Malignant mesothelioma with intracytoplasmic crystalline inclusions.

A 60-year-old female presented with a history of hoarseness, cough, chest pain, and dyspnea and a needle biopsy sample was submitted for histology. Light microscopy showed sheets of tumor cells with eosinophilic cytoplasm containing multiple crystals and eccentrically located nuclei. Electron microscopy showed large intracytoplasmic crystalloid inclusions. No crystalloid structures were found extracellularly. The tumor cells also had long slender microvilli and cell junctions, the features being consistent with a malignant epithelial mesothelioma. In the authors' experience this is a rare finding. The clinical information initially received was poor and electron microscopy was essential in making the correct diagnosis.