Unusual features of metastatic atypical carcinoid of the larynx.

This report describes a case of atypical carcinoid of the larynx with metastatic tumor to cervical lymph nodes showing features similar to paraganglioma. Immunohistochemically, both the primary and metastatic tumor were positive for epithelial membrane antigen, cytokeratin, neuron-specific enolase, chromogranin, synaptophysin, calcitonin and carcinoembryonic antigen. The sustentacular cells in pseudo-cell ball ("Zellballen") formations were shown by a positive S-100 marker. Electron microscopic analysis revealed numerous neuroendocrine granules measuring 150-250 nm in diameter. Clinical features, histological appearance, histochemical, immunohistochemical and ultrastructural findings, as well as differential diagnosis are discussed.