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Prostate MRI and PI-RADS

In PI-RADS 2.1 the deciding sequence in the peripheral zone is DWI and in the transition zone T2, dynamic enhancement only upgrades a score of 3 to 4 in the peripheral zone, and a score of 4–5 leads to targeted biopsy.

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Why it matters in the exam

Pre-biopsy multiparametric MRI is now recommended in a man with suspected prostate cancer: it detects clinically significant cancer and guides targeted biopsy. The 1–5 score expresses the likelihood of significant cancer. In the peripheral zone, where most tumours arise, the dominant sequence is DWI and ADC; in the transition zone the dominant sequence is T2, because benign hyperplasia confounds diffusion. Positive dynamic enhancement (DCE) upgrades a lesion from score 3 to score 4 in the peripheral zone only. A peripheral zone tumour appears as a dark focus on T2 with restricted diffusion; in the transition zone — a dark T2 focus "like erased charcoal" with ill-defined margins.

After biopsy, wait at least 6 weeks before MRI, because haemorrhage disturbs reading. Extraprostatic extension is sought on T2: capsular bulge, irregularity, a long tumour–capsule contact (above about 15 mm) and obliteration of the rectoprostatic angle. Seminal vesicle invasion: low T2 signal within the vesicles, restricted diffusion, and spread along the ejaculatory duct. With a normal MRI or a score of 1–2 and a low PSA density, avoiding biopsy may be considered.

Staging: PSMA PET-CT is preferred over CT and bone scan in high risk to detect lymph nodes and metastases. Active surveillance uses repeated MRI. Bladder cancer: MRI with the VI-RADS score assesses muscle invasion. Testicular tumour: after US, CT of the chest, abdomen and pelvis for staging — retroperitoneal nodes around the renal vessels are the first station. A man with high PSA and a palpable nodule still needs biopsy regardless of MRI.

Key points

Peripheral — DWI; transition — T2.
DCE upgrades 3 to 4 only in the peripheral zone.
PI-RADS 4–5 — targeted biopsy.
6 weeks after biopsy before MRI.
PSMA PET-CT for staging in high risk.

Summary table

Zone	Dominant sequence	Tumour appearance	Note
Peripheral	DWI and ADC	Dark T2 focus with restricted diffusion	Positive DCE upgrades 3 to 4
Transition	T2	Erased charcoal, ill-defined margins	Benign hyperplasia confounds diffusion
Extraprostatic extension	T2	Bulge, contact longer than 15 mm, obliterated angle	Changes stage
Seminal vesicles	T2 and DWI	Low signal in the vesicle	Stage T3b
After biopsy	—	Haemorrhage	Wait at least 6 weeks

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Sources

ACR–ESUR–AdMeTech PI-RADS, version 2.1 (2019) — Dominant sequences and assessment categories
EAU–EANM–ESTRO–ESUR–ISUP–SIOG Guidelines on Prostate Cancer, 2024 — Pre-biopsy MRI

Sources are given for further reading; the text is written afresh and not copied from them.

Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.