In the past two decades, technological innovations related to scientific research in the diagnosis of prostate cancer (PCa) have allowed magnetic resonance imaging (MRI) to become the current main imaging modality for the detection, localization, staging, grading and response assessment to therapy [
1‐
4]. Great interest has been shown in multiparametric MRI (mp-MRI), which combines anatomic T2-weighted (T2W) imaging with functional techniques. The detection of PCa on T2W can be confounded by false-positive findings such as prostatitis, post-biopsy haemorrhage, benign prostatic hyperplasia, fibrosis, radiation and hormonal tissue changes [
5,
6]. In order to improve the diagnostic accuracy of PCa imaging, functional MR imaging techniques have been applied, such as Diffusion-Weighted MR Imaging (DWI) [
7‐
9], proton (1H) MR Spectroscopic Imaging (MRSI) [
10‐
12], and Dynamic Contrast-Enhanced MR Imaging (DCE-MRI) [
13]. The combination of anatomic, biological and metabolic information offered by multiparametric MRI (mp-MRI) provides a promising imaging tool for improving many aspects of PCa management. Moreover, mp-MRI has recently also been proposed as a tool that is more useful than other imaging procedures for the diagnosis of local recurrence of PCa after radiation treatment or radical prostatectomy [
14‐
18]. In order to allow for a standardized interpretation, and to objectively visualize the contribution of mp-MRI to predict the presence of significant cancer, a scoring system similar to that employed successfully by breast radiologists (BI-RADS) [
19], has been designed for mp-MRI (PI-RADS) [
20]. In this scoring system, every imaging technique (T2W, DW, DCE-MRI and MRSI) is scored on a five-point scale, based on the probability that a combination of mp-MRI findings on T2w, DWI and DCE findings correlates with the presence of a clinically significant cancer on each portion of the gland, as recently illustrated on the PI-RADS v2. Because of multiple diagnostic misunderstandings that may arise from the individual parameters forming the study protocol, the system of “score” with PI-RADS was introduced. Each value assigned to each sequence is weighted in relation to the sequence considered to be “dominant” for each zone of the gland; the DWI is considered the main sequence for the peripheral zone (PZ), while the T2 is the main sequence for the transition zone (TZ). An accurate assessment of an mp-MRI, in addition to the PI-RADS score, requires a comprehensive evaluation of the gland, including unavoidable knowledge of anatomy, pathology and clinical data in order to avoid certain diagnostic pitfalls, both false-positive and false-negative interpretations, that prostate MRI can show [
21]. In this paper, we present a collection of pitfalls of interpreting prostate mp-MRI and propose a series of solutions for difficult cases (Tables
1 and
2).
Table 1
Pitfalls classification based on categories before treatment
1. Pitfalls in primary diagnosis | 1. Bilateral basal hypointense zones (moustache sign) |
2. Median posterior hypointense area at the middle third of the gland |
3. Transition zone prostate cancer versus BPH foci of stromal hyperplasia |
4. Ectopic BPH nodule |
5. Granulomatous prostatitis after intravesical instillation of BCG |
6. Hypertrophic anterior fibromuscular stroma |
7. Periprostatic venous plexus and neurovascular bundle |
2. Pitfall in the staging | 1. T3 versus T2 (overlapping with pitfalls in primary diagnosis: granulomatous prostatitis, periprostatic venous plexus and neurovascular bundle) |
5. Bone findings |
6. Controversial on lymph nodes |
3. Artifacts/iatrogenic changes | 1. Mispositioned endorectal coil |
2. Post-biopsy changes |
3. Lymphoceles |
Table 2
Pitfalls classification based on categories after treatment
4. Pitfalls after surgical treatment | 1. Residual glandular tissue |
2. Fibrosis |
3. Retained seminal vesicles |
4. Sealed off veins |
5. Prominent periprostatic venous plexus |
6. Residual verumontanum |
5. Pitfalls after radiation/hormone deprivation therapy and after focal therapies | 1. RT-induced capsular irregularity may hinder evaluation of extracapsular extension |
2. Focal regions of T2-hypointensity may represent treated tumour and not local recurrence |
3. Focal therapies-induced enhancing of reactive prostate tissue may hamper the assessment of persistent/residual disease |