V. Rendell1, A. Awe1,2, M. Lubner2, E. Winslow1 1University Of Wisconsin,Department Of Surgery,Madison, WI, USA 2University Of Wisconsin,Department Of Radiology,Madison, WI, USA
Background: Determining surveillance and treatment plans for indeterminate pancreatic cystic lesions (PCs) is challenging due to an overall lack of understanding of their natural history. Clinical guidelines use unidimensional size thresholds and growth criteria, but the correlation between cyst size and malignant potential has been variable. It is unclear if unidimensional size changes accurately capture true volumetric changes of PCs, which may better predict clinical risk. We aimed to determine if changes in maximum axial diameter (MAD) of PCs accurately reflect changes in volume.
Methods: We performed an imaging search at our institution from 2012-2013 for contrast-enhanced CT or MR scans demonstrating a PC>1cm. We selected the first and most recent scan for patients with two studies >1 year apart. Pseudocysts and solid tumors were excluded. Imaging analysis of PCs was performed using a novel analytics software, HealthMyne, to measure MAD, volume, sphericity, and surface area. To compare changes in MAD to changes in volume, the estimated change in volume over time based on MAD was calculated as follows: eΔvol = 4π(MADtime 2/2)3/3 – 4π(MADtime 1/2)3/3. The difference between measured (actual) change in volume, (Δvola = voltime2 – voltime1) and estimated change in volume was used to calculate the absolute value of the percent difference in volume change: %diffabs = ? (eΔvol – Δvola)/Δvola? x 100% . The %diffabs by high vs low PC sphericity and surface area to volume ratio (SA:V) were compared by chi-square analysis.
Results: 153 patients had two scans, an average of 4.1 years apart (SD 2.7 years). PCs had an average MAD of 2.1cm (SD 1.0cm) on the first scan, and 2.5cm (SD 1.3cm) on the last scan. In total, 9 PCs (6%) decreased in size over time. The average change in MAD per year was 1.0mm/yr (SD 2.5mm/yr) or 5.7%/year (SD 13%/yr). The PCs had an average volume of 5.3cm3 (SD 10.1cm3) on the first scan and 9.2 cm3 (SD 16.7cm3) on the last scan. The average change in volume per year was 0.88 cm3/yr (SD 2.5 cm3/yr) or 4%/yr (SD 87%/yr). For 60 (39%), the actual volume change was larger than the estimated volume change. Sixty-four PCs (42%) had a >100% absolute difference between estimated and measured volumes changes. PCs with high sphericity had significantly better concordance between estimated and actual volumes, but no significant difference was found by SA:V (Table 1).
Conclusions: For many PCs, estimating volume changes using MAD has poor concordance with actual changes in cyst volume. When following PCs over time, volumetric changes may provide better assessments of changing cyst size. The value of volumetric measurements for risk stratification of PCs is in need of further study.
