Orbital schwannoma with fluid-fluid levels on MRI.

A 40-year-old man presented with a progressively growing left orbital mass producing proptosis. Orbital MRI revealed a large bilobed mass that was isointense with respect to the extraocular muscles on T1-weighted images and demonstrated heterogenous contrast enhancement. T2-weighted images revealed a markedly heterogenous internal appearance with fluid-fluid levels. The mass was completely excised in one piece. Histopathologically, the encapsulated tumor consisted mostly of spindle-shaped tumor cells with elongated nuclei forming bundles without obvious mitosis. Richly cellular areas were consistent with the Antoni A pattern, and more hypocellular edematous areas were consistent with the Antoni B pattern. Hemorrhagic and cystic areas were seen within the tumor. The tumor cells stained diffusely positive with S-100 protein. Findings were consistent with the diagnosis of orbital schwannoma. Fluid-fluid levels are usually seen in some vascular and bone tumors and soft tissue lesions. Fluid-fluid levels have previously been reported to occur in intracranial but not in orbital schwannomas. This case demonstrates that orbital schwannoma can also display fluid-fluid levels on MRI, which were thought to be due to intralesional hemorrhage in this case.