(BMJ)—A 10-year-old boy presented with R scrotal pain of 20 hours’ duration. No fever, vomiting, hx of trauma. Exam: No scrotal swelling/redness. Cremasteric reflex normal. Bilateral testes in vertical lie, soft. Tender, mobile blue area near upper pole of R testis. What’s the dx?
Hemorrhagic hydrocele
Torsion of appendix testis
Epididymitis
Testicular torsion
Incarcerated inguinal hernia
You are correct. The blue dot sign (BDS), due to necrosis in torsion of appendix testis (TAT), appears as a small, tender area of blue discoloration on the superior testicular pole. If not immediately apparent, it may be better observed by manipulating the testis downward into an area where overlying skin is thinner and inner structures are more visible.

The BDS is specific to TAT. This fact, combined with the absence of testicular torsion sx (such as testicular swelling, a high-riding position, lack of the cremasteric reflex, N/V, testicular tenderness, and hardness of the testis on palpation), the absence of scrotal edema or redness characteristic of epididymitis, and the absence of a firm mass extending from the groin to the scrotum, which would have indicated an incarcerated inguinal hernia, pointed to the dx of TAT. U/S confirmed normal testes with normal blood flow.

Emergency Medicine Journal 2021;38:578-586