Diagnostic confirmation of adult sinonasal rhabdomyosarcoma through comprehensive immunohistochemical profiling: a case report.

BACKGROUND

Adult sinonasal rhabdomyosarcoma (RMS) is an exceptionally rare and aggressive malignancy originating from mesenchymal cells. It poses a significant diagnostic challenge due to its morphological and immunohistochemical overlap with other small round blue cell tumors, such as neuroendocrine carcinoma and olfactory neuroblastoma. Accurate diagnosis requires a high index of suspicion, advanced imaging, and comprehensive histopathology aided with immunohistochemistry (IHC) for specific myogenic markers like Myogenin and MyoD1.

CASE PRESENTATION: A 27-year-old male presented with recurrent epistaxis and headache. MRI revealed an enhancing ethmoidal mass with intracranial extension. Following endoscopic surgery, initial pathology suggested neuroendocrine carcinoma. However, a detailed IHC panel showed strong nuclear positivity for MyoD1 and myogenin, confirming RMS. The tumor had a high Ki-67 index (~ 70%). FISH testing was negative for FOXO1 rearrangement, favoring embryonal subtype. Postoperative imaging confirmed complete resection. The patient received adjuvant chemotherapy and radiotherapy.

CONCLUSION

This case underscores the diagnostic difficulty of sinonasal RMS. A definitive diagnosis is contingent upon integrating imaging findings with histopathology and an extensive IHC panel to identify myogenic differentiation. Once confirmed, prompt, multimodal therapy administered through a specialized multidisciplinary center is critical for managing this aggressive neoplasm and optimizing patient outcome.