Purpose: To describe the sequential imaging findings and diagnostic utility of ultrasound and contrast-enhanced magnetic resonance imaging in a rare pediatric case of superinfected macrocystic lymphatic malformation of the gluteal region following minor trauma. Materials and methods: A 2-year-old girl with a pre-existing diagnosis of macrocystic lymphatic malformation in the gluteal region presented with acute onset of severe localized pain, fever, and erythema after sustaining blunt trauma. Laboratory tests demonstrated leukocytosis and elevated C-reactive protein, supporting the clinical suspicion of secondary infection. Initial ultrasound evaluation revealed multiple cystic lesions without internal vascularity, accompanied by surrounding soft-tissue edema. Given the concern for secondary infection, a follow-up ultrasound was performed 72 hours later, demonstrating increased vascularity of the cyst walls and internal echogenic debris consistent with superinfection. Subsequently, contrast-enhanced magnetic resonance imaging confirmed abscess formation, characterized by peripheral contrast enhancement, restricted diffusion, and extensive inflammatory changes in the surrounding soft tissues. Results: Integration of sequential imaging findings enabled early and accurate diagnosis of abscess formation within the macrocystic lymphatic malformation. This facilitated prompt initiation of targeted conservative treatment, including intravenous antibiotics and image-guided percutaneous drainage, effectively avoiding emergency surgical intervention and its potential complications. Conclusion: In pediatric patients with macrocystic lymphatic malformations, minor trauma may precipitate secondary infection and abscess development. A stepwise imaging strategy, beginning with ultrasound and supplemented by contrast-enhanced magnetic resonance imaging, is critical for early detection, precise lesion characterization, and guidance of appropriate management to minimize morbidity and improve clinical outcomes.