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Article of the week: Getting to the core of the matter with PIRADS scoring

Every week the Editor-in-Chief selects the Article of the Week from the current issue of BJUI. The abstract is reproduced below and you can click on the button to read the full article, which is freely available to all readers for at least 30 days from the time of this post.

In addition to the article itself, there is an accompanying editorial written by prominent members of the urological community. This blog is intended to provoke comment and discussion and we invite you to use the comment tools at the bottom of each post to join the conversation.

If you only have time to read one article this week, it should be this one.

Histology core-specific evaluation of the European Society of Urogenital Radiology (ESUR) standardised scoring system of multiparametric magnetic resonance imaging (mpMRI) of the prostate

Timur H. Kuru*, Matthias C. Roethke, Philip Rieker*, Wilfried Roth, Michael Fenchel, Markus Hohenfellner*, Heinz-Peter Schlemmer and Boris A. Hadaschik*

*Department of Urology, University Hospital Heidelberg, Department of Radiology, German Cancer Research Center (DKFZ), and Institute of Pathology, University of Heidelberg, Heidelberg, Germany

Link to Video: MRI-Navigated Stereotactic Prostate Biopsy

OBJECTIVES

• To evaluate the Prostate Imaging Reporting and Data System (PIRADS) in multiparametric magnetic resonance imaging (mpMRI) based on single cores and single-core histology.

• To calculate positive (PPV) and negative predictive values (NPV) of different modalities of mpMRI.

PATIENTS AND METHODS

• We performed MRI-targeted transrectal ultrasound-guided perineal prostate biopsies on 50 patients (mean age 66 years, mean PSA level of 9.9 ng/mL) with suspicion of prostate cancer. The biopsy trajectories of every core taken were documented in three dimensions (3D) in a 3D-prostate model.

• Every core was evaluated separately for prostate cancer and the performed biopsy trajectories were projected on mpMRI images.

• PIRADS scores of 1177 cores were then assessed by a histology ‘blinded’ uro-radiologist in T2-weighted (T2W), dynamic contrast-enhanced (DCE), diffusion-weighted imaging (DWI) and magnetic resonance spectroscopy (MRS).

RESULTS

• The PIRADS score was significantly higher in cores positive for cancer than in negative cores.

• There was a significant correlation between the PIRADS score and histopathology for every modality.

• Receiver operating characteristic (ROC) analysis showed excellent specificity for T2W (90% peripheral zone/97% transition zone) and DWI (98%/97%) images regardless of the prostate region observed. These numbers decreased for DCE (80%/93%) and MRS (76%/83%).

• All modalities had NPVs of 99%, if a PIRADS score threshold of 2 (for T2W, DCE, and MRS) or 3 (for DWI) was used. However, PPVs were low.

CONCLUSIONS

• Our results show that PIRADS scoring is feasible for clinical routine and allows standardised reporting.

• PIRADS can be used as a decision-support system for targeting of suspicious lesions.

• mpMRI has a high NPV for prostate cancer and, thus, might be a valuable tool in the initial diagnostic evaluation.

 

Read Previous Articles of the Week

 

Editorial: Too many men still undergo needless prostate biopsy

Multiple studies have shown that only one in three or four men with a raised PSA level prove to have prostate cancer and many men suffer potentially life-threatening complications from transrectal prostate biopsy. There is an urgent need for better risk stratification of men with elevated PSA levels. Any such test should have a high negative predicative value (NPV; small number of significant cancers missed) but also a high positive predictive value (PPV; i.e. the yield would be high and there would be very few false positives) to diminish the number of unnecessary biopsies. Multiparametric MRI (mpMRI) of the prostate, especially with a stronger 3 T magnet, has been advocated for this purpose. The parameters refer to the separate MRI sequences used, typically at least three. Sequences can not only study the anatomy of the gland (standard T2-weighted MRI), but there is also a measure of the tissue cellularity (diffusion-weighted MRI), vascularity (dynamic contrast-enhanced MRI) or biochemistry (magnetic resonance spectroscopy). Initial data have shown promise but the changes seen on these various sequences can be subtle and interpretation is subjective. Naturally observer experience plays a large part but a standardised scoring system, the so called Prostate Imaging Reporting and Data System (PIRADS) system, has been proposed to improve reporting performance [1]. Each parameter is scored on a scale of 1–5 according to the likelihood of cancer. Scoring systems are always a compromise between the NPV and PPV, and so far there is no agreement where the threshold for each parameter should be set. In the original document, the authors proposed that a score of 4 or 5 signifies a high likelihood or almost certainty of cancer, whilst scores of 1 or 2 denote a high likelihood of benign tissue. A score of 3 is evens. The paper by Kuru et al. [2] shows a high NPV only when the threshold was set at the low level of 2 for each parameter. Predictably, at this threshold the PPV was extremely low, and therefore many men would still undergo unnecessary biopsy. Another similar paper advocated a mean threshold of 3, but even then the PPV was 38% with a NPV of 95% [3]. Both these papers are retrospective studies, in particular the MRI readings were done retrospectively. Nevertheless, the low PPV is disappointing. The results of prospective studies with multiple readers are keenly awaited and I hope that that these will find a higher PPV for mpMRI, and we can to move to an era when fewer men undergo needless prostate biopsy.

Uday Patel
St George’s Hospital, London, UK

References

  1. Barentsz JO, Richenberg J, Clements R et al. ESUR prostate MR guidelines 2012. Eur Radiol 2012; 22: 746–757
  2. Kuru T, Roethke M, Rieker P et al. Histology core-specific evaluation of the European Society of Urogenital Radiology (ESUR) standardised scoring system of multiparametric magnetic resonance imaging (mpMRI) of the prostate. BJU Int 2013; 112:1080–1087
  3. Portalez D, Mozer P, Cornud F et al. Validation of the European Society of Urogenital Radiology scoring system for prostate cancer diagnosis on multiparametric magnetic resonance imaging in a cohort of repeat biopsy patients. Eur Urol 2012; 62: 986–996
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