Cardiac neuroendocrine tumor with absence of sustentacular cells: immunohistochemical and ultrastructural findings.

A 68-year-old male presented with increased shortness of breath and intermittent chest pain. Cardiac catheterization along with echocardiogram imaging demonstrated 3-vessel coronary artery disease with severe left ventricular dysfunction and critical aortic stenosis. During coronary artery bypass surgery, a tumor was identified at the sulcus between the aorta and the right atrial appendage. This highly vascular tumor extended over the right coronary artery, prompting biopsy and further resection. Light microscopic evaluation showed packets of uniform round neoplastic cells without evidence of necrosis or increased mitotic figures. Immunohistochemical studies were positive for synaptophysin and weakly positive for chromogranin. Pankeratin, S-100, and GFAP stains were all negative. Ultrastructural examination of the neoplasm demonstrated numerous electron-dense secretory granules within the cytoplasm of the tumor cells. These secretory granules varied in size from 60 to 210  nm, with halos encircling many of them, suggesting the likelihood of epinephrine or norepinephrine granules. Within the specimen, abundant vascular spaces were identified, but no sustentactular cells were present. The patient agreed to undergo genetic testing, and a mutation in the succinate dehydrogenase complex subunit B (SDHB) was identified. This confirmed the molecular diagnosis of hereditary paraganglioma/pheochromocytoma syndrome. Now two years out from surgery, this patient continues to be asymptomatic in spite of the fact that his tumor was only partially resected.