THALAMUS

The thalamus is a diencephalic structure that is easily visualized in the same plane as the BPD measurement.

ULTRASOUND

• Two hypoechoic structures on either side of the midline.
• Hypoechoic.
• Their central location allows the sonographer to evaluate the symmetry of structures in both hemispheres as well as the correct imaging plane for measuring the BPD.
• The width of the thalamus increases with gestational age.
• The two thalami are separate structures.
  Fusion of the thalami is present in alobar holoprosencephaly.

Normal thalami - unfused
Fused thalami in holoprosencephaly