A 5 year old male presents with a right sided non-axial proptosis.
Fig 1 shows the MRI scan confirming the presence of an extensive right medial anterior orbital mass.
The patient undergoes an urgent biopsy.
1. Summarise the findings in Figs 2 and 3
2. What is the differential diagnosis of the features seen in Figs 2 and 3?
3. Fig 4 is a desmin stain and Fig 5 is a MyoD1. What is the diagnosis?
4. Which cytogenetic changes are found in this lesion?
1. Figs 2 and 3 show a small round blue cell tumour with an alveolar architcture.
2. The differential diagnosis at this location includes: alveolar rhabdomyosarcoma, embryonal rhabdomyosarcoma, lymphoma/leukaemia, Ewings Sarcoma/PNET, desmoplastic small round cell tumour, neuroblastoma, small cell/neuroendocrine carcinoma, olfactory neuroblastoma, extrarenal rhabdoid tumour.
3. Alveolar rhabdomyosarcoma.
4. t(2;13) (q35;q14)-60 % of cases and t(1;13) (p36; q14)-10/15% of cases, leads to fusion of FOXO1 with PAX3 or PAX7, leading to chimeric proteins that act as transcription factors.