What is the normal splenic index on ultrasonography for adults and the age‑specific normal ranges in children?

Normal Splenic Index on Ultrasonography

The normal splenic index (calculated as length × width × thickness × 0.523) is ≤480 cm³ in adults, with a coronal oblique length cutoff of <12 cm being highly sensitive for excluding splenomegaly. 1

Adult Normal Values

Single Linear Measurements

• Splenic length: Upper limit of normal is 11 cm in 95% of healthy adults 2
• Splenic width: Upper limit of normal is 7 cm in 95% of healthy adults 2
• Splenic thickness: Upper limit of normal is 5 cm in 95% of healthy adults 2
• Calculated weight via rotation ellipsoid formula: <190 g in 95% of patients 2

Splenic Index Calculation

• The splenic index uses the formula: length × width × thickness × 0.523 3
• Normal splenic index: ≤480 cm³ 1
• Craniocaudal length >9.5 cm and width >10.6 cm suggest splenomegaly when used as single cutoff values 1

Optimal Measurement Technique

• Right lateral decubitus (RLD) position provides the most accurate correlation with true splenic volume 4
• Splenic width measured on longitudinal section in RLD position shows the strongest correlation with CT volume (r=0.89) 4
• Splenic length in RLD position also correlates well with CT volume (r=0.86) 4

Pediatric Age-Specific Normal Ranges

Upper limits of normal splenic length by age (measured as greatest longitudinal distance from dome to tip at the hilum in coronal plane): 5

Infants

• 3 months: ≤6.0 cm 5
• 6 months: ≤6.5 cm 5
• 12 months: ≤7.0 cm 5

Children

• 2 years: ≤8.0 cm 5
• 4 years: ≤9.0 cm 5
• 6 years: ≤9.5 cm 5
• 8 years: ≤10.0 cm 5
• 10 years: ≤11.0 cm 5
• 12 years: ≤11.5 cm 5

Adolescents and Young Adults

• 15+ years (girls): ≤12.0 cm 5
• 15+ years (boys): ≤13.0 cm 5

Clinical Application and Pitfalls

Diagnostic Accuracy Considerations

• Coronal oblique length ≥12 cm has 97.8% sensitivity but only 34.1% specificity for splenomegaly, with 91% positive predictive value 1
• Splenic index is the most reliable measurement for diagnosing splenomegaly, superior to single linear measurements 1
• Three-dimensional ultrasonography provides improved accuracy over traditional two-dimensional techniques for irregularly shaped spleens 3

Important Caveats

• Two-dimensional sonographic estimations consistently overestimate splenic volumes compared to three-dimensional measurements 3
• Physical examination has limitations in obese patients where palpation and percussion are less reliable 6
• When ultrasound findings are equivocal, contrast-enhanced CT is the gold standard for definitive splenic assessment 6