Paraganglioma of the urinary bladder is a rare
tumor with characteristic histologic and immunohistochemical features. However, in our experience, it may be misdiagnosed as urothelial
cancer because of 1) its frequent involvement of the muscularis propria; 2) morphology that may suggest urothelial
cancer in transurethral resection specimens, particularly if there are artifactual changes induced by that procedure; 3) failure of pathologists to include it in their differential diagnosis when evaluating a
bladder tumor; and 4) only a minority of the cases are associated with symptoms that might prompt consideration of the diagnosis. Distinction between
paraganglioma and urothelial
cancer is important because of likely different therapeutic options. In this report, we describe our experience with the histopathology of
paragangliomas of the urinary bladder with emphasis on the histologic features that have led to their being misdiagnosed as conventional urothelial
cancer and, most importantly, those that will help pathologists recognize this rare
tumor of the bladder. Fifteen cases of
paraganglioma of the urinary bladder were studied, 11 of them consult cases. They affected patients (8 male, 7 female) with a mean age of 49.5 years; only two had symptoms suggestive of the diagnosis, including
hypertension during cystoscopy and episodic
headache. Three consult cases were submitted with a diagnosis of "
transitional cell carcinoma" and 4 with a diagnosis only of "
bladder tumor." Histologically, "zellballen" and diffuse patterns were present in 12 (80%) and 3 (20%) of the cases. A delicate fibrovascular stroma was obvious in 14 (93%) cases. Other patterns included irregular nests and pseudorosette formation.
Tumor necrosis, significant
cautery artifact, and muscularis propria invasion were present in 1 (7%), 3 (20%) cases, and 10 (67%) cases, respectively. All 15
tumors were composed of large polygonal cells with abundant granular cytoplasm. Focal clear cells were present in 3 (20%). The nuclei were mostly uniform, although occasional pleomorphic nuclei were seen in 6 (40%) cases, and 2 (13%) had frequent pleomorphic nuclei. Mitoses were rare overall, and no abnormal mitotic figures were found. The major histologic features that led to misdiagnosis included a diffuse growth pattern, focal clear cells,
necrosis, and muscularis propria invasion, with significant
cautery artifact compounding the diagnostic problems. Immunohistochemically, 2 of 2
tumors were positive for
neuron-specific enolase, 9 of 10
tumors for
chromogranin, and 2 of 3
tumors for
synaptophysin; 3 of 3
tumors were negative for
cytokeratin and 1 of 1
tumor negative for HMB-45.
Paraganglioma of the urinary bladder may be misdiagnosed as urothelial
cancer, but a careful search for the characteristic histologic features and, if necessary, supportive immunohistochemical studies, should lead to a correct diagnosis.