Rhabdomyosarcoma

• Most common primary orbital malignancy in childhood

  • Third most common solid extracranial tumour of childhood (after Wilm’s tumour and neuroblastoma)

• Relatively good prognosis

• M>F

• Can affect the orbit, eyelids, conjunctiva and rarely the uveal tract

• Originates from primitive pluripotent mesenchymal cells

• Generally well circumscribed with occasional areas of haemorrhage

• Usually intraconal or within superior orbit

Histological types

• Embryonal (84%): good prognosis

  • Cellular and myxoid areas, central nucleus and highly eosinophilic cytoplasm

• Alveolar (9%): worst prognosis

  • Loosely adherent eosinophilic rhabdomyoblasts

• Pleomorphic (very rare, typically occurs in adults)

  • Best prognosis

• Botyroid (4%)

Immunohistochemical stains

• Desmin
• Muscle-specific actin
• Myoglobin

Clinical features

• Presents as non-axial proptosis which can be rapid onset, chemosis, eyelid discolouration, ophthalmoplegia. Only 10% experience pain

Imaging

• CT/MRI: well-defined mass with bony destruction

Management:

• Biopsy
• Systemic workup
• Surgical excision: only if small and encapsulated lesion
• Combined radio/chemotherapy: mainstay