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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)
          |
    PI-RADS 1-2        PI-RADS 3         PI-RADS 4-5
    No biopsy      Consider biopsy    MRI-TRUS fusion
    (monitor)      (clinical factors)  targeted biopsy
                                           |
                                   Histological diagnosis
                                           |
                               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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IMAGING OF BRONCHOGENIC CARCINOMA

RGUHS Radiology PG Exam - 10 Marks

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INTRODUCTION

• Detection and characterization
• Local staging (T descriptor)
• Nodal staging (N descriptor)
• Distant metastasis staging (M descriptor)
• Treatment planning and response assessment

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IMAGING MODALITIES USED

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A. CHEST RADIOGRAPHY (CXR)

1. Peripheral tumours
2. Central tumours
3. Intrathoracic staging features

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1. PERIPHERAL TUMOURS (~40% of bronchogenic Ca)

• Most are approximately spherical or oval
• Lobulation - common; indicates uneven growth in different parts
• Dumb-bell shape or two adjacent nodules may be seen
• Pancoast (superior sulcus) tumour may resemble apical pleural thickening

• Seen in tumours of any size; best demonstrated on CT
• Squamous cell carcinoma - most commonly cavitates
• Wall is thick and irregular (unlike thin-walled benign cysts)
• CT distinguishes malignant from benign cavities by wall thickness (>15 mm = malignant)

• Rare on CXR; seen on CT in 6-10% of cases
• May represent pre-existing calcified granuloma engulfed by tumour
• Amorphous/cloud-like = dystrophic tumour calcification (<10%)
• Calcified tumours are usually large (≥5 cm)

• Air bronchogram / bubble lucencies / pseudo-cavitation: adenocarcinoma
• Ground-glass opacity (GGO): more common in adenocarcinoma; may be pure GGO
• Mucocele / mucoid impaction: dilated mucus-filled bronchi distal to obstruction
• Ill-defined edges resembling pneumonia: some adenocarcinomas

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2. CENTRAL TUMOURS

• Common presenting feature
• May reflect: proximal tumour mass, lymphadenopathy, consolidated lung, or combination
• A mass superimposed on hilum → increased hilar density (summation sign)
• "Dense hilum sign": only radiographic finding in some cases - must inspect lateral film
• Lateral CXR is essential when dense hilum is suspected

• Obstruction of major bronchus → combination of atelectasis + secretion retention + opacity
• Collateral air drift may partially/completely prevent collapse

1. Golden S sign (Reverse S sign): When RUL collapses due to a central mass, the minor fissure bulges outward (over the hilar mass) while collapsing medially - creating an S-shape. Classic for right upper lobe bronchial carcinoma
2. Pneumonia confined to one lobe persisting >2-3 weeks without resolution
3. Recurring pneumonia in the same lobe - until proven otherwise = underlying carcinoma
4. Absent air bronchograms within the collapsed lobe (secretions fill the bronchi)
5. Visible mass with bronchial stenosis on CT
6. Mucus-filled dilated bronchi (branching tubular low-density structures = "finger in glove") on CT
7. Drowned lobe: opacified lobe larger than normal (build-up of infected secretions)

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Diagram to Draw in Exam (ESSENTIAL):

GOLDEN S SIGN - Right Upper Lobe Collapse with Central Mass
 
Normal position                  RUL collapse + central mass
of minor fissure:                (Golden S sign):

_____Trachea_____               _____Trachea_____
  |               |               |               |
  |               |               |        ___/   |
  |    RUL        |               |  RUL  /       |
  |_______________|               |______/ Mass   |
  |  Right hilum  |               |  Central |    |
  |               |               |  mass    |    |
  |               |               |          |    |

Minor fissure =                  Minor fissure bulges
horizontal line                  outward over mass = S shape

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B. CT SCAN (Primary Staging Modality)

CT Features for T-Staging (8th edition AJCC/UICC TNM):

CT Features for N-Staging:

• Short-axis diameter >10 mm = enlarged (95th percentile)
• Simple but imperfect criterion - many causes of benign node enlargement (TB, sarcoid, reactive hyperplasia)
• Sensitivity 55-60%, Specificity 80% for CT nodal staging

CT Signs of Mediastinal Invasion:

• Visible tumour deep within mediastinal fat
• Tumour surrounds mediastinal vessels (aorta, pulmonary artery, SVC, oesophagus, carina)
• Glazer criteria: <3 cm contact with mediastinum + preserved mediastinal fat plane = likely no invasion
• >3 cm contact / >90° circumference of vessel involvement = likely invasion

CT Signs of Chest Wall Invasion:

• Bone destruction - definitive for invasion
• Large soft-tissue mass extending into chest wall - definitive
• Contact with pleura alone: does NOT confirm invasion
• Obliteration of extrapleural fat plane = strongly suggests invasion
• Preserved extrapleural fat plane (Fig. 8.23) = likely no invasion
• CT sensitivity for chest wall invasion = ~60%

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C. PET-CT (¹⁸F-FDG)

• Nodal staging (superior to CT alone)
• Detection of distant metastases
• Identification of occult disease before planned surgery
• Recurrence detection
• Response assessment

• Higher sensitivity and specificity for nodal disease
• Detects metabolically active disease in normal-sized nodes
• Identifies distant metastases (skeleton, adrenal, liver, contralateral lung)
• Decision analysis: identifies inoperable patients, avoiding unnecessary thoracotomy
• PET/CT = single study covering skull base to upper thigh

• CT acquisition: usually low-dose unenhanced (for co-registration)
• PET acquisition: 5-7 bed positions, 3-5 minutes each (~35 minutes total)
• Modern systems: significantly faster acquisition

• False positives: active inflammation, granulomas (TB, sarcoid), reactive hyperplasia
• Brain metastases: high background FDG activity - MRI preferred
• Small lesions <8 mm: limited resolution
• Carcinoid tumours: may be FDG-negative (low metabolic activity)

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D. MRI

• T1WI axial: Shows anatomy, tumour vs. fat planes
• T2WI coronal: Extension into root of neck, brachial plexus
• Gadolinium-enhanced T1WI: Vessel/nerve enhancement
• Respiratory-gated sequences
• Advantages of current MDCT (multiplanar reformats) have reduced need for MRI

• Similar accuracy to CT using size criteria alone
• STIR imaging: 93% sensitivity, 87% specificity for malignant nodes (signal difference between normal and pathological nodes)
• Limited advantage over modern MDCT for routine nodal staging

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E. SKELETAL (BONE) SCINTIGRAPHY

• Tc-99m MDP bone scan: sensitive for skeletal metastases; positive before X-ray changes
• Largely replaced by ¹⁸F-FDG PET-CT for whole-body staging
• NaF PET-CT: more sensitive than bone scan for bone metastases

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F. ULTRASOUND

• Chest wall: detects invasion by showing fixity of tissue to pleura during respiration
• Supraclavicular lymph nodes: USG ± FNA improves sensitivity for N3 detection
• Routine use recommended by some centres to improve preoperative staging

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G. ENDOBRONCHIAL ULTRASOUND (EBUS)

• Assesses size, morphology of mediastinal nodes
• Guides fine-needle aspiration of aortopulmonary, subcarinal, posterior mediastinal nodes
• Greater sensitivity and specificity than CT/PET-CT in some series
• Now first-line for mediastinal node biopsy (replaced mediastinoscopy)

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STAGING SUMMARY TABLE (8th Edition TNM)

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OVERALL IMAGING ALGORITHM (RGUHS - Exam Diagram)

SUSPECTED BRONCHOGENIC CARCINOMA
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    CHEST X-RAY (CXR) - First investigation
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    Peripheral mass / Central opacity / Hilar enlargement
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    CONTRAST-ENHANCED CT THORAX + UPPER ABDOMEN
    (T + N staging, assess local invasion)
             |
    ┌─────────────────────────────────────┐
    |         PET-CT (¹⁸F-FDG)           |
    |   Nodal staging + distant mets      |
    |   (except brain)                    |
    └─────────────────────────────────────┘
             |
    ┌─────── SPECIFIC INDICATIONS ────────┐
    | MRI: Pancoast, chest wall, brain    |
    | EBUS: Mediastinal node biopsy       |
    | USG: Chest wall, supraclavicular    |
    | Bone scan: If PET-CT unavailable    |
    └─────────────────────────────────────┘
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    TISSUE DIAGNOSIS (bronchoscopy/CT-guided biopsy)
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    MULTIDISCIPLINARY TEAM DISCUSSION
             |
    Surgery / Radiotherapy / Chemotherapy /
    Targeted therapy / Palliative care

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SPECIAL PATTERNS

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SUMMARY BOX (For Last-Minute Revision)

• First investigation: CXR
• Primary staging tool: CECT thorax (MDCT)
• Best for nodal staging: PET-CT
• Best for Pancoast/chest wall invasion: MRI
• Best for brain metastases: MRI
• Best for bone metastases: PET-CT > Bone scan
• Key CXR signs: Corona radiata, Golden S sign, dense hilum, pleural tail, lobar collapse
• Cavitation: Squamous cell carcinoma most common; thick irregular wall
• Nodal criterion: Short-axis >10 mm on CT = enlarged
• Mediastinal invasion on CT: <3 cm contact + preserved fat = likely no invasion
• Pleural effusion = M1a (confirm by cytology unless another cause proven)
• TNM system: 8th edition AJCC/UICC used for NSCLC and SCLC

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