associated with trauma is followed by a pain-free period after which pain returns On examination, scrotal erythema, edema, and tenderness of the epididymis may be found In this noninfectious variety of epididymitis, the urinalysis is negative Sonography is helpful to rule out any more severe injury and will demonstrate hyperemia associated with the inflammation Treatment is supportive Incarcerated Inguinal Hernia Incarcerated inguinal hernias are herniations of bowel and omentum into the scrotum which present with pain and a scrotal mass Their diagnosis and treatment are discussed in Chapters 39 Inguinal Masses and 119 Genitourinary Emergencies Henoch–Schönlein Purpura Occasionally, a child may be seen with a petechial rash on the scrotum as the initial presentation of this systemic vasculitic syndrome, characterized by nonthrombocytopenic purpura, arthralgia, renal disease, abdominal pain, and gastrointestinal bleeding More typically, the rash begins on the lower extremities or buttocks and later may involve the scrotum If the associated swelling is not great, the cord structures and testes can be felt to be uninvolved and normal In other cases with severe swelling, surgical exploration may be necessary to rule out testicular torsion, which rarely has been noted to coexist When skin lesions are present, the diagnosis of Henoch–Schönlein purpura (HSP) must be suspected Occasionally, an acutely painful scrotum is the dominant presenting symptom Ultrasound may help rule out testicular torsion in these instances For a more detailed discussion of HSP management, see Chapter 100 Renal and Electrolyte Emergencies Other Causes of a Painful Scrotum Referred pain to the scrotum can present as acute scrotal pain without scrotal swelling, tenderness, or mass The somatic nerves that innervate the scrotum are the genitofemoral, ilioinguinal, and posterior scrotal nerves A retrocecal appendicitis is an uncommon, but important cause of referred pain Other considerations may include urolithiasis, retroperitoneal processes like tumor, lumbar, or sacral nerve compression, or pain following hernia repair CAUSES OF PAINLESS SCROTAL SWELLING Hydrocele