PMC4861865_01
Plain radiographs in frontal (A) and lateral (B) projections show a soft-tissue shadow (upward arrow) in the interosseous space causing scalloping and erosion (right arrow) of the midshaft of the left ulna.
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Plain radiography of the left forearm in frontal and lateral projections (Figs. 1A and B) showed a soft-tissue shadow in the interosseous space causing scalloping and erosions of the midshaft of the ulna.
Nonontrast CT of the left forearm in reformatted coronal (A) and sagittal (B) views shows a well-defined, soft-tissue density (curved arrow) lesion involving the intermusclar compartment and causing scalloping and erosion of the adjacent ulnar cortex (right arrow).
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Noncontrast CT of the left forearm in a reformatted coronal and sagittal view (Figs. 2A and B) demonstrated a relatively well-defined, soft-tissue-density lesion involving the intermuscular compartment of the left forearm in the dorsal aspect of the ulna.
MRI of the left forearm in axial T1W (A), T2W (B), and T1 FAT (C) SAT shows a well-defined intermuscular lesion (arrowhead) involving the dorsal aspect of the ulna. The lesion is hyperintense on T1 and T2 W, and not suppressed on fat-saturated images. The lesion is seen to cause scalloping and cortical irregularity of the ulna with a mild intramedullary extension (arrow).
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T1W fat-suppressed images (Fig. 3B). The lesion was hyperintense to the adjacent muscle on T2-weighted images (Fig. 3C). The lesion was seen to anteriorly displace and impinge on the anterior intraosseous nerve, and posteriorly displace the extensor muscles of the forearm.
MRI of left forearm in coronal (A) and sagittal (B) T2W STIR shows well-defined, hyperintense, intermuscular lesion involving the dorsal aspect of ulna (curved arrow) causing scalloping and cortical irregularity with a mild intramedullary extension (left arrow).
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Intraoperative image shows the soft-tissue tumor (white arrow) resected with the ulnar bone (curved arrow).
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The tumor was excised completely (Fig. 5) and sent for histopathological examination.
Histopathological examination shows a well-circumscribed lesion composed of spindle cells arranged in a whorled pattern. The cells show an elongated nucleus with a moderate amount of eosinophilic cytoplasm (H & E x 200).
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Initial microscopic examination (Fig. 6) revealed a well-circumscribed lesion composed of spindle cells arranged in a whorled pattern.
Immunohistochemical staining shows strong reactivity to smooth muscle actin (H & E x100).
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Further immunohistochemical (IHC) staining showed strong reactivity for vimentin, smooth-muscle actin, and desmin, and a negative reaction against S-100 that favored a diagnosis of leiomyoma (Fig. 7).