Fine needle aspiration cytology of primary lymphoid lesions of the orbit: Report of four cases

Background: The role of fine needle aspiration cytology (FNAC) in diagnosis and differentiation of primary orbital lymphoid lesions is debatable, and little literature exists on cytodiagnosis of orbital lymphoid lesions. Cases: Four patients with orbital lesions underwent routine FNAC. In 3 cases, histopathologic examination was performed with immunohistochemistry (IHC). Cytologic features and diagnoses were correlated with histopathologic diagnoses. Two were cytologically diagnosed with low-grade non-Hodgkin lymphoma (NHL) and 2 with pseudolymphoma and inflammatory pseudotumor, respectively. Of the 2 cases of histologically diagnosed NHL, 1 had concordant diagnosis and the other had a false negative diagnosis of pseudolymphoma; both showed significant increase in mast cells, with neoplastic lymphoid cells exhibiting a higher N:C ratio and coarser chromatin texture. The case cytologically interpreted as suspicious for NHL was identified as a pseudolymphoma on histology (false positive). The case of inflammatory pseudotumor, in which biopsy was not performed, responded well to corticosteroids, strengthening the cytologic diagnosis. Conclusion: FNAC diagnosis and differentiation of benign vs. malignant primary orbital lymphoid lesions is often difficult. Careful cytologic interpretation with respect to certain subtle cytologic details is needed in minimizing false positive or false negative diagnoses. In difficult situations, IHC using suitable immunomarkers proves highly useful.