Histological examination reveals an encapsulated expansile tumor which is seen to compress the normal thyroid tissue around it. The tumor is composed of nests of cells separated by fine fibrous septa. The cells are large and brightly eosinophilic, with a granular cytoplasm and a low nuclear to cytoplasmic ratio. In most areas the nuclei are rather monomorphic, with coarse chromatin features and singular prominent eosinophilic nucleoli. Focally, there is nuclear atypia suggesting aneuploidy, but mitotic figures are not easily found. There are focal areas where there seems to be invasion into the capsule, and in one region, frank breaching of the capsule is seen. The tumor appears to track along the blood vessels as they pierce the capsule. Angiolymphatic invasion is identified.