38 yo male complaining of an upper lumbar mass for 2 months, inflammatory type, painful, irradiating to the left knee. MRI discloses a paravertebral left mass with extension to medullary canal.

Male de 38 ans, se plaignant depuis 2 mois d'une masse douloureuse lombaire haute, avec irradiation de la douleur au genou gauche. L'IRM rvle une masse paravertbrale gauche de D12 L1 avec expansion intracanalaire.

A surgical biopsy is performed.

Une biopsie chirurgicale est ralise.

Imprints for the material submitted (Hematoxylin-Phloxin)

Empreintes du materiel biopsique (Hematoxyline-Phloxine)

Diff-Quick.

HE

PAS- Diastase

CD 99

Diagnosis: Primitive Neuro-Ectodermal Tumor

Facts about PNET (Extraskeletal Ewing's sarcoma )

• PNET are morphologically indistinguishable from Ewing's sarcoma of the skeletal system. Most of the patients are adolescents or young adults, and the usual sites of involvement are the soft tissues of the lower extremity and paravertebral region. The course is aggressive and distant metastases are common, particularly to lung and skeleton.
• the presence of a consistent chromosomal translocation (11;22), present in about 90% of the cases, which leads to the production of a chimeric transcript that recognizes a cell membrane protein of yet unknown function (p30/32 MIC 2; CD99),
• tumors located in bone are more likely to exhibit a more undifferentiated phenotype, whereas those located in soft tissues( Neuroepithelioma) including most thoracopulmonary examples (Askin), tend to display various degrees of neuroepithelial differentiation. The prognosis seems to be the same.
• The differential diagnosis of Ewing's sarcoma/PNET of soft tissues includes embryonal and alveolar rhabdomyosarcoma (especially the solid variant of the latter), malignant lymphoma, and the rhabdoid tumor.

(Ackermann's Surgical Pathology, 8th Ed.)