Thalamic volume measurement in normal fetuses using three-dimensional sonography.

PURPOSE

Brain thalami are important for a wide range of sensorimotor and neuropsychiatric functions. This study was carried out to calculate normative values for thalami volume during fetal life.

METHODS

Fetal thalami volumes were measured using 3D ultrasound in 122 normal, singleton fetuses at 20(+0) -34(+6) weeks' gestation. Virtual Organ Computer-aided AnaLysis (VOCAL) was used to obtain a sequence of six sections of each thalamus, starting from the transthalamic view of the brain at an axial plane. Thalamic contour was drawn manually. Volume contrast imaging was used to enhance image quality when needed. The volume of the thalamus distal to the transducer was also measured by a second operator in 30 randomly selected cases, blind to the measurements of the first, to calculate interobserver agreement.

RESULTS

Thalamic volume increased with gestational age, following a quadratic equation (R(2) = 0.83). There was no significant difference in volume between the right and left thalamus. The mean volume of each thalamus increased from 0.45 ml at 20(+0) weeks, to 1.39 ml at 28(+0) weeks, to 2.17 ml at 34(+0) weeks. The 95% limits of interobserver agreement for thalamic volume were -14.3% to +17.2%.

CONCLUSIONS

The increase in thalamic volume with gestation can be described adequately by a quadratic equation. The moderate interobserver repeatability is attributed to the similar echogenicity between the thalamus and its surrounding structures.