Histological views of the resected adrenal tumor and its intravascular invasion. A. High power (400 ×) view of the resected adrenal tumor. The resected adrenal pheochromocytoma shows chromaffin cells with a classic nested and trabecular architecture. Other characteristic morphologic features include nuclear enlargement and hyperchromasia with cytoplasm that is both oncocytic (pink and granular) in some cells and basophilic (blue) in others. B. Intra-vascular invasion of tumor (400 ×). Pheochromocytoma cells seen within a blood vessel. Vascular invasion is not a reliable indication of a malignant pheochromocytoma. Only metastatic disease to regional lymph nodes or distant sites (most commonly ribs, spine, liver and lung) will define this tumor as a malignant lesion.