Malignant paraganglioma of the rectum: The first case report and a review of the literature

Figure 1 Histological features. A-B: The tumor was composed of sheets or organoid nests of large polygonal cells surrounded by a rich network of delicate arborizing vasculature, generating a characteristic “zellballen” (A: HE, × 100; B: HE, × 400); C: Focal nuclear pleomorphism (HE, × 400); D: Confluent tumor necrosis (HE, × 100); E: Vascular invasion (HE, × 400); F: Metastases of lymph nodes (HE, × 100).

Figure 2 Immunohistochemistry. A: The tumor cells exhibited diffuse and strong expression of chromogranin A; B: S100 protein highlighted the presence of slender sustentacular cells located at the periphery of the tumor nests; C: The Ki67 index was approximately 20%; D: CD34 outlined the rich vascular network.