Background: Malacoplakia was first described by Michaelis and Gutmann in 1902 and further characterized by Von Hansemann, who coined the term malacoplakia to describe the soft, yellow-tan, raised plaques he encountered in a case involving the urinary bladder.11
Case: Fine needle aspiration cytology of a case of malacoplakia of the thyroid gland was performed on a 60-year-old woman. Fine needle aspiration demonstrated histiocytes with abundant granular cytoplasm that were eosinophilic with hematoxylin-eosin stain. Many of the cells contained numerous round, regular-appearing inclusions, which ranged in size from 4 to 10 microns in diameter. Many of these inclusions demonstrated the characteristic concentric appearance of Michaelis-Gutmann bodies. The inclusions were strongly positive for periodic acid-Schiff stain and stained weakly with Von Kossa stain. Clinically and radiologically the lesion mimicked a malignant neoplasm by virtue of its large size and destruction of adjacent cervical vertebrae. The diagnosis was ascertained only after surgical excision.
Conclusion: This is the first report of fine needle aspiration cytology of malacoplakia of the thyroid. The case demonstrates how difficult it may be to diagnose this rare entity, regardless of its characteristic features. It also underscores the point that malacoplakia may occur anywhere in the body and should always be considered when round, concentric intracytoplasmic inclusions are seen within histiocytes.