zellballen zellballen a zellballen is a small nest of chromaffin cells or chief cells with pale eosinophilic staining. zellballen are separated into groups by segmenting bands of fibrovascular stroma, and are surrounded by supporting sustentacular cells. a zellballen pattern is diagnostic for paraganglioma or pheochromocytoma. zellballen is german for "ball of cells".