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A case of crystal-storing histiocytosis (CSH) associated with mucosa-associated lymphoid tissue (MALT) lymphoma of orbit is reported. The patient was a 53-year-old man who presented with an 8-year history of a slowly enlarging tumor in his right orbit. Histopathologic 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, showing prominent plasmacytoid differentiation. Immunohistochemical analysis demonstrated that the spindle-shaped cells were CD68-positive histiocytes containing abundant crystals in their cytoplasm, consistent with the diagnosis of CSH. The aggregates of atypical lymphoid cells were diagnosed as MALT lymphoma based on their immunophenotype. Although CSH is a well-recognized manifestation in lymphoproliferative disorders, CSH complicated by MALT type of ocular adnexal lymphoma has rarely been reported. Given the rarity of this, every case presenting with such crystal-storing histiocytes warrants a thorough search for a hidden lymphoid dyscrasia.

Crystal-storing histiocytosis is an uncommon form of nonneoplastic histiocytic proliferation that in most patients complicates an underlying lymphoproliferative or plasma cell disorder. Lung is a common site of involvement in patients with localized disease. We present an illustrative example from a 54-year-old woman with an asymptomatic solitary lung nodule. The tumor was characterized by sheets of histiocytes with abundant cytoplasm expanded by distinctive eosinophilic inclusions. Focal necrosis was present. Aggregates of monocytoid lymphocytes and clusters of peribronchiolar plasma cells were overshadowed by the histiocytic infiltrate. Immunohistochemical stains showed CD68 staining in nonneoplastic histiocytes and CD20 staining in monocytoid lymphocytes. In situ hybridization studies showed κ light-chain restriction in plasma cells. These results, combined with the histologic findings, supported the diagnosis of crystal-storing histiocytosis complicating marginal zone lymphoma of mucosa-associated lymphoid tissue. We review the literature pertaining to pulmonary crystal-storing histiocytosis, highlighting the differential diagnosis for this rare phenomenon.

Massive crystal deposition is unusual in lymphoproliferative disorders. In this report, a mucosa-associated lymphoid tissue (MALT) low-grade B-cell lymphoma of the parotid gland containing large numbers of crystal-storing histiocytes is described. The patient, an 81-yr-old female, presented with a history of long-standing left parotid gland enlargement. FNA cytology of the tumor showed a lymphoplasmacytic infiltrate and sheets of large benign histiocytes with abundant eosinophilic intracytoplasmic inclusions. Paraffinsection immunohistochemistry performed on the cell block demonstrated that the histiocytic cells were immunoreactive for the KP-1 (CD-68) antibody and monotypic for cytoplasmic IGM and L-light chain. The cytological diagnosis was consistent with a low-grade B-cell lymphoma with plasmacytic differentiation associated with crystal-storing histiosis. A periparotid lymph node was biopsied and showed involvement by a monocytoid B-cell lymphoma with plasmacytic differentiation and crystal-storing histiocytosis in the pericapsular region.