A clinicopathologic study of paragangliomas of the urinary bladder: can the clinical behavior of the tumor be predicted?

Paraganglioma of the urinary bladder is rare but even more unusual as no singular histologic feature is consistently characteristic of malignancy. Addi-tionally, paragangliomas can manifest in hypertensive crisis for clinicians resecting the tumors in unusual locations without proper histologic diagnosis. Herein we report nine cases of paraganglioma of the urinary bladder with immunohistologic study and follow-up information, including one rare malignant case with liver metastasis. Comparison of the immunohistologic features reveal that the malignant case shows the common features suggested by both the Pheochromo-cytoma of the Adrenal Gland Scaled Score (PASS) and Grading of Adrenal Pheochromocytoma and Extra-adrenal Paraganglioma (GAPP) system. The predomi-nant histopathologic features of malignant cases were large irregular nests with focal spindle tumor cells and a diffusely infiltrative growth pattern between smooth muscle of the urinary bladder wall with multiple necrotic areas and a high proliferative index. Eight cases without metastasis showed the classic zellballen of benign paragangliomas without irregular nests and well-demarcated nodules either in the submucosa or between smooth muscle bundles with no diffuse infiltration. We discuss the histopathologic and immunohistochemical features detecting malignant behavior, and comprehensi-vely review the previously published cases of malignant paraganglioma of the urinary bladder. In summary, we assess some clinicopathologic features which might help to predict which neoplasms are more likely to behave in a clinically aggressive manner to avoid adverse outcomes in this rare tumor's resection.