Cystic hygroma and occipital meningocele are both differential diagnosis for an antenatally detected cystic collection noted on the posterior aspect of the head and neck.
A simple differentiation can be made based on the contents and presence of septations:
- cystic hygroma will present as a well-defined anechoic thin-walled cyst with multiple septations and a characteristic midline septum representing the nuchal ligament
- an occipital meningocele will appear as a well-defined anechoic area with no septations and is seen in direct continuity with a defect in the calvaria
