Extracranial complications is a classification of adverse medical conditions or pathological sequelae that manifest anatomically outside the cranial vault. As a research concept, it delineates a distinct domain of study focused on the etiology, pathophysiology, clinical presentation, diagnosis, management, and prognosis of these complications, which can arise from a variety of primary diseases or conditions and affect diverse extracranial structures. This concept is significant for understanding the systemic impact of diseases, guiding clinical interventions, and improving patient outcomes by distinguishing these peripheral manifestations from those occurring within the cranium.