Slow-flow malformation, lymphatic type

Slow-flow malformation, lymphatic type — also commonly known as lymphatic malformation (LM) or historically as cystic hygroma or lymphangioma — is a congenital vascular anomaly characterized by abnormal development of the lymphatic system. These malformations consist of dilated lymphatic channels and cysts that fail to connect properly to the normal lymphatic drainage system. They are classified as slow-flow vascular malformations, distinguishing them from high-flow lesions such as arteriovenous malformations. Lymphatic malformations most commonly affect the head and neck region (particularly the cervical area), axilla, mediastinum, and extremities, though they can occur in virtually any body site including the abdomen, retroperitoneum, and bones. They are typically present at birth or become apparent in early childhood. Clinically, they present as soft, compressible masses that may be macrocystic (large cysts), microcystic (small cysts), or mixed. Key symptoms include swelling, disfigurement, pain, and functional impairment depending on location. Complications can include infection (cellulitis or abscess), intralesional bleeding, compression of adjacent structures (such as the airway), and lymphatic fluid leakage. These malformations tend to grow proportionally with the child but may enlarge suddenly due to infection, trauma, or hormonal changes. Treatment is guided by the size, location, and type of lymphatic malformation. Macrocystic lesions often respond well to sclerotherapy, in which agents such as doxycycline, bleomycin, or OK-432 (picibanil) are injected directly into the cysts to induce shrinkage. Microcystic and mixed lesions are more challenging to treat and may require surgical excision, though complete removal is often difficult due to infiltration of surrounding tissues. Sirolimus (an mTOR inhibitor) has emerged as a promising medical therapy, particularly for extensive or refractory lymphatic malformations, and has shown efficacy in reducing lesion volume and symptoms. Multidisciplinary management involving vascular anomaly specialists, surgeons, interventional radiologists, and other specialists is recommended for optimal care.

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