Lateral neck masses in children fall into 3 broad categories: congenital, inflammatory, and neoplastic. The differential for a soft, compressible, congenital lateral neck mass includes most commonly, branchial cleft or dermoid cysts, along with ranulas, superior mediastinal cysts, pharyngoceles, laryngoceles, and vascular anomalies including hemangiomas, vascular malformations, or phlebectasias. 1 We present a lateral neck mass that was initially diagnosed as a branchial cleft cyst but was later correctly diagnosed as a lymphatic malformation (LM) and was treated nonsurgically.A 6-year-old female was referred for a right neck mass. She was a full-term child without previous hospitalizations or surgeries. Examination revealed a 4-cm discrete, soft, compressible mass in the right lateral neck posterior to the middle onethird of the sternocleidomastoid muscle, extending inferiorly to the supraclavicular fossa. A computed tomography (CT) neck with contrast showed a well-circumscribed, fluid-filled, cystic mass, posterior, and deep to the right sternocleidomastoid, extending from the level of the hyoid superiorly to the clavicle inferiorly ( Figure 1) with medial displacement and compression of the right internal jugular vein and right lobe of the thyroid. A magnetic resonance imaging (MRI) showed a septated, macrocystic mass with blood-fluid levels (Figure 2), and the diagnosis of macrocystic LM was made that was amenable for sclerotherapy. She underwent sclerotherapy under general anesthesia with a total of 500 mg of doxycycline and 1 mL of 3% Sotradecol (STS) in foam, which she tolerated without complications. At 1-month follow-up, no residual LM was palpated.Lymphatic malformations are congenital, low-flow vascular anomalies filled with chyle that consist of collections of abnormal lymphatic vessels composed of normal appearing, flattened endothelial layers. 2,3 First described in 1843 by Werhner, these lesions were originally termed cystic hygromas or lymphangiomas. They were reclassified as LMs by the International Society for the study of vascular anomalies. 2 Lymphatic malformations can present as late as early childhood, though up to 60% are noted at perinatally and almost 90% by the age of 2. 2 The majority occur in the head and neck and fall into 3 categories: marocystic where all loculations are >2 mL, microcystic where all loculations are <2 mL, and mixed lesions. 3 Lymphatic malformations grow proportionally with the child, lack the proliferative phase of hemangiomas, and are associated with continued, steady growth rather than spontaneous regression. 4 Lymphatic malformations typically exist as soft, easily compressible, cystic lateral neck masses, similar to branchial cleft cysts, dermoid cysts, and other vascular malformations. 1 Unlike venous malformations or air-filled anomalies such as larynogceles and pharyngoceles, LMs will not increase in size with Valsalva and are not compressible. They also lack the bruit that is characteristic of high-flow vascular malformations. 3 Lymphatic malformations are...