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PG DMRD Year-1 Radiology Diagnosis - January 2025

Complete Model Answers

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QUESTION 1 (30 marks)

Anatomy of the Biliary Tree, Radiological Evaluation of Obstructive Jaundice in a 40-year-old Male, and Differential Diagnosis

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A. ANATOMY OF THE BILIARY TREE

• Bile canaliculi (between hepatocytes) drain into bile ductules (canals of Hering)
• These drain into interlobular bile ducts, then segmental ducts
• Right and Left hepatic ducts emerge at the porta hepatis
• The right hepatic duct drains the right lobe (anterior segment = segments V, VIII; posterior segment = VI, VII)
• The left hepatic duct is longer (3 cm) and drains segments II, III, IV (quadrate lobe)

• Common hepatic duct (CHD): Formed by union of right and left hepatic ducts; 2-3 cm long; runs in the free edge of the lesser omentum
• Cystic duct: Joins CHD from the right; 3-4 cm long; contains the spiral valve of Heister; enters CHD at an acute angle
• Common bile duct (CBD): 7-11 cm long; 4 key parts:
  • Supraduodenal (in hepatoduodenal ligament, with portal vein and hepatic artery)
  • Retroduodenal (behind first part of duodenum)
  • Pancreatic (in groove on posterior surface of pancreatic head)
  • Intraduodenal (oblique intramural course through ampulla of Vater, controlled by Sphincter of Oddi)
• Normal CBD diameter: Up to 6 mm (increases to 10 mm post-cholecystectomy)
• Gallbladder: Pear-shaped (7-10 cm long); fundus, body, infundibulum (Hartmann's pouch), neck

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B. RADIOLOGICAL EVALUATION OF OBSTRUCTIVE JAUNDICE

1. Ultrasound Abdomen (FIRST-LINE investigation)

• Cheapest, no radiation, bedside availability
• Key findings in obstruction:
  • Dilated CBD (>6 mm) - confirms biliary obstruction
  • Intrahepatic biliary radicle dilatation (IHBRD): "Too many tubes" sign - bile ducts alongside portal vein branches give parallel channel sign
  • Level of obstruction: Can determine whether obstruction is at porta hepatis, mid-CBD, or lower CBD
  • Gallstones: Hyperechoic foci with posterior acoustic shadowing
  • Pancreatic head mass: Hypoechoic, dilated pancreatic duct (double duct sign)
  • CBD: Measure at porta hepatis in right intercostal view
• Limitation: Gas, obesity, overlying structures may obscure lower CBD

2. MRCP (Magnetic Resonance Cholangiopancreatography) - SECOND-LINE, gold standard non-invasive

• Heavy T2-weighted sequences (fluid appears bright - "white bile duct" technique)
• No contrast, no radiation, no intervention needed
• Shows entire biliary tree - intrahepatic and extrahepatic
• Key findings:
  • Exact level and cause of obstruction
  • "Rat-tail" stricture: Pancreatic carcinoma
  • Smooth tapering: Chronic pancreatitis / stricture
  • Filling defects (dark on T2): CBD stones
  • Hilar stricture: Klatskin tumor - Bismuth classification
  • Primary sclerosing cholangitis: Beaded, pruned-tree appearance
• Sensitivity: 95% for choledocholithiasis, >90% for malignant obstruction

3. CT Abdomen (Contrast-enhanced - CECT)

• Excellent for pancreatic head masses, lymphadenopathy, vascular invasion, liver metastases, staging
• Protocol: Triple phase - plain, arterial, portal venous phases
• Findings:
  • "Double duct sign": Simultaneous dilatation of both CBD and pancreatic duct - highly suggestive of periampullary carcinoma
  • Mass in pancreatic head: Iso/hypodense to pancreas, hypovascular
  • Gallbladder carcinoma: Irregular wall thickening or mass replacing gallbladder
  • Cholangiocarcinoma: Hilar mass, peripheral enhancement
  • Portal vein involvement, hepatic artery encasement (unresectable criteria)

4. ERCP (Endoscopic Retrograde Cholangiopancreatography)

• Combined diagnostic and therapeutic modality
• Gold standard for lower CBD stones (can extract at same sitting)
• Visualizes ampulla directly
• Diagnostic: Cholangiogram, cytology brushing
• Therapeutic: Sphincterotomy, stone extraction, biliary stenting (plastic/metal), balloon dilatation
• Risk: Pancreatitis (3-5%), bleeding, perforation, cholangitis

5. PTC (Percutaneous Transhepatic Cholangiography)

• Used when ERCP fails or for high/hilar obstruction
• Fluoroscopy-guided needle into dilated intrahepatic duct
• Opacifies the biliary system above the obstruction
• Therapeutic: PTBD (Percutaneous transhepatic biliary drainage) - external or internal-external

6. Endoscopic Ultrasound (EUS)

• Best for small ampullary lesions, small CBD stones, local staging of pancreatic head tumors
• FNA/biopsy possible

7. Nuclear Medicine - HIDA Scan (Hepatobiliary Iminodiacetic Acid)

• Tc-99m labeled HIDA injected IV; secreted in bile
• Shows bile flow in real-time
• Useful for:
  • Post-operative bile leaks
  • Biliary atresia in neonates
  • Biliary dyskinesia

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C. DIFFERENTIAL DIAGNOSIS OF OBSTRUCTIVE JAUNDICE

1. Choledocholithiasis (CBD stone) - commonest overall
2. Carcinoma of head of pancreas - painless progressive jaundice + Courvoisier's sign (palpable non-tender gallbladder)
3. Cholangiocarcinoma
4. Periampullary carcinoma
5. Chronic pancreatitis - benign stricture

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QUESTION 2 (30 marks)

Diagnostic and Therapeutic Role of Radiology in a 70-year-old Man with Lower GI Bleeding

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INTRODUCTION

1. Diverticular disease (most common - 40%)
2. Angiodysplasia (arteriovenous malformations)
3. Colorectal carcinoma
4. Ischemic colitis
5. Hemorrhoids / anorectal disease
6. Inflammatory bowel disease

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A. DIAGNOSTIC RADIOLOGY IN LOWER GI BLEEDING

1. CT Angiography (CTA) - First-line Imaging

• Thin-slice (0.5-1 mm) MDCT
• Three phases: Plain (baseline), Arterial phase (20-25 sec), Portal venous phase (60-70 sec)
• Contrast medium: 80-120 mL iodinated contrast at 4-5 mL/sec
• Can detect bleeding rates as low as 0.3-0.4 mL/min

• Active bleeding: Extravasation of contrast ("blush") into bowel lumen - increases in density from arterial to delayed phase
• Shows precise location in the colon
• Identifies the bleeding vessel (branch of superior or inferior mesenteric artery)
• Identifies underlying cause: diverticular disease, mass, AVM

• Fast, widely available, non-invasive
• Maps the bleeding site for targeted intervention
• Rules out other causes (obstruction, perforation, ischemia)
• Grainger & Allison's Diagnostic Radiology - CTA for acute gastrointestinal bleeding is now standard of care

2. Radionuclide Imaging (Nuclear Scintigraphy)

• RBCs labeled with Tc-99m; injected IV
• Imaging over 24 hours (intermittent or continuous)
• Most sensitive - can detect bleeding as slow as 0.1 mL/min
• Uses: Low-grade/intermittent bleeding where CTA may be negative
• Findings: Area of focal accumulating radiotracer ("hot spot") moving with peristalsis

• Taken up by liver/spleen; bowel lumen has none - bleeding appears as "hot" activity
• Very rapid clearance limits imaging to first 30 minutes
• Less used than RBC scan

3. CT Colonography (Virtual Colonoscopy)

• Used in stable patients after acute bleeding settles
• 3D reconstruction of colon using CT data
• Detects polyps >6 mm, masses, diverticula
• Used when optical colonoscopy fails or is incomplete

4. Conventional Angiography (Digital Subtraction Angiography - DSA)

• After positive CTA or nuclear scan
• Catheter placed via femoral artery into SMA or IMA
• Diagnostic: Shows contrast extravasation, AVMs, early draining vein
• Detects bleeding at 0.5-1.0 mL/min

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B. THERAPEUTIC RADIOLOGY (INTERVENTIONAL RADIOLOGY)

1. Transcatheter Embolization

• Most important therapeutic role in LGIB
• Performed after identification of bleeding vessel on DSA
• Technique: Super-selective catheterization using microcatheters (2.7-2.8 Fr) into the bleeding branch
• Embolic agents used:
  • Microcoils (most common for LGIB) - mechanical occlusion
  • Gelfoam pledgets - temporary hemostasis
  • Polyvinyl alcohol (PVA) particles
  • N-butyl cyanoacrylate (NBCA glue) - for refractory cases
• Super-selective embolization minimizes risk of bowel ischemia
• Technical success: 85-95%
• Clinical success: 70-90% (rebleeding rate 15-25%)
• Complication: Colonic ischemia (1-4% with super-selective technique)

2. Vasopressin Infusion (Vasoconstrictive Therapy)

• Historically used; now largely replaced by embolization
• Catheter left in SMA/IMA; vasopressin infused at 0.2-0.4 U/min
• Causes mesenteric vasoconstriction, reduces arterial flow to bleeding site
• Temporary effect - rebleeding on stopping infusion (50% rate)
• Risk: Systemic hypertension, cardiac ischemia, mesenteric ischemia

3. TIPS (Transjugular Intrahepatic Portosystemic Shunt)

• For LGIB secondary to portal hypertension / ectopic varices
• Creates shunt between portal and hepatic vein to decompress portal system

4. Percutaneous Drainage

• For pericolic abscess from diverticulitis causing bleeding

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C. MANAGEMENT ALGORITHM (70-year-old male)

Lower GI Bleeding
    ↓
Hemodynamic resuscitation + Labs
    ↓
CTA Abdomen/Pelvis (FIRST imaging)
    ↓
Active blush seen? → YES → Conventional DSA + Embolization
    ↓
No active bleed seen?
    ↓
Colonoscopy (elective) OR Tc-99m RBC scan if intermittent
    ↓
Source found → Colonoscopic therapy / Surgery

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QUESTION 3 (20 marks)

A: Double Contrast Barium Enema - Technique, Advantages and Disadvantages over CT

B: Imaging Findings in Ulcerative Colitis and Crohn's Disease

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PART A: DOUBLE CONTRAST BARIUM ENEMA (DCBE)

Definition

Patient Preparation

• Low-residue diet 2 days before
• Clear liquid diet day before
• Bowel preparation: Magnesium citrate, bisacodyl suppository, or polyethylene glycol
• NPO after midnight

Technique (Step by Step)

• Check adequacy of bowel preparation
• Baseline to detect calcification, perforation

• Rectal tube inserted per rectum
• High-density barium (80-100% w/v, low viscosity) slowly instilled under fluoroscopic guidance
• Fill up to the mid-transverse colon (approximately 300-400 mL)

• Barium tap closed; air introduced via rectal tube
• This distends the colon and pushes barium to coat the walls

• Patient rotated through multiple positions (supine, prone, right and left decubitus, obliques, erect)
• Each rotation uses gravity to coat each segment with barium
• Order: Right lateral, left lateral, prone, supine, erect

• Each segment examined; spot films taken
• Complete colonic coating from rectum to ileocaecal valve
• Terminal ileum often refluxes with barium (ileocaecal incompetence)

• AP, PA, lateral and oblique views
• Rectosigmoid: Lateral view most important

Interpretation of DCBE Views

• Barium pools in dependent portion (white/opaque)
• Air fills non-dependent portion (black)
• Mucosa coated by barium at air-barium interface
• Normal: Smooth haustral folds, no filling defects

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ADVANTAGES of DCBE over Contrast-Enhanced CT Colon (CT Colonography)

DISADVANTAGES of DCBE compared to CT

1. No extracolonic information - Cannot detect liver metastases, lymphadenopathy, peritoneal disease
2. Operator dependent - Skill-intensive; poor preparation leads to missed lesions
3. Cannot biopsy - Only diagnostic; CT can guide biopsy
4. Bulky/sessile lesions - CT better for annular carcinoma, staging
5. Post-surgical anatomy - CT better after bowel resection
6. Rectal lesions - Not well evaluated (catheter tip obscures area)
7. Patient compliance - Elderly patients find rotation difficult
8. Ileoscopy - Cannot directly visualize ileum (DCBE may show terminal ileum on reflux only)
9. Cannot detect mural/serosal disease - CT shows mural thickening, pericolic fat stranding
10. Virtual colonoscopy - CT colonography now preferred for polyp detection screening

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PART B: IMAGING FINDINGS IN ULCERATIVE COLITIS (UC) AND CROHN'S DISEASE

ULCERATIVE COLITIS - Imaging Features

• Starts in rectum (rectum ALWAYS involved) and extends proximally in continuous fashion
• Pancolitis (entire colon) in severe cases

• Early: Fine mucosal granularity (sandpaper pattern) - first sign
• Moderate: Superficial ulcers (collar-stud ulcers), mucosal edema
• Severe: Extensive ulceration - "cobblestone" pattern
• Chronic changes:
  • Loss of haustrations - "lead pipe" colon (featureless, smooth, shortened colon)
  • Pseudopolyps / inflammatory polyps (islands of regenerating mucosa surrounded by ulcerated areas)
  • Shortened, narrow colon
  • Widened retrorectal space (>15 mm)
  • "Collar-stud" ulcers: Superficial ulcer communicating with submucosal tunnel

• Continuous circumferential wall thickening
• Mucosal enhancement (target sign or halo sign)
• Pericolonic fat stranding
• Shortened colon
• Toxic megacolon (severe complication): Colonic dilatation >6 cm, loss of haustrations, mucosal irregularity

• Wall thickening with layered enhancement
• Useful for pre-surgical assessment

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CROHN'S DISEASE - Imaging Features

• "Skip lesions" - any part of GI tract from mouth to anus
• Terminal ileum most commonly involved (70%)
• Rectum often SPARED
• Asymmetric, eccentric involvement

• Earliest finding: Aphthoid ulcers (tiny ulcers with surrounding edema halo - 1-3 mm) - seen in transverse colon
• Deep ulcers: Longitudinal and transverse ulcers - "cobblestone" appearance (due to deep linear ulcers + mucosal islands between)
• Fissures and fistulae: Deep trans-mural fissures; enterocutaneous, enterovesical, enteroenteric fistulae
• String sign of Kantor: Severe narrowing of terminal ileum due to spasm/fibrosis
• Pseudodiverticula: On the anti-mesenteric border due to asymmetric fibrosis
• Skip lesions: Normal areas between diseased segments

• Segmental bowel wall thickening (asymmetric)
• Mesenteric fat proliferation - "creeping fat" (fibro-fatty proliferation of mesentery)
• Mesenteric hypervascularity - "comb sign" (engorged vasa recta)
• Abscess formation (pericolic/psoas)
• Fistula tracts
• Terminal ileal thickening + narrowing

• Better soft tissue contrast, no radiation (important in young patients)
• T2-bright wall thickening = active inflammation
• T1 post-contrast enhancement of wall
• DWI (Diffusion Weighted Imaging) - areas of restricted diffusion in active disease

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COMPARISON TABLE: UC vs. CROHN'S on Imaging

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QUESTION 4 (20 marks)

A: Imaging Evaluation and Differential Diagnosis of Wilms' Tumour

B: Definition of Endometriosis and Imaging Findings of Pelvic Endometriosis

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PART A: WILMS' TUMOUR (NEPHROBLASTOMA)

Definition and Overview

• Incidence: 6-7% of all childhood cancers; 95% of kidney cancers in children under 15
• Age: Typically under 5 years (median 3.5 years); peak at 3-4 years
• Gender: Slightly more common in females
• Associated syndromes:
  • WAGR syndrome (Wilms, Aniridia, Genitourinary anomalies, intellectual disability) - WT1 gene deletion
  • Denys-Drash syndrome - WT1 mutation
  • Beckwith-Wiedemann syndrome - WT2 gene; macroglossia, hemihypertrophy, organomegaly
  • Perlman syndrome
• Bilateral in 5-7%

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IMAGING EVALUATION

1. Ultrasound (First-line imaging)

• Findings:
  • Large, well-defined, heterogeneous intrarenal mass
  • Mixed echogenicity (solid and cystic components due to necrosis, hemorrhage)
  • Compresses and distorts remaining normal kidney (claw sign)
  • IVC and renal vein thrombus in 4-10% - must be assessed (color Doppler)
  • Contralateral kidney evaluation for bilateral tumor
• Doppler: Color Doppler shows tumor vascularity; assess IVC for tumor thrombus extension
• Limitation: Cannot reliably detect lung metastases or lymph nodes

2. CECT Abdomen and Chest (Staging - Standard of care)

• Primary tumor:
  • Large heterogeneous mass arising from kidney
  • Enhancing solid components + non-enhancing necrotic/hemorrhagic areas
  • "Claw sign" - rim of normal enhancing renal parenchyma around the mass
  • Intrarenal origin distinguishes from neuroblastoma (which displaces kidney)
  • Calcification in ~10% (eggshell or amorphous - less common than neuroblastoma)
• Staging on CT:
  • Stage I: Tumor confined to kidney, completely excised
  • Stage II: Extends beyond kidney, completely excised
  • Stage III: Residual non-hematogenous tumor, nodes positive
  • Stage IV: Hematogenous mets (lung > liver > bone > brain)
  • Stage V: Bilateral tumors
• IVC thrombus: CT shows filling defect in IVC - surgical planning essential
• Lymph nodes: Retroperitoneal, para-aortic
• Liver: Hepatic metastases
• Lung CT: Primary staging site for metastases (nodular lesions)

3. MRI

• Preferred in children to reduce radiation
• T1: Heterogeneous signal
• T2: High signal areas (necrosis, cystic)
• Gadolinium enhancement of solid components
• Superior for IVC thrombus characterization
• Better for bilateral tumor and residual disease assessment

4. Nuclear Medicine

• Tc-99m DMSA/DTPA scan: Assesses functional renal tissue
• FDG-PET: Not standard; used for recurrence evaluation

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DIFFERENTIAL DIAGNOSIS OF RENAL MASS IN A CHILD

• Wilms: Intrarenal origin, kidney displaced/distorted but remains; IVC thrombus
• Neuroblastoma: Adrenal/paraaortic origin, encases and displaces (does not arise from) kidney, calcification >90%, VMA elevated, crosses midline more commonly

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PART B: ENDOMETRIOSIS - DEFINITION AND IMAGING FINDINGS

Definition

• Prevalence: 10-15% of women of reproductive age; 25-50% of infertile women
• Pathogenesis theories: Retrograde menstruation (Sampson's theory - most accepted), coelomic metaplasia, lympho-vascular spread
• Classification (ASRM/rASRM): Stage I (minimal) to Stage IV (severe) based on laparoscopic scoring
• Sites: Ovaries most common, followed by posterior cul-de-sac (pouch of Douglas), uterosacral ligaments, bladder, rectosigmoid, small bowel, lungs (rare)

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IMAGING FINDINGS IN PELVIC ENDOMETRIOSIS

A. Ultrasound (First-line imaging)

• Endometrioma (Chocolate cyst):
  • Homogeneous low-level echoes ("ground glass" appearance) - classic finding
  • Thick wall, posterior acoustic enhancement
  • May have hyperechoic wall foci (cholesterol crystals)
  • No or minimal internal vascularity on Doppler
  • Bilateral in 30%
  • Size: 2-20 cm
• Deep infiltrating endometriosis (DIE):
  • Hypoechoic nodules in rectovaginal septum, uterosacral ligaments
  • Uterine fixation (fixed, retroverted uterus)
  • Loss of sliding sign (adhesions) - dynamic transvaginal US
• Adenomyosis (endometriosis within myometrium):
  • Enlarged uterus, globular appearance
  • Heterogeneous myometrium, myometrial cysts
  • Thickened junctional zone

B. MRI - Gold Standard for Deep Infiltrating Endometriosis (DIE)

• T1-weighted: High signal (bright) due to methemoglobin (subacute blood products) - pathognomonic
• T2-weighted: Low to intermediate signal (T2 shading) - due to recurrent hemorrhage and hemosiderin layering
• "T2 shading sign" - progressively lower signal on T2 compared to simple cysts - indicates old blood
• "T1 bright, T2 dark" = classic endometrioma

• Uterosacral ligaments: Thickened, irregular, low T2 signal; most common DIE site
• Rectovaginal nodule: Low T2 signal nodule in the rectovaginal septum; may show spiculated margins
• Bladder endometriosis: Low T2 signal nodule on posterior bladder wall, best seen on T2 sagittal
• Bowel endometriosis (rectosigmoid): Tethering, thickening, low signal nodule on anterior wall of rectosigmoid
• Peritoneal implants: Small T1-bright deposits on peritoneal surfaces
• Ovarian endometrioma: Bilateral "kissing ovaries" (adherent to posterior uterus)

• Pelvic MRI with 3 Tesla preferred
• Small field of view
• T1 fat-suppressed (FS) sequences essential - high signal persists after fat suppression confirming blood products
• T2 sagittal, axial, coronal
• DWI to assess for malignant transformation (endometrioma-associated clear cell/endometrioid carcinoma)

C. CT

• Less useful for endometriosis
• May show complex pelvic mass, adhesions, bowel involvement
• Used for surgical planning; MRI always superior

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COMPLICATIONS OF ENDOMETRIOSIS (Imaging clues)

• Infertility: Tubal occlusion on hysterosalpingography
• Malignant transformation: 1% risk; suspect if rapid growth, solid component, septal thickening in endometrioma on MRI
• Bowel obstruction: Rectosigmoid involvement - narrowed lumen on CT

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SUMMARY TABLE: IMAGING MODALITIES BY CONDITION

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