Zonal anatomy and age-related changes
To correctly interpret tomograms, it is necessary to understand the structure of the prostate gland, as tumors are distributed unevenly:
- Peripheral zone (peripheral zone). Occupies the posterior-inferior parts, appearing as a hyperintense (bright) crescent on T2-weighted images. This is where 75–80% of cancer foci are located. It is also the main site for the development of prostatitis, which often mimics a tumor on imaging and is the primary differential diagnosis.
- Transition zone (transition zone). Located anteriorly and superiorly, around the urethra. About 20–25% of tumors arise here. With age, this specific zone enlarges due to benign prostatic hyperplasia (BPH), forming nodules and compressing adjacent structures.
- Central zone (central zone). In young men, it merges with the transition zone, but with the development of BPH, it becomes compressed and displaced toward the base of the gland.
- Anterior fibromuscular stroma. Consists of connective tissue and smooth muscle, and contains no glandular tissue.
Multiparametric MRI (mpMRI)
To date, mpMRI is the primary diagnostic imaging modality for suspected Carcinoma prostatae. The PROMIS study proved that this approach improves the detection of dangerous tumors and helps avoid many unnecessary biopsies.
The mpMRI protocol includes anatomical and functional sequences:
- T2-weighted images (T2WI) — for assessing zonal anatomy and the capsule.
- Diffusion-weighted images (DWI) — for assessing cellular density (tumors restrict water diffusion).
- Dynamic contrast-enhanced (DCE) imaging — for assessing vascularization.
It is recommended to use 3 T field strength scanners for the study, as they provide a better signal-to-noise ratio. The use of an endorectal coil increases the cost of the procedure, deforms the gland, and causes discomfort, so modern protocols recommend doing without it.
PI-RADS v2 system
The PI-RADS system is used to standardize MRI descriptions. It assesses the probability of clinically significant cancer, defined as a tumor with a Gleason score ≥7, a volume ≥0.5 cm³, or extraprostatic extension.
The scale includes 5 categories:
- PI-RADS 1: The presence of cancer is highly unlikely.
- PI-RADS 2: Unlikely.
- PI-RADS 3: Intermediate probability (indeterminate risk).
- PI-RADS 4: High probability.
- PI-RADS 5: Very high probability.
The scoring depends on the zone. In the peripheral zone, the dominant sequence is DWI. In the transition zone, T2WI plays the primary role. Contrast enhancement (DCE) is of secondary importance, but is used for upgrading: if DWI in the peripheral zone yields a score of 3, positive contrast enhancement increases the final score to PI-RADS 4. Similarly, in the transition zone, DWI data can increase the score from 3 to 4.
Histopathology and Gleason score
Imaging methods only indicate suspicious areas, but the definitive diagnosis is established exclusively by a pathologist following a biopsy. A characteristic feature of prostate cancer is that it rarely forms a distinct nodule — tumor cells intermingle with normal glands.
The aggressiveness of adenocarcinoma is assessed using the Gleason system (Gleason score). The physician identifies the dominant microscopic pattern and the most aggressive non-dominant pattern (on a 5-point scale). Their sum (ranging from 2 to 10) determines the biological aggressiveness of the tumor (e.g., 3+4=7).
In modern practice, the 5-tiered ISUP Grade group system is used:
- ISUP 1: Gleason 3+3 (baseline, least aggressive)
- ISUP 2: Gleason 3+4
- ISUP 3: Gleason 4+3
- ISUP 4: Gleason 4+4, 3+5, 5+3
- ISUP 5: Gleason 4+5, 5+4, 5+5
Clinical risk stratification
After obtaining MRI and biopsy data, the patient is assigned to a specific clinical risk group (according to EAU or AUA classifications).
This combines three factors:
- Blood PSA level.
- Stage based on clinical and MRI data (e.g., organ-confined tumor ≤T2 or extraprostatic extension ≥T3).
- ISUP prognostic grade group (or Gleason sum).
For example, patients with PSA <10, stage T1–T2a, and ISUP 1 are classified into the low-risk group. Conversely, a PSA ≥20, stage ≥T3, or ISUP 4–5 automatically places the patient in the high-risk group, which requires aggressive treatment.
Briefly: answers to topical questions
What anatomical structures are affected in stage T3 prostate cancer?
In stage T3 prostate cancer, the tumor extends beyond the organ capsule and affects adjacent structures. The following anatomical formations are involved in the pathological process:
- Prostate capsule — extracapsular (extraprostatic) extension occurs.
- Bladder neck — microscopic involvement is observed.
- Seminal vesicles (Seminal vesicles) — tumor invasion occurs (stage T3b).
- Lateral sulci — the tumor invades them upon extending beyond the gland.
- Periprostatic adipose tissue — is infiltrated during extracapsular extension.
To which lymph nodes and organs does typical metastasis of prostate cancer occur?
Typical metastasis of prostate cancer occurs to regional and distant lymph nodes, as well as to the bones of the skeleton.
- Pelvic lymph nodes — are regional, and may be involved singly or multiply.
- Inguinal, iliac, and para-aortic lymph nodes — are involved at later stages.
- Bones of the axial skeleton — the most common site of extranodal metastases.
- Spine, pelvis, and ribs — typical zones of osteoblastic (sclerotic) involvement.
Which diseases must be differentiated from prostate cancer based on MRI findings?
Based on MRI findings, prostate cancer must be differentiated from benign and inflammatory changes described in the sources.
- Chronic prostatitis — the main differential diagnosis when prostate cancer is suspected; it can be asymptomatic, cause a rise in PSA, and mimic BPH.
- Benign prostatic hyperplasia (BPH) is characterized by enlargement of the transition zone due to adenomatous and stromal nodules.
- Post-biopsy hematomas / hemorrhage appear as T1-hyperintense areas and can impair staging due to low signal on T2-weighted imaging.
- Granulomatous prostatitis, scars, and atrophy are listed among benign changes of the peripheral zone on T2-weighted imaging.
What are the contraindications to multiparametric MRI of the prostate gland?
The sources do not list specific contraindications strictly for multiparametric prostate MRI; general limitations and contraindications to MRI are specified.
- Pacemaker / incompatible cardiac pacemaker is listed as a contraindication to MRI.
- Other implants that are contraindications to MRI are indicated in the source together with pacemakers.
- Severe claustrophobia is indicated as a reason for the impossibility or limitation of performing MRI.
- Recent prostate biopsy is not termed a contraindication, but acts as a confounding factor: to reduce false-positive results for extracapsular extension, a 6-week interval between biopsy and MRI is recommended.
P-DWI, T-T2: DWI is the primary sequence in the peripheral zone, and T2-weighted imaging in the transition zone.
Class and exam questions
Can a definitive diagnosis of cancer be made based on MRI alone?
No, diagnostic imaging only identifies lesions and assesses risks. A diagnosis of cancer is established exclusively histopathologically following a biopsy.
What does a PI-RADS 3 score mean?
This is an intermediate category meaning that the probability of clinically significant prostate cancer is equivocal.
Why is contrast used in prostate MRI if the main sequences are T2 and DWI?
Dynamic contrast-enhanced (DCE) MRI plays an auxiliary role. It is used to upgrade the risk category (from 3 to 4) in equivocal cases in the peripheral zone.
What else to study on this topic
- Criteria for extracapsular extension and T2 vs T3 staging on MRI
- Features of detecting tumors of the anterior fibromuscular stroma
- Differential diagnosis of chronic prostatitis and cancer in the peripheral zone
- Methodology for performing MRI-guided targeted biopsy
- The role of PET/CT in searching for distant metastases of prostate cancer
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