Prenatal Diagnosis of Third and Fourth Branchial Apparatus Anomalies: Case Series and Comparison with Lymphatic Malformation.

Background And Purpose: Third and fourth branchial apparatus anomalies are rare congenital anomalies. The purpose of this study was to investigate imaging features of these lesions on fetal MR imaging in comparison with lymphatic malformations, the major competing differential diagnosis in these cases.

Materials And Methods: A retrospective review of our institutional fetal MR imaging database between 1997 and 2019 resulted in 4 patients with confirmed third and fourth branchial apparatus anomalies and 14 patients with confirmed lymphatic malformations. The imaging features were reviewed by consensus, and the Fisher exact test was used to evaluate statistically significant differences between these 2 populations.

Results: Four cases of third and fourth branchial apparatus anomalies were imaged at 29 weeks 1 day (range, 23 weeks 1 day to 33 weeks 4 days). All 4 cases demonstrated unilateral, unilocular cysts without reduced diffusion or hemorrhage and a medially directed beaked contour that tapered between the spine and airway at the level of the piriform sinus. Compared with 14 cases of fetal lymphatic malformations imaged at 27 weeks 6 days (range, 21 weeks 3 days to 34 weeks 6 days), third and fourth branchial apparatus cysts were significantly more likely to be unilocular (< .005) and to have a medially beaked contour (< .005). The combination of features of unilateral, unilocular, and medially beaked contour was observed only in the fetuses with third and fourth branchial apparatus cysts (< .001).

Conclusions: The presence of a left-sided unilocular cyst with a medially beaked contour tapering at the level of the piriform sinus suggests the diagnosis of third and fourth branchial apparatus anomaly. Accurate diagnosis in the prenatal period allows proper counseling, genetic work-up, and treatment, potentially sparing patients from recurrent infections and associated morbidity.