Giant intranuclear granules in human megakaryocytes: an ultrastructural study.

The appearance of "giant perichromatin granules" to date has been considered pathognomonic of nasopharyngeal angiofibroma. We present the finding of giant intranuclear granules in human megakaryocytes. The patient was a 34-year-old woman with a diagnosis of Sebastian platelet syndrome. The bone marrow aspirate showed an increased number of megakaryocytes. Ultrastructural study revealed giant perichromatin-like granules in the nuclei of 80% megakaryocytes. These granules were round or oval and size ranged 230 to 540 nm. Further studies are needed in our patient to determine the significance of these granules.