Zellballen pattern is seen in?

Ans. is 'a' i.e., Pheochromocytoma * Pheochromocytoma is composed of polygonal to spindle shaped chromaffin cells or chief cells, clustered with sustentacular cells into small nests or alveoli (zellballen) by a rich vascular network. The nuclei are usually round to ovoid, with a stippled "salt & pepper" chromatin that is characteristic of most neuroendocrine tumors.* Zellballen pattern is also seen in paraganglioma.