Cytologic diagnosis of rhabdomyosarcoma in a child with a pleural effusion - A case report

BACKGROUND: A pleural effusion in children is usually caused by infectious diseases; malignant effusion is very uncommon. In a case of a malignant effusion in a child, a pleura-based metastasis of a neoplasm with a typically high prevalence in childhood has to be considered. Examples are neuroblastoma, nephroblastoma, Wilms' tumor, hepatoblastoma, malignant germ cell tumor and rhabdomyosarcoma. CASE: A 4-year old boy presented with a unilateral pleural effusion. Cytologic examination of the effusion revealed malignant small round cells admixed with very large cells with atypical nuclei. In formalin-fixed cell blocks prepared for immunocytochemistry the cells expressed desmin and myf-4. The cytologic diagnosis was consistent with metastatic rhabdomyosarcoma. Subsequent computed tomography revealed a mass above the diaphragm, which was biopsied. Histologic examination of a needle biopsy specimen confirmed the diagnosis of rhabdomyosarcoma. Molecular examination revealed a PAX3-FKHR fusion transcript specific to the alveolar type of rhabdomyosarcoma. CONCLUSION: This case illustrates the usefulness of immunocytochemistry on cell block preparations in diagnosing difficult cases of effusion cytology.