What is the significance of the splenic index in clinical practice?

Significance of Splenic Index in Clinical Practice

The splenic index, calculated as the product of transverse diameter and its perpendicular diameter on ultrasound, is a valuable clinical parameter for assessing splenomegaly and serves as an important component in predicting portal hypertension, particularly when combined with liver stiffness measurements and platelet count in the LSPS score (liver stiffness × spleen size/platelet count).

Definition and Measurement

• The splenic index (SI) is calculated by multiplying the transverse diameter and its perpendicular diameter measured on the maximum cross-sectional image of the spleen using ultrasound 1
• SI correlates well with actual splenic volumes in resected specimens, making it a reliable non-invasive measurement of spleen size 1
• Alternative measurement methods include splenic length (upper limit of normal being 9.76 cm) and volumetric assessment, with normal spleen volume averaging 236.89 ± 77.58 mL 2, 3

Clinical Significance in Portal Hypertension

• Splenomegaly is related to increased splenic venous pressure due to portal hypertension, as well as fibrosis and tissue proliferation of the spleen itself 4
• The LSPS score (liver stiffness × spleen size/platelet count) is a validated tool designed by Korean researchers to predict clinically significant portal hypertension (CSPH) with high accuracy (AUC 0.92) 4
• Spleen size assessment is crucial in calculating this score, which outperforms other non-invasive parameters in identifying patients with esophageal varices and different degrees of portal hypertension 4

Role in Predicting Esophageal Varices

• Spleen size, when combined with other parameters in the LSPS score, helps predict the presence of esophageal varices, which is critical for risk stratification in cirrhotic patients 4
• Studies have shown that spleen stiffness (SS) and liver stiffness (LS) measurements are more accurate than other non-invasive parameters in identifying patients with esophageal varices 4
• The combination of spleen size assessment with platelet count provides better diagnostic performance than either parameter alone 4

Hemodynamic Assessment

• Splenic impedance indices (resistive index and pulsatility index) measured by Doppler ultrasound reflect portal vein blood flow resistance and correlate significantly with portal resistance 5
• These indices are increased in cirrhotic patients and correlate with the severity of portal hypertension 5
• Patients with large esophageal varices show higher splenic impedance indices compared to those without or with small varices 5

Utility in Various Clinical Conditions

• The splenic index is useful in evaluating spleen size in patients with liver disease, blood disorders, collagen diseases, and autoimmune conditions 1, 6
• Splenomegaly can be present in high percentages of these patients even when the spleen is not large enough to be palpable, making imaging assessment particularly valuable 1
• In hematologic disorders, particularly myeloproliferative neoplasms, accurate spleen measurement is critical for disease staging, treatment response assessment, and monitoring disease progression 7

Grading Splenomegaly

• Volumetric thresholds of 314.47 mL and 430.84 mL can be used to define mild and massive splenomegaly, respectively 3
• Grading the SI provides characteristic distributions for patients with different types of diseases, aiding in differential diagnosis 1, 6
• Automated volumetric assessment of the spleen has shown high accuracy (95.2% volume overlap) compared to manual measurements and may improve splenomegaly detection compared to traditional methods 3

Clinical Applications in Trauma

• Spleen size assessment is important in trauma settings to evaluate the extent of injury and guide management decisions 4
• In the World Society of Emergency Surgery (WSES) classification of splenic trauma, spleen size is considered when evaluating the degree of injury and determining the appropriate management approach 4

Limitations and Pitfalls

• Determination of splenic involvement is not always reliable because a spleen considered normal in size may still contain pathology, while an enlarged spleen may reflect variations in anatomy, blood volume, use of hematopoietic growth factors, or causes other than the primary suspected condition 4
• Radiologists may disagree in approximately 23% of cases when diagnosing splenomegaly by visual inspection, highlighting the importance of standardized measurements 3
• The sensitivity of radiologists in detecting mild splenomegaly (66.6%) is significantly lower than for massive splenomegaly (99.0%), emphasizing the value of objective measurements 3

Emerging Applications

• EUS-guided splenic artery embolization has been reported as a treatment for portal hypertension and hypersplenism, with post-procedure imaging showing reduction in vein diameter and improvement in cytopenias 4
• Spleen stiffness assessment is emerging as a promising non-invasive tool for predicting the presence of esophageal varices and the degree of portal hypertension in cirrhotic patients 4