Is Varicocele Truly Unilateral? Contralateral Involvement and Bilateral Testicular Effects in Male Infertility: A Narrative Review

Background/Objectives: Varicocele is usually clinically left-sided, but imaging and mechanistic studies suggest that contralateral venous reflux or bilateral testicular effects may be more common than physical examination indicates. This narrative review critically examines whether varicocele-associated infertility is better conceptualized as an asymmetric disorder with potential bilateral anatomical or functional involvement and considers the implications for diagnosis and treatment. Methods: PubMed/MEDLINE and Scopus were searched from inception to 21 June 2026 for studies on varicocele laterality, bilateral and subclinical disease, color Doppler ultrasonography, venography, and unilateral versus bilateral repair. Reference lists and contemporary clinical guidelines were also reviewed. Because the included studies differed substantially in patient selection, age, operator technique, diagnostic criteria, and reference standards, reported bilateral rates were not interpreted as head-to-head estimates of diagnostic sensitivity or as pooled prevalence estimates. Results: Physical examination identifies predominantly left-sided clinical disease. Bilateral involvement is reported more frequently when both sides are assessed using Doppler ultrasonography or venography, but estimates vary widely across referral-enriched and highly selected cohorts. Human and experimental evidence supports several mechanisms by which a clinically unilateral lesion may have bilateral functional effects, including shared scrotal hyperthermia, oxidative stress, endocrine disturbance, and venous cross-communication. Bilateral repair is consistent with standard treatment criteria when both varicoceles are clinically palpable. In men with a clinical left varicocele and non-palpable right-sided reflux, comparative evidence is mixed, and current guidelines do not support routine treatment of imaging-only disease. Conclusions: Varicocele is best viewed as an asymmetric disorder that may be anatomically or functionally bilateral in selected men, rather than as a universally bilateral disease. Deliberate bilateral clinical assessment and standardized bilateral ultrasonography when imaging is clinically indicated may improve phenotyping and operative planning. However, contralateral imaging abnormalities should not automatically be converted into a surgical indication.