Targeted biopsy of the prostate.

Diagnostic multiparametric MRI of the prostate has steadily evolved over the last three decades and can now reliably depict the dominant tumor in most men with prostate cancer. In response, several methods of targeted biopsy to direct tissue sampling of suspected tumor foci seen at multiparametric MRI have been developed and successfully tested in recent years, including software-assisted MRI-ultrasound (US) fusion biopsy and direct MRI-guided in-bore biopsy. These advances are leading to a sea change in the approach to prostate cancer diagnosis, with the traditional approach of blind systematic biopsy increasingly being replaced by MRI directed targeted biopsy. This review aims to describe the current status of targeted biopsy, with an emphasis on the relative accuracy of different techniques. The results of several critical large multicenter trials are presented, while unanswered questions that require more research are highlighted.

Prototype Description and Ex Vivo Evaluation of a System for Combined Endorectal Magnetic Resonance Imaging and In-Bore Biopsy of the Prostate.

ABSTRACT: We describe early ex vivo proof-of-concept testing of a novel system composed of a disposable endorectal coil and converging multichannel needle guide with a reusable clamp stand, embedded electronics, and baseplate to allow for endorectal magnetic resonance (MR) imaging and in-bore MRI-targeted biopsy of the prostate as a single integrated procedure. Using prostate phantoms imaged with standard T 2 -weighted sequences in a Siemens 3T Prisma MR scanner, we measured the signal-to-noise ratio in successive 1-cm distances from the novel coil and from a commercially available inflatable balloon coil and measured the lateral and longitudinal deviation of the tip of a deployed MR compatible needle from the intended target point. Signal-to-noise ratio obtained with the novel system was significantly better than the inflatable balloon coil at each of five 1-cm intervals, with a mean improvement of 78% ( P < 0.05). In a representative sampling of 15 guidance channels, the mean lateral deviation for MR imaging-guided needle positioning was 1.7 mm and the mean longitudinal deviation was 2.0 mm. Our ex vivo results suggest that our novel system provides significantly improved signal-to-noise ratio when compared with an inflatable balloon coil and is capable of accurate MRI-guided needle deployment.

Metabolic activity diffusion imaging (MADI): II. Noninvasive, high-resolution human brain mapping of sodium pump flux and cell metrics.

We introduce a new 1 H2 O magnetic resonance approach: metabolic activity diffusion imaging (MADI). Numerical diffusion-weighted imaging decay simulations characterized by the mean cellular water efflux (unidirectional) rate constant (kio ), mean cell volume (V), and cell number density (ρ) are produced from Monte Carlo random walks in virtual stochastically sized/shaped cell ensembles. Because of active steady-state trans-membrane water cycling (AWC), kio reflects the cytolemmal Na+ , K+ ATPase (NKA) homeostatic cellular metabolic rate (c MRNKA ). A digital 3D "library" contains thousands of simulated single diffusion-encoded (SDE) decays. Library entries match well with disparate, animal, and human experimental SDE decays. The V and ρ values are consistent with estimates from pertinent in vitro cytometric and ex vivo histopathological literature: in vivo V and ρ values were previously unavailable. The library allows noniterative pixel-by-pixel experimental SDE decay library matchings that can be used to advantage. They yield proof-of-concept MADI parametric mappings of the awake, resting human brain. These reflect the tissue morphology seen in conventional MRI. While V is larger in gray matter (GM) than in white matter (WM), the reverse is true for ρ. Many brain structures have kio values too large for current, invasive methods. For example, the median WM kio is 22s-1 ; likely reflecting mostly exchange within myelin. The kio •V product map displays brain tissue c MRNKA variation. The GM activity correlates, quantitatively and qualitatively, with the analogous resting-state brain 18 FDG-PET tissue glucose consumption rate (t MRglucose ) map; but noninvasively, with higher spatial resolution, and no pharmacokinetic requirement. The cortex, thalamus, putamen, and caudate exhibit elevated metabolic activity. MADI accuracy and precision are assessed. The results are contextualized with literature overall homeostatic brain glucose consumption and ATP production/consumption measures. The MADI/PET results suggest different GM and WM metabolic pathways. Preliminary human prostate results are also presented.

Intermediate-term oncological outcomes after a negative endorectal coil multiparametric MRI of the prostate in patients without biopsy proven prostate cancer.

PURPOSE: Investigate the intermediate-term oncological outcome after negative multiparametric MRI (mpMRI) of the prostate in patients without biopsy proven prostate cancer (PCa). METHODS: The retrospective study included 121 patients with negative mpMRI (Prostate Imaging Reporting and Data System version 2.1 category<3) performed at our institution between 2012 and 2017 without known biopsy proven PCa. Clinical and pathological data were collated including post-MRI prostatic tissue diagnoses with highest Grade Group and most recent prostate specific antigen (PSA) levels up to any definitive prostate cancer treatment. Mean PSA velocities between patients with and without a subsequent diagnosis of Grade Group 2 or higher (GG2+) PCa were compared, and an optimal threshold value was calculated. RESULTS: Outcome data available included PSA values in 117 patients and prostate tissue sampling in 52 patients. Over a median follow up interval of 49.8 months, only 11 of 121 patients (9.1%) were diagnosed with GG2+ PCa, 10 patients (8.3%) with GG1 PCa, and 31 patients (25.6%) had negative prostate tissue samples. Mean PSA velocity was significantly higher in the patients diagnosed with GG2+ PCa (3.87 ng/mL/year) compared to those not diagnosed with GG2+ PCa (-0.71 ng/mL/year, p < 0.001). A threshold PSA velocity of 0.27 ng/mL/year had a 100% sensitivity and 69.8% specificity for GG2+ PCa (AUC: 0.898). CONCLUSION: <10% of patients with negative mpMRI without prior biopsy proven PCa were diagnosed with GG2+ PCa over median follow up of over four years and were associated with PSA velocity of ≥0.27 ng/mL/year. PSA monitoring may be a reasonable management strategy in patients with a negative mpMRI without biopsy proven PCa.

MRI appearance of BRCA-associated prostate cancer.

Despite advances in diagnosis and treatment, prostate cancer remains the second leading cause of cancer related mortality in men. Prognosis is variable and dependent on several clinical and genetic factors, including BRCA gene mutations. Recent clinical studies have reported that BRCA-associated prostate cancer is a more aggressive subtype with a higher probability of nodal involvement and distant metastases at the time of diagnosis, but radiological findings have not been described. Accurate recognition of those tumors could help guide clinical management and prompt testing and counseling for BRCA mutations. We have recently encountered four patients with BRCA-associated prostate cancer who underwent multiparametric MRI. The MRI appearances of these tumors, which were generally locally advanced and aggressive in appearance, are presented to facilitate recognition of BRCA-associated prostate cancer and guide potential genetic testing and counseling.

Cowper's gland hyperplasia: A potential pitfall at MRI of the prostate.

MRI features are presented in a multicenter retrospective series of five patients with a unilateral masslike lesion seen in the genitourinary diaphragm at MRI performed for known or suspected prostate cancer. In all cases, the lesion appeared as an encapsulated 1.3 to 3.0 cm mass of heterogeneous low or intermediate T2 signal intensity in the genitourinary diaphragm, and targeted biopsy demonstrated benign Cowper's gland tissue. This entity is a potential imaging pitfall that could result in a diagnosis of an exophytic nodule of benign prostatic hyperplasia or local spread of prostate cancer. We present these cases to facilitate correct identification of Cowper's gland hyperplasia as an occasional finding at MRI of the prostate.

Performance of transgluteal CT-guided biopsy of prostate lesions in men without rectal access: A retrospective study.

OBJECTIVE: To retrospectively study the performance of CT-guided biopsy of target prostate lesions at a single institution. METHODS: Between May 2016 and February 2021, we retrospectively identified all men without rectal access who underwent transgluteal CT-guided biopsy of PIRADS 4 or 5 targets detected on multiparametric MRI (n = 9). Clinical, radiological, and pathological details were collected by review of the electronic medical record, and included age, pre-biopsy prostate specific antigen (PSA) value, prior biopsy history, biopsy targeting technique and procedural details, complications, and final histologic diagnosis. Two targeting techniques were used: Localizing with anatomic landmarks or localizing with contrast enhancement. RESULTS: Mean patient age was 69 years (range, 49-74) and mean PSA was 14.6 ng/mL (range 7-23). Four lesions were targeted using anatomic landmarks and 5 were targeted using contrast enhancement. All biopsies were technically successful and all resulted as prostate cancer. Three biopsies showed Gleason 6 cancer and 6 biopsies showed clinically significant prostate cancers with Gleason 7 or above. There were no major complications. 7 patients went on to definitive treatment with surgery or radiation. CONCLUSION: Transgluteal CT-guided biopsy of MRI detected prostate lesions diagnoses clinically significant prostate cancer without complication and therefore should be considered for patients without a rectum.

In-Bore Versus Fusion MRI-Targeted Biopsy of PI-RADS Category 4 and 5 Lesions: A Retrospective Comparative Analysis Using Propensity Score Weighting.

BACKGROUND. Few published studies have compared in-bore and fusion MRI-targeted prostate biopsy, and the available studies have had conflicting results. OBJECTIVE. The purpose of this study was to compare the target-specific cancer detection rate of in-bore prostate biopsy with that of fusion MRI-targeted biopsy. METHODS. The records of men who underwent in-bore or fusion MRI-targeted biopsy of PI-RADS category 4 or 5 lesions between August 2013 and September 2019 were retrospectively identified. PI-RADS version 2.1 assessment category, size, and location of each target were established by retrospective review by a single experienced radiologist. Patient history and target biopsy results were obtained by electronic medical record review. Only the first MRI-targeted biopsy of the dominant lesion was included for patients with repeated biopsies or multiple targets. In-bore and fusion biopsy were compared by propensity score weights and multivariable regression to adjust for imbalances in patient and target characteristics between biopsy techniques. The primary endpoint was target-specific prostate cancer detection rate. Secondary endpoints were detection rate after application of propensity score weighting for cancers in International Society of Urological Pathology (ISUP) grade group 2 (GG2) or higher and detection rate with the use of off-target systematic sampling results. RESULTS. The study sample included 286 men (in-bore biopsy, 191; fusion biopsy, 95). Compared with fusion biopsy, in-bore biopsy was associated with significantly greater likelihood of detection of any cancer (odds ratio, 2.28 [95% CI, 1.04-4.98]; p = .04) and nonsignificantly greater likelihood of detection of ISUP GG2 or higher cancer (odds ratio, 1.57 [95% CI, 0.88-2.79]; p = .12) in a target. When off-target sampling was included, in-bore biopsy and combined fusion and systematic biopsy were not different for detection of any cancer (odds ratio, 1.16 [95% CI, 0.54-2.45]; p = .71) or ISUP GG2 and higher cancer (odds ratio, 1.15 [95% CI, 0.66-2.01]; p = .62). CONCLUSION. In this retrospective study in which propensity score weighting was used, in-bore MRI-targeted prostate biopsy had a higher target-specific cancer detection rate than did fusion biopsy. CLINICAL IMPACT. Pending a larger prospective randomized multicenter comparison between in-bore and fusion biopsy, in-bore may be the preferred approach should performing only biopsy of a suspicious target, without concurrent systematic biopsy, be considered clinically appropriate.

MRI of prostatic urethral mucinous urothelial carcinoma: Expanding the differential diagnosis for T2 hyperintense prostatic masses.

We report the case of a 66-year-old previously healthy man presenting with blood and mucus in his urine. Cystoscopy revealed a mass in the prostatic urethra, and endoscopic biopsy showed adenocarcinoma in situ with mucinous features. Endorectal multiparametric prostate MRI demonstrated a 1.9 cm T2 hyperintense mass in the peripheral zone of the left prostatic apex with extension into the urethral lumen. No diffusion restriction or early enhancement was seen in the mass. Radical prostatectomy was performed, and final pathology demonstrated a mucin-producing urothelial adenocarcinoma arising from the prostatic urethra. The peripheral zone T2 hyperintense abnormality correlated with abundant pools of mucin extending into the prostatic stroma and surrounded by neoplastic prostatic glandular cells. We conclude prostatic urethral mucinous urothelial carcinoma should be included in the differential diagnosis for T2 hyperintense prostatic masses.

Variability of the Positive Predictive Value of PI-RADS for Prostate MRI across 26 Centers: Experience of the Society of Abdominal Radiology Prostate Cancer Disease-focused Panel.

Background Prostate MRI is used widely in clinical care for guiding tissue sampling, active surveillance, and staging. The Prostate Imaging Reporting and Data System (PI-RADS) helps provide a standardized probabilistic approach for identifying clinically significant prostate cancer. Despite widespread use, the variability in performance of prostate MRI across practices remains unknown. Purpose To estimate the positive predictive value (PPV) of PI-RADS for the detection of high-grade prostate cancer across imaging centers. Materials and Methods This retrospective cross-sectional study was compliant with the HIPAA. Twenty-six centers with members in the Society of Abdominal Radiology Prostate Cancer Disease-focused Panel submitted data from men with suspected or biopsy-proven untreated prostate cancer. MRI scans were obtained between January 2015 and April 2018. This was followed with targeted biopsy. Only men with at least one MRI lesion assigned a PI-RADS score of 2-5 were included. Outcome was prostate cancer with Gleason score (GS) greater than or equal to 3+4 (International Society of Urological Pathology grade group ≥2). A mixed-model logistic regression with institution and individuals as random effects was used to estimate overall PPVs. The variability of observed PPV of PI-RADS across imaging centers was described by using the median and interquartile range. Results The authors evaluated 3449 men (mean age, 65 years ± 8 [standard deviation]) with 5082 lesions. Biopsy results showed 1698 cancers with GS greater than or equal to 3+4 (International Society of Urological Pathology grade group ≥2) in 2082 men. Across all centers, the estimated PPV was 35% (95% confidence interval [CI]: 27%, 43%) for a PI-RADS score greater than or equal to 3 and 49% (95% CI: 40%, 58%) for a PI-RADS score greater than or equal to 4. The interquartile ranges of PPV at these same PI-RADS score thresholds were 27%-44% and 27%-48%, respectively. Conclusion The positive predictive value of the Prostate Imaging and Reporting Data System was low and varied widely across centers. © RSNA, 2020 Online supplemental material is available for this article. See also the editorial by Milot in this issue.

Impact of Direct MRI-Guided Biopsy of the Prostate on Clinical Management.

OBJECTIVE. The purpose of this study is to investigate the impact of direct MRI-guided biopsy of the prostate on clinical management in practice. MATERIALS AND METHODS. We retrospectively identified 127 patients with unknown (n = 98) or untreated prostate cancer with a Gleason score of 6 (n = 29) who underwent direct MRI-guided biopsy of the prostate at our institution between August 2013 and January 2018, after initial multiparametric endorectal MRI examination revealed one or more Prostate Imaging Reporting and Data System (PI-RADS or PI-RADSv2) category 4 or 5 target lesion. All available medical and imaging records were reviewed to determine pertinent clinical details, biopsy findings, and postbiopsy management. RESULTS. The mean patient age was 68 years (interquartile range, 63-73 years). Findings from MRI-guided biopsy were positive for 93 of 127 patients (73%), with prostate cancer of Gleason score of 7 or higher diagnosed in 84 of these 93 patients (90%). When stratified by clinical scenario, the rate of positive biopsy findings was 66% (57/86) for patients who had negative findings from one or more prior transrectal ultrasound-guided biopsies, 83% (10/12) for biopsy-naive patients, and 90% (26/29) for patients undergoing active surveillance. Overall, 90 of 127 patients (71%) received a new (n = 67) or upgraded (n = 23) diagnosis of prostate cancer, and 57 of these 90 patients (63%) proceeded to receive treatment with prostatectomy, radiation, or androgen deprivation therapy. CONCLUSION. The results of this study suggest that direct MRI-guided biopsy is associated with high rates of significant prostate cancer detection and subsequent definitive treatment across common clinical scenarios and should be considered an important supplementary diagnostic tool in the appropriate setting.

MRI of prolapsed polypoid adenomyoma: Expanding the differential diagnosis for the broccoli sign.

We report a 44 year old previously healthy premenopausal woman who presented with a three month history of vaginal bleeding and a 5 cm vaginal mass obscuring the cervix on physical examination. Ultrasound evaluation was non diagnostic. Pelvic MRI demonstrated a 6 cm soft tissue mass in the vagina prolapsed from the uterine cavity with a visible connecting stalk, which is termed the broccoli sign. The initial radiological differential diagnosis included prolapsed uterine malignancy or leiomyoma. Surgical pathology revealed a polypoid adenomyoma. We conclude polypoid adenomyoma should be included in the differential diagnosis for prolapsed uterine tumor demonstrating the broccoli sign.

Dominant intraprostatic cancer confirmed by direct MRI-guided biopsy: Concordance with histopathological findings.

PURPOSE: To investigate the concordance between dominant intraprostatic cancer seen on endorectal multiparametric MRI and confirmed by MRI-targeted biopsy with histopathological findings at radical prostatectomy, since existing literature has emphasized the miss rather than the concordance rate of MRI. MATERIALS AND METHODS: We retrospectively identified 20 patients who underwent radical prostatectomy after a dominant intraprostatic cancer focus was identified at endorectal multiparametric MRI and confirmed by MRI-targeted biopsy. Concordance was determined by comparing the location and Gleason grade group of dominant tumor at MRI with the location and Gleason grade group determined at histopathological review. RESULTS: Mean patient age was 65 years (range, 48 to 76) and median serum prostatic specific antigen level was 9.4 ng/mL (range, 4.6 to 58.0). In all 20 patients, the location of dominant tumor based on MRI and targeted biopsy corresponded with the dominant tumor location at histopathology. In 9 patients, Gleason grade group was the same at targeted biopsy and final histopathology. In 9 patients, final Gleason grade group was higher and in two patients it was lower. CONCLUSION: Our preliminary results suggest dominant tumor as determined by endorectal multiparametric MRI and confirmed by a positive MRI-targeted biopsy has high concordance with histopathological findings at radical prostatectomy for location, and reasonable concordance for Gleason grade group.

ACR Appropriateness Criteria® Pretreatment Staging of Muscle-Invasive Bladder Cancer.

Muscle-invasive bladder cancer (MIBC) has a tendency toward urothelial multifocality and is at risk for local and distant spread, most commonly to the lymph nodes, bone, lung, liver, and peritoneum. Pretreatment staging of MIBC should include imaging of the urothelial upper tract for synchronous lesions; imaging of the chest, abdomen, and pelvis for metastases; and MRI pelvis for local staging. CT abdomen and pelvis without and with contrast (CT urogram) is recommended to assess the urothelium and abdominopelvic organs. Pelvic MRI can improve local bladder staging accuracy. Chest imaging is also recommended with chest radiograph usually being adequate. FDG-PET/CT may be appropriate to identify nodal and metastatic disease. Chest CT may be useful in high-risk patients and those with findings on chest radiograph. Nonurogram CT and MRI of the abdomen and pelvis are usually not appropriate, and neither is radiographic intravenous urography, Tc-99m whole body bone scan, nor bladder ultrasound for pretreatment staging of MIBC. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

ACR Appropriateness Criteria® Post-treatment Follow-up Prostate Cancer.

Diagnosis and management of prostate cancer post treatment is a large and complex problem, and care of these patients requires multidisciplinary involvement of imaging, medical, and surgical specialties. Imaging capabilities for evaluation of men with recurrent prostate cancer are rapidly evolving, particularly with PET and MRI. At the same time, treatment options and capabilities are expanding and improving. These recommendations separate patients into three broad categories: (1) patients status post-radical prostatectomy, (2) clinical concern for residual or recurrent disease after nonsurgical local and pelvic treatments, and (3) metastatic prostate. This article is a review of the current literature regarding imaging in these settings and the resulting recommendations for imaging. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Case series of collapsed simple renal cysts potentially simulating cystic malignancy at CT.

The radiological differential diagnosis for complex renal cysts seen at CT generally includes cystic malignancy or renal abscess. We have encountered five cases of complex-appearing renal cysts at CT where serial imaging and clinical outcome favored a diagnosis of a collapsed benign simple renal cyst. We present these cases to broaden the differential diagnosis for complex renal cysts seen at CT, highlighting the importance of careful correlation with prior imaging to assist in correct recognition of collapsed simple cysts and potentially allowing for conservative management or surveillance.

Endorectal MR imaging of prostate cancer: Evaluation of tumor capsular contact length as a sign of extracapsular extension.

OBJECTIVE: To evaluate the length of contact between dominant tumor foci and the prostatic capsule as a sign of extracapsular extension at endorectal multiparametric MR imaging. MATERIALS AND METHODS: We retrospectively identified 101 patients over a three-year interval who underwent endorectal multiparametric prostate MR imaging prior to radical prostatectomy for prostate cancer. Two readers identified the presence of dominant tumor focus (largest lesion with PI-RADS version 2 score of 4 or 5), and measured the length of tumor capsular contact and likelihood of extracapsular extension by standard criteria (1-5 Likert scale). Results were analyzed using histopathological review as reference standard. RESULTS: Extracapsular extension was found at histopathological review in 27 patients. Reader 1 (2) identified dominant tumor in 79 (73) patients, with mean tumor capsular contact length of 18.2 (14.0) mm. The area under the receiver operating characteristic curve for identification of extracapsular extension by tumor capsular contact length was 0.76 for reader 1 and 0.77 for reader 2, with optimal discrimination at values of 18 mm and 21 mm, respectively. In the subset of patients without obvious extracapsular extension by standard criteria (Likert scores 1-3), corresponding values were 0.74 and 0.66 with optimal thresholds of 24 and 21 mm. CONCLUSION: Length of contact between the dominant tumor focus and the capsule is a moderately useful sign of extracapsular extension at endorectal multiparametric prostate MR imaging, including the subset of patients without obvious extracapsular extension by standard criteria, with optimal discrimination at threshold values of 18 to 24 mm.

Direct magnetic resonance imaging-guided biopsy of the prostate: lessons learned in establishing a regional referral center.

MRI-targeted biopsy of the prostate appears to have the potential to reduce the high rates of underdiagnosis and overdiagnosis associated with the current diagnostic standard of transrectal ultrasound guided systematic biopsy. Direct or "in bore" MRI-guided biopsy is one of the three methods for MRI-targeted core needle sampling of suspicious, generally Pi-RADS 4 or 5, foci within the prostate, and our early experience suggests the approach demonstrates substantial utility and promise in the care of patients with prostate cancer. We performed direct MRI-guided biopsies in 50 patients within 19 months of establishing the first referral center for this service in our region. Our preliminary results indicate the service can be easily grown due to unmet demand, primarily in patients with a negative traditional systematic biopsy but with a concerning focus at MRI (30 of 50; 60%). Other applications include evaluation of patients who are on active surveillance (n=14; ten upgraded to higher Gleason score at MRI-guided biopsy), who are biopsy naïve (n=5; all positive at MRI-guided biopsy), or post focal therapy (n=1; positive for recurrent tumor at MRI-guided biopsy). With careful patient selection and technique, we have achieved a favorable overall positive biopsy rate of 73% (37 of 50), with 84% (31 of 37) positive biopsies demonstrating Gleason score 7 or greater disease. Large multicenter comparative trials will be required to determine the relative accuracy and appropriate utilization of direct MRI guided biopsy in the care pathway of patients with known or suspected prostate cancer.

Performance characteristics of magnetic resonance imaging without contrast agents or sedation in pediatric appendicitis.

BACKGROUND: Magnetic resonance imaging (MRI) has emerged as a promising modality for evaluating pediatric appendicitis. However optimal imaging protocols, including roles of contrast agents and sedation, have not been established and diagnostic criteria have not been fully evaluated. OBJECTIVE: To investigate performance characteristics of rapid MRI without contrast agents or sedation in the diagnosis of pediatric appendicitis. MATERIALS AND METHODS: We included patients ages 4-18 years with suspicion of appendicitis who underwent rapid MRI between October 2013 and March 2015 without contrast agent or sedation. After two-radiologist review, we determined performance characteristics of individual diagnostic criteria and aggregate diagnostic criteria by comparing MRI results to clinical outcomes. We used receiver operating characteristic (ROC) curves to determine cut-points for appendiceal diameter and wall thickness for optimization of predictive power, and we calculated area under the curve (AUC) as a measure of test accuracy. RESULTS: Ninety-eight MRI examinations were performed in 97 subjects. Overall, MRI had a 94% sensitivity, 95% specificity, 91% positive predictive value and 97% negative predictive value. Optimal cut-points for appendiceal diameter and wall thickness were ≥7 mm and ≥2 mm, respectively. Independently, those cut-points produced sensitivities of 91% and 84% and specificities of 84% and 43%. Presence of intraluminal fluid (30/33) or localized periappendiceal fluid (32/33) showed a significant association with acute appendicitis (P<0.01), with sensitivities of 91% and 97% and specificities of 60% and 50%. For examinations in which the appendix was not identified by one or both reviewers (23/98), the clinical outcome was negative. CONCLUSION: Rapid MRI without contrast agents or sedation is accurate for diagnosis of pediatric appendicitis when multiple diagnostic criteria are considered in aggregate. Individual diagnostic criteria including optimized cut-points of ≥7 mm for diameter and ≥2 mm for wall thickness demonstrate high sensitivities but relatively low specificities. Nonvisualization of the appendix favors a negative diagnosis.