The clivus-supraocciput angle: a useful measurement to evaluate the shape and size of the fetal posterior fossa and to diagnose Chiari II malformation.
OBJECTIVE
To obtain a nomogram of the clivus-supraocciput angle as a basis for the diagnosis of Chiari II malformation in fetuses with ventriculomegaly.


METHODS
A cross-sectional study was undertaken on 310 normal pregnant women of 16-34 weeks' gestation. A mid-sagittal section of the fetal skull was obtained and the angle between the clivus and the supraocciput was measured. Forty-four fetuses with ventriculomegaly due to various causes (13 Chiari II malformation, 12 dysgenesis of the corpus callosum, 7 aqueductal stenosis, 6 borderline ventriculomegaly, 3 Dandy-Walker malformation, 2 porencephaly, 1 schizencephaly) were also included in the study and the values of the angle found in the pathological cases were compared with those found in the normal population.


RESULTS
The clivus-supraocciput angle did not change during gestation and was almost constant with an average value of 79.3 +/- 6 degrees. All cases of Chiari II malformation showed a value below the 5th centile of our nomogram.


CONCLUSIONS
The evaluation of the posterior fossa and particularly the measurement of the clivus-supraocciput angle is a useful parameter to differentiate the various causes of fetal ventriculomegaly and particularly to recognize Chiari II malformation.
D'Addario
V
V
IV Unit of Obstetrics and Gynecology, University Medical School of Bari, 70124 Bari, Italy. v.daddario@gynecology4.uniba.it
Pinto
V
V
Del Bianco
A
A
Di Naro
E
E
Tartagni
M
M
Miniello
G
G
Serio
G
G
D000293:Adolescent; D000328:Adult; D001139:Arnold-Chiari Malformation / Q000175:diagnosis*; D002552:Cerebral Ventricles / Q000002:abnormalities; D003388:Cranial Fossa, Posterior / Q000000981:diagnostic imaging / Q000473:pathology*; D003430:Cross-Sectional Studies; D003616:Dandy-Walker Syndrome / Q000175:diagnosis; D003937:Diagnosis, Differential; D005865:Gestational Age; D006801:Humans; D008279:Magnetic Resonance Imaging; D016216:Ultrasonography, Prenatal