What are the pathologic differential diagnoses of granular cell tumors (GCTs)?

Updated: Dec 29, 2018
  • Author: Vladimir O Osipov, MD; Chief Editor: E Jason Abel, MD  more...
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Answer

Some schwannomas and neurofibromas may show granular changes in parts, but the changes are never extensive enough to create a major diagnostic challenge. Moreover, schwannomas are encapsulated, and other stigmata of von Recklinghausen disease associated with neurofibromas are absent in patients with granular cell tumors.

Benign granular cell tumors may exhibit some superficial resemblance to rhabdomyomas and hibernomas. However, upon critical analysis, they do not show cytoplasmic striations or vacuoles and are negative for skeletal muscle markers and fat stains.

Intracranial granular cell tumors (the posterior pituitary is a noteworthy site for granular cell tumors) may be mistaken for granular variants of glial tumors but can be differentiated based on their negativity for glial fibrillary acid protein.

Granular cell variants of basal cell carcinoma, melanoma, leiomyoma, leiomyosarcoma, dermatofibrosarcoma, angiosarcoma, fibrous histiocytoma, and ameloblastoma can sometimes be indistinguishable from granular cell tumors if examined with routine light microscopy. A battery of immunohistochemical stains is needed to make a specific diagnosis. Granular cell tumors are positive for S-100 protein and negative for epithelial, melanocytic, smooth muscle, dendritic cell, and endothelial markers.

Malignant granular cell tumors can sometimes mimic alveolar soft part sarcoma because of their organoid growth pattern and periodic acid-Schiff (PAS)–positive intracellular crystalloids. The rhomboid crystalloids with their characteristic lattice pattern, observed ultrastructurally in alveolar soft part sarcoma, are absent in granular cell tumors.


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