Radiology of Renal Tuberculosis (TB of Kidney) - RGUHS PG Answer

Introduction

Radiological Investigations

1. Plain X-ray KUB (Kidney, Ureter, Bladder)

• Lobar (lobular) calcification - pathognomonic of end-stage renal TB. Calcium deposits follow the lobar architecture of the kidney ("putty kidney" or autonephrectomy pattern)
• Scattered intraparenchymal calcifications or "pseudo-calculi" (calcified caseous material)
• Ureteral calcification (intramural, in nondilated ureters - distinguishes from schistosomiasis where calcified ureters are dilated)
• Calcified psoas abscess (in cases with perinephric spread)
• Renal calculi have higher incidence in TB

Key sign: Lobar pattern of calcification is pathognomonic of end-stage/healed renal TB on plain film

2. Intravenous Urography (IVU) / CT Urogram

Early Changes:

Late/Advanced Changes:

Ureteral Changes (IVU):

• Multiple ureteric strictures (commonest finding after calyceal changes)
• "Beaded" or "corkscrew" ureter
• Ureteral calcification (in nondilated ureter - unlike schistosomiasis)
• Hydronephrosis/hydroureter distal to stricture

Bladder (Cystogram):

• Reduced bladder capacity - "Thimble bladder" (contracted fibrosed bladder) - classic late finding
• Irregular bladder wall with filling defects (ulcers/tubercles initially around ureteric orifices and trigone)

3. Ultrasonography (USG)

4. CT Scan (CT Urogram / MDCT)

Key CT advantage: CT identifies calcifications, renal scars, and urothelial lesions better than any other modality; can substitute for retrograde pyelography when ureteric orifice is strictured.

5. MRI

• Limited role compared to CT
• Useful when CT is contraindicated (e.g., contrast allergy, pregnancy)
• T2W: Hyperintense cavities; low signal calcifications
• Post-gadolinium: Enhancement of urothelium and granulomas
• Diffusion-weighted imaging (DWI): Restricted diffusion in granulomas

6. Nuclear Medicine (DMSA Scan)

• Assesses differential renal function
• Important before deciding on nephrectomy (function <10-15% in affected kidney = poor prognosis)
• Shows reduced uptake in areas of scarring/non-function

Summary: Radiological Staging (IVU/CT)

Pathognomonic Signs (High-Yield for RGUHS)

References

• Bailey and Love's Short Practice of Surgery, 28th Edition (GUTB chapter)
• Merchant S, et al. "Tuberculosis of the genitourinary system - Urinary tract tuberculosis: Part I & II." Indian Journal of Radiology and Imaging, 2013

Radiology of Tuberculosis of the Kidney

Introduction & Pathogenesis

General Imaging Principles

• Papillary necrosis and parenchymal destruction
• Presence of three or more of the following is highly suggestive of TB:
  1. Pelvicalyceal thickening
  2. Ulceration
  3. Fibrosis with or without stricture
• Calcification occurs in 40-70% of cases

Modality-by-Modality Imaging Findings

1. Plain Radiograph (X-ray KUB)

• Renal calcification - may be focal, multifocal, or complete
• Putty kidney (end-stage): reniform-shaped radio-opaque calcified mass occupying the entire kidney - dystrophic calcifications fill the entire non-functioning kidney

2. Intravenous Urography (IVU) / Excretory Urography

• Loss of calyceal sharpness (mucosal oedema)
• Minor calyceal dilatation
• Papillary necrosis - moth-eaten appearance of calyces (contrast tracks into necrotic papilla)

• Infundibular strictures - obstruct renal segments, creating phantom calyx against a background of normal renal tissue
• Strictures distort the collecting system, creating cavities and contour deformities
• Ureteric strictures (multiple sites, beaded/corkscrew appearance)
• Hydronephrosis / hydroureter
• Poor or non-functioning kidney (autonephrectomy)

• Calcification - thin rim around a necrotic area or complete parenchymal replacement
• Autonephrectomy - completely non-functioning calcified kidney
• IVU can detect parenchymal calcification, cavitary lesions, infundibular stenosis with amputated calyces, or pelvicalyceal stenosis with hydronephrosis

Note: CT is not as sensitive as excretory urography for detecting early urothelial changes

3. Computed Tomography (CT) - Investigation of Choice

4. Ultrasonography (USG)

• Focal hyperechoic or hypoechoic renal masses (granulomas/tuberculomas)
• Diffuse parenchymal hyperechogenicity from calcification
• Renal abscess formation
• Loss of corticomedullary differentiation
• Urothelial thickening of the collecting system
• Hydronephrosis
• A lesion may be missed if isoechoic to the parenchyma

Limitation: USG is less sensitive than IVU or CT for subtle urothelial changes and early calcification

5. Magnetic Resonance Imaging (MRI)

• Depicting TB cavities, sinus tracts, and fistulous communications
• Assessing extrarenal spread

• T1W: Hypointense (lesion); may be isointense to parenchyma
• T2W: Thick, irregular, hypointense peripheral wall with intralesional fluid-debris level
• Post-Gd contrast: Rim enhancement and subtle internal septal enhancement
• TB granulomas appear as mildly enhancing soft-tissue masses

End-Stage Renal TB: Putty Kidney / Autonephrectomy

High-Yield Summary for RGUHS

Key point (Grainger & Allison): "The presence of three or more of the following is highly suggestive of TB: pelvicalyceal thickening; ulceration; and fibrosis with or without stricture."

TB of Ureter, Bladder and Urethra - Radiology

TUBERCULOSIS OF THE URETER

Pathological basis

Plain X-ray KUB

• Ureteral calcification - intramural, in a nondilated ureter

  This distinguishes TB from schistosomiasis (where the calcified ureter is dilated)

• Faint upper ureteral calcification alongside any renal calcification = good marker of renal TB

IVU / CT Urogram - Ureteric Findings

MRI - Ureteric TB

• Severe hydronephrosis and hydroureter proximal to stricture (T2W coronal MIP)
• Complex obstructing ureterocele in the distal ureter with internal "webs"
• Ureteric wall thickening with enhancement

TUBERCULOSIS OF THE BLADDER

Pathological basis

1. Hyperaemia near the ureteral orifice
2. Superficial ulcers + granulomatous changes involving all layers (pancystitis)
3. Healing by fibrosis at the ureteral orifice → refluxing "golf-hole" ureter
4. Extensive fibrosis of the bladder wall → "thimble bladder" (capacity <20 mL in severe cases)

IVU / Cystogram Findings

CT Findings - Bladder TB

• Diffuse circumferential mural thickening with post-contrast enhancement
• Small bladder capacity
• Dystrophic bladder wall calcification (late)
• Perivesical stranding if perivesical inflammation present
• Fistula formation (vesico-colic, vesico-cutaneous) - late complication
• CT can identify calculi, diverticula and complications including fistula/abscess

USG - Bladder TB

• Thickened bladder wall (>5 mm with full bladder)
• Reduced bladder capacity
• Post-void residual urine elevated
• Hyperechoic foci in wall = calcification

MRI - Bladder TB

• Diffuse mural thickening
• T2W: thickened wall with intermediate signal
• Gadolinium: differential enhancement - generally less enhancement than urothelial tumour
• Sagittal MRI best demonstrates bladder capacity and wall thickening

TUBERCULOSIS OF THE URETHRA

• Rare - usually secondary to bladder or prostatic TB
• Urethral stricture: single or multiple
• May present as urinary obstruction, poor urinary stream
• IVU / Urethrogram (RGU/MCU): urethral narrowing, irregular stricture
• Associated periurethral abscess or fistula can occur
• In males - periurethral abscess, fistula formation
• CT/MRI: periurethral soft tissue thickening, abscess, fistulous tracts

Summary of Named Signs - High Yield

Key teaching point (Grainger & Allison): Fibrotic strictures of infundibula, renal pelvis and ureters are highly suggestive of TB. The presence of three or more features (pelvicalyceal thickening, ulceration, fibrosis ± stricture) is needed for imaging diagnosis.

• Grainger & Allison's Diagnostic Radiology (Ch. 26 & 27) - Renal TB, MR Urography
• Comprehensive Clinical Nephrology, 7th Edition (Ch. 54) - Urinary TB: Pathogenesis, IVU findings
• Bailey & Love's Short Practice of Surgery, 28th Ed. (Ch. 81, 83) - Cystogram images

Pyeloureteritis Cystica - Radiology (15 Marks)

Definition

Pathology / Histological Basis

(Knowing this is essential for understanding the imaging)

• Cyst walls are transparent macroscopically
• Contents: mucoproteinaceous fluid
• Surrounding stroma: lymphocytic infiltrate
• No atypia, no goblet cells, no malignant features

✏️ DRAWABLE DIAGRAM 1 - Pathogenesis (Cross-Section of Urothelium)

UROTHELIUM (transitional cells)
     │
     │  Chronic irritation (stones/UTI)
     ▼
┌────────────────────────────────────────────┐
│  NORMAL      │   VON BRUNN'S NESTS formed  │
│  SURFACE     │   → buds into lamina propria│
│  UROTHELIUM  │                             │
│──────────────│─────────────────────────────│
│              │   ┌──────┐   ┌──────┐       │
│  LAMINA      │   │ cyst │   │ cyst │       │
│  PROPRIA     │   │(fluid│   │(fluid│       │
│              │   └──────┘   └──────┘       │
│──────────────│─────────────────────────────│
│  MUSCULARIS  │                             │
└────────────────────────────────────────────┘
     Cysts project INWARD into lumen
     → filling defects on IVU/CT urogram

Aetiology / Associations

Clinical Features

• Most often an incidental finding
• Symptoms are those of the underlying cause (UTI, stones)
• Haematuria (microscopic/gross)
• Diagnosis confirmed on ureteroscopy or imaging

Radiological Findings

1. Intravenous Urography (IVU) / Retrograde Pyelography (RGP)

✏️ DRAWABLE DIAGRAM 2 - IVU Appearance

       RENAL PELVIS
   ┌──────────────────┐
   │  ○  ○  ○  ○      │  ← smooth round lucent filling defects
   │     ○    ○       │     in renal pelvis = PYELITIS CYSTICA
   └────────┬─────────┘
            │ URETER (not dilated)
     ───────┤○──────
     ───────┤ ○─────     ← smooth oval filling defects
     ───────┤○──────        projecting inward
     ───────┤ ○─────        = "scalloping" of walls
     ───────┤○──────     ← bead-like / string of beads
     ───────┤ ○─────
            │
       BLADDER

2. CT Urogram (CTU) - Now the Preferred Modality

• Punctate rounded filling defects (2-3 mm) in the collecting system on excretory phase
• Best visualised in bone window settings - uniform tiny filling defects are clearly resolved
• Cysts contain fluid density (too small to measure HU reliably)
• No ureteric wall thickening (unlike ureteritis/TB)
• No perinephric stranding
• No obstruction / hydroureter
• CT is superior to IVU for detecting associated stones/cause

3. Ultrasound (USG)

• Limited utility for this condition
• May show subtle echogenic foci along the urothelial lining
• Cysts are too small to individually characterise on USG
• Can identify hydronephrosis if present (though usually absent)
• Useful for identifying associated stones (the causative factor)

4. MRI

• Not routinely used
• May show subtle filling defects on MR urography (T2W heavily weighted sequences)
• Role is mainly for equivocal cases or when CT is contraindicated

Differential Diagnosis of Multiple Filling Defects in Ureter / Renal Pelvis

✏️ DRAWABLE DIAGRAM 3 - Key Differentiating Features

MULTIPLE FILLING DEFECTS IN URETER

┌─────────────────────────────────────────────────────────┐
│                                                         │
│  SMOOTH + UNIFORM + SMALL (2-3mm)                       │
│  + NO OBSTRUCTION + BILATERAL + STABLE                  │
│                       ↓                                 │
│          PYELOURETERITIS CYSTICA ✓                      │
│                                                         │
├─────────────────────────────────────────────────────────┤
│                                                         │
│  IRREGULAR + ASYMMETRIC + ENHANCING                     │
│  + CAUSES OBSTRUCTION + PROGRESSES                      │
│                       ↓                                 │
│          UROTHELIAL CARCINOMA ✗                         │
│                                                         │
├─────────────────────────────────────────────────────────┤
│                                                         │
│  CHANGE POSITION / DISAPPEAR on repeat imaging          │
│                       ↓                                 │
│          CLOTS / AIR BUBBLES ✗                          │
│                                                         │
└─────────────────────────────────────────────────────────┘

Key Radiological Points to Emphasise in Exam

1. Pyeloureteritis cystica is listed as a false positive for upper tract urothelial carcinoma (Grainger & Allison, Table 31.2) - making correct recognition clinically important
2. IVU demonstrates it well due to small lesion size - IVU is stated as particularly useful for "pyeloureteritis cystica" in Smith & Tanagho's General Urology (p. 104)
3. CTU excretory/delayed phase is the modern investigation of choice - bone window settings improve detection
4. Stability on follow-up and negative urine cytology are reassuring features
5. No treatment required for PUC itself - treat the underlying cause (stones, UTI)

Summary Box (15-Mark Answer Checklist)

• Grainger & Allison's Diagnostic Radiology - Table 31.2 (False-positive UTUC diagnoses, including ureteritis cystica)
• Smith & Tanagho's General Urology, 19e - IVU clinical applications + Fig. 6-33 (CTU ureteritis cystica)
• Journal of Clinical Imaging Science - Radiologic-Pathologic Correlation of Ureteritis Cystica