November 28, 2019
A 49-year-old patient with new-onset bilateral lower extremity weakness with preserved continence and saddle sensation
Peripheral Primitive Neuroectodermal Tumor
- Background:
- The peripheral primitive neuroectodermal tumor (pPNET) is a member of the Ewing sarcoma family of tumors—a highly aggressive and undifferentiated small blue cell tumor, which can be challenging to identify.
- The nonembryonal extraosseous types of the intradural extramedullary space represent fewer than 50 reported cases.
- Clinical Presentation:
- The most common presentation corresponds with compression of the affected site (in this case, early signs of cauda equina syndrome due to lumbar and conus involvement).
- Tumors can reoccupy the excision site within days to weeks if surgical margins are incomplete.
- Key Diagnostic Features:
- MRI is the best imaging modality for characterization. T1WI demonstrates hypointensity with variable hyperintensity of hemorrhagic components, while T2WI demonstrates hyperintensity of solid components, with heterogeneous postcontrast enhancement.
- Pathologic evaluation will reveal strong neuron-specific enolase and CD99 positivity, and chromogranin A negativity; EWS-FLI fusion protein confirms identity.
- Differential Diagnoses:
- Ependymoma: spinal widening, T1 hypointensity to isointensity, T2 hyperintensity commonly with hemorrhagic cap sign, heterogeneous enhancement
- Meningioma: dural tail sign, T2 hypointensity to isointensity, avid homogeneous enhancement
- Peripheral nerve sheath tumors: split fat sign, possible target sign on cross-section, T2 hyperintensity, solid/heterogeneous enhancement
- Drop and non-CNS metastases: nodularity and postcontrast “sugar coating” appearance along cauda equina nerve roots due to leptomeningeal enhancement
- Treatment:
- Surgical resection followed by chemoradiation (commonly vincristine, doxorubicin, cyclophosphamide, ifosfamide, etoposide)
- FDG-PET/CT shows favorable results in staging pPNETs that can micrometastasize and may otherwise be missed by previous techniques like blind bone marrow aspiration biopsy.
