PMC3459257_01
CT of the chest revealing a 2.0 x 2.0 cm nodular mass on the right peripheral upper lobe.
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fig1
A chest computed tomography (CT) scan detected a nodular lesion of about 2.0 cm in diameter in the right upper lobe (Figure 1).
(a, b) The excised tumor, measuring 2.0 x 2.0 cm, appeared as a well-circumscribed nodular lesion with a whitish color and focal central hemorrhage. (c, d) Histological findings for the removed tumor revealed uniform small round to oval cells with a centrally located nucleolus, a clear cytoplasm, and clear cell borders. Branching vessels with a hemangiopericytomatous pattern (HPC-pattern) were also evident.
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fig2
The removed tumor was solbid and whitish, measured 2.0 x 2.0 cm, and showed focal hemorrhaging and no necrotic changes (Figures 2(a) and 2(b)). The excised tumor had irregularly branched or dilated vessels that formed the so-called hemangiopericytomatous pattern (Figures 2(c) and 2(d)).
(a-c) Immunostaining revealing that the tumor cells showed a diffuse positive expression of alphaSMA and h-caldesmon at the cell membrane and cytoplasm but were negative for chromogranin A. (d) CD34 was found to be only focally positive in perivascular tumor cells.
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fig3
 By immunostaining, the tumor cells were positive for alpha smooth muscle actin, h-caldesmon, muscle specific actin (HHF-35), laminin, type IV collagen, and vimentin, but negative for cytokeratin (AE1/AE3), epithelial membrane antigen (EMA), TTF-1, surfactant apoprotein A, S-100 protein, synaptophysin, and chromogranin A (Figures 3(a)-3(d)).
Electron microscopy revealed that the tumor cells contained pinocytotic vesicles and a dense patch lining at the basement membrane.
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fig4
By electron microscopy, pinocytotic vesicles and dense patches were revealed along the basement membranes (Figure 4), suggestive of smooth muscle differentiation of the tumor cells. 