Possible identification of third stromal component in extraadrenal paraganglioma: myofibroblast in fibrous band and capsule.

Sustentacular and dendritic cells are known as the stromal components of extraadrenal paraganglioma. We identified a third stromal component in such a case. A 66-year-old Japanese woman complained of abdominal pain. The tumor was discovered near the right adrenal gland in the retroperitoneum. Histologically, the tumor consisting of round to oval neoplastic cells with eosinophilic cytoplasm proliferating with a "zellballen" pattern. Sustentacular cells were positive for S-100. Dendritic cells positive for HLA-DR were seen among the neoplastic nests. Additionally, many alpha-smooth muscle actin (ASMA)-positive and hcaldesmon-negative stromal cells, namely, myofibroblasts, were distributed in the capsule and fibrous band. Ultrastructurally, myofibroblasts contained many myofilaments and dense bodies in the cytoplasm. Finally, we identified the third stromal component, namely, myofibroblasts, in the extraadrenal paraganglioma. These myofibroblasts may play a role in the stromal response of host against neoplasm or the regulation of tumor growth.