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A standardized method to measure the membranous urethral length (MUL) on MRI of the prostate with high inter- and intra-observer agreement

  • Magnetic Resonance
  • Published:
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Abstract

Objectives

The membranous urethral length (MUL), defined as the length between the apex and penile base as measured on preoperative prostate magnetic resonance imaging (MRI), is an important predictor for urinary incontinence after radical prostatectomy. Literature on inter- and intra - observer agreement of MUL measurement is limited. We studied the inter- and intra-observer agreement between radiologists using a well-defined method to measure the MUL on the prostate MRI.

Methods

Prostate cancer patients underwent a preoperative MRI and robot-assisted radical prostatectomy (RARP) at one high-volume RARP center. MUL measurement was based on well-defined landmarks on sagittal T2-weighted (anatomical) images. Three radiologists independently performed MUL measurements retrospectively in 106 patients blinded to themselves, to each other, and to clinical outcomes. The inter- and intra-observer agreement of MUL measurement between the radiologists were calculated, expressed as intra-class correlation coefficient (ICC).

Results

The initial inter-observer agreement was ICC 0.63; 95% confidence interval (CI) 0.28–0.81. Radiologist 3 measured the MUL mean 3.9 mm (SD 3.3) longer than the other readers, interpreting the caudal point of the MUL (penile base) differently. After discussion on the correct anatomical definition, radiologist 3 re-assessed all scans, which resulted in a high inter-observer agreement (ICC 0.84; 95% CI 0.66–0.91). After a subsequent reading by radiologists 1 and 2, the intra-observer agreements were ICC 0.93; 95% CI 0.89–0.96, and ICC 0.98; 95% CI 0.97–0.98, respectively. Limitation is the monocenter design.

Conclusions

The MUL can be measured reliably with high agreement among radiologists.

Key Points

• After discussion on the correct anatomical definition, the inter- and intra - observer agreements of membranous urethral length (MUL) measurement on magnetic resonance imaging (MRI) were high.

• A reproducible method to measure the MUL can improve the clinical usefulness of prediction models for urinary continence after RARP which may benefit patient counselling.

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Abbreviations

ICC:

Intra-class correlation coefficient

ICIQ-SF:

International consultation of incontinence short form

MRI:

Magnetic resonance imaging

MUL:

Membranous urethral length

PCa:

Prostate cancer

RARP:

Robot-assisted radical prostatectomy

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Acknowledgements

We would like to acknowledge Erik-Jan Rijkhorst for his technical support in anonymizing the MRI scans and preparing software for the measurements.

Funding

The authors state that this work has not received any funding.

Author information

Authors and Affiliations

  1. Department of Urology, Netherlands Cancer Institute – Antoni van Leeuwenhoek Hospital, Plesmanlaan 121, 1066CX, Amsterdam, the Netherlands

    Hans Veerman, Marinus J. Hagens, Henk G. van der Poel & Pim J. van Leeuwen

  2. Department of Urology, Amsterdam University Medical Centers location Boelelaan, Amsterdam, the Netherlands

    Hans Veerman, Marinus J. Hagens, Henk G. van der Poel & André N. Vis

  3. Prostate Cancer Network Netherlands, Amsterdam, the Netherlands

    Hans Veerman, Marinus J. Hagens, Henk G. van der Poel, Pim J. van Leeuwen & André N. Vis

  4. Department of Radiology, Diakonessenhuis Utrecht, Utrecht, the Netherlands

    Caroline M. Hoeks

  5. Department of Radiology, Netherlands Cancer Institute - Antoni van Leeuwenhoek Hospital, Amsterdam, the Netherlands

    Stijn W. T. J. P. Heijmink, Ivo G. Schoots, Margriet C. de Haan & Thierry N. Boellaard

  6. Department of Radiology, Erasmus Medical Center, Rotterdam, the Netherlands

    Ivo G. Schoots

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  1. Hans Veerman
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Correspondence to Hans Veerman.

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The scientific guarantor of this publication is Henk van der Poel and Ivo Schoots.

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The authors of this manuscript declare no relationships with any companies whose products or services may be related to the subject matter of the article.

Statistics and biometry

No complex statistical methods were necessary for this paper.

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Institutional Review Board approval was obtained. IRB number IRBd20-069.

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• performed at one institution

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Veerman, H., Hagens, M.J., Hoeks, C.M. et al. A standardized method to measure the membranous urethral length (MUL) on MRI of the prostate with high inter- and intra-observer agreement. Eur Radiol 33, 3295–3302 (2023). https://doi.org/10.1007/s00330-022-09320-2

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