Background: Rhabdomyomas are rare benign tumors of striated muscle and include cardiac and extracardiac types. Extracardiac rhabdomyomas are divided in three subtypes (adult, fetal, genital). The adult type is usually found in the head and neck regions of elderly persons. Misinterpretations in initial diagnosis of adult rhabdomyomas on fine needle aspiration have been reported.
Case: A 64-year-old man presented with gurgling and difficulty swallowing for approximately 3 months. Computed tomography and magnetic resonance imaging showed a 5.8-cm solid mass located in the right parapharyngeal space. Fine needle aspiration smears were cellular, showing cohesive clusters of cells with scattered individual cells. Cells had abundant eosinophilic glassy cytoplasm, peripherally placed round nuclei, and prominent nucleoli. Many traversing vessels were noted, but cross-striations were not seen. The cell block demonstrated clusters of cells with abundant eosinophilic granular cytoplasm, some with clear and/or vacuolated cytoplasm, and possible cross-striations. Tumor cells were positive for desmin. The lesion closely resembled normal muscle tissue. Electron microscopy showed many cells containing actin and myosin filaments with Z-band material.
Conclusion: Correct diagnosis can be achieved with a combination of awareness of the lesion, familiarity with the characteristic cytologic features, and application of appropriate immunohistochemistry markers. Classic electron microscopic findings can support the diagnosis.