Course Map: Soft Tissue Tumors: Rhabdomyosarcoma

Rhabdomyosarcoma
This is the common sarcoma of childhood; it usually presents as polypoid masses in the trigone-bladder neck area (sarcoma botryoides) and is typically of the embryonal type. There is an invasive proliferation of undifferentiated cells in a myxoid stroma with a subepithelial zone of concentrated tumor cells (the cambium layer). Diagnostic strap cells with cross striations may not be found, particularly in biopsies, but a diagnosis can generally be established by immunohistochemsitry (desmin, MyoD1, and myoglobin are most commonly used).
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	Figure 1: The polypoid gross appearance is typical of sarcoma botryoides.
	Figure 2: Rhabdomyosarcoma, bladder neck.
	Figure 3: The polyps illustrated in Figures 1 and 2 will usually show a concentration of small, dark - staining, undifferentiated cells forming a band immediately beneath the surface urothelium (the cambium layer). The deeper tissue is edematous, with widely scattered tumor cells.
	Figure 4: A fascicle of the muscularis propria is seen in the center of the field. It is invaded by small dark tumor cells. In a pediatric patient or young adult with a bladder neck tumor, rhabdomyosarcoma would be suspected. On the far left, a cell has a wisp of pink cytoplasm (rhabdomyoblast--arrow). The diagnosis is rhabdomyosarcoma.
	Figure 5: This shows a strap cell near the center of the field. It shows cross striations (arrow). In most cases, these are not seen, especially in biopsies, and the diagnosis will require immunohistiochemistry.