An isolated orbital mass with proptosis and diplopia: an uncommon metastasis from intracranial olfactory neuroblastoma in a Chinese patient

Purpose: Olfactory neuroblastoma (ONB) is a rare neuroectodermal malignant neoplasm that originates from the olfactory sensory epithelium. In reported cases involving the orbit, the primary neoplasms could invade the orbits through bone destruction or cranio-orbital communication anatomical structure. The present study reports a rare case of orbital metastatic tumor arising from an intracranial ONB in a Chinese patient, which is the first case demonstrating an uncommon route of ONB involving the orbit. Patient and methods: A 62-year-old man with a right orbital tumor was diagnosed as having a secondary tumor arising from intracranial ONB. Clinical examination, including ocular imaging examination, and histopathological and immunohistochemical studies were performed. Results: In the ocular examination, a focal, firm, nontender swelling with ill-defined margins in the right orbit was found on palpation. Proptosis, limited eyeball movement, and visual loss were also observed. The unenhanced computed tomography scan showed a homogeneous, isolated, ill-defined soft tissue neoplasm in the right orbit. The histopathological study revealed irregularly shaped nests of tumor cells surrounded by avascularized fibrous stroma. The monomorphic malignant tumor cells are small round blue cells that are slightly larger than mature lymphocytes, with a very high nuclear to cytoplasmic ratio. The immunohistochemical staining for tumor cells was positive for synaptophysin, chromogranin A, cluster of differentiation 56 (CD56), cytokeratin, vimentin, S-100 protein, and negative for epithelial membrane antigen, and cluster of differentiation (CD99). Conclusion: This is so far the first Chinese case of orbital metastasis from intracranial ONB that has ever been reported. Metastasis might be another route of ONB invading the orbit besides direct invasion.