDG PET/CT. However, their study was limited by their retrospective design in the form of retrospective assessment of preferred treatment before and after FDG PET/CT which would reflect that the categories used for decision and change in management might be inappropriate and underestimated .
A unique feature in the present study is that in group A, the additional diagnostic value of FDG-PET/CT study was compared with conventional imaging that performed within 30 days before FDG PET/CT examination to minimize the possibility of disease progression between the two imaging studies.
Post-diuretic FDG PET/CT when was done pre and post-therapy for patients in group B was able to give us a proper evaluation of the primary bladder lesion besides its role in the detection of metastasis in the rest of the body, which helped in proper decision making and accurate therapeutic plan for these patients.
One more advantage over the other studies is that pathological staging for all patients who showed response and proceeded to radical surgery was compared to post-therapeutic clinical staging by PET/CT evaluating its efficacy in the staging of MIBC patients.
Another good feature of the current study is that the 35 patients included in the study were evaluated prospectively within a clear treatment plan according to the most recent guidelines which make the changes in the treatment plans and treatment decisions appropriate and accurate, allowing for true evaluation of the clinical impact of additional diagnostic information from FDG PET/CT.
However, this study is limited by the small number of the included patients and future studies with the larger patient samples are required to assess the efficacy of delayed post-diuretic 18F FDG PET/CT imaging in the initial diagnosis and follow-up of MIBC patients.