The DOMINANT sequence depends on the zone — diffusion in the peripheral zone, T2 in the transition zone — and getting that backwards inverts the score.
Orient first
- Assessment is ZONE-DEPENDENT and this is the single most common source of error. In the PERIPHERAL zone, DWI/ADC is the dominant sequence and T2 is secondary. In the TRANSITION zone, T2 is dominant and DWI is secondary.
- Dynamic contrast enhancement is a TIE-BREAKER, not a primary sequence: it upgrades an equivocal peripheral-zone lesion and does little else.
- Suspicious peripheral-zone findings are focal, markedly hypointense on T2, with marked restriction — low ADC and high b-value signal — and a non-circumscribed shape.
- In the transition zone, benign hyperplastic nodules are ENCAPSULATED and well-defined; a suspicious lesion is a lenticular or ill-defined homogeneous moderately hypointense area — the "erased charcoal" appearance.
- HAEMORRHAGE after biopsy mimics and obscures tumour for weeks; T1-bright material in the gland must be recognised before scoring anything.
Acquire the study
- High-resolution T2 in three planes, DWI with a high b-value and an ADC map, and dynamic contrast-enhanced sequences.
- Wait an adequate interval after biopsy — commonly quoted as at least 6 weeks — because post-biopsy haemorrhage degrades the study.
- Antispasmodic where available, and patient preparation to reduce rectal gas, which distorts the DWI at the posterior peripheral zone.
- Confirm which sequence you are on before judging any signal — see the MRI sequence primer.
- Check that the high b-value images are of usable quality before relying on them.
The manoeuvre
- Review T1 FIRST for post-biopsy haemorrhage and note where it is.
- Identify the zone of any lesion — peripheral, transition, central or anterior fibromuscular stroma — before scoring it.
- For a PERIPHERAL zone lesion, score on DWI/ADC and use T2 as supporting; apply dynamic contrast only to an equivocal score.
- For a TRANSITION zone lesion, score on T2 and use DWI as supporting.
- Measure the lesion in its largest dimension on the sequence on which it is best seen, and say which sequence that was.
- Assess EXTRAPROSTATIC EXTENSION: capsular bulge, irregularity, breach, and neurovascular bundle involvement.
- Assess the seminal vesicles for low T2 signal and restricted diffusion.
- Assess pelvic nodes and the visible bones — bone metastases are frequently visible and frequently missed on these studies.
- Assign a category using a named system, state the version, and mark the lesion on a sector map.
What confirms it
- A high-category lesion is one that is dominant on the ZONE-APPROPRIATE sequence and measures 1.5 cm or more, or shows definite extraprostatic extension.
What licenses you to exclude it
- ⚠️ A negative study does not exclude clinically significant cancer, particularly anteriorly and in a large gland. State the residual risk rather than issuing an all-clear.
- A study performed too soon after biopsy is degraded by haemorrhage and should be reported as limited, with a recommendation to repeat.
- Severe rectal gas artefact on DWI makes the posterior peripheral zone non-diagnostic — say so rather than scoring it.
The classic misread
- Scoring a transition-zone lesion on diffusion, or a peripheral-zone lesion on T2.
- Scoring through post-biopsy haemorrhage.
- Using dynamic contrast as a primary rather than a tie-breaking sequence.
- Not looking at the bones.