An 8-year-old boy presents with rapidly progressive unilateral proptosis over three weeks, with eyelid swelling and a firm mass in the superonasal orbit. There is no fever, and the white cell count is normal. Biopsy shows small round blue cells with rhabdomyoblasts. The MOST likely diagnosis is:

• A Embryonal rhabdomyosarcoma ✓
• B Alveolar soft part sarcoma
• C Orbital cellulitis
• D Granulocytic sarcoma (chloroma)

Explanation

Embryonal rhabdomyosarcoma is the most common primary malignant orbital tumour of childhood, presenting as rapidly progressive proptosis over days to weeks, classically superonasal, mimicking inflammation without infective signs. Histology shows small round blue cells with cross-striated rhabdomyoblasts. Granulocytic sarcoma also grows fast in children but signals underlying leukaemia and stains positively for myeloperoxidase, which distinguishes it histologically from rhabdomyosarcoma.

Reference: Kanski's Clinical Ophthalmology, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.