This 3rd trimester fetus has round cystic anechoic image in the pituitary fossa, 25 by 27 mm. The cyst expands the polygon of Willis but the cyst demonstrates no flow.

The following images suggested an downward extension of the cyst towards the nasopharyngeal cavity.

Findings:

Cyst in the suprasellar region, not vascular with possible extension towards the nasopharynx.

Few condition can present this way:

1. A cystic craniopharyngioma (rare)
2. A Rathke's cleft cyst with a craniopharyngeal canal
3. An arachnoid cyst

Normal delivery of a male newborn weighing 3200 g occurred at 39 weeks. The newborn had no complications and normal head circumference. The neurological examination was normal. The MRI confirmed an arachnoid cyst