What are the differential diagnoses for a 2-year-old boy with a firm, painless testicular swelling?

Differential Diagnosis for Firm, Painless Testicular Swelling in a 2-Year-Old Boy

In a 2-year-old boy presenting with firm, painless testicular swelling, the primary differential diagnoses are testicular tumor (most commonly yolk sac tumor), followed by hydrocele, epididymal cyst, and less commonly testicular torsion with delayed presentation or post-torsion changes. 1, 2, 3

Primary Diagnostic Considerations

Testicular Tumor (Most Critical to Rule Out)

Yolk sac tumor is the most common testicular malignancy in this age group, accounting for 70-80% of pediatric testicular germ cell tumors, and characteristically presents as a firm, painless scrotal mass. 2, 3

• Ultrasound findings: Typically shows a solid, ovoid, homogeneous, well-circumscribed, isoechoic or hypoechoic intratesticular mass with increased internal vascularity on color Doppler 2, 4
• Critical diagnostic marker: Serum alpha-fetoprotein (AFP) is markedly elevated (often >300 ng/ml, can exceed 4,000 ng/ml) and is essential for initial diagnosis 2, 4, 3
• Age consideration: Benign tumors are more frequent in prepubertal boys, but malignant tumors must always be excluded 3

Common pitfall: Yolk sac tumors can be misdiagnosed on ultrasound as orchitis due to heterogeneous echogenicity and abundant blood flow, making AFP measurement mandatory in any child with testicular enlargement 2

Extratesticular Benign Lesions

• Hydrocele: Most common extratesticular cause of painless scrotal swelling; ultrasound shows anechoic fluid collection surrounding the testis 5
• Spermatocele/Epididymal cyst: Appears as well-defined cystic structure separate from testicular parenchyma 5, 6
• Testicular cystic lesions: Include epidermoid cyst, simple cyst, or cystic dysplasia; ultrasound shows mainly cystic component with well-defined borders and echogenic rim 3, 6

Testicular Torsion (Less Likely but Time-Critical)

While typically presenting with acute pain, testicular torsion can occasionally present with delayed or minimal pain, resulting in a firm, swollen testis 7, 1

• Key distinguishing features: History of sudden onset (even if pain has subsided), negative Prehn sign, and ultrasound showing decreased or absent blood flow with possible "whirlpool sign" 1, 8
• Critical time window: Requires surgical intervention within 6-8 hours to prevent testicular loss 7, 1
• Age distribution: Has bimodal distribution with peaks in neonates and postpubertal boys, making it less common but still possible at age 2 7, 1

Diagnostic Algorithm

Immediate Steps:

1. Obtain serum AFP level immediately - This is non-negotiable in any child with testicular swelling to rule out yolk sac tumor 2, 4, 3

2. Perform scrotal ultrasound with Doppler - First-line imaging to differentiate intratesticular from extratesticular lesions and assess vascularity 1, 8, 5

   • Intratesticular solid mass = presumed malignant until proven otherwise 3, 5
   • Extratesticular cystic lesion = likely benign 5
   • Absent/decreased blood flow = consider torsion even without typical pain presentation 1

3. Assess for systemic symptoms and progression - Rapid enlargement or systemic symptoms increase suspicion for malignancy or torsion 8, 2

Key Imaging Interpretation:

Findings suggesting malignancy: Inhomogeneous, hypoechoic, poorly circumscribed intratesticular mass with increased vascularity 3, 5

Findings suggesting benign lesion: Mainly cystic component, well-defined borders, echogenic rim, or normal to increased echogenicity compared to healthy parenchyma 3, 6

Critical caveat: These ultrasound findings may overlap, and AFP level is essential for definitive differentiation 2, 3

Management Pathway

• If intratesticular solid mass identified: Urgent urology referral for radical inguinal orchiectomy; testis-sparing surgery may be considered only for small, clearly benign-appearing lesions with normal AFP and frozen section confirmation 3, 6

• If extratesticular lesion: Can often be managed conservatively or with testis-sparing surgery 5, 6

• If torsion suspected: Immediate urological consultation for surgical exploration, regardless of imaging findings if clinical suspicion is high 1, 8

Bottom line: Any firm testicular mass in a 2-year-old requires immediate AFP measurement and scrotal ultrasound, with urgent urology referral if an intratesticular lesion is identified, as yolk sac tumor is the most common and most critical diagnosis to establish promptly 2, 4, 3