Tissue eosinophilia and eosinophil degranulation in orbital pseudotumor

To investigate the participation of the eosinophil in orbital pseudotumor, the authors studied surgical biopsy specimens from nine patients with pseudotumor. Surgical biopsy specimens of orbital tissue from four patients with Graves' ophthalmopathy and autopsy specimens of orbital tissue from six patients without orbital diseases served as controls. Eosinophil infiltration and degranulation were assessed by immunofluorescence staining of formalin-fixed, paraffin-embedded tissues for the cytotoxic eosinophil granule major basic protein. Eosinophil infiltration and extracellular major basic protein deposition were evident in all orbital pseudotumor specimens. In contrast, no eosinophil infiltration or extracellular major basic protein deposition was present in any of the ten control specimens. These findings indicate that eosinophil degranulation is found in orbital pseudotumor, and they also identify yet another clinical entity where eosinophil infiltration and degranulation are associated with fibrosis.