Clinical features
- Usually presents before the age of 2
- 50% congenital
- Axial regions and extremities
- Male predominance
- Rapid growth
- Extensive local invasion
Cytopathology
- Cellularity and degree of pleomorphism depends on the histological grade
- Cells with ovoid to elongated nucleus
- Fine granular chromatin
- Small nucleoli
- Scant to moderate uni or bipolar cytoplasm
- Nuclear atypia
- Necrosis
- Mitosis are frequent , although not important to prognosis
- Immunocytochemistry
- Vimentin: Positive
- Smooth muscle actin: Positive( focal)
- Desmin: Positive ( focal)
- S100 Protein: Positive( focal)
- CD34: Positive( focal)
- Factor XIIIa: Positive
Genetic studies
- t(12;15)(p13;q25)- ETV6-NTRK3 gene fusion (in 70%)
- Trisomy of chromosome 11
- Variable trisomy’s of chromosomes 17 and 20 or 8 and 10
Differential Diagnosis
- Nodular fasciitis
- Typical clinical presentation
- Highly characteristic metachromatic myxoid stroma
- Cells loosely and haphazardly arranged in fragments
- Fibromatosis
- Less cellularity than fibrosarcoma
- Bland spindle nuclei
- Inconspicuous nucleoli
- Absence of mitosis
- Embryonal Rhabdomyosarcoma
- Myxoid stroma
- Desmin: Positive
- Myo-D1: Positive
- Synovial Sarcoma
- Cytokeratins: Positive
- t(X; 18) (p11.2; q11)
Main points
- Identical to congenital mesoblastic nephroma
- 90% survival
- 40-50% recur
- 10% metastasize (typically to the lung)
Treatment: complete excision