Confocal laser scanning microscopy (CLSM) offers the advantage of quasi-theoretical resolution due to absence of interference with out-of-focus light. Prerequisites include minimal tissue autofluorescence, either intrinsic or induced by fixation and tissue processing, and minimal background fluorescence due to nonspecific binding of the fluorescent label. To eliminate or reduce autofluorescence, three different reagents, ammonia-ethanol, sodium borohydride, and Sudan Black B were tested on paraffin sections of archival formaldehyde-fixed tissue. Paraffin sections of biopsy specimens of human bone marrow, myocardium, and of bovine cartilage were compared by CLSM at 488-nm, 568-nm and 647-nm wavelengths with bone marrow frozen sections fixed either with formaldehyde or with glutaraldehyde. Autofluorescence of untreated sections related to both the specific type of tissue and to the tissue processing technique, including fixation. The reagents' effects also depended on the type of tissue and technique of tissue processing, including fixation, and so did the efficiency of the reagents tested. Therefore, no general recipe for the control of autofluorescence could be delineated. Ammonia-ethanol proved most efficient in archival bone marrow sections. Sudan Black B performed best on myocardium, and the combination of all three reagents proved most efficient on paraffin sections of cartilage and on frozen sections fixed in formaldehyde or glutaraldehyde. Sodium borohydride was required for the reduction of unwanted fluorescence in glutaraldehyde-fixed tissue. In formaldehyde-fixed tissue, however, sodium borohydride induced brilliant autofluorescence in erythrocytes that otherwise remained inconspicuous. Ammonia-ethanol is believed to reduce autofluorescence by improving the extraction of fluorescent molecules and by inactivating pH-sensitive fluorochromes. The efficiency of borohydride is related to its capacity of reducing aldehyde and keto-groups, thus changing the fluorescence of tissue constituents and especially of glutaraldehyde-derived condensates. Sudan Black B is suggested to mask fluorescent tissue components.

The aetiology of primary B-cell lymphomas of the thymus is enigmatic. Although thymic follicular lymphoid hyperplasia (TFH) is commonly associated with myasthenia gravis (MG), lymphoma is not a complication of this condition. The present paper reports a high frequency of monoclonal B-cell populations (6 of 18 cases; 33%) in micronodular thymoma (MNT), a peculiar thymic epithelial neoplasm with a B-cell-rich stroma, while B cells were consistently polyclonal in TFH (25 cases) and other types of thymomas (15 cases) (p < 0.001). An intratumoural lymphoma could be identified in three of the six monoclonal MNTs. Sequencing of the monoclonal IgH chain revealed partially overlapping VDJ gene usage in MNT and thymic mucosa-associated lymphoid tissue (MALT) lymphomas. The neoplastic epithelium of MNTs, but not of TFH and other types of thymoma, expressed high levels of dendritic cell, T-cell, and B-cell chemoattractants, such as CCL18, CCR6, and CCL20. It is concluded that abnormal chemokine expression in an epithelial tumour, MNT, can promote the recruitment of MALT, the emergence of monoclonal B cells, and, eventually, the subsequent development of mediastinal lymphomas. More generally, the concept that expression of a 'high-risk' spectrum of chemokines due to local or genetic factors may interfere with B-cell homeostasis and may contribute to MALT lymphoma development in chronic inflammatory states is proposed.

Eccrine angiomatous hamartoma (EAH) is an exceedingly rare benign tumor-like lesion prevalent in childhood which may produce pain and marked sweating. Although an aggressive treatment is not generally indicated, surgery may be considered in severe cases. In this report we present novel morphological findings by immunophenotyping, document the first MRI findings in EAH and emphasize the importance of preoperative imaging of such lesions.

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We report 18 cases of lipomatous meningioma occurring in patients aged 14 to 79, most being females (72%). Sixteen were supratentorial and 2 involved the spinal meninges. Follow-up ranged from 1 to 120 months. Fifteen patients were cured with surgery alone and 3 (17%) experienced a recurrence at 7, 8 and 24 months. Of these, one died with disease 4 years after resection of the primary lesion. Histologically, 12 tumors were meningothelial, 3 transitional, 2 showed myxoid stromal changes and 1 was microcystic. The 2 spinal tumors were atypical. The proportion of fatty cells ranged from 10 to 90%. These resembled mature adipocytes or less commonly lipoblasts. Xanthomatous meningothelial cells were also noted in 6 tumors (30%). Both conventional meningothelial as well as lipid-laden cells exhibited epithelial membrane antigen immunoreactivity. In addition, occasional cells resembling mature adipocytes showed reactivity for S-100 protein. Ultrastructurally, lipidization of neoplastic cells varied from intracytoplasmic lipid droplets to a single massive globule. Moreover, lipid-laden meningothelial cells featured interdigitating cell membranes and well-formed desmosomes. Lipid droplets were not membrane-bound. In that metaplasia denotes differentiation of one mature cell type to another, lipid accumulation in meningiomas cannot be considered true metaplasia since their lipid-laden cells retain the immunophenotype and ultrastructural features of meningothelium. We suggest that this distinctive subset of meningiomas be termed "lipidized meningiomas" rather than being included in the metaplastic category.