Which immunohistochemical marker combination is MOST characteristic of olfactory neuroblastoma (esthesioneuroblastoma) distinguishing it from other small round blue cell tumors of the sinonasal region?

• A CD99 positive, CK negative (Ewing's sarcoma pattern)
• B Synaptophysin and chromogranin A positive (neuroendocrine markers), S100 positive in sustentacular cells, CK negative ✓
• C CK positive, CD3 positive, EBV positive (NK/T-cell lymphoma)
• D WT1 positive, CD56 positive, desmin positive (rhabdomyosarcoma)

Explanation

Olfactory neuroblastoma shows: synaptophysin and chromogranin A positivity (neuroendocrine markers), S100 positivity in sustentacular cells at the periphery of tumor lobules (helpful in distinguishing from sinonasal neuroendocrine carcinoma which lacks sustentacular cells), and negativity for CK. Homer Wright pseudorosettes (neuroblastic rosettes) and Flexner-Wintersteiner rosettes may be seen. The sustentacular S100+ cells are pathognomonic.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.