Cystic hygroma, also referred to as lymphatic malformation or lymphangioma, is a rare congenital anomaly characterized by the presence of fluid-filled sacs resulting from abnormal development of the lymphatic system. These cystic masses are typically soft, compressible, and transilluminant. They most often appear in the head and neck region but can occur anywhere along the lymphatic vessels. Although cystic hygromas are generally benign, their location and size can cause significant functional and cosmetic concerns, especially in infants and young children. 

The understanding of cystic hygroma has evolved considerably over the decades, thanks to advances in prenatal imaging, genetics, and minimally invasive treatment techniques. This article provides an in-depth review of cystic hygroma, including its etiology, embryology, clinical features, diagnosis, management options, prognosis, and preventive strategies. The information aims to serve healthcare professionals, medical students, and interested readers seeking detailed knowledge of this complex condition. 

Cystic hygroma is a type of lymphatic malformation that results from sequestration or improper connection of lymphatic channels during embryonic development. It is characterized by multiloculated, thin-walled cystic spaces filled with lymphatic fluid. These cysts may vary in size from a few millimeters to large masses that distort normal anatomy. 

Key features: 

• Nature: Benign congenital lymphatic malformation. 

• Structure: Multiloculated, fluid-filled cystic spaces. 

• Common locations: Neck (especially posterior triangle), axilla, mediastinum, groin. 

• Onset: Usually present at birth or within the first two years of life. 

• Growth pattern: May enlarge rapidly, particularly due to infection or hemorrhage. 

The condition may be isolated or associated with other anomalies, including chromosomal abnormalities and syndromic conditions. 

Embryology and Pathogenesis 

The lymphatic system develops during the 5th to 6th week of gestation from lymph sacs that sprout from the veins. These lymph sacs subsequently connect with each other and the venous system, forming a functional lymphatic network. 

In cystic hygroma: 

• There is a failure of these lymphatic sacs (particularly the jugular lymph sacs) to establish proper communication with the venous system. 

• This leads to sequestration of lymphatic tissue, which progressively dilates to form cystic spaces. 

These malformations consist of endothelium-lined channels that fail to communicate normally with the main lymphatic network, resulting in lymph accumulation and cyst formation. 

Epidemiology 

• Incidence: Approximately 1 in 6,000 to 1 in 16,000 live births. 

• Sex distribution: No significant gender predilection. 

• Ethnicity: No specific racial predilection has been reported. 

• Prenatal detection: Increasingly identified during routine obstetric ultrasounds in the first or second trimester. 

Cystic hygroma primarily results from embryological defects rather than environmental factors. However, several risk factors and associations have been recognized: 

Genetic associations: 

• Turner syndrome (45,X) 

• Down syndrome (Trisomy 21) 

• Noonan syndrome 

• Trisomy 13 and 18 

• Other rare chromosomal abnormalities 

Other associations: 

• Fetal hydrops (generalized fetal edema) 

• Congenital heart defects 

• Polyhydramnios (excess amniotic fluid) 

Acquired cases: 

Rarely, lymphatic malformations resembling cystic hygroma can arise in adults following trauma, infection, or radiation, although these are not true congenital cystic hygromas. 

The presentation of cystic hygroma varies depending on its size, location, and associated anomalies. 

Common features: 

• Soft, fluctuant mass: Usually non-tender, compressible, and transilluminant. 

• Skin over mass: Normal unless inflamed or infected. 

Symptoms related to mass effect: 

• Respiratory distress (especially with large cervical or mediastinal lesions compressing airway). 

• Dysphagia (difficulty swallowing) due to esophageal compression. 

• Cosmetic deformity, which may be a source of parental anxiety. 

Prenatal presentation: 

• Seen as a cystic mass on ultrasound. 

• May be associated with hydrops fetalis. 

• Poor prognosis if hydrops or major chromosomal anomalies are present. 

Complications: 

• Infection (cellulitis or abscess formation). 

• Hemorrhage into the cyst leading to rapid enlargement. 

• Airway compromise due to mass effect. 

Classification 

Cystic hygromas (lymphatic malformations) are classified based on the size of cystic spaces: 

Macrocystic (formerly called cystic hygroma): 

• Cyst size > 2 cm.  

• Multiloculated, fluid-filled, large cystic spaces. 

Microcystic:  

• Cyst size < 2 cm.  

• Small, sponge-like network of lymphatic channels. 

Mixed type:  

• Contains both macrocystic and microcystic components. 

This classification is important because treatment response varies by type.

Prenatal diagnosis 

• Ultrasound: First-line imaging modality. Cystic hygroma appears as a multiloculated, thin-walled, cystic mass, often septated. 

• Fetal MRI: Occasionally used to define extent and relation to vital structures. 

• Amniocentesis/chorionic villus sampling: Recommended when a cystic hygroma is detected prenatally, to assess for chromosomal abnormalities. 

Postnatal diagnosis 

• Physical examination: Soft, compressible, transilluminant mass. 

• Ultrasound: Useful for initial evaluation, delineation of cystic vs. solid components. 

• MRI: Modality of choice for preoperative planning; superior in defining the lesion’s extent, deep tissue involvement, and relation to neurovascular structures. 

• CT scan: Occasionally used; less favored due to radiation exposure. 

Differential diagnosis 

• Branchial cleft cyst 

• Hemangioma  

• Teratoma 

• Thyroglossal duct cyst 

• Dermoid cyst 

• Lymphadenopathy 

The management of cystic hygroma depends on: 

• Size and location of the lesion 

• Presence of symptoms 

• Rate of growth 

• Cosmetic and functional considerations 

Observation 

• Small, asymptomatic lesions can be monitored over time.  

• Some may regress spontaneously, although this is uncommon. 

Surgery 

• Traditionally considered the mainstay of treatment.  

• Aim: Complete excision of the lesion while preserving vital structures.  

• Challenges: The lesion often infiltrates surrounding tissues, which can make complete removal difficult. If excision is incomplete, there is a high recurrence rate, reported to be up to 15–20%. Additionally, surgery carries the risk of damaging important nerves such as the facial, hypoglossal, and accessory nerves. 

• Surgery is preferred for large symptomatic lesions, lesions unresponsive to sclerotherapy, or recurrent or infected lesions 

Sclerotherapy 

• Minimally invasive and increasingly favored for macrocystic lesions. 

• Agents include OK-432 (picibanil) — derived from group A streptococcus; bleomycin; doxycycline; and ethanol.  

• Mechanism: Induces local inflammation → fibrosis → obliteration of cystic spaces. 

• Advantages: Avoids extensive surgery and lowers complication rates.  

• Limitations: Less effective for microcystic or mixed lesions and multiple sessions often required. 

Emerging treatments  

• Laser therapy for superficial microcystic components.  

• Radiofrequency ablation.  

• Sirolimus (mTOR inhibitor) for complex or refractory lymphatic malformations. 

Management of airway compromise  

• Emergency tracheostomy in severe cases.  

• Prenatal EXIT (Ex Utero Intrapartum Treatment) procedure for massive neck masses threatening airway at delivery. 

The outcome for cystic hygroma varies: 

Favorable prognosis: 

• Isolated macrocystic lesions amenable to sclerotherapy or surgery. 

• No associated chromosomal abnormalities. 

Poor prognosis: 

• Lesions associated with fetal hydrops. 

• Lesions associated with chromosomal abnormalities. 

• Large lesions causing airway compromise. 

Recurrence is a concern, especially with incomplete surgical excision or mixed-type lesions. 

• Airway obstruction (can be life-threatening). 
• Cosmetic disfigurement. 
• Psychological distress for patients and families. 
• Recurrent infections. 
• Hemorrhage into the cyst. 
• Chylothorax or chylous ascites (rare, with intra-thoracic or intra-abdominal lesions). 

Since cystic hygroma is congenital and linked to developmental anomalies: 

• Prevention: No known preventive measures to avoid primary occurrence. 

• Genetic counseling: Important for families with affected children, especially if associated with chromosomal abnormalities. 

Prenatal detection allows: 

• Early counseling about prognosis. 
• Planning for delivery at a tertiary center with pediatric surgery and neonatology teams. 

Cystic hygroma is a rare but significant congenital malformation of the lymphatic system, with a wide spectrum of clinical presentations and outcomes. Advances in prenatal imaging and molecular diagnostics have enhanced our ability to detect and characterize these lesions early. Treatment has evolved from radical surgery to include less invasive approaches such as sclerotherapy, offering improved outcomes with reduced morbidity. 

Management should be tailored to the individual, considering the lesion’s size, location, type, associated anomalies, and the expertise of the treating team. Multidisciplinary collaboration among pediatric surgeons, interventional radiologists, geneticists, and neonatologists is essential for optimal care. 

Further research is needed to refine medical therapies, improve recurrence rates, and understand the genetic mechanisms underlying cystic hygroma. Continued progress will enhance quality of life for affected individuals and their families. 

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