Cystic Hygroma (Lymphatic Malformation)

Lymphatic malformation (LM), historically called cystic hygroma, is a slow-flow congenital vascular malformation arising from sequestered lymphatic tissue that fails to communicate with the central lymphatic system. LMs are classified by cyst size: macrocystic (cysts >2 cm), microcystic (<2 cm), or mixed. About 50% are present at birth and 90% by age 2. Sites include posterior cervical triangle (most common), axilla, mediastinum, retroperitoneum, mesentery, scrotum, and tongue. Generalized lymphatic anomalies (Gorham-Stout, kaposiform lymphangiomatosis) involve bone and viscera.

Clinical features include soft, fluctuant, transilluminating, painless mass with sudden enlargement during upper respiratory infection (lymphangitis) or intracystic bleeding. Macrocystic LMs are amenable to sclerotherapy with high cure rates; microcystic and mixed LMs are more challenging. Complications include airway compromise, dysphagia, recurrent infection (cellulitis, abscess), intracystic hemorrhage causing rapid enlargement, and chylous effusion in mediastinal/retroperitoneal LMs.

MRI is the imaging modality of choice showing T2 hyperintense, multilocular, lobulated cysts with septa and possible fluid–fluid levels (hemorrhage). Sclerotherapy with OK-432 (picibanil), doxycycline, bleomycin, or ethanol is first-line for macrocystic LMs (>80% response). Surgical excision is reserved for accessible localized lesions or after sclerotherapy fails. Sirolimus (mTOR inhibitor) is highly effective for extensive, complex, microcystic, or generalized lymphatic anomalies, with 70–80% partial response rate. Antibiotic prophylaxis is given for recurrent cellulitis. Antenatal diagnosis warrants chromosomal evaluation (Turner, trisomies).