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Rhabdomyosarcoma (RMS) is an aggressive tumor that develops from mesenchymal cells of uncertain origin and can occur in any anatomic location of the body where there is skeletal muscle. It is the most common soft-tissue mesenchymal malignant tumor involving the orbit in children. The most common subtype is embryonal, which accounts for about 60% to 70% of cases. It is believed that this subtype arises from undifferentiated mesenchymal progenitor cells that have the capacity to differentiate into striated muscle. For ophthalmic RMS most cases arise in the orbit with only 3% occurring in the eyelids, mostly as extensions from anterior orbital tumors. Clinically, orbital RMS presents as acute to subacute progressive proptosis over days to weeks, often with ptosis, eyelid edema, and ophthalmoplegia. Eyelid RMS presents as a firm, immobile, non-tender mass with eyelid swelling and occasional ulceration, chemosis, superficial bleeding, and ecchymosis. Treatment of orbital lesions is with systemic chemotherapy, combined with radiation therapy in older children. 

Rhabdomyosarcoma of the left orbit and eyelid
Rhabdomyosarcoma of the right orbit with eyelid ptosis and hypoglobus
CT showing sn intraconal rhabdomyosarcoma
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