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

Hans Veerman*, Marinus J. Hagens, Caroline M. Hoeks, Henk G. van der Poel, Pim J. van Leeuwen, André N. Vis, Stijn W.T.J.P. Heijmink, Ivo G. Schoots, Margriet C. de Haan, Thierry N. Boellaard

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

1 Citation (Scopus)


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.

Original languageEnglish
Pages (from-to)3295-3302
Number of pages8
JournalEuropean Radiology
Issue number5
Early online date13 Dec 2022
Publication statusPublished - May 2023

Bibliographical note

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

Publisher Copyright:
© 2022, The Author(s), under exclusive licence to European Society of Radiology.


Dive into the research topics of 'A standardized method to measure the membranous urethral length (MUL) on MRI of the prostate with high inter- and intra-observer agreement'. Together they form a unique fingerprint.

Cite this