Fetal cerebellum: US appearance with advancing gestational age.

Abstract

To evaluate the change in ultrasonographic (US) appearance of the fetal cerebellum with advancing gestation. A total of 291 normal fetuses of uncomplicated pregnancies were evaluated at gestational ages (GAs) between 15 and 41 weeks with a 3.75-MHz transabdominal curvilinear probe. After the transcerebellar view was obtained, the transverse cerebellar diameter (TCD) was measured and the images were stored. On hard-copy US images, cerebella were assigned three grades of appearance. These grades were analyzed in relation to GA and TCD. Inter- and intraobserver variations were assessed in 91 randomly selected cases. Cerebella in 137 (47.1%), 71 (24.4%), and 83 (28.5%) of 291 subjects were classified as grade I (hypoechoic, "eyeglass" shape), grade II (intermediate echogenicity, "dumbbell" outline), and grade III (hyperechoic, "fan" shape), respectively. With advancing gestation, the dominant grade changed from I to III gradually and progressively. The median GA and TCD, respectively, were 22 weeks and 22 mm for grade I, 29 weeks and 35 mm for grade II, and 36 weeks and 46 mm for grade III. These differences were statistically significant (P <.001). The agreements within inter- and intraobserver estimations were 96% (87 of 91) and 95% (86 of 91), respectively. A gradual change in US appearance of the fetal cerebellum is seen with advancing gestation.