Bleomycin has nowadays been more and more widely used in the sclerotherapy of LMs, which has been proven to be primarily dose dependent. The investigators aim to compare the efficacy and safety of different concentrations of Bleomycin in the sclerotherapy of LMs for pediatric patients.

Lymphatic malformations (LMs) are vascular anomalies that arise from abnormal embryonic development of the lymphatic system and might present as dilated lymphatic channels or cysts lined by lymphatic endothelial cells. With an estimated incidence of approximately 1/4000-1/2000, LMs can occur at any site in the lymphatic system, in which head, neck and axilla were mostly detected and have been reported to account for over 75%. Based on the location and size of the lesion and the extent of involvement, LMs may be asymptomatic with incidental detection, or chronic abdominal pain and distension due to their compression of surrounding structures, or critical and even fatal secondary to their volvulus, hemorrhage, infection and rupture. Surgical excision is a definitive treatment for LMs, while it may be difficult at times because of the infiltrative nature of the lesions, leading to a high incidence of complications like vital organ injuries, nerve injuries, bleeding, infection scar formation, and recurrences. Sclerotherapy is a simpler alternative to tedious surgical excision treatment for LMs and avoids the complications related to surgery. As an anticancer drug extracted from Streptomyces verticillus, Bleomycin has been more and more widely used in the sclerotherapy of LMs for pediatric patients, which has been proven to be primarily dose dependent. However, the optimum concentration of Bleomycin in the sclerotherapy of LMs for pediatric patients has not been strictly validated, due to the lack of high-quality RCT studies. The investigators aim to compare the efficacy and safety of different concentrations of Bleomycin in the sclerotherapy of LMs for pediatric patients.

Inclusion Criteria:

• Male or female participants less than 14 years of age at the time of informed consent/assent form was signed.
• Participants whose parents have voluntarily given written consent and participants who provided assent (if applicable) after the study has been explained to them.
• Participants with LMs of all sites measured and confirmed via imaging at screening, with rapid progression, resluting in obvious symptoms or dysfunction, which could not be radically resected and could be treated by sclerotherapy.

Exclusion Criteria:

• Penicillin allergy.
• Vascular tumors or combined vascular malformations.
• Participants who may have had surgical or sclerotherapy treatment by other hardeners.
• LMs growing slowly, without obvious symptoms or dysfunction, which does not need to be treated prematurely.