Third ventricle: size and appearance in normal fetuses through gestation.
OBJECTIVE
To define the size and appearance of the normal fetal third ventricle.


METHODS
The third ventricle was prospectively assessed in 441 consecutive normal second- and third-trimester fetuses. The fetuses were divided into six gestational age ranges. Data regarding the size and configuration of the third ventricle were analyzed for each group.


RESULTS
The third ventricle was seen in 435 of 440 (98.9%) fetuses. It appeared as a single echogenic line between the thalami in 171 (38.9%) fetuses, as parallel echogenic lines outlining a fluid-filled lumen in 243 (55.2%) fetuses, and as divergent lines delineating a V-shaped fluid-filled structure in 21 (4.8%) fetuses. The single-line configuration was most common early in the second trimester. Later in pregnancy, the ventricle walls could be discerned as separate parallel or divergent lines outlining a fluid-filled lumen. The average width of the ventricle was relatively constant at approximately 1 mm from 12 to 28 weeks. After this time, it enlarged, reaching a maximum 1.9 mm.


CONCLUSIONS
The third ventricle can be imaged in most second- and third-trimester fetuses. Its size and configuration evolve through the second and third trimesters. This evolution must be considered in the evaluation of normality. At any gestational age, a third ventricle greater than 3.5 mm in width should be viewed with concern for abnormality.
Hertzberg
B S
BS
Department of Radiology, Duke University Medical Center, Durham, NC 27710, USA.
Kliewer
M A
MA
Freed
K S
KS
McNally
P J
PJ
DeLong
D M
DM
Bowie
J D
JD
Kay
H H
HH
D000015:Abnormalities, Multiple; D061085:Agenesis of Corpus Callosum; D006502:Budd-Chiari Syndrome / Q000000981:diagnostic imaging; D002552:Cerebral Ventricles / Q000002:abnormalities / Q000000981:diagnostic imaging / Q000196:embryology*; D003337:Corpus Callosum / Q000000981:diagnostic imaging; D005314:Embryonic and Fetal Development; D004677:Encephalocele / Q000000981:diagnostic imaging; D005260:Female; D005315:Fetal Diseases / Q000000981:diagnostic imaging; D005865:Gestational Age; D006801:Humans; D015588:Observer Variation; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D011446:Prospective Studies; D013788:Thalamus / Q000000981:diagnostic imaging / Q000196:embryology; D016216:Ultrasonography, Prenatal