Transient echogenicity of neonatal renal papillae: updating normal age range with current ultrasound technology

Author

Lu Mao

Published

January 19, 2025

Statistical analysis

Categorical variables are summarized using counts and percentages. Continuous variables are summarized using means and standard deviations. The distributions of factors like age of patient, prematurity, congenital heart disease, and ultrasound probe are summarized by degree of severity of echogenicity (right, left, and overall). The relationship between these factors and echogenicity is assessed using linear trend tests or Fisher exact tests. Statistical significance is defined as a two-sided p-value < 0.05. All analyses are performed using R version 4.1.1.

Patient characteristics

The study population included 101 patients. Their characteristics are summarized in Table 1. Overall echogenicity is defined as the maximum degree of severity between the right and left renal pyramids.

Table 1: Characteristics of the study population.
Characteristic Female, N = 381 Male, N = 631 Overall, N = 1011
Race


    White 30 (79%) 49 (80%) 79 (80%)
    Black 2 (5.3%) 5 (8.2%) 7 (7.1%)
    Hispanic/Latino 3 (7.9%) 4 (6.6%) 7 (7.1%)
    Asian 2 (5.3%) 2 (3.3%) 4 (4.0%)
    Other 1 (2.6%) 1 (1.6%) 2 (2.0%)
    Unknown 0 2 2
Ethnicity


    Not Hispanic/Latino 34 (89%) 52 (83%) 86 (85%)
    Hispanic/Latino 4 (11%) 11 (17%) 15 (15%)
Prematurity 10 (26%) 14 (22%) 24 (24%)
Age of patient (days) 4 (2, 28) 3 (1, 20) 3 (1, 24)
Echogenicity (right)


    None 33 (87%) 48 (76%) 81 (80%)
    Mild 3 (7.9%) 8 (13%) 11 (11%)
    Moderate 1 (2.6%) 4 (6.3%) 5 (5.0%)
    Severe 1 (2.6%) 3 (4.8%) 4 (4.0%)
Echogenicity (left)


    None 26 (81%) 31 (70%) 57 (75%)
    Mild 4 (13%) 7 (16%) 11 (14%)
    Moderate 1 (3.1%) 3 (6.8%) 4 (5.3%)
    Severe 1 (3.1%) 3 (6.8%) 4 (5.3%)
    Unknown 6 19 25
Echogenicity (overall)


    None 31 (82%) 46 (73%) 77 (76%)
    Mild 5 (13%) 10 (16%) 15 (15%)
    Moderate 1 (2.6%) 4 (6.3%) 5 (5.0%)
    Severe 1 (2.6%) 3 (4.8%) 4 (4.0%)
Ultrasound probe


    9L 5 (14%) 13 (22%) 18 (19%)
    C2-9 0 (0%) 1 (1.7%) 1 (1.1%)
    C3-10 0 (0%) 1 (1.7%) 1 (1.1%)
    L2-9 3 (8.6%) 2 (3.4%) 5 (5.3%)
    L8-18i 1 (2.9%) 0 (0%) 1 (1.1%)
    LA2-14A 1 (2.9%) 0 (0%) 1 (1.1%)
    M6-15 1 (2.9%) 0 (0%) 1 (1.1%)
    ML4-20 3 (8.6%) 0 (0%) 3 (3.2%)
    ML6-15 20 (57%) 41 (69%) 61 (65%)
    S4-10 1 (2.9%) 1 (1.7%) 2 (2.1%)
    Unknown 3 4 7
Congenital heart disease 14 (37%) 14 (22%) 28 (28%)
Exam type


    US Abdomen Complete 27 (71%) 40 (63%) 67 (66%)
    US Abdomen - RUQ 5 (13%) 17 (27%) 22 (22%)
    Other 6 (16%) 6 (9.5%) 12 (12%)
Follow-up ultrasound 10 (26%) 15 (24%) 25 (25%)
Echogenicity at follow-up


    No 8 (80%) 11 (73%) 19 (76%)
    Mild 2 (20%) 2 (13%) 4 (16%)
    Moderate 0 (0%) 2 (13%) 2 (8.0%)
    Unknown 28 48 76
1 n (%); Median (IQR)

Factors correlated with echogenicity

The distributions of factors like age of patient, prematurity, congenital heart disease, and ultrasound probe are summarized by degree of severity of echogenicity (right, left, and overall) in Table 2.

Table 2: Predictors of echogenicity of renal pyramids.
Overall
Characteristic1 None, N = 771 Mild, N = 151 Moderate, N = 51 Severe, N = 41 p-value1
Age of patient (days) 4 (1, 27) 2 (1, 17) 1 (1, 1) 2 (2, 2) 0.019
Prematurity 20 (26%) 4 (27%) 0 (0%) 0 (0%) 0.2
Congenital heart disease 25 (32%) 1 (6.7%) 2 (40%) 0 (0%) 0.14
Ultrasound probe



0.8
    9L 16 (23%) 1 (6.7%) 1 (20%) 0 (0%)
    C2-9 1 (1.4%) 0 (0%) 0 (0%) 0 (0%)
    C3-10 1 (1.4%) 0 (0%) 0 (0%) 0 (0%)
    L2-9 3 (4.3%) 2 (13%) 0 (0%) 0 (0%)
    L8-18i 1 (1.4%) 0 (0%) 0 (0%) 0 (0%)
    LA2-14A 1 (1.4%) 0 (0%) 0 (0%) 0 (0%)
    M6-15 1 (1.4%) 0 (0%) 0 (0%) 0 (0%)
    ML4-20 2 (2.9%) 0 (0%) 1 (20%) 0 (0%)
    ML6-15 42 (60%) 12 (80%) 3 (60%) 4 (100%)
    S4-10 2 (2.9%) 0 (0%) 0 (0%) 0 (0%)
    Unknown 7 0 0 0
1 Linear trend test or Fisher exact test.
Right
Characteristic1 None, N = 811 Mild, N = 111 Moderate, N = 51 Severe, N = 41 p-value1
Age of patient (days) 4 (1, 26) 3 (2, 24) 1 (1, 1) 2 (2, 2) 0.039
Prematurity 22 (27%) 2 (18%) 0 (0%) 0 (0%) 0.11
Congenital heart disease 25 (31%) 1 (9.1%) 2 (40%) 0 (0%) 0.2
Ultrasound probe



>0.9
    9L 16 (22%) 1 (9.1%) 1 (20%) 0 (0%)
    C2-9 1 (1.4%) 0 (0%) 0 (0%) 0 (0%)
    C3-10 1 (1.4%) 0 (0%) 0 (0%) 0 (0%)
    L2-9 4 (5.4%) 1 (9.1%) 0 (0%) 0 (0%)
    L8-18i 1 (1.4%) 0 (0%) 0 (0%) 0 (0%)
    LA2-14A 1 (1.4%) 0 (0%) 0 (0%) 0 (0%)
    M6-15 1 (1.4%) 0 (0%) 0 (0%) 0 (0%)
    ML4-20 2 (2.7%) 0 (0%) 1 (20%) 0 (0%)
    ML6-15 45 (61%) 9 (82%) 3 (60%) 4 (100%)
    S4-10 2 (2.7%) 0 (0%) 0 (0%) 0 (0%)
    Unknown 7 0 0 0
1 Linear trend test or Fisher exact test.
Left
Characteristic1 None, N = 571 Mild, N = 111 Moderate, N = 41 Severe, N = 41 p-value1
Age of patient (days) 3 (1, 21) 2 (1, 8) 1 (1, 2) 2 (2, 2) 0.038
Prematurity 16 (28%) 4 (36%) 0 (0%) 0 (0%) 0.2
Congenital heart disease 25 (44%) 1 (9.1%) 2 (50%) 0 (0%) 0.081
Ultrasound probe



0.7
    9L 12 (23%) 1 (9.1%) 1 (25%) 0 (0%)
    C2-9 1 (1.9%) 0 (0%) 0 (0%) 0 (0%)
    C3-10 1 (1.9%) 0 (0%) 0 (0%) 0 (0%)
    L2-9 3 (5.8%) 2 (18%) 0 (0%) 0 (0%)
    LA2-14A 1 (1.9%) 0 (0%) 0 (0%) 0 (0%)
    ML4-20 1 (1.9%) 0 (0%) 1 (25%) 0 (0%)
    ML6-15 31 (60%) 8 (73%) 2 (50%) 4 (100%)
    S4-10 2 (3.8%) 0 (0%) 0 (0%) 0 (0%)
    Unknown 5 0 0 0
1 Linear trend test or Fisher exact test.

It is clear that the degree of echogenic renal pyramids (each side and overall) is negatively correlated with patient age. The boxplots of patient age by echogenicity of renal pyramids are shown in Figure 1.

Figure 1: Boxplots of patient age by echogenicity of renal pyramids
Figure 2: Frequency plot of echogenic pyramids according to age prematurity.