Rhabdomyosarcoma. Cytomorphology, subtyping and differential diagnostic dilemmas

To identify morphologic characteristics and architectural patterns of rhabdomyosarcoma (RMS), to attempt a subclassification from fine needle aspiration biopsy (FNAB) smears and to point out some differential diagnostic problems.

We reviewed all positive cytologic material from 53 patients with RMS whose diagnoses were histologically and/or immunocytochemically confirmed. We analyzed several morphologic features and identified architectural patterns of smears.

Among alveolar RMS, we identified two major architectural patterns: one containing completely dissociated cells and one containing many chance formations. Among the embryonal type, the predominant architectural pattern contained large tissue fragments with abundant eosinophilic material and various numbers of dissociated cells. The pattern of only dissociated cells was similar to the one seen in the alveolar type. The relative proportion of poorly to better and well-differentiated rhabdomyoblasts varied in both types and in all patterns.

RMS exhibits a variety of morphologic pictures regarding cellular morphology and architectural patterns, even within the same histologic subtype. Therefore, a reliable subclassification into alveolar and embryonal RMS cannot be made from FNAB smears. The embryonal type can be suggested in cases containing large tissue fragments with abundant eosinophilic material and small, tightly packed cells with oval nuclei. However, all cases suspected to be RMS must always be confirmed immunocytochemically since they could be confused with some benign and malignant tumors with similar morphology.