Cystic hygroma

A cystic hygroma (CH) refers to a type of congenital lymphangioma (lymphovascular malformation).

Epidemiology 

They usually occur in the fetal - infantile and paediatric populations with most lesions presenting by the age of two. The estimated prevalence in the fetal population is at ~ 0.2 - 3 %. 

Clinical presentation

Patients in the infantile or paediatric populations can present with pain, dyspnoea, infection, haemorrhage or respiratory compromise.

Pathology

They are thought to arise from delayed development / maldevelopment - failure to communicate with the venous system of the lymphatic system of the neck. Like other lymphangiomas, there are endothelial lined cavernous lymphatic spaces. They are microscopically comprised of endothelium lined cystic spaces with scanty stroma. They can significantly vary in size. Lymphatic vascular malformations may be mixed with other forms of vascular malformation, including capillary or venous. 

Location

They occur most commonly in the neck - which is then also termed nuchal cystic hygroma ( occurs in ~ 80% of cases) ⁷ and axilla, with only 10% of cases extending to the mediastinum ^2,3 and only 1% confined to the chest ¹. 

Associations

Associated anomalies can be common

• aneuploidic anomalies : 50 - 80 % of cystic hygromas can be associated with an aneuploidic abnormality
  • Turner syndrome : most frequent aneuploidic association
  • Down syndrome : second most frequent aneuploidic association
  • trisomy 13
  • trisomy 18 
  • triploidy ¹¹
• non aneuploidic
  • congenital cardiac anomalies : 
    • aortic coarctation : commonest cardiovascular anomaly
    • hypoplastic left heart syndrome
  • pentalogy of Cantrell ⁸
  • Apert syndrome
  • Cornelia de Lange syndrome
  • fetal alcohol syndrome
  • Fryns syndrome ¹¹
  • lethal multiple pterygium syndrome
  • limb hypertrophy
  • Noonan syndrome
  • Pena Shokeir syndrome ¹¹

Radiographic features

They are usually well circumscribed and are of fluid density. Cystic hygromas may also have an infiltrative appearance, and may be uni or multilocular. The density can also be variable with a combination of fluid, soft-tissue density and fat. 

Antenatal ultrasound

On antenatal ultrasound they may present as a nuchal cyst and may show septations + / - evidence of fetal anasarca / hydrops fetalis. The presence of septations may indicate a poorer outcome. Greater volumes ( > 75 mm³ according to one study ⁹) are thought to correlate with increased karyotypic abnormality and poorer fetal outcome ^9-10.

CT

Commonly seen as a hypo-attenuating ill defined cystic mass.

MRI

Reported signal characteristics include

• T1 : predominantly low signal - unless there are haemorrhagic components
• T2 : predominantly high signal 
• T1 C+ (Gd) : no enhancement on any component except occasional faint enhancement of rim

Complications

• development of non-immune hydrops fetalis : which often indicates a poorer prognosis
• respiratory obstruction from pharyngeal oedema ¹¹

Treatment and prognosis

Management may be by surgical excision or by injection with OK-432, a preparation containing Streptococcus pyogenes antigens, which induces an inflammatory response and subsequent obliteration of the abnormal cavities. Most fetuses with cystic hygromas have a poor prognosis although it may improve in utero on its own in a very small proportion of cases. Spontaneous remission does not necessarily exclude an abnormal karyotype.

Differential diagnosis

Considerations on antenatal ultrasound include

• cervical teratoma
• occipital encephalocoele
• cervical meningocoele