Unilateral testicular swelling can occur due to the same reasons you may have bilateral testicular swelling torsion, infection, fluid collection, or hernia so it is not very helpful in determining the etiology. More useful in evaluating acute swelling is the nature and timing of the onset of pain, the particular area of the testicle that is swollen, and the presence of fever and lower urinary tract symptoms (e.g. frequency, urgency, painful urination). While a less common cause of swelling, a persistently enlarged testicle should be evaluated to exclude a malignant growth.