INI 1 Retained Sinonasal Undifferentiated Carcinoma Masquering as Alveolar Rhabdomyosarcoma -A Rare Case Series
DOI:
https://doi.org/10.52783/jns.v14.2963Keywords:
Alveolar rhabdomyosarcoma, Sinonasal, CarcinomaAbstract
Background: Sinonasal Undifferentiated carcinoma (SNUC) is a rare, aggressive malignancy of the sinonasal tract. Its clinical and histopathological presentation can often mimic other malignant tumors, including alveolar rhabdomyosarcoma (ARMS), which is characterized by small round cells and rhabdoid morphology. Distinguishing between these entities is crucial for appropriate treatment and prognosis. This case series highlights instances where SNUC was initially misdiagnosed as alveolar rhabdomyosarcoma due to overlapping morphological features but was ultimately identified through immunohistochemical (IHC) analysis, particularly with the retention of INI1 expression.
Case Presentation: We present a series of three cases with sinonasal tumors initially presented with symptoms such as epistaxis, nasal obstruction, and facial pain. Imaging studies revealed masses involving the maxillary sinuses and nasal cavities, suggestive of aggressive sinonasal tumors. Initial biopsies showed small round cells arranged in sheets and nests, with some cells exhibiting rhabdoid morphology, leading to a preliminary diagnosis of high-grade undifferentiated tumors, including alveolar rhabdomyosarcoma. However, further immunohistochemical analysis, including markers such as EMA, pancytokeratin (AE1/AE3), and INI1, revealed retained INI1 expression, which is characteristic of sinonasal undifferentiated carcinoma. The diagnosis of SNUC was confirmed, and treatment plans were adjusted accordingly.
Results: All three cases demonstrated INI1 retention, which helped distinguish SNUC from other differential diagnoses, such as alveolar rhabdomyosarcoma and sinonasal undifferentiated tumors. Immunohistochemistry proved essential in guiding accurate diagnosis, particularly in differentiating SNUC from mimicking malignancies. The Ki-67 index was notably high in all cases, reflecting the aggressive nature of the tumors.
Conclusion: This rare case series underscores the importance of a comprehensive diagnostic approach, including immunohistochemistry, in differentiating sinonasal undifferentiated carcinoma from other malignancies like alveolar rhabdomyosarcoma. Retention of INI1 expression is a key marker for diagnosing SNUC, even when it presents with histological features that overlap with more common sinonasal malignancies. Timely and accurate diagnosis is critical for appropriate management and prognosis.
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