Giant mixed vascular lymphatic malformation in a pediatric patient: a case report.

Background: Giant Mixed vascular lymphatic malformation-is a relatively rare congenital anomaly, particularly in pediatric populations. Mediastinal vascular malformations are uncommon in children, and their exact incidence remains poorly defined in the literature. It is not a true neoplasm but rather a low-flow vascular malformation arising from aberrant development of the vascular system during embryogenesis. Due to nonspecific clinical manifestations (e.g., cough, dyspnea) and the deep location of the mediastinum-adjacent to the heart, great vessels, and airways-diagnosis and management pose considerable challenges. Misdiagnosis is common, potentially leading to inappropriate treatment and life-threatening complications. Thus, accurate preoperative imaging is essential for developing safe and effective treatment strategies. Case Description: We report the case of a 3-year-old girl who presented with a persistent cough lasting more than 20 days. Imaging revealed a cystic-solid mass measuring approximately 53 mm × 37 mm × 67 mm in the left middle-upper mediastinum. Contrast-enhanced computed tomography (CT) showed mild progressive enhancement of the lesion, with distinct "branch-like" vascular structures communicating with the left brachiocephalic vein, consistent with a low-flow vascular malformation. No definite arterial feeding vessel was identified. The mass was well-demarcated from the aorta and heart but caused localized compression and narrowing of the left main bronchus. These imaging findings were consistent with a low-flow vascular malformation. A biopsy obtained via video-assisted thoracoscopic surgery (VATS) confirmed the diagnosis of mixed vascular malformation. Given the high-risk location adjacent to vital mediastinal structures, complete surgical resection was considered extremely hazardous. The multidisciplinary team therefore adopted a non-surgical approach consisting of oral sirolimus as targeted therapy. Following treatment, the child's cough improved significantly. Conclusions: This case illustrates that in children with cystic-solid mediastinal masses, the presence of "progressive enhancement" and "clearly enhanced vascular channels" on contrast-enhanced CT or magnetic resonance imaging (MRI) should raise suspicion for vascular malformations. Comprehensive imaging assessment is fundamental for accurate diagnosis and formulation of individualized management. For complex mediastinal vascular malformations with high surgical risk, oral sirolimus represents a safe and effective targeted therapeutic alternative, capable of alleviating symptoms and controlling disease progression.