Cystic Hygroma

Definition

A cystic hygroma is a congenital thin-walled cyst containing lymphatic fluid, arising from failure of the primitive lymphatic tree to connect to the venous system — the blind lymphatic pouch dilates to form a macrocystic lymphatic malformation (also called cystic lymphangioma, lymphatic hamartoma, or hygroma cysticum). It is multiloculated, lined by endothelium, and most commonly involves the posterior neck/jugular lymphatic sacs.

Epidemiology & Pathogenesis

Incidence: 1:100 pregnancies in the first trimester; septated subtype in 1:285 pregnancies
Arises from failure of the jugular lymphatic sac to drain into the venous system → lymphatic obstruction → cystic dilation
Can occur anywhere along the lymphatic system: posterior neck (most common), axilla, mediastinum, groin, retroperitoneum

Clinical Features

Prenatal (most commonly detected):

Anechoic, fluid-filled posterior neck mass — septated or simple
A thick midline nuchal ligament band is characteristic (separating bilateral jugular sacs)
May engulf the fetal head cephalad, or extend caudad over the dorsum
Associated with fetal hydrops in severe cases

Postnatal:

Soft, translucent, cystic neck mass, often large
Can distort the airway — potentially life-threatening
Prone to sudden enlargement from intracystic hemorrhage or infection (becomes tender, tense, purple/yellow)

Associated Anomalies (Prenatal)

Structural anomalies in ~34% of first-trimester cases:

Category	Specifics
Aneuploidy (50%)	Turner syndrome (45,X) — 28.3%; Trisomy 18 — 19.4%; Trisomy 13 — 9%; Triploidy — 4.5%
Cardiac anomalies	72.7% of structural abnormalities — hypoplastic left/right heart, TOF, VSD, complex defects; 4.3% major CHD in euploid fetuses
Syndromes	Noonan syndrome, Roberts syndrome, Cornelia de Lange, others
Other	Skeletal abnormalities, fetal hydrops, IUFD

Imaging

Ultrasound (Key Diagnostic Features)

Anechoic, fluid-filled cavities in the posterior neck
Thick or thin internal septations
Thick midline nuchal ligament (Turner syndrome classic)
May be multiloculated

Septated cystic hygroma on transverse fetal ultrasound — anechoic cystic mass in posterior cervical region with internal septation dividing fluid into compartments

Large cystic hygroma with hydrops — septated nuchal cystic structure with diffuse fetal edema

Turner syndrome — bilateral cystic neck mass with thick midline nuchal ligament

MRI

Useful postnatally to define extent of lymphatic channels and airway relationship.

Differential Diagnosis

Thickened nuchal translucency (non-septated)
Neural tube defects (posterior encephalocele, cervical meningocele)
Cystic teratoma
Hemangioma
Thyroglossal duct cyst / branchial cleft cyst
Laryngocele
Fetal hydrops

Management

Antenatal

Detailed fetal anatomy survey to identify associated anomalies
Fetal echocardiogram (cardiac anomalies present in majority of structural abnormalities)
Genetic testing — amniocentesis or CVS for karyotype/chromosomal microarray
Serial ultrasounds for growth, hydrops, polyhydramnios from esophageal compression, progression
Assess airway relationship for birth planning

Delivery

If large cystic neck mass compromises the airway: EXIT procedure (ex utero intrapartum treatment) — secures airway while uteroplacental circulation is maintained

Postnatal / Pediatric Surgical

Complete surgical excision with meticulous isolation and ligation of lymphatic branches; avoid blunt/electrocautery dissection (risk of recurrence/infection)
When complete excision is not feasible: sclerotherapy with bleomycin, doxycycline, or OK-432 (Picibanil, derived from Streptococcus pyogenes)
Sirolimus (mTOR inhibitor) is emerging as a pharmacologic option, particularly for cervicofacial disease

Prognosis

Highly variable — depends on karyotype, associated anomalies, and trimester at detection
In the presence of aneuploidy or hydrops: poor prognosis, high rate of IUFD
Euploid fetuses with isolated hygroma: better outcome but still significant risk of CHD
Spontaneous resolution can occur (particularly with small, non-septated lesions early in pregnancy)
A 2025 systematic review (PMID: 40389136) confirmed that perinatal outcomes are strongly stratified by chromosomal status and presence of hydrops
A 2025 review (PMID: 40190084) highlighted the genetic link between cystic hygroma, nuchal translucency, and congenital heart disease via cardiac lymphatic abnormalities

Sources: Creasy & Resnik's Maternal-Fetal Medicine (8e); Sabiston Textbook of Surgery; Dermatology 2-Volume Set (5e); Thompson & Thompson Genetics in Medicine (9e)

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