Comparing the Likert score and Prostate Imaging Reporting And Data System (PI - RADS score) to assess the likelihood of prostate cancer based on multiparametric MRI

Two scoring systems are commonly used to evaluate the likelihood of prostate cancer on multiparametric MRI:

• Prostate Imaging Reporting And Data System version 2 (PI-RADS_v2) uses explicit criteria based on a zonal multiparametric MRI (mpMRI) dominant sequence (e.g. diffusion-weighted imaging in the peripheral zone (PZ) and T2 weighted imaging in the transition zone) to rate the suspicion of prostate cancer on a 5-point scale and
  
• a subjective 5-point Likert assessment, based on each mpMRI sequence equally (unlike the use of dominant sequence in PIRADS_v2) and adapted to the radiologist's experience for overall impression

Both 5-point scales define the likelihood for the presence of prostate cancer, as follows

• (1) highly unlikely,
• (2) unlikely,
• (3) equivocal,
• (4) likely,
• (5) highly likely

PI-RADS and Likert are both 1-5 scales used to communicate the likelihood of clinically significant prostate cancer found on an MRI. While they share the same scoring range, they differ in how that score is calculated.

The two systems are highly correlated; a high score on one usually matches a high score on the other. However, PI-RADS is a rigid, rules-based system designed for international consistency, whereas Likert is a subjective, "gestalt" assessment often used in the UK.

PI-RADS scale

A standardized, algorithmic approach using specific MRI sequences based on the anatomical zone of the lesion.

• Peripheral Zone (PZ):
  • score is determined primarily by DWI (Diffusion)
• Transition Zone (TZ):
  • score is determined primarily by T2W (Structural) imaging
• Structural Criteria:
  • an upgrade from score 4 to 5 is strictly defined by a size threshold of 1.5 cm or evidence of extraprostatic extension

Likert scale

• similar to PI-RADS, the Likert scale is based on a 5-point score meant to reflect the probability of prostate cancer being present
  • athough image interpretation incorporates the findings considered suspicious by PI-RADS, no specific criteria are provided to define each risk category
    • therefore, to some extent, much is left at the discretion of the radiologist and it is considered a “gestalt” assessment
      • as such, it can be tweaked according to the experience of the reader as well as parameters beyond imaging appearance, such as age, PSA, PSA density and previous biopsy results
  • different from PI-RADS, given its relatively free form, there is not a unified document providing specific guidelines such as the concept of zone-specific dominant MRI pulse sequence
  • note also that a lesion can be classified as risk category 5 regardless of size, whereas PI-RADS requires a minimum size of 15 mm
• PI-RADS has been proposed specifically for treatment-naïve patients, the flexibility resulting from the lack of specific criteria in the Likert scale also allows the use of Likert scales in other settings such as suspected disease recurrence after radiation or focal therapy (3)

Key differences include the incorporation of clinical information into Likert assessment and an equal evaluation of all multiparametric (mp) MRI sequences, in contrast to the zone-specific dominant sequence paradigm of PI-RADS (4).

A study comparing the use of PI-RADs versus the Likert assessment concluded (4):

• both Likert and PI-RADS scoring systems have a high detection of clinically signficant prostate cancer at a cut-off positive MRI score ≥3
  • however, Likert scoring by experienced radiologists resulted in lower positive call rate, but with equivalent outcomes, and therefore could help reduce the number of unnecessary biopsies performed

Notes:

• in the "grey zone" of a PI-RADS 3 or Likert 3 result, PSA density (PSAD) acts as the critical clinical tie-breaker to determine whether a patient should undergo an immediate biopsy or move to active surveillance (5)

Reference:

1. Renard-Penna R et al. Prostate imaging reporting and data system and Likert scoring system: multiparametric MR imaging validation study to screen patients for initial biopsy. Radiology 2015; 275: 458-68.
2. Rosenkrantz AB et al. Comparison of interreader reproducibility of the prostate imaging reporting and data system and likert scales for evaluation of multiparametric prostate MRI. AJR Am J Roentgenol 2013; 201: W612-W618.
3. Desai S, Costa DN. PI-RADS and Likert scales for structured reporting in multiparametric MR imaging of the prostate. Br J Radiol. 2022 Mar 1;95(1131):20210758. doi: 10.1259/bjr.20210758.
4. Zawaideh JP et al. Comparison of Likert and PI-RADS version 2 MRI scoring systems for the detection of clinically significant prostate cancer. Br J Radiol. 2020 Aug;93(1112):20200298.
5. Nazir MA et al. Evaluating Prostate-Specific Antigen (PSA) Density Thresholds for Detecting Clinically Significant Prostate Cancer in Prostate Imaging Reporting and Data System (PI-RADS) 3 Lesions: A Retrospective Cohort Study. Cureus. 2025 Nov 9;17(11):e96432.