MR Urography (MRU) - Radiology

Definition

Two Main Techniques

1. Static-Fluid (Anatomical) MRU

• Uses heavily T2-weighted sequences (e.g., HASTE/SSFSE - Half-Fourier Acquisition Single-Shot Turbo Spin-Echo)
• Fluid-filled structures (urine, CSF, bile) appear bright white due to long T2 relaxation time
• Does NOT require contrast injection
• Best for: demonstrating hydronephrosis, hydroureter, duplex systems, congenital anomalies
• Works well even in non-dilated or poorly functioning systems
• A thick-slab (60 mm) coronal oblique sequence gives the "urogram" overview

2. Excretory (Functional) MRU

• Uses T1-weighted gradient-echo sequences after IV gadolinium contrast injection
• Mimics conventional intravenous urography/pyelography
• Dynamic contrast-enhanced (DCE) sequences capture: arterial phase → corticomedullary phase → excretory phase
• Provides differential renal function (DRF), renal output efficiency, time-to-peak enhancement
• Strongly correlates with radionuclide scintigraphy (correlation coefficient ~0.95)

Typical MRU Protocol Sequences

Indications

Primary Indications

1. Hydronephrosis - primary indication; assessment of obstructive uropathy
2. Pregnancy with suspected ureteric calculus - avoids radiation; CT contraindicated
3. Children - avoids radiation burden in the developing patient
4. Iodinated contrast contraindicated - previous anaphylaxis, severe renal impairment (though gadolinium also carries NSF risk in GFR <30)
5. Upper tract urothelial carcinoma (UTUC) - when CT urography (CTU) is contraindicated
6. Haematuria workup - alternative when CTU not possible
7. Congenital urogenital anomalies - ectopic ureters, duplex kidneys, cloacal malformations (pre-operative anatomy)
8. Post-trauma - integrity of urinary tract
9. Genitourinary TB - tract assessment
10. Renal masses - cyst characterisation, VHL syndrome follow-up
11. Neuropathic bladder - when spinal imaging also required
12. Frequent UTIs - structural assessment

In Children Specifically (Table 72.6, Grainger & Allison)

• Abdominal/pelvic mass diagnosis and follow-up
• Acute pyelonephritis complications (if USS inconclusive)
• Spinal imaging + neuropathic bladder assessment
• Complex urogenital/cloacal malformations
• Post-trauma urine leak evaluation

Advantages of MRU

Limitations of MRU

MRU vs Other Modalities

Role in Specific Conditions

Acute Flank Pain / Suspected Ureteric Colic

• Pregnant patients after inconclusive USS
• Combined USS + KUB is first approach in pregnancy, with MRU if needed
• Unenhanced CT remains gold standard for stone protocol

Upper Tract Urothelial Carcinoma (UTUC)

• CTU is optimal (sensitivity 67-100%, specificity 93-99%)
• MRU is the alternative when CTU is contraindicated
• Both RCR and ACR guidelines prefer CTU as first-line for haematuria workup

Obstructive Uropathy

• MRU shows hydronephrosis and functional drainage impairment
• Sensitivity 0.75 after intravenous contrast (Campbell-Walsh)
• Functional MRU can replace scintigraphy (MAG3 renogram) in many paediatric centres

Textbook Images

Summary Points (Exam-Focused)

• MRU uses two strategies: static T2-fluid imaging (no contrast) + excretory T1-Gadolinium imaging
• Primary indication: hydronephrosis / obstructive uropathy evaluation
• Radiation-free - safe in pregnancy and children; preferred when CTU contraindicated
• Cannot reliably detect stones - CT urography remains superior for calculi
• Full functional MRU requires hydration, diuretic, catheterisation, dynamic T1 sequences
• Functional MRU correlates with MAG3 renogram; DRF correlates coefficient ~0.95
• DWI adds value for pyelonephritis, masses, obstruction assessment
• In UTUC: CTU is first-line; MRU is alternative when CTU not feasible

Sonological Evaluation of Extratesticular Scrotal Lesions

Introduction

• Intratesticular mass: Generally considered malignant until proven otherwise
• Extratesticular mass: Only 3-6% are malignant in adults; majority are benign

Technique

• Transducer: High-frequency linear array (9-15 MHz)
• Patient position: Supine, scrotum supported on a towel between the thighs
• Grey-scale US: Both longitudinal and transverse planes; bilateral comparison ("sunglasses view" or "buddy shot")
• Colour/Power Doppler: Essential for vascularity assessment, differentiating torsion from inflammation, and characterising solid masses
• Valsalva maneuver: Performed during Doppler for varicocele assessment

A. CYSTIC EXTRATESTICULAR LESIONS

1. Hydrocele

• Anechoic (non-reflective) fluid collection surrounding the anterior and lateral aspects of the testis
• May contain swirling low-level echoes from cholesterol crystals
• Congenital hydrocele: Patent processus vaginalis in neonates; usually resolves spontaneously
• Acquired hydrocele: Secondary to infection, trauma, tumour, or idiopathic
• Multiloculated hydrocele: May resemble organising haematoma; septations seen
• US indicated when hydrocele prevents clinical palpation of the testis (to exclude underlying malignancy)

2. Epididymal Cyst / Spermatocele

• Both result from dilated epididymal tubules
• Spermatocele: Retention cyst of the head of epididymis; contains sperm; usually found in the caput
• Epididymal cyst: May occur anywhere in the epididymis; does NOT contain sperm

• Well-defined, discrete, anechoic (non-reflective) fluid-containing structure
• Single or multiple; posterior acoustic enhancement
• Located adjacent to the testis in the epididymis
• Large cysts may superficially resemble a hydrocele

3. Pyocele

• Rare complication of epididymo-orchitis
• Results from communication between an infected hydrocele and the tunica vaginalis lining

• Complex, often heavily loculated fluid collection
• Multiple low-level internal echoes due to pus
• Thick irregular walls
• Associated epididymal/testicular abscess

4. Haematocele / Organising Haematoma

• Blood within the tunica vaginalis, usually post-traumatic

• Septated, complex collection with variable echogenicity
• Hyperechoic acutely, becoming more complex over time
• May be indistinguishable from a multiloculated hydrocele

B. SOLID EXTRATESTICULAR LESIONS

5. Epididymitis (Acute)

• Enlarged epididymis (focal or diffuse involvement)
• Heterogeneous and hypoechoic echotexture compared to normal
• The tail and body are most commonly affected
• Associated reactive hydrocele common
• Scrotal wall thickening/oedema

• Increased colour flow in ALL cases of acute epididymitis - key diagnostic feature
• None of the cases of scrotal pain WITHOUT epididymitis demonstrate this finding
• Doppler differentiates epididymitis from testicular torsion (which shows absent flow)
• If orchitis co-exists (epididymo-orchitis), the testis also shows increased vascularity

6. Varicocele

• Multiple serpiginous, tubular anechoic structures in the spermatic cord, posterior and superior to the testis
• Pampiniform venous diameter >3 mm = abnormal
• Increased diameter on Valsalva manoeuvre / upright position
• Colour Doppler: Retrograde (reversed) venous flow on Valsalva maneuver = diagnostic criterion
• Subclinical varicoceles not palpable on clinical exam can be detected by US + Doppler

Isolated right-sided varicocele on US warrants CT abdomen to exclude retroperitoneal mass causing venous compression.

7. Epididymal Tumours

• Well-defined, solid mass
• Echotexture similar to or slightly hyperechoic compared to testis
• Usually no increased Doppler flow
• Size ranges from 3 mm to 5 cm
• Location: tail of epididymis most commonly

• Seen following vasectomy, trauma, or infection
• Solid, well-defined, hypoechoic extratesticular mass ≤1 cm
• Located in epididymis or along vas deferens

8. Spermatic Cord Lipoma

• Most common spermatic cord "mass"
• Appears as echogenic fatty tissue within the cord
• No internal vascularity on Doppler

9. Splenogonadal Fusion

• Extratesticular solid lesion adjacent to the upper pole of the left testis
• Colour Doppler may show a central feeding vessel branching outward (splenic-type pattern)
• Nuclear medicine (99mTc sulphur colloid scan) confirms ectopic splenic tissue
• Can be mistaken for intratesticular solid lesion, leading to unnecessary orchiectomy if not recognised preoperatively

10. Post-Vasectomy Changes

• Normal late post-vasectomy finding: epididymal enlargement in ~45% of men
• Epididymis appears enlarged but otherwise normal in echogenicity
• No increased Doppler flow (distinguishes from epididymitis)

C. MISCELLANEOUS EXTRATESTICULAR CONDITIONS

Testicular Torsion (Paratesticular component)

• While the testicle itself is involved, the spermatic cord twisting produces extratesticular changes
• Twisted, oedematous spermatic cord may be visible as a "whirlpool sign" on Doppler
• Absent or markedly reduced testicular blood flow on Colour Doppler = torsion
• Reactive hydrocele may be present

Fournier Gangrene (Scrotal Wall)

• Necrotising fasciitis of perineum/scrotum
• US shows thickened scrotal wall with dirty shadowing/gas within scrotal wall
• CT preferred for full extent assessment

D. SUMMARY TABLE

Summary Points (RGUHS Exam)

1. US is the first-line imaging for all extratesticular scrotal lesions - no radiation, real-time, cheap
2. Key role: Determine intratesticular vs extratesticular location (malignancy risk differs dramatically)
3. Extratesticular masses are predominantly benign in adults but 50% malignant in children
4. Hydrocele = most common extratesticular cystic lesion; anechoic fluid surrounding testis anteriorly and laterally
5. Epididymitis: Enlarged heterogeneous epididymis + increased Colour Doppler flow (differentiates from torsion)
6. Varicocele: Tubular anechoic structures >3 mm + retrograde flow on Valsalva on Doppler
7. Adenomatoid tumour = most common solid epididymal tumour
8. Pyocele = emergency - complex loculated collection with pus echoes
9. Doppler US is essential for all solid extratesticular lesions and acute scrotal pain
10. Isolated right varicocele on US warrants CT to exclude retroperitoneal pathology

Sonological Evaluation of Extratesticular Scrotal Lesions

Introduction (1 mark)

• Intratesticular mass → generally malignant until proven otherwise
• Extratesticular mass → only 3-6% malignant in adults; majority benign
• Exception: In children, 50% of extratesticular solid masses are malignant (usually rhabdomyosarcoma)

Technique

• High-frequency linear array transducer: 9-15 MHz
• Patient: supine, scrotum supported on a towel
• Grey-scale + Colour/Power Doppler imaging
• Bilateral comparison ("sunglasses/buddy shot" - both testes side-by-side)
• Valsalva manoeuvre during Doppler for varicocele

A. CYSTIC EXTRATESTICULAR LESIONS (3 marks)

1. Hydrocele

• Most common cause of scrotal swelling
• Congenital: Patent processus vaginalis in neonates; usually resolves spontaneously
• Acquired: Secondary to infection, trauma, tumour, or idiopathic

• Anechoic (non-reflective) fluid surrounding the anterior and lateral aspects of the testis
• May contain swirling low-level echoes (cholesterol crystals)
• Multiloculated hydrocele may mimic organising haematoma
• US indicated when size prevents clinical palpation of testis (to exclude underlying tumour)

Longitudinal view: anechoic hydrocele surrounding the normal testis anteriorly and laterally

2. Epididymal Cyst / Spermatocele

• Spermatocele = retention cyst of caput (head) of epididymis; contains spermatozoa
• Epididymal cyst = may occur anywhere in epididymis; does NOT contain sperm; single or multiple

• Well-defined, discrete, anechoic fluid structure with posterior acoustic enhancement
• Located adjacent to the testis within the epididymis
• Large cysts may superficially resemble a hydrocele

Well-defined anechoic spermatocele/epididymal cyst in the head of the epididymis

3. Pyocele

• Complex, heavily loculated fluid collection
• Multiple low-level internal echoes due to pus
• Thick, irregular walls
• Associated epididymal or testicular abscess
• Must be urgently communicated to the clinical team - risk of Fournier gangrene

Pyocele: complex loculated collection with internal low-level echoes following acute epididymitis

4. Haematocele

• Blood within the tunica vaginalis, usually post-traumatic

• Septated, complex collection; variable echogenicity
• Acutely hyperechoic; becomes more complex/septated over time
• May be indistinguishable from multiloculated hydrocele

B. SOLID EXTRATESTICULAR LESIONS (4 marks)

5. Acute Epididymitis

• Enlarged epididymis (whole or focal - body/tail most commonly)
• Heterogeneous, hypoechoic echotexture compared to normal
• Associated reactive hydrocele and scrotal wall thickening

• Increased colour flow demonstrated in ALL cases of acute epididymitis
• None of the cases without epididymitis show this - highly specific
• Differentiates epididymitis (increased flow) from testicular torsion (absent flow) - critical distinction

Fig 33.17 - Acute epididymitis: body and tail (arrowed) are heterogeneous and enlarged. Testis is normal.

6. Varicocele

• Multiple serpiginous, tubular anechoic structures posterior and superior to testis in the spermatic cord
• Diameter increases in upright position and with Valsalva

• Pampiniform vein diameter >3 mm = abnormal
• Retrograde (reversed) venous flow on Valsalva manoeuvre = diagnostic
• Detects subclinical varicoceles not palpable clinically

Note: Isolated right-sided varicocele on US must prompt CT abdomen to exclude a retroperitoneal mass causing venous obstruction.

7. Adenomatoid Tumour (Most Common Solid Epididymal Tumour)

• Comprises ~30% of all paratesticular neoplasms
• Benign; usually found in the tail of epididymis

• Well-defined, solid mass; size 3 mm to 5 cm
• Echotexture similar to or slightly hyperechoic compared to testis
• No significant increase in Doppler flow
• No internal vascularity

8. Sperm Granuloma

• Chronic inflammatory reaction to extravasated sperm
• Increased incidence following vasectomy, trauma, or infection

• Solid, well-defined, hypoechoic extratesticular mass ≤1 cm
• Located in the epididymis or along the vas deferens
• Avascular on Doppler

9. Splenogonadal Fusion

• Extratesticular solid lesion adjacent to upper pole of left testis
• Colour Doppler: central feeding vessel branching outward (splenic vascular pattern)
• Confirmed by 99mTc sulphur colloid nuclear medicine scan

C. SUMMARY TABLE (1 mark)

Conclusion (1 mark)

1. Localise a lesion as extratesticular (excluding malignancy in most adult cases)
2. Characterise it as cystic or solid
3. Assess vascularity in real-time with Doppler