Scrotal Sonography – Comprehensive Study Notes

NORMAL ANATOMY & SONOGRAPHIC APPEARANCE

• Scrotum is divided into two hemiscrota, each containing testis + epididymis + spermatic cord.
• Average adult testis: ovoid, approx. $5 \times 3 \times 2\ \text{cm}$.
  • Gray-scale US: homogeneous, medium-level echoes.
• Epididymis
  • Lies posterolateral to testis; subdivided into head, body, tail.
  • Head: triangular; iso- to slightly hyperechoic relative to testis.
• Tunica albuginea
  • Fibrous capsule → thin echogenic line around testis.
  • Infolding forms mediastinum testis (linear hyperechoic band along long axis on side of epididymis).
• Rete testis
  • Network within mediastinum; drains to epididymis via $10 !–! 15$ efferent ductules.
  • Tubular ectasia ⇒ multiple tiny anechoic spheres/tubes; may extend extra-testicular post-vasectomy.
• Tunica vaginalis: outer parietal & inner visceral layers; normally only a trace of fluid separates them.
• Appendages (normal variants; risk of misdiagnosis as masses)
  • Appendix testis: Müllerian remnant at upper pole.
  • Appendix epididymis: mesonephric remnant on epididymal head.
  • Visualised when hydrocele fluid outlines them.

VASCULAR ANATOMY

• Arterial supply
  • Testicular (internal spermatic) arteries → capsular & centripetal branches (major supply).
  • Deferential artery (from vesicular) & cremasteric artery (from inferior epigastric) → mainly epididymis/peritesticular tissues.
• Venous drainage
  • Pampiniform plexus → testicular veins.
  • Right vein → IVC; left vein → left renal vein.

VARICOCELE

• Definition: Dilated pampiniform plexus (> $2\ \text{mm}$ diameter).
• Epidemiology: Predominantly left-sided.
• Clinical: Soft mass ↑ with upright posture/valsalva.
• Gray-scale: serpiginous anechoic channels; Color Doppler shows augmented flow on Valsalva.
• Red flags: sudden onset, right-sided, non-reducible supine ⇒ search for retroperitoneal tumor obstructing testicular vein.

EMBRYOLOGY & DEVELOPMENTAL DISORDERS

• Cryptorchidism (maldescent)
  • Incidence at birth $\approx 3.68\%$; at $1\ \text{yr}=1.06\%$.
  • Location: $80\%$ inguinal canal, $20\%$ abdomen.
  • Risks: infertility & testicular CA (absolute risk $3!–!5\%$).
  • Orchiopexy recommended < $2\ \text{yrs}$; reduces infertility risk, not cancer.
  • US: atrophic, hypoechoic, oval mass along canal/abdomen.
• Polyorchidism
  • < $100$ cases in literature; supernumerary testis separate but identical on US; MRI confirms.
  • Complications: torsion, $\approx5\%$ malignancy; fertility implications.

FLUID COLLECTIONS & CYSTIC LESIONS

• Hydrocele
  • Serous fluid between tunica vaginalis layers; no mass effect.
  • Simple (patent processus vaginalis in infants) vs complex (due to trauma, infection, tumor).
• Encysted hydrocele of spermatic cord
  • Anechoic mass superior to testis/epididymis.
• Epididymal cyst vs Spermatocele
  • Identical sonographically (simple/sep­tated).
  • Spermatocele: only at head; contains sperm; fibromuscular wall.
  • Epididymal cyst: anywhere; mesothelial lining.
• Intratesticular cyst
  • Incidence $8!–!10\%$; men > $40\ \text{yrs}$; usually $2\ \text{mm} \to 2\ \text{cm}$, solitary or multiple.
• Tunica albuginea cyst: small ($2!–!5\ \text{mm}$), often palpable peripheral simple cyst.

ACUTE SCROTUM

• Need to distinguish torsion (surgical emergency) vs epididymo-orchitis (medical Rx).

Torsion

• Age peak $12!–!18\ \text{yrs}$.
• Types: Intravaginal (bell-clapper deformity; bilateral risk) vs extravaginal (perinatal).
• Salvage window: < $6\ \text{h}$ ⇒ high; $>12!–!24\ \text{h}$ dramatic drop.
• US: Enlarged hypoechoic testis, absent/decreased flow; compare to contralateral. Later: heterogeneous, peritesticular hyperemia.
• Caveat: spontaneous detorsion → normal or hyperemic flow (pitfall).

Epididymo-orchitis

• Age $20!–!30\ \text{yrs}$; retrograde infection (UTI, STI).
• US: Enlarged, hypoechoic epididymis ± testis; marked hyperemia; thickened skin; reactive hydrocele.
• Complications: abscess, testicular infarct, chronic sinus, infertility, calcifications.
• Tuberculous variant: heterogeneous, peripheral flow, sinus tract.

Fournier Gangrene

• Necrotizing fasciitis of perineum; M:F $10:1$.
• Risk factors: DM, alcoholism, HIV.
• US: echogenic subcutaneous gas; edematous wall; testes spared (separate blood supply).

TESTICULAR MASSES

General

• Most intratesticular tumors are hypoechoic; heterogeneity ↑ with size.
• Color Doppler adds limited value in adults; helpful in subtle pediatric lesions.

Malignant – Pediatric

• Yolk sac tumor (endodermal sinus)
  • Most common malignant tumor in boys < $3\ \text{yrs}$ (mean $18\ \text{mo}$).
  • ↑ Alpha-fetoprotein; heterogeneous mass with necrosis.
• Embryonal carcinoma & mixed GCT appear post-puberty.
• Benign teratoma may outnumber malignant tumors pre-puberty.
• Sex-cord stromal tumors (Leydig/Sertoli) = $10!–!30\%$ of malignancies.
• Leukemia/Lymphoma < $10\%$; bilateral; testes are sanctuary sites during chemo.

Malignant – Adult

• Peak age $20!–!34\ \text{yrs}$.
• $90!–!95\%$ germ-cell origin.
• Seminoma
  • Homogeneous hypoechoic nodule → diffuse enlargement; sharp margins; less necrosis/calc.
• Mixed germ-cell tumors
  • Heterogeneous, ill-defined, cystic/necrotic, calcifications; invade tunica.
• Burned-out tumor: regressed primary with scar/calcifications; accounts for $\approx10\%$ of apparent primary retroperitoneal GCTs.

Benign

• Epidermoid cyst: ‘onion-skin’ concentric rings; avascular.

EXTRATESTICULAR MASSES

Benign

• Lipoma (spermatic cord) – most common paratesticular tumor.
• Adenomatoid tumor (epididymal tail) – $\approx30\%$ extratesticular masses; variable echoes.
• Extratesticular epidermoid cyst – hypoechoic, well-circumscribed ± echogenic crystals.

Malignant

• Spermatic cord sarcomas (mesenchymal) – commonest malignant para-testicular lesions.
• Paratesticular rhabdomyosarcoma – most common in children; rapid growth.
• Mesothelioma & lymphoma can involve tunica/cord.

INGUINAL HERNIA

• Indications for US: equivocal exam, occult scrotal enlargement.
• Findings: Fluid/air-filled bowel loops with peristalsis or echogenic fat/omentum entering canal.

TRAUMA

• Hematocele: acute = hyperechoic; chronic = anechoic with septations; avascular.
• Intratesticular hematoma: focal hypoechoic mass; differentiate from tumor.
• Testicular rupture: irregular contour + heterogeneous parenchyma ± hematocele ⇒ urgent surgery (salvage $\approx90\%$ if early).

MICROLITHIASIS

• Numerous $(1!–!3\ \text{mm})$ non-shadowing echogenic foci; usually bilateral.
• Incidence: boys $0.16\%$; men $0.6!–!9\%$.
• Associated conditions: cryptorchidism, Down, Klinefelter, pulmonary alveolar microlithiasis.
• Reported relative CA risk $\approx2!–!20$; intensive US screening NOT cost-effective; recommend self-exam & routine care.

SCROTAL EDEMA & PEARLS

• Edema: thickened wall with alternating echogenic stripes (‘onion’); testes normal. Causes: CHF, cirrhosis, lymphedema, low albumin, obstruction.
• Scrotal pearl: mobile echogenic calcified body within hydrocele; composition Ca-Mg-phosphate; clinically insignificant.

ROLE & ADVANCES IN SCROTAL SONOGRAPHY

• High-frequency transducers (≥ $12\ \text{MHz}$) → exquisite gray-scale detail.
• Color/Power Doppler crucial for vascular disorders (torsion vs infection, varicocele).
• Real-time exam: dynamic maneuvers (Valsalva, standing) enhance varicocele detection & hernia confirmation.
• US guides management: emergent surgery (torsion/rupture), conservative therapy (infection), oncologic planning.

NUMBERS & EQUATIONS QUICK REFERENCE

• Normal testis: $5 \times 3 \times 2\ \text{cm}$.
• Varicocele vein: diameter > $2\ \text{mm}$.
• Efferent ductules: $10 !–! 15$.
• Cryptorchidism prevalence: birth $3.68\%$, $3\ \text{mo}=1.00\%$, $1\ \text{yr}=1.06\%$.
• Testicular tumor salvage window: < $6\ \text{h}$ torsion.
• Testicular cancer risk post-cryptorchidism: $3!–!5\%$.
• Microlithiasis CA relative risk: $2!–!20$.

CLINICAL PEARLS & METAPHORS

• Torsion mechanism likened to “clapper in a bell” (bell-clapper deformity).
• Epidermoid cyst pattern described as “onion skin.”
• Scrotal wall edema resembles “onion layers” on US.

ETHICAL & PRACTICAL IMPLICATIONS

• Early identification of torsion prevents loss of testis & infertility.
• Counseling families re: cryptorchidism timing of surgery & long-term cancer surveillance.
• Avoid over-screening microlithiasis; balance cost vs benefit.
• Recognition of Fournier gangrene mandates rapid multidisciplinary management (surgical debridement + broad-spectrum antibiotics).