An ultrastructural morphometric analysis of platelet giant and fusion granules in control subjects and patients with neoplastic myeloproliferative disorders

Abstract

Electron microscopy has made a significant contribution to our understanding of the normal and defective human platelet. The normal human platelet is ultrastructurally complex and although only 2-4 microns in diameter, contains many cell organelles and structural elements shared with muscle cells and neurons. Platelet organelles include mitochondria, microfilaments, microtubules, α-granules (contain fibrinogen and platelet factor 4), dense bodies (contain serotonin, ADP, ATP and calcium), a dense tubular system and open canalicular system (Fig. 1). An ultrastructural description of giant granules were first reported in 1960 in Willebrand-Jürgens disease. Fusion granules (giant, irregularly-shaped granules) resulting from an apparent "fusion of normal-sized α-granules have since been reported to be characteristic of platelets obtained from patients with preleukemia and myelomonocytic leukemia.Electron microscopic examination of normal platelets in our laboratory revealed occasional granules which also appear fused and irregular in shape.A qualitative assessment of what constitutes an abnormal granule is therefore subjective. The purpose of this study was to establish morphometric criteria which can be used to define the pathological nature of giant and fusion-type platelet granules, and to determine if patients with neoplastic myeloproliferative disorders can be distinguished from patients with a variety of benign conditions for diagnostic purposes.