10.3: Normograms for the urinary tract

Gurdarshdeep Singh Madan, Giriraj Singh, Namita Singh

1. Renal Measurement
- Antenatal
  - Appearance: Kidney should be less echogenic as compared to fetal liver and spleen. Corticomedullary differentiation is apparent at 20 weeks of gestation.
  - Renal circumference/Abdominal circumference = 0.27–0.30
  - (throughout gestation)
  - Renal pelvis: Measured on transverse image on maximum dimension of intrarenal pelvis. Renal pelvis is seen as anechoic fluid-filled structure in the centre of the renal sinus.
  - Normal measurements
    
    a) 16–27 weeks of gestation: <4 mm*
    
    b) >28 weeks of gestation: <7 mm*
  - Fetal renal lengths: Maximum long-axis measurement from upper to the lower pole, excluding adrenal glands. Approximately, it equals 4–5 fetal vertebra in length. Multiple studies have proven wide range of normalcy in the fetal renal length (See Table 10.3.1). Hence, the authors recommend labeling measurement beyond the 3SD as abnormal.
  - Antenatal renal parenchymal thickness assessment is subjective.
- Pediatric
  - Renal size: In pediatric age group, the renal length best correlates with height of the child/body surface area. Maximum long-axis distance is measured from upper pole to lower pole. The reference chart for renal length with respect to height is shown in Table 10.3.2.
  - Correlation coefficients for renal length/parenchymal width to body parameters (See Table 10.3.3)
  - Renal size and parenchymal thickness in children (See Table 10.3.4)
  - AP renal pelvis diameter (APRPD)
    
    Normal at 1 year of age is 3 mm.
    
    Normal at 18 years of age is 6 mm.
    
    99th percentile at less than 5 years of age is 10 mm.
    
    Renal assessment should be preferably done at least 48 hours after birth to prevent over-diagnosis of hydronephrosis.
    
    Appearances: Accentuated corticomedullary differentiation is normal appearance in the first 6 months. Medullary pyramids appear as hypoechoic triangles with base towards peripherally located echogenic renal cortex.
  - Normal Pediatric Renal Doppler Parameters
- Main renal artery
  - Peak systolic velocity: <180 cm/s (commonly between 60 and 100 cm/s)
  - Main renal artery–aortic ratio = <3.5:1
- Adult:
  - Renal Size
    
    The normal renal sizes (±2SD) are mentioned as table below.
  - Adult Renal Sizes on Ultrasound (in cm) (See Table 10.3.5)
    
    Renal length correlates well with height of the individual and the age. Taller individuals are likely to have renal lengths around upper limit of normal. Also, the renal size decreases with advancing age due to parenchymal reduction. They reduce at a rate of 1–2 mm per decade of life, starting from third decade till about seventh decade. Rate of reduction in renal size is more in eighth and ninth decades.
  - Renal cortical thickness is measured over the renal pyramids. It is normally > 1 cm in adults. This measurement gradually decreases with advancing age.
  - Normal Renal Doppler Parameters
- Main renal artery
  - Peak systolic velocity: <180 cm/s (commonly between 60 and 100 cm/s)
  - Main renal artery–aortic ratio = <3:1.
  - The angle of insonation during Doppler (Doppler angle) should be less than 60 degree.
- Intrarenal artery/segmental renal artery
  - RI = <0.7 (normal range between 0.55 and 0.7)
  - Low heart rates lead to reduced end diastolic flows and elevated RI. Hence, RI should be interpreted keeping the patient’s heart rate in mind.
  - Normal CT values
    
    Non-contrast renal attenuation: 33–45 HU
    
    Time to cortico-medullary equilibrium: 60 s
    
    Contrast excretion to calyceal system: 180 s
2. Criteria for Polycystic Kidney Disease
- Ultrasound Diagnostic Criteria for Autosomal Dominant Polycystic Kidney Disease1 (ADPKD1)
  - • At least two renal cysts (unilateral or bilateral) in an at-risk patient younger than 30 years
  - • At least two cysts in each kidney in an at-risk patient aged 30–59 years
  - • At least four cysts in each kidney in an at-risk patient aged >60 years
- Ultrasound Diagnostic Criteria for ADPKD in Patients with a Family History but Unknown Genotype
  - • Three or more (unilateral or bilateral) renal cysts in patients aged 15–39 years
  - • Two or more cysts in each kidney in patients aged 30–59 years
  - • At least four cysts in each kidney in an at-risk patient aged > 60 years
  - • Less than two renal cysts in at-risk individuals >40 years of age is sufficient to exclude the disease.
3. Criteria for Multicystic Renal Dysplasia: The following ultrasound criteria were described for reliable diagnosis of multicystic renal dysplasia. The first three have a sensitivity of 100%.
- • The presence of interfaces between cysts
- • Non-medial location of the largest cyst
- • Absence of an identifiable renal sinus
- • Multiplicity of oval or round cysts that do not communicate
- • Absence of parenchymal tissue.
4. CT Angiography of Renal Arteries
- Main renal artery originates from the lateral aspect of the abdominal aorta at the L1–2 level. The main renal artery splits into two to four branches at renal hilum.

Normal Range of Fetal Renal Lengths

Gestational Age (in weeks)	Right Kidney (±2SD) (in mm)	Left Kidney (±2SD) (in mm)	Right Kidney (±3SD) (in mm)	Left Kidney (±3SD) (in mm)	Mean Renal Length (±2SD) (in mm)
18					16–28
19					15–31
20	18.9–22.5	19.84–22.24	18–23.4	19.24–22.84	18–34
21	20.0–21.7	20.15–21.95	19.57–22.15	19.7–22.4	21–32
22	20.9–23.3	21.57–23.41	20.26–23.86	21.11–23.87	20–34
23	21.9–25.3	21.73–26.25	21.04–26.14	20.6–27.38	22–37
24	22.4–27.9	21.73–26.25	21.05–29.21	20.6–27.38	19–44
25	23.3–28.4	23.25–28.97	21.99–29.67	21.82–30.4	25–42
26	25.6–28.2	26.62–29.46	24.89–28.91	25.91–30.17	24–44
27	24.8–29.9	25.59–29.95	23.47–31.15	24.5–31.04	27–44
28	28.1–30.6	28.08–31.04	27.5–31.22	27.34–31.78	26–42
29	28.1–31.9	28.31–33.07	27.12–32.88	27.12–34.26	23–48
30	29.8–33.4	30.53–33.61	28.92–34.26	29.76–34.38	29–46
31	29.7–33.6	29.94–34.22	28.69–34.63	28.87–35.29	28–46
32	31.6–35.5	31.65–35.73	30.6–36.42	30.63–36.75	31–51
33	31.45–36.81	31.88–37.08	30.11–38.15	30.58–38.38	33–47
34	33.24–36.6	33.17–37.25	32.4–37.44	32.15–38.27	33–50
35	33.08–38.44	33.64–38.28	31.74–39.78	32.48–39.44	32–52
36	34.44–38.6	35.14–39.26	33.4–39.64	34.11–40.29	33–50
37	35.33–40.97	36.05–40.37	33.92–42.38	34.97–41.45	33–51
38	36.3–40.86	36.66–41.26	35.16–42	35.51–42.41	32–56
39	37.07–41.63	37.61–41.29	35.93–42.77	36.69–42.21	35–48
40	38.44–41.16	37.33–44.33	37.76–41.84	35.58–46.08	32–53
41	39.54–42.06	40.5–43.54	38.91–42.69	39.74–44.3	39–51