Fetal cerebellum: US appearance with advancing gestational age

PURPOSE: To evaluate the change in ultrasonographic (US) appearance of the fetal cerebellum with advancing gestation. MATERIALS AND METHODS: A total of 291 normal fetuses of uncomplicated pregn ancies were evaluated at gestational ages (GAs) between 15 and 41 weeks wit h a 3.75-MHz transabdominal curvilinear probe. After the transcerebellar vi ew was obtained, the transverse cerebellar diameter (TCD) was measured and the images were stored. On hard-copy US images, cerebella were assigned thr ee grades of appearance. These grades were analyzed in relation to GA and T CD. Inter- and intraobserver variations were assessed in 91 randomly select ed cases. RESULTS: Cerebella in 137 (47.1%), 71 (24.4%), and 83 (28.5%) of 291 subjec ts were classified as grade I (hypoechoic, "eyeglass" shape), grade II (int ermediate echogenicity, "dumbbell" outline), and grade III (hyperechoic, "f an" shape), respectively. With advancing gestation, the dominant grade chan ged from I to III gradually and progressively. The median GA and TCD, respe ctively, were 22 weeks and 22 mm for grade 1, 29 weeks and 35 mm for grade II, and 36 weeks and 46 mm for grade Ill. These differences were statistica lly significant (P <.001). The agreements within inter- and intraobserver e stimations were 96% (87 of 91) and 95% (86 of 91), respectively. CONCLUSION: A gradual change in US appearance of the fetal cerebellum is se en with advancing gestation.