What is the most likely diagnosis for a baby with a red, inflamed hemiscrotum, viable testis, and thick, oedematous cord?

Most Likely Diagnosis: Testicular Torsion

The most likely diagnosis is testicular torsion (Option A), as the thick and oedematous cord is the pathognomonic finding that distinguishes this surgical emergency from other causes of acute hemiscrotum in infants. 1

Key Diagnostic Features Supporting Testicular Torsion

Spermatic Cord Findings

• The thick, oedematous cord is the critical distinguishing feature that points directly to testicular torsion, representing the twisted and swollen spermatic cord 1
• This finding corresponds to the "whirlpool sign" seen on ultrasound, which is the most specific sign of torsion with 96% sensitivity 2
• The cord thickening results from extravaginal twisting of the spermatic cord that compromises blood flow, particularly common in the neonatal/infant period 1

Testicular Viability

• The viable testis at exploration indicates either early presentation (within the critical 6-8 hour window) or partial torsion 2
• Testicular viability does not exclude torsion—in fact, early surgical exploration is precisely when the testis is most likely to be salvageable 1
• Complete torsion >450 degrees results in absent arterial and venous flow, but partial torsion can present with diminished flow while maintaining some viability 2

Age-Specific Considerations

• Testicular torsion has a bimodal distribution with peaks in neonates and postpubertal boys 2, 1
• In infants, torsion is primarily extravaginal, occurring prenatally or perinatally, accounting for approximately 10% of pediatric testicular torsion cases 1
• The infant age group makes testicular torsion more likely than epididymo-orchitis, which is overwhelmingly more common in adults 2

Why Other Diagnoses Are Less Likely

Torsion of Testicular Appendage (Option D)

• While torsion of testicular appendage is the most common cause of acute scrotal pain in prepubertal boys 2, it would not present with a thick, oedematous cord 3
• The appendage torsion presents as an enlarged, homogeneously echogenic appendix testis located medial or posterior to the epididymal head, not cord thickening 3
• The "blue dot sign" (pathognomonic for appendage torsion) is only seen in 21% of cases and represents the ischemic appendage itself, not cord pathology 2

Epididymo-orchitis (Option B)

• Epididymitis/epididymo-orchitis would show an enlarged epididymis with increased blood flow on Doppler, not a thick cord 2
• This condition is rare in infants and should be diagnosed with caution in the prepubertal male 4
• The gradual onset of pain typical of epididymitis contrasts with the acute presentation of torsion 2

Incarcerated Inguinal Hernia (Option C)

• An incarcerated hernia would present with a palpable mass extending into the inguinal canal, not isolated cord thickening 5
• The clinical presentation would include bowel obstruction symptoms and a different physical examination pattern 5

Critical Management Implications

Immediate Surgical Intervention Required

• Surgical exploration and detorsion must be performed within 6-8 hours of symptom onset to prevent permanent ischemic damage 2, 1
• The salvage rate for the affected testicle depends on the degree of torsion and duration of ischemia 1
• Bilateral orchiopexy should be performed during surgery to prevent contralateral torsion, as the Bell clapper deformity is found in 82% of patients with torsion 2

Common Pitfall to Avoid

• Never delay surgical exploration based on testicular viability alone—the finding of a viable testis at exploration is actually the optimal scenario and confirms appropriate early intervention 1
• False-negative Doppler evaluations can occur in 30% or more of cases, particularly with partial torsion or early presentation 2
• In infants, normally reduced intratesticular blood flow can make Doppler interpretation challenging 2