An ultra-late maxillofacial cavity following multimodal treatment for adult head and neck rhabdomyosarcoma: a case report with a 16-year follow-up.

Objective: To report a rare case of a patient with adult rhabdomyosarcoma (RMS) in the craniofacial region who developed a very late-stage left maxillofacial cavity after 16 years of multimodal treatment, and to systematically investigate the potential causal relationship between this complication and previous radiotherapy. Methods: A detailed report is presented on the diagnosis and treatment process of a 46-year-old female patient. A comprehensive evaluation framework was employed to analyze causality, encompassing temporal correlation, spatial alignment with the original radiation field, exclusion of alternative etiologies, and biological plausibility. Results: Approximately 16 years after the initial radiotherapy, the patient developed soft tissue defects and cavity formation in the core area of the original high-dose irradiation field. Although tissue biopsy was not performed due to post-radiotherapy site bleeding and patient constitution risks, imaging studies showed a high degree of consistency between the lesion and the previous radiotherapy area, with no evident evidence of tumor recurrence or primary infection, consistent with the pathophysiological process of radiation-induced tissue necrosis. Conclusion: Despite the exceedingly long latency period, based on the conclusive spatial correlation, reasonable exclusion of other etiologies, and well-established radiobiological mechanisms, there is a "highly probable" causal relationship between the maxillofacial cavity and previous radiotherapy. This case serves as a warning that for long-term surviving RMS patients, extremely late radiation injury represents a serious complication risk that cannot be ignored.