Cystic hygroma and increased nuchal translucency

Definition

Nuchal translucency basics

• Nuchal translucency (NT) is a subcutaneous collection of fluid in the nuchal region that can be visualised in every fetus in the first trimester and is therefore not a sign of pathology per se.
• The proposed causes include immature lymphatic drainage, possible cardiac insufficiency, and specific connective tissue properties.
• The measurement is time-sensitive because the nuchal translucency resolves after 14 weeks, meaning the screening cannot be performed later.

• Nuchal translucency is a transient collection of fluid under the skin of the fetal neck, measured at a crown-rump length of 45 to 84 mm, and is not a structural anomaly.
• Cystic hygroma is a developmental anomaly of the lymphatic system with fluid in the nuchal region that can extend along the length of the fetus and show septations.

Classification

• A nuchal translucency of 3 mm or more is a high risk factor for aneuploidy; values at or above the 99th centile (3.5 mm or more) are found in about 1% of pregnancies.
• Septation does not reliably distinguish cystic hygroma from increased nuchal translucency.

Aetiopathogenesis

Aetiology

• Fluid collections arise when interstitial fluid production exceeds return via the lymphatic vessels; cystic hygroma results from jugular-lymphatic obstruction.
• A nuchal translucency at or above the 99th centile is associated with chromosomal anomalies, monogenic conditions such as RASopathies and, in euploid fetuses, with cardiac and other malformations.

Diagnosis

Typical imaging findings

• Ultrasound: Behind the fetal head and neck there is an extensive anechoic fluid collection far beyond the extent of a normal nuchal translucency. It extends far dorsally; the measuring line is marked.
• Ultrasound: Large anechoic sacs lie on both sides of the neck, divided into chambers by thin walls. The fluid extends far around the neck and is clearly more than a narrow nuchal fold.

• Nuchal translucency is measured in a midsagittal view of the fetal face.
• Investigations include karyotyping, chromosomal microarray analysis and a multigene RASopathy panel, together with careful anatomical assessment and early and repeated fetal echocardiography.

Keep learning in the app

Further reading (selection)

1. Diagnostics 2022: A Pain in the Neck: Lessons Learnt from Genetic Testing in Fetuses Detected with Nuchal Fluid Collections, Increased Nuchal Translucency versus Cystic Hygroma (PubMed Central)
2. DocCheck Flexikon, Nackentransparenz

Cross-references