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RADIOLOGY PG EXAM ANSWERS - PROSTATE GLAND

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Q1. MULTIPARAMETRIC MRI (mpMRI) IN PROSTATE MALIGNANCY (10 Marks)

Introduction

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Sequences in mpMRI (the "Multi" Parameters)

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1. T1-Weighted Imaging (T1WI)

• Prostate parenchyma is isointense on T1 - no anatomical detail
• Primary use: detect post-biopsy haemorrhage (T1 hyperintense foci)
• Larger FOV up to aortic bifurcation: assess lymph nodes and bone metastases
• A minimum 6-week interval between biopsy and MRI is advised to reduce false-positive T2 staging due to haemorrhage

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2. T2-Weighted Imaging (T2WI)

• High-resolution, multiplanar (axial, sagittal, coronal), slice thickness 3 mm, no gap
• Depicts zonal anatomy of the prostate, seminal vesicles, capsule
• Peripheral Zone (PZ): Normal = homogeneous intermediate-to-high signal; thin T2-hypointense rim = capsule
  • PCa appears as focal low signal intensity area
  • High-grade tumours (Gleason 4/5): lower SI; Low-grade (Gleason 2/3): mildly hypointense/isointense
• Transition Zone (TZ): Heterogeneous due to BPH ('organised chaos')
  • PCa sign: ill-defined homogeneous T2 hypointense lesion = 'Erased Charcoal Drawing Sign'
  • Also: lenticular/fusiform anterior lesion, spiculated margins, loss of pseudocapsule
• T2WI is the dominant (primary) sequence for Transition Zone in PI-RADS v2

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3. Diffusion-Weighted Imaging (DWI) + ADC Map

• Shows random Brownian motion of water molecules
• PCa has high cell density → restricted diffusion → bright on high b-value DWI, dark on ADC map
• ADC values are inversely proportional to diffusion restriction; PCa has significantly lower ADC than normal tissue
• High-grade tumours (Gleason 4/5) show lower ADC than low-grade tumours
• Recommended b-values: 50-100 s/mm², 800-1000 s/mm², and computed/acquired ≥1400 s/mm²
• DWI is the dominant (primary) sequence for Peripheral Zone in PI-RADS v2
• Slice thickness ≤4 mm, in-plane dimension ≤2.5 mm

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4. Dynamic Contrast-Enhanced MRI (DCE)

• Gadolinium-based contrast: exploits tumour angiogenesis (VEGF-driven)
• PCa shows early, intense enhancement + early washout compared to normal parenchyma
• Role: minor/adjunct when T2WI and DWI quality is good
• Key role: upgrades a PI-RADS 3 peripheral zone lesion to PI-RADS 4 if DCE is positive
• Does NOT influence scoring at PI-RADS 1, 2, 4, or 5
• Clinically significant cancer cannot be excluded solely based on absent early enhancement

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PI-RADS v2 Scoring System

• Peripheral Zone: DWI is dominant; DCE can upgrade DWI 3 → PI-RADS 4
• Transition Zone: T2WI is dominant; DWI 5 can upgrade T2 score 3 → PI-RADS 4

PI-RADS v2 Flowchart (Grainger & Allison, Fig. 32.3)

                    PI-RADS Assessment Category
                           |
    PERIPHERAL ZONE        |          TRANSITION ZONE
    (DWI dominant)         |          (T2WI dominant)
                           |
    DWI Score 1 ---------> PI-RADS 1 <--------- T2 Score 1
    DWI Score 2 ---------> PI-RADS 2 <--------- T2 Score 2
    DWI Score 3 + DCE- --> PI-RADS 3 <--------- T2 Score 3 + DWI ≤4
    DWI Score 3 + DCE+ --> PI-RADS 4 <--------- T2 Score 3 + DWI 5
    DWI Score 4 ---------> PI-RADS 4 <--------- T2 Score 4
    DWI Score 5 ---------> PI-RADS 5 <--------- T2 Score 5

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Technical Requirements

• Field strength: 3 Tesla preferred (better SNR, spatial/temporal resolution)
• 1.5T acceptable without endorectal coil
• Endorectal coil: Optional - improves SNR but causes prostate deformation, artefacts, patient discomfort
• External phased-array coil recommended
• Protocol: T2WI + DWI + DCE (mandatory); T1WI (optional)

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Clinical Applications

1. Primary detection - triage to avoid unnecessary biopsy (PROMIS trial: 27% of patients avoided biopsy)
2. Targeted biopsy guidance - via cognitive fusion, MRI/TRUS software fusion, or "in-bore" MRI biopsy
3. Local staging - extracapsular extension, seminal vesicle invasion
4. Active surveillance - monitor low-risk disease
5. Treatment planning - radiation therapy targeting (MRI volumes 10% smaller than CT)
6. Post-treatment recurrence - T2WI for biochemical recurrence localisation

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Q2. TRANSRECTAL USG vs MRI OF THE PROSTATE GLAND (10 Marks)

Introduction

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Comparison Table

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TRUS - Details

• 7-10 MHz bi-planar transducer inserted transrectally
• Sagittal + transverse planes
• Volume calculation: prolate ellipsoid formula = L × W × H × 0.523

• Peripheral zone: uniform hypoechoic (central gland echogenic)
• Surgical capsule: echogenic line
• Seminal vesicles: symmetrical paired structures superior-posterior

1. Prostate volume measurement (essential for PSA density calculation)
2. TRUS-guided systematic biopsy - 12-core extended sextant biopsy (gold standard access route for random biopsy)
3. Colour Doppler - increased vascularity at tumour sites
4. TRUS + Elastography - tissue stiffness mapping
5. Contrast-enhanced TRUS - emerging technique
6. Guidance for brachytherapy seed implantation
7. Drainage of prostatic abscess

• 60-70% of PCa is isoechoic to background (invisible)
• Cannot assess anterior prostate, apex, or periurethral zone adequately
• Cannot assess extracapsular extension reliably
• Operator-dependent
• Cannot differentiate cancer from prostatitis, BPH nodules

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MRI - Details (See also Q1 and Q4)

1. Superior soft tissue contrast
2. Better zonal anatomy depiction
3. Accurate capsular assessment - extracapsular extension (ECE), seminal vesicle invasion (SVI)
4. Identifies anterior and transition zone tumours
5. Multi-parametric functional data (DWI, DCE)
6. Systematic staging via PI-RADS
7. Nodal and bone marrow assessment on T1WI
8. RDOG study: MRI shows higher sensitivity and specificity than endorectal ultrasound for ECE detection

• Best of both worlds: MRI identifies suspicious lesion, TRUS guides real-time needle
• Software-based image co-registration
• Three techniques: (a) In-bore MRI biopsy, (b) Cognitive fusion, (c) MRI/TRUS software fusion
• Allows targeted biopsy of PI-RADS 3-5 lesions

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Diagram to Draw in Exam:

PROSTATE IMAGING COMPARISON

TRUS                              MRI
├─ 7-10 MHz transducer            ├─ 1.5T / 3T magnet
├─ Transrectal approach           ├─ External phased-array coil
├─ Real-time guided biopsy        ├─ mpMRI protocol
├─ Volume measurement             ├─ T2WI: anatomy + staging
├─ Doppler vascularity            ├─ DWI: cancer detection
└─ Limited cancer detection       └─ DCE: vascularity

MRI-TRUS FUSION BIOPSY:
[MRI lesion map] + [Real-time TRUS] = Targeted needle placement

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Q3. DEVELOPMENT AND IMAGING MODALITIES OF PROSTATE GLAND (10 Marks)

A. EMBRYOLOGICAL DEVELOPMENT

• The prostate develops from the urogenital sinus (endodermal origin)
• Outgrowths of urogenital sinus epithelium invade the surrounding urogenital mesenchyme
• Begins at 10-12 weeks of gestation
• Development is androgen-dependent (dihydrotestosterone / DHT via 5-alpha reductase)
• Full secretory function only at puberty under testosterone influence

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B. ANATOMY (McNeal's Zonal Anatomy - 1981)

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Diagram to Draw in Exam (Zonal Anatomy - ESSENTIAL):

PROSTATE ZONAL ANATOMY - Axial View (Mid-gland)
         ANTERIOR
    ___________________
   |  ANTERIOR        |
   |  FIBROMUSCULAR   |
   |  STROMA (AFS)    |
   |___________________|
   |  TRANSITION  |CZ |
   |  ZONE  (TZ)  |   |  <- Ejaculatory ducts
   |______________|___|
   |                   |
   |  PERIPHERAL ZONE (PZ)       |
   |___________________________|
         POSTERIOR
         (Palpable on DRE)

Urethra runs through centre of TZ

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C. IMAGING MODALITIES FOR PROSTATE

1. Plain X-Ray

• Not useful for prostate itself
• May show prostatic calcifications (corpora amylacea)
• IVU: Indentation on bladder base in BPH

2. Ultrasound (TRUS)

• First-line imaging for prostate
• Volume measurement, biopsy guidance
• Normal appearance: PZ hypoechoic, CG echogenic
• Colour Doppler: vascularity in PCa
• Limitations: PCa often isoechoic, operator-dependent

3. CT Scan

• NOT useful for primary tumour detection - poor soft tissue contrast
• Staging role: lymph node assessment (N staging), osseous metastases
• CT is primary for N/M staging in high-risk PCa
• Cannot distinguish tumour from BPH within prostate

4. MRI (mpMRI - See Q1 and Q4 for details)

• Gold standard for local staging
• T2WI: anatomy, capsular integrity
• DWI: tumour detection
• DCE: vascularity
• PI-RADS v2 reporting
• 3T preferred; no endorectal coil needed at 3T

5. Bone Scintigraphy (Tc-99m MDP)

• Standard for bone metastases detection
• Recommended for: PSA >20, Gleason >7, T3/T4 disease
• Hot spots at sites of osteoblastic metastases
• Superscan in widespread disease

6. PET-CT

• Choline PET-CT: Early PCa, biochemical recurrence
• PSMA PET-CT (Ga-68 PSMA): Highly sensitive for PCa; PCa cells overexpress PSMA
  • Superior to bone scan + CT for staging and restaging
  • Increasingly preferred over choline PET
  • Detects disease at PSA levels as low as 0.2 ng/mL
• NaF PET-CT: Bone-specific, more sensitive than bone scan for skeletal metastases

7. TRUS-Guided Biopsy

• 12-core extended sextant systematic biopsy
• MRI-TRUS fusion for targeted biopsy

8. Multiparametric TRUS (mpTRUS)

• Analogous to mpMRI: combines B-mode + Doppler + contrast enhancement + elastography
• Emerging alternative/complement to mpMRI

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Q4. MRI OF THE PROSTATE GLAND (10 Marks)

Introduction

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Technical Requirements

• 3T preferred (higher SNR, better spatial and temporal resolution)
• 1.5T is acceptable without endorectal coil
• 3T without endorectal coil = diagnostic quality equivalent to 1.5T with endorectal coil

• External phased-array pelvic coil - standard of care
• Endorectal coil (optional): improves SNR but deforms prostate, increases cost, patient discomfort, artefacts

• Metallic implants, pacemakers, claustrophobia
• Post-biopsy waiting: 6 weeks (haemorrhage resolution)

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MRI Sequences and Protocols

1. T1-Weighted Imaging

• Prostate isointense: no zonal anatomy
• Detects post-biopsy haemorrhage (T1 hyperintense)
• Large FOV: nodal + bone marrow assessment
• Fat-saturation versions: improves nodal detection

2. T2-Weighted Imaging (Anatomical Sequence)

• Key sequence for anatomy and staging
• Multiplanar: axial (mandatory), coronal, sagittal
• Slice thickness 3 mm, no gap; in-plane ≤0.7 mm × 0.4 mm
• FOV 12-20 cm, covering prostate + seminal vesicles

• Focal low signal intensity area
• High-grade: markedly low SI
• Low-grade: mildly hypointense or isointense

• 'Erased charcoal drawing' sign - ill-defined homogeneous T2 hypointense lesion
• Lenticular/fusiform anterior lesion
• Spiculated/irregular margins
• Loss of pseudocapsule

T2WI PI-RADS Categories (Peripheral Zone) - Fig. 32.5, Grainger & Allison

• 1: Uniform hyperintense (normal)
• 2: Linear/wedge-shaped hypointensity, indistinct margin
• 3: Heterogeneous, non-circumscribed, rounded moderate hypointensity
• 4: Circumscribed, homogeneous, moderate hypointensity, <1.5 cm
• 5: Same as 4 but ≥1.5 cm OR definite extraprostatic extension

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3. Diffusion-Weighted Imaging (DWI)

• High b-value images: Restricted diffusion = bright signal (cancer)
• ADC map: Restricted diffusion = dark (low ADC value); inverse relationship
• Cancer has HIGH cell density → RESTRICTED diffusion → HIGH signal on DWI, LOW ADC

• Normal PZ: high ADC (fluid-rich tubular structures, especially >50 years)
• PCa: significantly lower ADC than normal tissue
• High-grade PCa (Gleason 4/5): lower ADC than low-grade (Gleason 3)

• 2: Non-focal hypointense ADC
• 3: Focal, mildly/moderately hypointense ADC + iso/mildly hyperintense high b-value DWI
• 4: Focal, markedly hypointense ADC + marked hyperintensity on high b-value, <1.5 cm
• 5: Same as 4 but ≥1.5 cm or extraprostatic extension

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4. Dynamic Contrast-Enhanced MRI (DCE)

• Early, intense enhancement + early washout (type 3 curve)
• Due to increased vascular permeability and AV shunting

• Positive DCE = focal area of earlier onset enhancement than surrounding normal tissue
• DCE upgrades PZ PI-RADS 3 to PI-RADS 4 (the only upgrade role)
• Does NOT influence PI-RADS 1, 2, 4, or 5 scoring
• Visual assessment of early enhancement phase is recommended
• Gadolinium: dose 0.1 mmol/kg, temporal resolution <10 seconds per dynamic phase

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Staging with MRI - TNM

• Irregular or spiculated margin
• Asymmetric neurovascular bundle
• Obliteration of rectoprostatic angle
• Direct tumour extension beyond capsule

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MRI in Prostate Cancer Pathway

Elevated PSA / Abnormal DRE
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    mpMRI (PI-RADS scoring)
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    PI-RADS 1-2        PI-RADS 3         PI-RADS 4-5
    No biopsy      Consider biopsy    MRI-TRUS fusion
    (monitor)      (clinical factors)  targeted biopsy
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                                   Histological diagnosis
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                               Staging MRI (T/N/M staging)
                                           |
                      Treatment planning (surgery / RT / surveillance)

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MRI in Active Surveillance

• Serial mpMRI monitoring for low-risk PCa on active surveillance
• Detects disease upgrading or progression
• Guides repeat biopsy only when PI-RADS changes

MRI vs CT vs Bone Scan for Staging

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Prostate MRI - Summary Box (for quick revision)

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