Prostate imaging recurrence reporting

Last revised by Joachim Feger on 11 Feb 2022

Prostate imaging recurrence reporting (PI-RR) or prostate MRI for local recurrence reporting is a structured reporting scheme similar to the Prostate Imaging-Reporting and Data System (PIRADS) v2.1 on multiparametric prostate MRI for the detection of local recurrence after radical prostatectomy or radiation therapy 1

Following the PIRADS v2.1 score 2 and the Likert scales PI-RR comprises a five-point scale for the mpMRI evaluation of the prostate after radiation therapy and the postoperative prostatic site after prostatectomy 1:

  • PI-RR 1: very low likelihood of recurrence
  • PI-RR 2: low likelihood of recurrence
  • PI-RR 3: uncertain
  • PI-RR 4: high likelihood of recurrence
  • PI-RR 5: very high likelihood of recurrence

The reporting criteria are founded on anatomical and functional imaging findings similar to the PIRADS score with anatomical criteria being based on lesion location size and shape and functional criteria on cellularity and vascularity assessed with diffusion-weighted imaging and dynamic contrast enhancement respectively 1.

The post-radiation prostate is usually smaller and characterized by a less evident distinction between benign and malignant tissue. General radiographic features of local recurrence include 1:

  • mass-like lesion
  • capsular bulging
  • lesion at the site of the previous tumor

Prostate imaging recurrence reporting overall assessment after radiation therapy is mainly subject to diffusion-weighted imaging (DWI) and dynamic contrast enhancement (DCE) 1

The overall PI-RR score is determined by the sequence with the highest score. 

Lesions that are characterized by both diffusion restriction (DWI score 4) and increased vascularity (DCE score 4) are considered highly suspicious and are upgraded from PI-RR 4 to PI-RR 5 1.

Due to possible radiation-induced inflammatory changes which might lead to false-positive results multiparametric prostate MRI should not be done until three months after radiation therapy 1.

T2 weighted images are considered the non-dominant sequence in prostate imaging recurrence reporting. They are not counted towards the overall score but can help in the detection and localization of suspicious lesions as well as the comparison to findings in previous examinations 1. Therefore the acquisition of T2 weighted images is recommended in three planes 1.

Local recurrence can appear slightly hypointense on T2 weighted imaging compared to the irradiated prostatic tissue, this finding however is unspecific and hypointense lesions.

  1. no abnormality or lesions different from the background
  2. linear wedge-shaped or diffuse moderate hypointensities, remaining BPH nodules
  3. mass-like or focal mildly hypointense lesions, any lesion that does not fit into another category
  4. mass-like or focal moderate to marked hypointensity at a location different from the primary tumor site
  5. mass-like or focal moderate to marked hypointensity at the primary tumor site

Similar to the native prostate diffusion-weighted imaging (DWI) plays a major role in the detection of local recurrence after radiation therapy. It can be hampered due to early radiation-related inflammatory effects in the first 6 weeks after radiation therapy or seed implants 1.

The signal intensity of the irradiated prostate is visually compared to the average signal of remaining prostate tissue elsewhere in the same histologic zone 1.

  1. no abnormality or lesions visible on high b-value and the ADC map
  2. diffusely high signal on high b-value and low signal on the ADC map
  3. either focal high signal on high b-value or focal low signal on the ADC map but not both
  4. focal diffusion restriction at a location different from the primary site
  5. focal diffusion restriction at the primary tumor site

Unlike in the native prostate and the original PI-RADS v2.1, dynamic contrast enhancement plays a major role in prostate imaging recurrence reporting after radiation therapy 1. However, during the initial three months, radiation-induced inflammatory changes can lead to increased blood flow which can give false-positive results 1

  1. no enhancement
  2. heterogeneous or diffuse enhancement
  3. mass-like or focal late enhancement
  4. mass-like or focal early enhancement at a location different from the primary site
  5. mass-like or focal early enhancement at the primary tumor site

Radiographic features and forms of recurrent tumor after radical prostatectomy can be quite variable and include the following 1

  • nodular or plaque-like lesions 
  • spherical or hemispherical masses
  • asymmetric perianastomotic soft-tissue thickening
  • signal intensity between the pelvic muscles and the surrounding tissues

Local recurrence can be found anywhere within the prostatectomy site and is commonly observed in the following locations1:

  • perianastomotic area
    • around the bladder neck
    • membranous urethra
    • vesicorectal space
  • seminal vesicle remnants

Prostate imaging recurrence reporting overall assessment after radical prostatectomy is mainly subject to dynamic contrast enhancement (DCE) and also to diffusion-weighted imaging (DWI) 1

The overall PI-RR score is mainly determined by dynamic contrast enhancement (DCE) but an upgrade from PI-RR 2 to PI-RR 3 or PI-RR 3 to PI-RR 4 is considered appropriate if there is a definite diffusion restriction with a high signal on high b-value and a low signal on the ADC map 1.

Similar to cases after radiation therapy T2 weighted imaging is considered a non-dominant sequence in prostate imaging recurrence reporting and is not included in the overall assessment score. Nevertheless, a likelihood rating for local recurrence has been defined 1:

  1. normally configured low signal vesicourethral anastomosis and seminal vesicle remnants
  2. diffusely thickened vesicourethral anastomosis or seminal vesicle remnants with or without coarse scar tissue
  3. mass-like or focal symmetric high signal changes of the anastomosis or seminal vesicle site
  4. mass-like or focal asymmetric lesions in the anastomotic area or the seminal vesicle site at a location different from the primary tumor
  5. mass-like or focal asymmetric lesions in the anastomotic area or the seminal vesicle site at the primary tumor site

Diffusion-weighted imaging (DWI) plays an important role in the detection of local recurrence after radical prostatectomy in the combination with other sequences 1. Evaluation can be hampered by geometric distortion due to susceptibility artefacts e.g. by surgical clips 1.

  1. no abnormality or lesions visible on high b-value and the ADC map
  2. diffusely high signal on high b-value and low signal on the ADC map
  3. either focal high signal on high b-value or focal low signal on the ADC map but not both
  4. focal diffusion restriction at a location different from the primary site
  5. focal diffusion restriction at the primary tumor site

Unlike in the native prostate and the original PI-RADS v2.1, dynamic contrast enhancement plays the dominant role in prostate imaging recurrence reporting after radical prostatectomy 1. Local recurrences after prostatectomy tend to enhance sooner and at a faster rate 1.

  1. no enhancement
  2. heterogeneous or diffuse enhancement
  3. mass-like or focal late enhancement
  4. mass-like or focal early enhancement at a location different from the primary site
  5. mass-like or focal early enhancement at the primary tumor site

The radiological report should include a description of the following features:

  • form and size of the finding
  • PI-RR overall score
  • after radiation therapy
    • location of findings in relation to the primary tumor site
  • after radical prostatectomy
    • location of findings in a clock position, with the vesicourethral anastomosis as the center

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