Normal Variant Residual Germinal Matrix in Extremely Premature Infants: Radiographic Features and Imaging Pitfalls

Background As radiology volume from premature patients increases, previously undescribed imaging findings may be identified, posing diagnostic dilemma to the pediatric radiologist. Objective The primary goal of our study is to characterize the previously undescribed imaging finding of subependymal echogenicity at the floor of the frontal horns, which we postulate represents normal variant embryologic remnant residual germinal matrix. Furthermore, we hope to equip the pediatric radiologist with diagnostic criteria to distinguish this normal variant from pathology. Materials and methods Retrospective review of neonates at our institution over a 10 year period was performed to identify extremely premature infants who received head ultrasounds during their hospital stay. Clinical data from EPIC was collected on these patients in addition to retrospective review of their head ultrasound images. Results Literature review of neuroembryology and observed involution of the frontal horn subependymal echogenicity on sequential imaging inform our hypothesis that this imaging finding represents normal variant residual germinal matrix. Two-thirds of the 210 included extremely premature infants demonstrated this finding, which was frequently misinterpreted as grade 1 germinal matrix, intra-choroidal or intra-ventricular hemorrhage. Residual matrix was concomitantly present with additional pathology in 29.4% of the patients. Conclusion Previously undescribed subependymal echogenicity at the floor of the frontal horns is favored to represent normal variant embryologic remnant residual germinal matrix. Since this finding may be misinterpreted as germinal matrix, intra-choroidal or intra-ventricular hemorrhage, it is essential for the interpreting radiologist to be aware of this normal variant and not confuse it for pathology.