Background: Few sinonasal malignancies can manifest, histologically, as clear cell neoplasia. The most likely such tumor to be encountered is metastatic renal cell carcinoma. Primary sinonasal tumors that can appear as clear cell malignancies include squamous cell carcinoma and mucoepidermoid carcinoma. Primary salivary clear cell carcinoma occurs almost exclusively in the oral cavity and has not been described in the nasal cavity.
Objective: To report a unique sinonasal clear cell malignancy that mimicked metastatic renal carcinoma.
Study design: Case report.
Outcome measurements: Radiography, histology, histochemistry, immunohistochemistry, and electron microscopy.
Results: Histologically, the tumor was identical to renal cell carcinoma. No evidence of renal malignancy was found by abdominal computed tomographic scan or gadolinium-enhanced magnetic resonance imaging. Histochemistry confirmed the presence of tumor glycogen but no mucin. Immunohistochemistry confirmed strong expression of low- and high-molecular-weight keratin and S100, and no vimentin expression. Electron microscopy showed tumor myofibroblastic differentiation and cytoplasmic glycogen, neutral lipid vacuoles, and cholesterol.
Conclusions: There was no clinical evidence of renal cell carcinoma. The immunohistochemical and ultrastructural findings were inconsistent with the diagnosis of renal cell carcinoma and showed features also inconsistent with the diagnosis of primary salivary clear cell carcinoma. We therefore conclude that this tumor represents a new and distinct entity, notable in its presentation as a "counterfeit renal cell carcinoma."