Renal Extramedullary Hematopoiesis in Mast Cell Leukemia with Bone Marrow Fibrosis

Figure 2

Bone marrow biopsy reveals mastocytosis. (a) H&E stain shows a patchy distribution of areas with atypical mast cell infiltrates, concentric fibrosis (dashed line), and granulocyte-rich areas (bold line). Trabeculae shows signs of beginning osteosclerosis with focal spikes and paratrabecular apposition of new bone (osteosclerosis grade 1). (b) Gomori stain damasks a diffuse and dense increase in reticulin with extensive intersections, occasionally with focal bundles of thick fibres, associated to focal myelofibrosis (MF-2), particularly in the mast cell-rich area. (c) H&E stain shows infiltrates of atypical spindle-shaped mast cells without metachromatic granules and without blast-like appearance. (d) Giemsa stain exposes atypical mast cells, some of which still contain metachromatic granules. (e) Immunohistochemical staining for CD117 highlights atypical mast cell infiltrates (encircled by the dashed line). (f) Immunohistochemical staining for MPO highlights patchy granulocyte-rich area (encircled by a bold line). (g) Expression of mast cell tryptase is present within the atypical mast cell aggregates. (h) CD25 expression emphasizes the atypical immunophenotype of the mast cells.

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