[Pulmonary crystal-storing histiocytosis: a case report].

A 45-year-old female patient was found to have a nodule in the right lower lobe on physical examination. Chest CT showed the nodule was lobulated measuring 24 mm×23 mm, with obvious enhancement and adjacent pleural traction. As the PET-CT showed increased ¹⁸F-FDG uptake suggesting malignancy, the wedge resection of the right lower lobe was performed. Grossly, the mass was adjacent to the pleural area with indistinct boundary. On cut sections, the lesion was solid and tough, with a greyish-pink colour. Microscopically, the lesion had an ill-defined margin, and was composed of spindle and polygonoid histiocytes with rich eosinophilic cytoplasm similar to rhabdoid muscle cells. The cytoplasm of histiocytes was filled with diamond-shaped or club-shaped crystals. Immunohistochemistry (IHC) showed the histiocytes were positive for CD68, κ, λ, IgG, IgM and IgA. The patient had been followed up for 41 months and had shown neither recurrences nor new diseases. CSH is a rare non-neoplastic histiocytic proliferative disease. Pulmonary CSH should be differentiated from multiple diseases. Accurate pathological diagnosis depends on its morphology and immunophenotype. This disease is often related to potential lymphoproliferative or plasma cell disorder. After diagnosis, a systemic examination is required and long-term follow-up is recommended.