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Embryonal Rhabdomyosarcoma : Orbit

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The image shows embryonal rhabdomyosarcoma (RMS) of the orbit.

Introduction & Clinical Features: RMS is the most common orbital malignancy in children. The average age at presentation is 7 years. Orbital RMS often grows rapidly and can present with fulminant proptosis. Due to its rapid growth, it is sometimes mistaken clinically for an inflammatory process.

Locations: Superior orbit is more commonly involved. The tumor frequently erodes through the medial orbital wall. Some cases originate in the paranasal sinuses and involve the orbit secondarily. The tumor is fleshy, yellow or pink-tan and may have areas of hemorrhage or necrosis.

Histologic Types Most orbital RMS are embryonal type and consist of spindle cells arranged haphazardly in loose myxoid stroma as seen here. Cross-striations are seen in less than half of the cases. Rhabdomyoblasts, which appear as globoid cells with deeply eosinophilic cytoplasm, may be present (although they are not seen in this image). Botryoid variant of embryonal RMS is rare in this location and is usually associated with mucus membranes like conjunctiva. Alveolar RMS is also rare and usually involves inferior orbit. Pleomorphic and differentiated RMS (with abundant rhabdomyoblasts) are also uncommon in orbit and usually occur in adults.

Diagnosis & Treatment: The diagnosis of orbital RMS can be confirmed with immunostains (desmin, myogenin, MyoD1) on biopsy material. The management consists of adjuvant radiation and combination chemotherapy. With advances in non-surgical treatment modalities, orbital exenteration becomes necessary only in rare cases. The overall prognosis is good. The 3-yr survival rate is more than 90%.

Reference: Eagle Jr., Ralph C. (2017). Eye Pathology : An Atlas and Text - 3rd Edition; Philadelphia, PA. Wolters Kluwer.

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