PMC7607928_01
On coronal section of T2-weighted magnetic resonance imaging of arm, intermediate-to-high signal intensity observed in well- marginated mass of ulnar nerve region of triceps brachii, measuring 2.9x2.5 cm, was observed.
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F1
On T2-weighted imaging, intermediate-to-high signal intensity was observed (Figure 1).
On T1-weighted imaging, low-to-intermediate signal intensity with a signal somewhat higher than that of muscle was detected.
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F2
On T1-weighted imaging, low-to-intermediate signal intensity with a signal somewhat higher than that of the muscle was detected (Figure 2).
A mass in triceps muscle parenchyma, clearly isolated from surrounding muscle parenchyma, was found on operation field.
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F3
No infiltration into the parenchyma of the muscle was observed (Figure 3).
(a) Under light microscopy, myofibroblastic spindle cells, myofibroblasts, collagen, various plasma cells, lymphocytes, and histocytes were observed (H-E x40). (b) Spindle cells had an abundant cytoplasm and formed loose bundles of fibers in different directions. Small amounts of collagen were deposited in between, and owing to frequent infiltrations, density of cells was not particularly high, and no dysplasia of spindle cells was detected (H-E x400).
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F4
Under light microscopy, myofibroblastic spindle cells, myofibroblasts, collagen, various plasma cells, lymphocytes, and histocytes were observed (Figure 4a). Small amounts of collagen were deposited in between, and owing to frequent infiltrations, the density of the cells was not particularly high, and no dysplasia of spindle cells was detected (Figure 4b).
Immunohistochemical staining for differentiation showed spindle cells reacting negatively to VENTANA anaplastic lymphoma kinase immunohistochemistry (D5F3) (a) and positively to smooth muscle actin (b), S-100 protein (c), and cluster of differentiation 34 (d).
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F5
Hoffmann-La Roche, Basel, Switzerland) (Figure 5a) and positively to smooth muscle actin (SMA) (Figure 5b), S-100 protein (Figure 5c), and cluster of differentiation 34 (Figure 5d).