PMC3804802_01
T1-weighted magnetic resonance imaging of the right knee after administration of gadolinium.
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fig001
Magnetic resonance imaging (MRI) of the knee showed a solid mass of 1.2x2.4x2.1 cm extent adjacent to the dorsal joint capsule and the posterior cruciate ligament (PCL) (Figure 1, T1-weighted image after administration of gadolinium).
A) Small and middle sized arteries (arrow) with concentric proliferation of SMA positive spindle cells (inset; original magnification 200x) in the outer layers are seen accompanied by myxoid and collagenous connective tissue in the background (hematoxilin and eosin staining; original magnification 50x). B) Several small, whorly nodules (asterisks) consiting of histiocytoid bland cells and containing (arrow) some multinucleated giant cells of osteoclastic type (CD68 positive as seen in the upper inset; original magnification 200x) are seen in the center of the lesion (hematoxilin and eosin staining; original magnification 100x). These cells show partial nuclear expression of MITF (lower inset; original magnification 200x)
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fig002
The first and most striking feature was the presence of numerous thick-walled blood vessels (Figures 2A and 3A) with marked concentric proliferation of bland spindle cells with smooth muscle actin (SMA) (1A4 clone, Sigma; 1:20 000) (Inset Figure 2A) and desmin (not shown) expression. Figure 2B; clone PG-M1, DAKO; 1:50). Furthermore there were similar smaller nodules of cells, some of which appeared to be centered around a vascular lumen, almost giving the impression that these aggregates are vasculocentric. Interestingly, the histiocytoid cells expressed partially microphtalmia-associated transcription factor (MITF) (inset Figure 2B; clone C5+D5; Abcam Limited; 1:50), were weakly positive for S100 and negative for CD68, CD34, SMA, desmin. However, the typical angiomatous character of the lesion (as shown in Figure 2A and Figure 3A, respectively) didn't fit to a plexiform fibrohistiocytic tumor, and there was not seen the more orderly fascicular spindle cell component of the plexiform fibrohistiocytic tumor.
A) There are numerous thick-walled blood vessels (asterisks) with an outer concentric proliferation of bland spindle cells. Between these vessels, there is a diffuse spindle cell proliferation with a loosely myxoid or collagenous matrix (hematoxilin and eosin staining; original magnification 25x). B) Focally there are striking nodular aggregates (asterisks) of palely eosinophlic histiocytoid cells admixed with occasional osteoclastic giant cells (arrow) (hematoxilin and eosin staining; original magnification 100x).
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fig003
The first and most striking feature was the presence of numerous thick-walled blood vessels (Figures 2A and 3A) with marked concentric proliferation of bland spindle cells with smooth muscle actin (SMA) (1A4 clone, Sigma; 1:20 000) (Inset Figure 2A) and desmin (not shown) expression. However, the typical angiomatous character of the lesion (as shown in Figure 2A and Figure 3A, respectively) didn't fit to a plexiform fibrohistiocytic tumor, and there was not seen the more orderly fascicular spindle cell component of the plexiform fibrohistiocytic tumor.