Pheochromocytoma is a tumour that arises from the chromaffin cells of the adrenal medulla. Clinically, patients typically present with catecholamine excess, resulting in symptoms such as hypertension, headaches, and heart palpitations. It is considered benign if the tumour is localized to the adrenal gland and malignant if it has metastasized. Microscopically the tumour is made up of neuroendocrine cells with granular to basophilic cytoplasm. The tumour cells are arranged in small nests surrounded by a supporting network of sustentacular cells. This arrangement is known as “zellballen”. Small blood vessels are typically seen throughout the tumour. By immunohistochemistry, the tumour cells are positive for the neuroendocrine markers chromogranin and synaptophysin, and the supporting sustentacular cells stain positive for S100.