This report describes two examples of nodular histiocytic/ mesothelial hyperplasia as seen in transbronchial biopsy that initially led to serious consideration of neuroendocrine neoplasm or meningioma. The biopsies showed nodular collections of cohesive polygonal or round cells with ovoid or deeply grooved nuclei and a moderate amount of finely granular cytoplasm. Nuclear pleomorphism was mild. Immunohistochemical studies showed few cells staining for cytokeratin and the mesothelial marker HBME-1, whereas most cells were decorated by the histiocytic marker PG-M1 (CD68). This lesion appears to be identical to nodular mesothelial hyperplasia as described in hernia sacs and mesothelial/monocytic incidental cardiac excrescences, and we propose modifying the designation to "nodular histiocytic/mesothelial hyperplasia" to take into account the marked predominance of histiocytes over mesothelial cells. The clues to recognition of the true nature of the lesion are clinicopathologic correlation and identification of strips of low cuboidal (mesothelial) cells in the vicinity, and the diagnosis can be further confirmed by immunohistochemical staining. Nodular histiocytic/mesothelial hyperplasia probably results from irritation to the mesothelial lining by various causes leading to focal aggregation of histiocytes within retraction pockets or crevices of the serosal cavity.

Granulomatous slack skin is an extremely uncommon form of cutaneous T-cell lymphoma. We report a case occurring in a 29-year-old man, who had generalized, progressive skin lesions evolving to nodular swellings and folds in the flexural regions, and peripheral blood and marrow involvement. The biopsies were initially misinterpreted as xanthogranuloma or granulomatous inflammation. Histologically, the entire dermis and subcutis was infiltrated by non-necrotizing granulomas comprising mononuclear histiocytes, multinucleated giant cells and small lymphoid cells with irregularly folded nuclei, associated with loss of elastic fibres. The small lymphoid cells showed focal epidermotropism. Immunohistochemical studies showed that they were of T-lineage (CD3+, CD43+, CD45RO+). The multinucleated giant cells, which showed reactivity with the histiocytic markers CD68 and Mac387, were highlighted by intense, thick membrane staining with CD45, CD43 and CD45RO. Ultrastructurally, they exhibited features of macrophages with numerous surface villous processes and lysosomes. Greater awareness of this entity may facilitate more prompt and accurate diagnosis, obviating a futile search for a non-existent infective aetiology.

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gravidarum associated with a serum activity which stimulates human thyroid cells in vitro. Clin Endocrinol 1992; 36: 83-9