Introduction: Macrocystic lymphatic malformations (LM) are low-flow vascular lesions characterized by disorganized lymphatic tissue and the formation of cystic cavities. Despite being benign, these can cause symptoms or complications, there-fore requiring treatment. The initial management of choice is percutaneous sclerotherapy with ultrasound guidance. There are rare cases in which these lesions occur at the arch of the thoracic duct, presenting as a low cervical cystic mass. Objective: To describe, regarding two cases, the identification and management of LM located at the arch of the thoracic duct. Material and methods: A retrospective non-concurrent cohort analysis was performed, analyzing two cases of patients treated in our center with sclerotherapy with doxycycline and polidocanol for left supraclavicular LM. The diagnosis of these and the technique used in the procedure are described in detail. Results: In both cases, the diagnosis of lymphatic malfor-mation was confirmed, and the procedure was carried out without complications in the short or long term. Both had comple-te remission both clinically and on Doppler ultrasound, with ceasing of their initial symptoms. Conclusions: There is still a lack of knowledge concerning the topic of LM. Diagnosis is clinical-imaging, and LM of the arch of the thoracic duct, usually present themselves as a low cervical mass. These should ideally be studied initially with Doppler ultrasound and then with magnetic resonance imaging. The management of these should be multidisciplinary, using ultrasound-guided sclerothe-rapy as a first step.