Morphological CT and MRI characteristics of small cell neuroendocrine bladder cancers and their predictive factors for distinguishing from conventional urothelial carcinoma

Small cell neuroendocrine bladder cancers (SCBCs) are rare. The accurate preoperative diagnosis of SCBCs is critical because of their poor prognosis, and therapeutic approaches differ from those of urothelial carcinoma (UC). This study aimed to identify the imaging characteristics of SCBCs and determine the factors for their differential diagnosis. This was a retrospective observational study. This study enrolled 32 participants with SCBCs from September 2014 to July 2023 and 100 with UC from July 2022 to July 2023. Patient characteristics and imaging features from computed tomography (CT) and magnetic resonance (MRI) were reviewed and compared between the SCBC and UC groups. Univariable and multivariable analyses identified the predictive factors of SCBCs. Receiver operating characteristic (ROC) curve analysis was used to quantify the performance of these factors. Univariate analysis revealed significant differences in margins, serosal invasion, apparent diffusion coefficient (ADC) mean values, the invasion of the urinary meatus, ureteral invasion, hydroureter, and pelvic lymphatic metastasis between the SCBC and UC groups ( p < 0.05). Compared with UC, SCBCs were more likely to present with ill-defined margins, serosal invasion, low ADC values, invasion of the urinary meatus, ureteral invasion, hydroureter, and pelvic lymphatic metastasis. In logistic regression analysis, serosal invasion and pelvic lymphatic metastasis were independent factors distinguishing SCBCs from UC, with the model showing an area under the curve of 0.791 in ROC curve analysis. SCBCs were found to exhibit distinct imaging features. A bladder tumor with serosal invasion and pelvic lymphatic metastasis on CT and/or MRI is more likely to be SCBC than UC.