E1892. Beyond PIRADS for the Transition Zone: Additional Characteristics and Imaging Features of Transition Zone Prostate Cancer
Although interobserver agreement and sensitivity for prostate cancer in the peripheral zone is high, this is not the case for the transition zone. Even using PI-RADS, interobserver variability is relatively high and sensitivity can be quite a bit lower. Based on the literature, there are additional imaging features that can be used in conjunction with PI-RADS to help assist in the diagnosis of lesions in the transition zone.
Educational Goals / Teaching Points
Detection of malignancy in the transition zone is more difficult than the peripheral zone, with lower sensitivity and specificity, and lower interobserver agreement. Changes from PI-RADS v2.0 to v2.1 improves the detection and classification of lesions in the transition zone, both decreasing the miss rate and avoiding biopsy of benign lesions. Additional non-imaging parameters are crucial to determine your pre-test probability, especially the PSA density. Other considerations including lesion location, ADC value, and enhancement parameters have been suggested as adjuncts to transition zone lesion detection. Transition zone lesions tend to have a specific morphology and location within the gland, and this is theorized to be related to displacement from benign prostatic hyperplasia nodules.
Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
Current PI-RADS criteria focuses on the signal characteristics on T2 imaging and to a lesser extent the DWI. One of the most important and perhaps subjective parameters includes the shape of the lesion. Changes from PI-RADS v2.0 to v2.1 include more attention paid to DWI. Literature also suggests that location and quantitative degree of diffusion restriction can help improve proper identification and classification of transition zone lesions. Anterior, inferior, and peripheral location within the transition zone is associated with higher likelihood of being malignant, as are markedly low ADC values.
Accurate identification and diagnosis of transition zone clinically significant prostate cancer is difficult. The update from PIRADS 2.0 to 2.1 provided improvements, and additional parameters can be used to help guide interpretation and improve sensitivity and specificity.