Orchitis

Orchitis (plural: orchitides) is an infection of the testis, which is rarely isolated, and when in conjunction with the epididymis is called epididymo-orchitis.

Pathology

Usually, bacteria retrogradely seed into the testis from the bladder or prostate. It can also be secondary to viral infection (e.g. mumps, Coxsackie virus). 

Associations

• almost all cases are associated with epididymitis
• isolated orchitis can be seen in mumps, syphilis and brucellosis ⁶

Radiographic features

Ultrasound

Ultrasound is the gold standard investigation. When compared with the other testis in the 'sunglasses view' features of orchitis include relative: 

• hypoechogenicity: focal or diffuse
• hypervascularity: focal or diffuse
• swelling
• scrotal wall thickening

A complex/septated hydrocele can be seen in the ipsilateral scrotum. 

Differential diagnosis

• intermittent testicular torsion ⁵
  • ​reperfusion after intermittent torsion can present similarly on Doppler ultrasound with increased flow, but the patient's history allows differentiation
• primary testicular malignancy should be considered, especially with focal changes