Crystal-storing histiocytosis associated with MALT lymphoma of the ocular adnexa: a case report with review of literature.

We report a case of crystal-storing histiocytosis (CSH) associated with mucosa-associated lymphoid tissue (MALT) lymphoma of the ocular adnexa. The patient was an 81-year-old woman who presented with a 5-month history of a slowly enlarging tumor on her left lower eyelid. The tumor was 2 cm in the largest diameter, involving both inferior oblique and inferior rectus muscles. Histological examination revealed that the tumor was composed predominantly of sheets of spindle-shaped cells resembling striated muscle cells, and scattered aggregates of atypical lymphoid cells at the periphery of the tumor, showing prominent plasmacytoid differentiation. Immunohistochemical and ultrastructural analyses demonstrated that the spindle-shaped cells were CD68-positive histiocytes containing abundant rod-like and/or rectangular crystals in their cytoplasm, consistent with the diagnosis of CSH. The scattered aggregates of atypical lymphoid cells were diagnosed as MALT lymphoma based upon their immunophenotype, featuring diffusely positive staining for CD20, but negative for CD3, CD5, and CD10, and monotypic expression of IgM-kappa in cells with plasmacytoid differentiation. Although CSH is a well-recognized manifestation in lymphoproliferative disorders in the literature, CSH complicated by MALT lymphoma has only very rarely been reported. Given the rarity of this, difficulties in diagnosis may arise especially in cases where histiocytic proliferation overwhelms the underlying lymphoproliferative diseases.