Conjunctival Foreign Body Granuloma With Hemosiderin Deposition Mimicking Malignant Melanoma

To report a case of pigmented conjunctival foreign body granuloma with prominent hemosiderin deposition that clinically mimicked malignant melanoma.

Case report. Clinical examination, anterior segment optical coherence tomography (AS-OCT), histopathology with polarized light microscopy, Prussian blue iron staining, and immunohistochemistry for CD68, PRAME, and SOX10 were performed.

A 64-year-old man presented with a 2-week history of a pigmented mass on the temporal bulbar conjunctiva of the left eye, with no history of ocular trauma. Slit-lamp examination revealed an elevated, dome-shaped, gray-brown mass approximately 3 × 3 mm with prominent feeder vessels and a peripheral orange-brown halo. AS-OCT showed an elevated dome-shaped lesion with internal heterogeneous hyperreflectivity and posterior shadowing. Given the clinical features suspicious for conjunctival melanoma, wide local excision with 4-mm margins, partial sclerectomy, cryotherapy, and amniotic membrane reconstruction were performed. Histopathology unexpectedly demonstrated a foreign body granuloma with yellow crystal-like foreign material, multinucleated giant cells, and extensive hemosiderin deposition, confirmed by positive Prussian blue iron staining. Polarized light microscopy showed partial birefringence at the periphery. Immunohistochemistry showed strong CD68 positivity with both PRAME and SOX10 negative, excluding a melanocytic origin.

Pigmented conjunctival foreign body granuloma with hemosiderin can closely mimic conjunctival melanoma clinically and on AS-OCT. Histopathology, including iron staining and immunohistochemistry for CD68, PRAME, and SOX10, was useful for establishing the diagnosis.