Purpose or Case Report: It is well-established and widely observed that newborn infants imaged by ultrasound may show transiently increased echogenicity of the renal pyramids within the first week of life, up to 10 days, postulated to reflect reduced excretion of urine that has been observed early in life. Over the past decade, as ultrasound technology has improved, we have observed in routine practice that many infants without renal disease manifest this echogenicity for several weeks and sometimes over a month. The aim of this study is to establish a new expected age range during which healthy infants may show hyperechogenicity of the renal pyramids using modern ultrasound equipment.
Methods & Materials: This was a retrospective IRB approved study. An imaging database search identified newborn infants less than 8 weeks of age who underwent limited or complete abdominal imaging for non-genitourinary indications within our institution between January 1, 2022, and April 30, 2024. Subjects’ electronic charts were reviewed to record demographics and pertinent clinical information. Ultrasound imaging was reviewed independently by an experienced pediatric radiologist. Vendor of scanning machine and probe type if available, visibility of right and/or left kidney, and presence of echogenic pyramids on a scale (mild = involving less than one-third, moderate = less than two-thirds, extensive = greater than two-thirds), were recorded.
Results: 101 neonates with abdominal ultrasound images were randomly selected for preliminary chart and imaging review; 9 cases were excluded for renal diseases that were identified in the chart review; 29 cases were excluded for lack of satisfactory kidney visualization. The study population included 63 patients. All imaging was performed on GE Logiq E9 machines. 30 infants (48%) had no medullary hyperechogenicity; 33 (52%) had at least mild medullary hyperechogenicity. Hyperechogenicity of medullary pyramids inversely correlated with age (p value of 0.006). Moderate to extensive medullary echogenicity was only observed at 1 to 3 days of age; mild medullary echogenicity was observed up to 22 days of life. There was no statistically significant association between echogenic pyramids and prematurity, congenital heart disease, or type of ultrasound probe.
Conclusions: Retrospective review of ultrasounds in neonates shows that renal medullary hyperechogenicity may be observed in healthy infants for at least three weeks, longer than previously established.