Hyaline cell-rich chondroid syringoma: case report and review of the literature.

Hyaline cell-rich chondroid syringoma (HCRCS) is a rare benign cutaneous neoplasm composed of cells with eosinophilic hyaline cytoplasm and plasmacytoid features, the origin of which remains elusive. To the best of our knowledge, only eight cases of this entity have been reported so far, and none of them was submitted to a large panel of myoepithelial markers. We report on a case of a previously healthy 29-year-old male patient who presented with a slowly enlarging flesh-colored nodule on the palmar aspect of the tenar region of his left hand, measuring 2 cm in maximum diameter. The nodule was "shelled-out" and submitted to light microscopy, immunohistochemistry, and ultrastructural examination. Histopathologic analysis disclosed a lobulated neoplasm composed of hyaline cells with plasmacytoid features showing ovoid nuclei, with occasional invaginations, finely granular chromatin, and discrete nucleoli; the cytoplasm was deeply eosinophilic with occasional dot-shaped paranuclear hyaline inclusions. On immunohistochemical evaluation, hyaline cells were strongly and diffusely positive for S-100 protein, vimentin, pan (CAM 5.2) and high molecular weight (34betaE12) cytokeratins; these cells were focally positive for GFAP, maspin, neuron-specific enolase, and cytokeratin 14. Alpha-smooth muscle actin, epithelial membrane antigen, carcinoembryonic antigen, collagen IV, Gp100 (HMB-45), and p63 were negative in neoplastic hyaline cells. Ultrastructural analysis disclosed cells with ovoid nuclei showing occasional invaginations and nuclear pockets; the cytoplasm was rich in meshworks of non-bundling intermediate filaments and a variable amount of rough endoplasmic reticulum cisternae. Based on our findings and those previously reported, hyaline cells of HCRCS might posses an aberrant myoepithelial differentiation. Most importantly, pathologists need to be aware of the histologic and immunohistochemical features of HCRCS to avoid a misdiagnosis of highly malignant neoplams, such as malignant melanoma and extra-skeletal myxoid chondrosarcoma.