Rhabdomyosarcoma



Rhabdomyosarcoma











Alveolar rhabdomyosarcoma of the anterior mediastinum shows sheets of primitive small round blue cells with prominent retraction artifact resulting in an “alveolar” appearance.






High magnification of alveolar rhabdomyosarcoma of the mediastinum shows a large multinucleated cell in the center displaying hyperchromatic nuclei and abundant pink cytoplasm.


TERMINOLOGY


Abbreviations



  • Rhabdomyosarcoma (RMS)


Definitions



  • Primary malignant neoplasm of mediastinum showing features of striated muscle differentiation


ETIOLOGY/PATHOGENESIS


Pathogenesis



  • Pure cases may arise from totipotential stem cells within mediastinal soft tissue


  • Cases associated with teratomatous elements may arise from somatic transformation of germ cells


  • Cases associated with thymic carcinosarcomatous elements may arise from native thymic myoid cells


CLINICAL ISSUES


Site



  • Anterior mediastinum


Presentation



  • Cough


  • Chest pain


  • Dyspnea


  • Pleural effusion


  • Mostly affects young adults (mean: 23 years)


Treatment



  • Surgical excision


  • Adjuvant chemotherapy and radiation therapy


Prognosis



  • Highly aggressive tumors with short survival time


  • Rapid recurrence and metastases generally within 1st 6 months after diagnosis


  • Metastases most often involve lymph nodes but may also involve lung, pleura, bone, and abdominal viscera


IMAGE FINDINGS


General Features



  • Solid, unencapsulated expansile lesion with poorly defined, infiltrative borders


  • CT scans show large homogeneous mass displacing midline structures with pleural effusion


MACROSCOPIC FEATURES


General Features



  • Firm, poorly circumscribed, and infiltrative mass


  • Homogeneous, tan-gray cut surface


  • Areas of hemorrhage and necrosis


Size



  • 4-12 cm


MICROSCOPIC PATHOLOGY


Histologic Features



  • Tumors may appear de novo in pure form, or may be associated with germ cell, teratomatous, or carcinomatous elements


  • Pure, de novo tumors may show varied histology


  • Embryonal rhabdomyosarcoma



    • Sheets of “small round blue cells” with hyperchromatic nuclei and scant eosinophilic cytoplasm


    • Scattered immature rhabdomyoblasts characterized by comma-shaped cells with small, dark nuclei and bright pink rim of cytoplasm


    • Spindle cell variant of embryonal rhabdomyosarcoma is composed of atypical spindle cells set against myxoid stroma



  • Alveolar rhabdomyosarcoma



    • Solid sheets of “small round blue cells” supported by delicate fibrovascular stroma


    • Artifactual clefting of nests of small blue cells from periphery results in striking “alveolar” pattern


    • Scattered multinucleated tumor cells with large hyperchromatic nuclei are seen admixed with small blue tumor cells


  • Pleomorphic rhabdomyosarcoma



    • Bizarre atypical cells with large, pleomorphic, and irregular nuclei surrounded by abundant eosinophilic cytoplasm


    • Cells may show slender, tapering cytoplasmic processes resembling racquet cells


    • Only rarely will cells display cytoplasmic cross-striations


Cytologic Features

Jul 9, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Rhabdomyosarcoma

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