Ultrasound of the Pediatric Scrotum and Testes

Overview

Ultrasound = modality of choice for pediatric scrotum/testes
- High‐resolution anatomy + real-time perfusion
- $0$ ionising radiation, rapid and portable → crucial for acute pain/ torsion work-up
Key clinical contribution: distinguishes surgical emergencies (e.g. torsion) from conditions manageable conservatively (e.g. epididymitis)

Patient Preparation & Room Set-up

Review prior imaging; pre-populate patient details on machine
Warm room + warm gel → minimises:
- $\text{cremasteric reflex}$ (retracts testes)
- Rugose scrotal skin (esp. adolescents)
Draping/modesty:
- Towel under scrotum (forms “tray” & elevates)
- Cover penis/lower abdomen (also shields operator from urine sprays)
- Consider pre-warmed towels for comfort
Distraction devices for younger children: toys, lights, mobiles etc.

Transducer Choices & Imaging Parameters

High-frequency linear probes
- Neonate / infant: $18\,\text{MHz}$ or hockey-stick for near-field
- Older child/adolescent: $12–14\,\text{MHz}$ (adult probe)
Depth small ⇒ inherently high frame rate
Reduce persistence (frame averaging) ⇒ sharper images in wriggly kids
Activate “low-flow” or “micro-vascular” Doppler presets; neonatal flow often only a few pixels

Standard Examination Protocol

ALWAYS include transverse sweep showing both testes simultaneously (confirms two testes, detects diffuse echogenicity change)
Document:
- Long & transverse planes of each testis
- Epididymal head, body, tail
- Spermatic cord to deep ring; entire inguinal canal (unique pediatric addition – assesses patency of processus vaginalis)
- Colour & spectral Doppler of intratesticular and extra-testicular vessels
Scan kidneys in all testicular studies (shared embryologic origin → renal anomalies may coexist)

Embryology Recap

Testes develop retro-peritoneally near kidneys
Gubernaculum = fibro-muscular band anchoring lower pole to future scrotum
- Fetal growth ⇒ relative shortening ⇒ draws testis through inguinal canal
Processus vaginalis (peritoneal diverticulum) precedes descent, dilates tissues
- Normally obliterates proximally after birth
- Distal remnant = tunica vaginalis
Scrotal / canal layers = continuations of abdominal wall (external → internal oblique, transversalis etc.)

Testicular & Epididymal Anatomy

Size trajectory
- <1\,\text{mL} after 1 yr, minimal change $2–10$ yr, rapid pubertal enlargement
Shape: normal ovoid; rounded contour suggests oedema/ orchitis
Coverings
- Tunica albuginea (fibrous capsule)
- Septa radiate to mediastinum testis (~ $200–300$ lobules)
Seminiferous tubules → straight tubules → rete testis (often seen as tiny cystic foci medially in adolescents)
Epididymis posterolateral (head receives efferent ducts; body/tail = sperm maturation; exits as vas deferens)
Spermatic cord mnemonic “3-3-3-3”
- $3$ arteries: testicular, deferential, cremasteric
- $3$ nerves: genital branch of genitofemoral, sympathetic plexus, cremasteric
- $3$ fascial layers: external, cremasteric, internal spermatic fascia
- $3$ other: vas deferens, pampiniform plexus (veins), lymphatics
Vas deferens: thick, non-compressible, avascular tubular structure ⇒ common pitfall (mistaken for thrombosed vein)

Vascular Supply & Doppler

Testicular artery (from aorta) becomes capsular → centripetal arteries (to mediastinum) → centrifugal/recurrent arteries (return to periphery) ⇒ bidirectional colour (red/blue)
Additional supply: cremasteric & deferential arteries
Low-resistance arterial waveform: forward diastolic flow
Neonate: scant flow; use maximal colour sensitivity

Indications for Pediatric Scrotal US

Acute pain, swelling, erythema
Palpable mass
Undescended / absent testis
Trauma
Follow-up of known anomalies/tumours

Cryptorchidism (Undescended Testis)

Incidence: $1–6\%$ term neonates (↑ in prematurity); $\approx1\%$ persist at $1$ yr
Bilateral in $10–30\%$
Types
1. True (arrested descent) – usually within inguinal canal
2. Acquired (previously scrotal, ascends due to short cord/ fibrous processus remnant)
3. Ectopic (deviates off normal path: superficial inguinal, femoral, perineal, contralateral hemiscrotum)
4. Retractile (mobile; rests high but can be milked into scrotum without tension and stays briefly)
Sonographic search pattern
- High scrotal → superficial inguinal → canal (between deep & superficial rings) → deep ring/low abdomen
- Beware lymph node mimic in intra-abdominal position
US features: smaller ( $\approx30\%$ ), hypoechoic, possible microlithiasis; absent perfusion if torsed/atrophic
Management
- Orchidopexy optimal $6–18$ months (earlier = better fertility & lower malignancy)
- Risks if untreated: infertility, trauma, torsion, ↑ risk of seminoma (× $3$ pre-pubertal surgery, × $6$ post-puberty)
- Retractile testes → annual clinical follow-up (may become acquired undescended)

Epididymitis / Epididymo-Orchitis

Aetiology
- Bacterial (often STI in adolescents)
- Chemical (urine reflux)
- Traumatic
Starts in tail → head; may extend to testis
US:
- Enlarged, hypoechoic, hypervascular epididymis
- Reactive hydrocele, scrotal wall thickening common
- Orchitic extension → rounded, enlarged, heterogeneous testis with hyperaemia

Testicular Torsion

Twisting of cord → venous then arterial obstruction
Types
- Intravaginal (≈ $12–18$ yr; bell-clapper deformity)
- Extravaginal (neonates; entire tunica + cord twist near external ring)
Clinical
- Intravaginal: sudden severe pain, nausea/vomiting
- Extravaginal: painless red swelling; often late presentation or antenatal → non-viable
Time-critical: salvage best <6 h after onset
Sonographic hallmarks
- Whirlpool sign of twisted cord (best predictor)
- Absent or markedly reduced intratesticular flow; BUT partial torsion may retain arterial/venous signals → ALWAYS compare spectral waveforms (look for absent/ reversed diastolic flow)
- Enlarged, hypoechoic, heterogeneous, rounded testis; reactive hydrocele
Torsion–detorsion cycle: intermittent pain, hypervascular epididymis; spectral analysis critical

Scrotal Trauma

Intratesticular hematoma
- Focal iso/hypoechoic area, avascular on colour
- No tunica breach → conservative
Fracture
- Discrete linear hypoechoic cleft; tunica intact
- ~ $17\%$ visualised; CEUS helpful
Rupture
- Discontinuity/ crinkling of tunica albuginea, extrusion of seminiferous tubules
- Surgical repair mandatory
Ischaemia/ infarct
- Heterogeneous, poorly perfused; mimic torsion

All except isolated hematoma usually require surgery

Testicular Microlithiasis

Definition (ESUR): $\ge5$ micro-calcifications in one sonographic field (each $2–3\,\text{mm}$ )
Benign; present in $\sim50\%$ of germ-cell tumour patients but also many normals
Current consensus: no routine annual US unless additional risk factors (cryptorchidism, family history, contralateral tumour, hypospadias)

Hydroceles & Processus Vaginalis Variants

Fluid between parietal & visceral tunica vaginalis; often anterior due to posterior anchoring
Types
1. Vaginal (simple) – most common adult
2. Communicating/congenital – patent processus vaginalis; fluid tracks from peritoneum
3. Funicular – fluid along cord, stops proximal to testis
4. Infantile – distal sac + peri-testicular fluid; obliterated proximally
5. Encysted (cord) – closed both ends; may mimic epididymal cyst
Differentiate from: postoperative cord hematoma, epididymal cyst, inguinal hernia (look for fat/bowel sliding)
Large/ persisting sacs or associated hernia → surgical repair

Torsion of Testicular Appendages

Appendages
- Appendix testis (hydatid of Morgagni): Müllerian remnant, present $\sim80\%$ , superior pole; most common torsed appendage
- Appendix epididymis: Wolffian remnant $\sim25\%$ , head of epididymis
Age $7–12$ yr; localized superior pole tenderness; cremaster reflex intact
US: oval, enlarged, avascular mass between testis and epididymis; reactive hydrocele/scrotal thickening possible
Management: conservative (analgesia)

Testicular Tumours in Children

Germ-Cell Tumours

Seminoma: rare paediatric; homogenous hypoechoic, lobulated, vascular; good prognosis
Non-seminomatous (most common paediatric)
- Yolk-sac (peak $\approx2$ yr, $\sim30\%$ GCTs)
- Teratoma (benign if <4 yr; malignant post-puberty)
- Mixed, embryonal etc.
US: iso/hypoechoic, markedly heterogeneous, cystic areas, calcifications, hypervascular; scrotal wall usually NOT thickened
Any solid intratesticular mass ⇒ surgical exploration/ orchiectomy

Non-Germ-Cell (Sex-Cord / Stromal)

Leydig-cell (testosterone-producing) & Sertoli-cell tumours
- Peaks $5–10$ yr & $20–30$ yr
- Well-circumscribed hypoechoic nodules; hormonal signs (precocious puberty, gynecomastia)
- $\approx90\%$ benign yet excised due to malignancy potential

Metastases

Leukemia, lymphoma → diffuse enlargement, bilateral
Rare solid metastases: Wilms, neuroblastoma, retinoblastoma

Varicocele & Nutcracker Syndrome

Dilated pampiniform plexus (diagnosis: veins >2–3\,\text{mm}, increase with Valsalva)
In paediatrics, always assess left renal vein between $\text{SMA}$ & aorta
- Compression ("nutcracker phenomenon") elevates venous pressure → left varicocele
Document renal vein calibre & sluggish flow if suspected

Practical Pearls & Pitfalls

Never rely solely on colour for torsion – evaluate spectral Doppler diastolic flow
Confirm both testes in the same image; avoid scanning same testis twice in neonates
Vas deferens is avascular & non-compressible – do not mistake for thrombosed vein
Scrotal wall thickening favours inflammatory processes rather than tumour
Any persistent patent processus vaginalis: exclude hernia

Ethical & Clinical Relevance

Early diagnosis impacts fertility, cancer risk, organ salvage
Avoid unnecessary radiation in vulnerable age group
Accurate US differentiates conditions, reducing negative explorations & guiding timely surgery