Peripheral Primitive Neuroectodermal Tumor
Definition
- Small cell neoplasm with a spectrum of appearance from undifferentiated to forming rosettes. CD99 positive and contains characteristic translocations involving 22q12.
Alternate/Historical Names
- PNET
- Primitive neuroectodermal tumor
- Peripheral neuroectodermal tumor
- Ewing sarcoma
- Askin tumor
- Peripheral neuroepithelioma
- Ectomesenchymoma (variant of PPNET)
- Biphenotypic sarcoma (variant of PPNET)
Diagnostic Criteria
- CD99 positive in >90% of cases
- Glycogen present in 90% of cases
- Mitotic figures frequent (5-50/10 HPF)
- Undifferentiated appearance
- Small cells
- Round to oval nuclei
- Smooth nuclear membrane
- Fine chromatin
- Small nucleoli
- Small amount of clear to amphophilic cytoplasm
- Cell borders may be distinct
- Differentiated appearance
- Medium sized cells
- Moderate sized nuclei with moderate atypia
- Irregular nuclei
- Small to medium sized nucleoli
- Moderately abundant eosinophilic or amphophilic cytoplasm
- Homer-Wright rosettes
- Radiating fibrillar material surrounded by a ring of nuclei
- Pseudorosettes
- As for Homer-Wright rosettes but with a central blood vessel
- Other patterns
- May form alveolar or angiomatoid patterns
- Metaplastic cartilage or bone may infrequently be seen
- Skeletal muscle differentiation may be seen in the ectomesenchymoma variant
Richard L Kempson MD
Robert V Rouse MD
Department of Pathology
Stanford University School of Medicine
Stanford CA 94305-5342
Original posting:: February 2, 2007
