A 38-year-old man presents with a 6-month history of episodic headaches, profuse sweating, and palpitations associated with severe hypertension (BP 180/110 mmHg). A CT abdomen shows a 4 cm well-encapsulated left adrenal mass. The cut surface demonstrates a mottled appearance with alternating tan and dark areas, as marked **B** in the diagram. Plasma free metanephrines are markedly elevated. Which of the following best explains the histopathological appearance marked **B**?