We present a congenital plexiform cellular tumor with high mitotic activities arising in
the right thigh of a 3-days-old infant. This subcutaneous tumor measured 6.5 x 4.5 cm in
diameter with multinodular, whitish, elastic cut surface. Microscopically, the tumor was
composed of fascicles of closely packed uniform spindle cells with frequent nuclear palisadings.
The most remarkable finding was frequent mitoses(4-5/10 HPF). The tumor cells were strongly
positive for S-100 protein, myelin basic protein and vimentin, and weakly positive for Leu 7.
On electron microscopic examination, the spindle cells were found to be surrounded by continuous
basal lamina and had interlocking long cytoplasmic processes. Although the prognosis of this
tumor is difficult to predict, aggressive behavior such as recurrences may be suggested, but
it is less likely to be metastatic. Further accumulation of similar unusual cases may be helpful
in evaluation of its biologic behavior.
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