Purpose or Case Report: Nutcracker syndrome (NCS) results from left renal vein (LRV) compression, typically between the abdominal aorta and superior mesenteric artery. The use of ultrasonography (US) to aid in diagnosis can be challenging due to the dynamic nature of the nutcracker phenomenon (NCP) and variability of symptoms, which can fluctuate with changes in patient posture and respiration. Moreover, defining a reliable Doppler threshold in children remains underexplored. This study explores the added utility of Doppler peak systolic velocity (PSV) ratio to LRV diameters in the evaluation of suspected NCS.
Methods & Materials: All US studies performed for suspected NCS between Nov 2024- Sep 2025 were retrospectively reviewed. LRV diameters and PSV was measured at the renal hilum (H) and aortomesenteric level (AM), with the diameter (H/AM) and PSV ratios (AM/H) calculated. Both ratios were dichotomized at pre-specified thresholds of ≥5:1 to define a “positive” test for NCP, with clinical diagnosis also serving as reference standard. Diagnostic performance was evaluated using standard matrices, including area under the receiver-operating-characteristics curve (AUROC). Secondary outcomes included agreement between both ratios.
Results: Of 41 children (mean age 11.8 years, range 1.4-18.9 years), 22 (53.6%) were clinically diagnosed with NCS whilst 10 (24.4%) were indeterminate for NCS. The mean diameter and PSV ratios for children were 4.93 (range 1.31-11.0) and 3.65 (range 0.78-15.3) respectively (p=0.002). The AUROC of diameter and PSV ratios were 0.613 (95% CI 0.39–0.84) and 0.652 (95% CI 0.46–0.85) respectively, with no significant difference (p=0.80). PSV≥5:1 yielded 68.3% diagnostic accuracy, 40.9% sensitivity and 100% specificity, while LRV diameter≥5:1 achieved 63.4% diagnostic accuracy, 63.6% sensitivity and 63.2% specificity. When combined, both ratios achieved 74.1% diagnostic accuracy, 53.3% sensitivity and 100% specificity. Both ratios showed high positive correlation (Spearman’s r=0.54, p<0.001).
Conclusions: While the individual performance of LRV diameter and PSV ratios was modest, incorporating both parameters improved overall diagnostic accuracy and specificity, underscoring their complementary value. The addition of PSV ratio to standard diameter assessment enhances confidence in non-invasive diagnosis and may reduce reliance on CT or MR venography. Larger, prospective studies are warranted to refine pediatric-specific Doppler thresholds and validate combined criteria for clinical use.