Prostate Imaging-Reporting and Data System (PI-RADS)

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PI-RADS (Prostate Imaging–Reporting and Data System) is a structured reporting scheme for multiparametric prostate MRI in the evaluation of suspected prostate cancer in treatment naive prostate glands. This article reflects version 2.1 (v2.1), published in 2019 and developed by an internationally representative group involving the American College of Radiology (ACR), European Society of Urogenital Radiology (ESUR), and AdMeTech Foundation .

Assessment categories

A combination of imaging findings (T2W, DWI, and dynamic contrast enhancement [DCE]) predicts the probability of a cancer that is clinically significant, which is defined as the presence of any of the following :

Gleason score ≥7 (including 3+4 with prominent but not predominant Gleason 4 component)
volume >0.5 mL
extraprostatic extension

Each lesion is assigned a score from 1 to 5 indicating the likelihood of clinically significant cancer:

PI-RADS 1: very low (clinically significant cancer is highly unlikely to be present)
PI-RADS 2: low (clinically significant cancer is unlikely to be present)
PI-RADS 3: intermediate (the presence of clinically significant cancer is equivocal)
PI-RADS 4: high (clinically significant cancer is likely to be present)
PI-RADS 5: very high (clinically significant cancer is highly likely to be present)
PI-RADS X: component of exam technically inadequate or not performed

PI-RADS v2.1 does not contain management recommendations, as these decisions also depend on other factors such as prostate specific antigen, clinical history, local expertise, and patient preferences. However, in general, biopsy should be considered for PI-RADS 4 or 5 lesions, but not PI-RADS 1 or 2 lesions.

Radiographic appearance

Each lesion can be scored 1-5 on DWI and on T2W, as well as by the absence or presence of dynamic contrast enhancement. The contribution of these scores to the overall PI-RADS assessment differs depending on whether the lesion is located in the transition zone or peripheral zone of the prostate. For the transition zone, the PI-RADS assessment is primarily determined by the T2W score and sometimes modified by the DWI score. For the peripheral zone, the PI-RADS assessment is primarily determined by the DWI score and sometimes modified by the presence of dynamic contrast enhancement.

T2 weighted imaging (T2W) score

Transition zone

1: normal appearing transition zone (rare) or a round, completely encapsulated nodule ("typical nodule" of benign prostatic hyperplasia)
2: a mostly encapsulated nodule or a homogeneous circumscribed nodule without encapsulation ("atypical nodule"), or a homogeneous mildly hypointense area between nodules
3: heterogeneous signal intensity with obscured margins; includes others that do not qualify as 2, 4, or 5
4: lenticular or non-circumscribed, homogeneous, moderately hypointense, and <1.5 cm in greatest dimension
5: same as 4, but ≥1.5 cm in greatest dimension or definite extraprostatic extension/invasive behavior

For transition zone lesions, the overall PI-RADS assessment usually follows the T2W score, but scores of 2 or 3 can be upgraded by the DWI (see below).

Peripheral zone

1: uniform high signal intensity (normal)
2: linear or wedge-shaped hypointensity or diffuse mild hypointensity, usually indistinct margin
3: heterogeneous signal intensity or non-circumscribed, rounded, moderate hypointensity; includes others that do not qualify as 2, 4, or 5
4: circumscribed, homogeneous, moderate hypointensity, and <1.5 cm in greatest dimension
5: same as 4 but ≥1.5 cm in greatest dimension or definite extraprostatic extension/invasive behavior

For peripheral zone lesions, the T2W score is only used for the overall PI-RADS assessment if the DWI is inadequate or absent. Scores of 3 can be upgraded by presence of dynamic contrast enhancement.

Diffusion weighted imaging (DWI) score

Signal intensity in the lesion is visually compared to the average signal of normal prostate tissue elsewhere in the same histologic zone.

Transition zone or peripheral zone

1: no abnormality on ADC or high b-value DWI
2: linear/wedge shaped, hypointensity on ADC and/or hyperintensity on high b-value DWI
3: focal (discrete and different from background), mild/moderate hypointensity on ADC and/or mild/moderate hyperintensity on high b-value DWI; may be markedly hypointense on ADC or markedly hyperintense on high b-value DWI, but not both
4: focal, marked hypointensity on ADC and marked hyperintensity on high b-value DWI; <1.5 cm in greatest dimension
5: same as 4 but ≥1.5 cm in greatest dimension or definite extraprostatic extension/invasive behavior

For peripheral zone lesions, the overall PI-RADS assessment usually follows the DWI score, but a score of 3 can be upgraded by the presence of dynamic contrast enhancement (see below).

For transition zone lesions with a T2W score of 2 or 3, a DWI score that is two higher (i.e. 4 or 5, respectively) is used to upgrade the overall PI-RADS assessment by one point (i.e. to 3 or 4, respectively).

Dynamic contrast enhancement (DCE)

(-) negative:
- no early or contemporaneous enhancement, or
- diffuse multifocal enhancement not corresponding to a focal finding on T2W and/or DWI, or
- focal enhancement corresponding to a lesion demonstrating features of benign prostatic hyperplasia on T2W (including features of extruded benign prostatic hyperplasia nodule in the peripheral zone)
(+) positive:
- focal, and
- earlier than or contemporaneous with enhancement of adjacent normal prostatic tissues, and
- corresponds to suspicious finding on T2 and/or DWI

For peripheral zone lesions with DWI score of 3, the presence of dynamic contrast enhancement is used to upgrade the overall PI-RADS assessment category to 4.

Changes from prior versions

Changes from v1 to v2

Determining sequences for PZ and TZ were defined.

For the PZ, DWI is the primary determining sequence (dominant technique).

PI-RADS score for a PZ lesion is based on DWI unless the DWI score is PI-RADS 3
in this scenario, DCE is used to decide between PI-RADS 3 (no focal or early enhancement) or upgrade to PI-RADS 4 (focal and early enhancement present).

For the TZ, T2W is the primary determining sequence.

PI-RADS score for a TZ lesion is based on T2W unless the T2W score is PI-RADS 3
in this scenario, DWI is used to decide between PI-RADS 3 (DWI score <5) or upgrade to PI-RADS 4 (DWI score 5)

The number of mapping lesions was limited up to four findings with the highest PI-RADS Assessment Category of 3, 4, or 5. The index (dominant) intraprostatic lesion should be identified. Thus, a smaller lesion with extraprostatic extension should be defined as the index lesion despite the presence of a larger tumor with the identical PI-RADS Assessment Category.

MR spectroscopy does not form part of PI-RADS scoring.

The sector map of version 1 was revised for version 2.