Inflammatory Myofibroblastic Tumour of the Skull Base
(a) HES × 10: a dense proliferation of spindle cells, partly with an epithelioid aspect, arranged in well-organized fascicles suspended in a myxoid background and admixed with many inflammatory cells, mostly lymphocytes, plasma cells, eosinophils, and rare mast cells. (b) HES × 20: spindle cells present with few atypical features: prominent nucleolus, anisokaryosis, and modest mitotic activity. (c) immunostaining with smooth muscle actin (SMA): spindle cells present a cytoplasmic and diffuse positivity with SMA. (d) immunostaining with CD45 (antipanleukocytes) exhibits the significant lymphoplasmacytic population. FISH analysis was performed: no rearrangement for ALK-1 gene was noticed.