What is the differential diagnosis for acute left groin pain and testicular swelling with a palpable hard knot?

Differential Diagnosis for Left Groin and Testicular Pain with Palpable Hard Knot

The most critical diagnosis to rule out immediately is testicular torsion, which requires surgical intervention within 6-8 hours to prevent testicular loss, followed by epididymitis/epididymo-orchitis as the most common cause in adults, with additional considerations including inguinal hernia, testicular tumor, and segmental testicular infarction. 1

Immediate Life/Organ-Threatening Diagnosis

Testicular Torsion (Surgical Emergency)

• This is a surgical emergency requiring immediate urological consultation and surgical exploration within 6-8 hours of symptom onset to prevent permanent ischemic damage. 1
• Presents with abrupt onset of severe scrotal pain, often with nausea and vomiting 1, 2
• Physical examination reveals a high-riding, tender, swollen, and firm testicle 3
• Negative Prehn sign (pain NOT relieved with testicular elevation) distinguishes this from epididymitis 1
• The "hard knot" may represent the twisted spermatic cord or swollen, ischemic testis 2, 3
• Up to 50% of patients report previous similar episodes of intermittent torsion 3
• More common in adolescents and young adults, but can occur at any age 1
• Cremasteric reflex is typically absent in torsion 4

Most Common Diagnosis in Adults

Epididymitis/Epididymo-Orchitis

• Represents approximately 600,000 cases annually in the United States and is the most common cause of testicular pain in adults 1
• Characterized by gradual onset of pain over days to weeks, not sudden 1, 4
• Associated with urinary frequency, dysuria, and pain with ejaculation 4
• Positive Prehn sign (pain relief with testicular elevation) suggests this diagnosis 4
• Physical examination shows epididymal tenderness and swelling 4
• The "hard knot" may represent the enlarged, inflamed epididymis 4
• Cremasteric reflex remains present 4
• May have abnormal urinalysis, though normal urinalysis does not exclude the diagnosis 1, 4

Additional Critical Diagnoses to Consider

Incarcerated/Strangulated Inguinal Hernia

• Can present with groin pain and a palpable mass or "hard knot" in the groin/scrotal area 5
• May have associated nausea, vomiting, and inability to reduce the hernia 5
• Requires urgent surgical evaluation if strangulated 5

Testicular Tumor

• Presents as a painless or minimally painful hard mass within the testicle itself 5
• The "hard knot" would be intratesticularly located on examination 5
• Typically has a more insidious onset unless complicated by hemorrhage or infarction 5

Segmental Testicular Infarction

• Presents with acute testicular pain and swelling, can mimic torsion 1, 6
• Classic wedge-shaped avascular area on ultrasound, though may appear as round lesions 1
• Median age 37-38 years 1
• May present with a tender, swollen, high-riding testicle similar to torsion 6

Torsion of Testicular Appendage

• Most common cause of testicular pain in prepubertal boys 1
• Less likely in adults but still possible 1
• "Blue dot sign" is pathognomonic but only seen in 21% of cases 1

Diagnostic Algorithm

Immediate Clinical Assessment

• Determine timing and onset of pain: sudden onset suggests torsion, gradual onset suggests epididymitis 1, 4
• Assess for nausea, vomiting (suggests torsion) 2, 3
• Evaluate for urinary symptoms (suggests epididymitis) 4
• Check Prehn sign: relief with elevation suggests epididymitis, no relief suggests torsion 1, 4
• Assess cremasteric reflex: absent in torsion, present in epididymitis 4
• Palpate to localize the "hard knot": spermatic cord (torsion), epididymis (epididymitis), inguinal canal (hernia), or intratesticularly (tumor) 5, 3

Urgent Diagnostic Testing

• Obtain urinalysis and urine culture immediately, but do not delay imaging if torsion is suspected 4
• Duplex Doppler ultrasound is the first-line imaging study with sensitivity 69-96.8% and specificity 87-100% 1, 4
• Ultrasound should include:
  • Grayscale examination for testicular homogeneity and the "whirlpool sign" of twisted spermatic cord 1
  • Color/Power Doppler assessment comparing testicular perfusion to the contralateral side 1
  • Spectral Doppler analysis of upper, mid, and lower poles 1

Key Ultrasound Findings by Diagnosis

• Testicular torsion: decreased or absent blood flow, whirlpool sign, enlarged heterogeneous hypoechoic testis, ipsilateral hydrocele 1
• Epididymitis: enlarged epididymis with increased blood flow on Doppler, scrotal wall thickening 1, 4
• Segmental infarction: wedge-shaped avascular area 1, 6
• Tumor: solid intratesticularly mass with variable vascularity 5

Critical Clinical Pitfalls

• False-negative Doppler evaluations occur in 30% or more of cases, particularly with partial torsion, spontaneous detorsion, or early presentation 1
• Normal urinalysis does not exclude either testicular torsion or epididymitis 1, 4
• Significant overlap exists in clinical presentation between different causes of acute scrotal pain 1
• When clinical suspicion for torsion remains high despite normal Doppler, immediate urological consultation and surgical exploration should proceed 1, 4
• Do not delay imaging or surgical consultation if any clinical suspicion for torsion exists, as testicular viability is compromised after 6-8 hours 1, 4
• Prepubertal boys may have normally reduced intratesticular blood flow, leading to false-positive evaluations for torsion 1

Management Based on Diagnosis

If Testicular Torsion Confirmed or Highly Suspected

• Immediate urological consultation and urgent surgical exploration 1, 4
• Do not delay surgery for imaging if clinical suspicion is high 1
• Surgery involves detorsion, assessment of viability, and bilateral orchiopexy to prevent recurrence 1

If Epididymitis Diagnosed

• Initiate empiric antibiotic therapy immediately while awaiting culture results 4
• Scrotal elevation and support 4
• NSAIDs for pain control 4
• Bed rest until inflammation subsides 4
• Reassess within 48-72 hours: if pain worsens or fails to improve, reconsider torsion 4

If Hernia or Tumor Suspected

• Urgent surgical consultation for incarcerated hernia 5
• Urology referral for suspected testicular tumor 5