Magnetic resonance imaging evaluation of fetal maxillary sinuses

The growth of maxillary sinus is closely connected to the development of facial structures. However, its definition and reference standards on fetal magnetic resonance imaging (MRI) have not been analyzed so far. In this study, the objectives were to define and evaluate the fetal maxillary sinus (fMS) formation with MRI.

We reviewed T2-weighted coronal MRI images of 75 fetuses. The MRI features, time of appearance, and boundaries of fMS were defined. Craniocaudal and transverse diameters of both maxillary sinuses and bone biparietal diameters were measured and statistically evaluated.

In 150 fMS site analysis, 91 fMSs were identified. The fMSs were visualized as a hyperintense structures on T2-weighted image above the tooth bud. It first appeared at the 22nd gestational week, and in 4% (3/75) of fetuses, there was unilateral development. Mean craniocaudal length was 2.84 mm (1.1-4.8 mm), and mean transverse diameter was 2.67 mm (1.5-4.2 mm).

Magnetic resonance imaging features of fMS that should be sought for the assessment of craniofacial anatomy are identified in this study. Fetal maxillary sinuses can be observed as hyperintense structures on T2-weighted MRI images starting from 22 weeks of gestation. The growth of fMS follows a predictable course throughout gestation; however, the dimensions are larger than the previously reported ex vivo series.