Comparison of Magnetic Resonance Imaging to Transabdominal and Transrectal Ultrasound for Sizing of the Prostate
Samuel Helrich, BS1, Nishant Garg, MD1, Wesley Pate, MD1, Philip Barbosa, MD2, Shaun Wason, MD1.
1Boston University School of Medicine, Boston, MA, 2Beth Israel Deaconess Medical Center, Boston, MA.
INTRODUCTION: Prostate size is an important factor when considering diseases of the prostate. AUA guidelines (2018) for surgical management of benign prostatic hyperplasia (BPH) now include consideration of prostate volume measurement prior to surgical intervention. Multiple imaging modalities exist to estimate size, including transabdominal pelvic ultrasound (PUS), transrectal ultrasound (TRUS), and cross-sectional imaging with computed tomography (CT) and magnetic resonance imaging (MRI). Ultrasound is a quick, inexpensive, and accessible imaging modality. MRI has been used increasingly in detection and diagnosis of prostate cancer and provides more accurate measurement of prostate size. This study seeks to compare PUS and TRUS to MRI in estimation of prostate size.
MATERIALS & METHODS: We performed a single-center, retrospective study of 95 patients with PUS, TRUS, and MRI prostate sizing between August 15, 2013 and June 20, 2017 with IRB approval. Prostate volumes were derived from ellipsoid volume calculation (length x width x height x π/6). Correlation between MRI versus TRUS and PUS was calculated through the Pearson coefficient (PC). Reliability between each of the three modalities was analyzed through intraclass correlation coefficient (ICC). Agreement was assessed using Bland-Altman (BA) analysis, which is a visual representation of how much of the data falls between clinically defined limits of agreement (LOA) that we defined as ±10 cc. Data was further stratified by numerous other variables, including prostate size.
RESULTS: A total of 95 patients had MRI, TRUS, and PUS. Median age was 64, median BMI was 27 kg/m2, and median PSA value prior to PUS was 7.1 ng/mL. Nineteen (20%) were white, 42 (44%) were black, and 21 (22%) were Hispanic. Mean difference in volume estimate between MRI and TRUS (VolTRUS - VolMRI) was (6.1 ± 15.5) cc, and mean difference in volume estimate between MRI and PUS (VolPUS - VolMRI) was (5.5 ± 16.6) cc. PC for MRI vs. TRUS and MRI vs. PUS was 0.80 and 0.74, respectively. The ICC for all three modalities was 0.90 (0.86 - 0.92). BA analysis for MRI vs PUS and MRI vs TRUS showed that for prostates ≤50cc, greater than 80% of the data fell within the LOA. These percentages decreased with increased prostate size to 39% and 42% for prostates >50cc and ≤80cc and to 25% and 61% for prostates >80cc for MRI vs PUS and MRI vs TRUS, respectively.
CONCLUSIONS: MRI may be considered clinically interchangeable with TRUS and PUS for prostate sizing at prostate volumes ≤50cc, as BA analyses showed good agreement between imaging modalities in this range. PUS and TRUS remain good tests in initial assessment of prostate size. If minor changes in prostate size would drastically alter surgical management, we would not recommend US as the sole imaging choice. It is important to note that our conclusions are based on our LOA of ±10cc, and this may vary based on clinical scenario and provider comfort. When selecting modality for prostate sizing, one should consider all factors including the benefits and drawbacks of each type of imaging.
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