Histopathological Basis of Peritumoral Enhancement in Muscle-invasive Bladder Cancer.

PURPOSE: Peritumoral enhancement (PTE) on dynamic contrast-enhanced MRI is a highly specific imaging feature of muscle-invasive bladder cancer (MIBC). However, the histopathological basis of PTE remains unclear. This study aimed to elucidate the pathological substrates underlying PTE, by correlating MRI findings with quantitative histopathological analysis.

METHODS

This retrospective cross-sectional study included 14 patients with pathologically confirmed MIBC who underwent preoperative multiparametric MRI followed by radical cystectomy. PTE was assessed on preoperative dynamic contrast-enhanced MRI by 4 experienced radiologists, and its thickness was measured. Postoperatively, histopathological evaluation was performed in 3 regions: intratumoral area (ITA), peritumoral area (PTA), and non-tumoral muscularis propria (MP). Fibrosis was quantified using Masson trichrome staining, T-lymphocytes using CD8 immunohistochemistry, and microvessels using CD31 immunostaining. Quantitative spot-based analysis and continuous ROI-based spatial analysis were performed along the invasive front of the tumor. Regional comparisons were conducted using the Wilcoxon signed-rank test with Bonferroni correction.

RESULTS

PTE thickness on MRI ranged from 1 to 2 mm (median, 1.5 mm), spatially corresponding to the histologically defined PTA. The fibrosis area fraction was significantly higher in the PTA than the ITA and MP (all P < 0.001), with continuous spatial analysis demonstrating a distinct peak immediately outside the tumor invasive margin. T-lymphocyte counts and area fractions were significantly higher in both the ITA and PTA than in the MP, with no significant differences between the ITA and PTA. The number of microvessels was significantly higher in the PTA than in the MP, but did not differ significantly between the PTA and ITA. Microvessel density was significantly higher in the PTA than in both the ITA and MP.

CONCLUSION

PTE reflects localized stromal remodeling at the tumor invasive front, characterized predominantly by marked peritumoral fibrosis accompanied by increased microvessel density.