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AJNR Awards, New Junior Editors, and more. Read the latest AJNR updates

Case of the Week

Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada

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November 28, 2019
  • Description
  • Legends
  • Diagnosis
  • Brain Teaser
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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.

Suggested Reading

  1. Saeedinia S, Nouri M, Alimohammadi M, et al. Primary spinal extradural Ewing's sarcoma (primitive neuroectodermal tumor): report of a case and meta-analysis of the reported cases in the literature. Surg Neurol Int 2012;3:55, 10.4103/2152-7806.96154
  2. Treglia G, Salsano M, Stefanelli A, et al. Diagnostic accuracy of 18F-FDG-PET and PET/CT in patients with Ewing sarcoma family tumours: a systematic review and a meta-analysis. Skeletal Radiol 2012;41:249–56, 10.1007/s00256-011-1298-9
  3. Kühne T. Ewing sarcoma family of tumors. In: Imbach P, Kühne T, Arceci RJ, eds. Pediatric Oncology. Springer, Berlin, Heidelberg; 2006:165–70
  4. Wu JS, Hochman MG. Soft-tissue tumors and tumorlike lesions: a systematic imaging approach. Radiology 2009;253:297–316, 10.1148/radiol.2532081199
  5. Chan WP. Magnetic resonance imaging of soft-tissue tumors of the extremities: a practical approach. World J Radiol 2013;5:455–59, 10.4329/wjr.v5.i12.455.

Current Issue

American Journal of Neuroradiology: 46 (6)
American Journal of Neuroradiology
Vol. 46, Issue 6
1 Jun 2025
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