Abstract
<title>Abstract</title> <p>Background Factor XIII (FXIII) deficiency is a rare but life-threatening bleeding disorder that often poses a significant diagnostic challenge in clinical practice. Because FXIII acts at the final stage of the coagulation cascade to stabilize fibrin, its deficiency typically results in normal routine screening tests (PT, aPTT, INR, and fibrinogen). This creates a dangerous "diagnostic blind spot," particularly in pediatric trauma cases where persistent, unexplained hemorrhage may be the only clinical clue. Case Presentation: We report the case of an 8-year-old girl who developed a massive, progressively enlarging right gluteal and thigh hematoma (7.6 × 11.7 × 11.4 cm) following a minor sports injury. Despite initial surgical evacuation and selective arterial embolization at two referring hospitals, bleeding remained refractory. Upon transfer to our center, thromboelastography (TEG) revealed a progressive decline in maximum amplitude (MA nadir: 25.9 mm) and a severely reduced coagulation index (CI: −12.4), indicating critically impaired clot formation and strength. A comprehensive coagulation workup confirmed a markedly reduced FXIII antigen level of 20.3%, establishing the diagnosis of acquired FXIII deficiency. A multimodal management strategy was subsequently implemented: super-selective arterial embolization was performed followed by open hematoma evacuation and drainage, during which the evacuated blood exhibited a non-coagulating, "egg-drop-soup"-like appearance, further corroborating the underlying fibrin cross-linking defect. Concurrently, targeted hemostatic replacement therapy was administered using cryoprecipitate, fresh frozen plasma, and recombinant activated factor VIIa (rFVIIa). Hemostasis was ultimately achieved, and the patient regained full mobility at two-month follow-up. Conclusions This case underscores the "diagnostic odyssey" associated with FXIII deficiency and emphasizes that it must be considered in unexplained, refractory post-traumatic hemorrhage. A pragmatic, multidisciplinary approach combining interventional embolization, surgical evacuation, and targeted hemostatic support offers a critical life-saving paradigm for managing this rare coagulopathy.</p>