Pheochromocytoma : Zellballen pattern
The histologic appearance of pheochromocytomas can be quite variable. In a typical case, the tumor consists of polygonal or spindle cells arranged in small nests (Zellballen) surrounded by sustentacular cells (best seen with S-100 immunostain; see image 35). The nests are separated by a delicate fibrovascular stroma. The nuclei are round or oval and have prominent nucleoli.