Unilateral and Bilateral Undescended Testicle: Why Are They Managed Differently?

For undescended testicle, the question "how many sides?" is just as decisive as "where?" In a unilateral case, the other testicle in the scrotum functions normally; there is a backup for growth, hormone production, and future reproduction. In a bilateral case, there is no such backup; both testicles have remained in a warm environment, and the outcome depends on protecting both together.

The large majority of cases are unilateral. If the other testicle is in the scrotum and of normal size, hormone testing is not routinely needed; planning is based on examination findings. If the testicle is palpable, inguinal orchiopexy (through a groin incision) or, in selected cases, scrotal orchiopexy (fixing the testicle in the scrotum) is planned; if it is not palpable, examination under anesthesia and, if needed, laparoscopy (a minimally invasive method) with descent in the same session are performed.

In a bilateral case, the sperm precursor cells of both testicles are affected by the warm environment. The literature reports that sperm count and paternity rate are significantly lower in men with a history of bilateral undescended testicle than in those with a unilateral history. For this reason, guidelines place particular emphasis on early surgery in bilateral cases, aiming to bring both testicles down into the scrotum within the 6-to-12-month window.

When neither testicle can be felt in a newborn, this is no longer only a urology question. In these babies, differences of sex development and, in particular, certain conditions in hormone production that require urgent treatment must be ruled out; for this reason, hormonal and, when needed, genetic evaluation is carried out together with pediatric endocrinology in the first days of life. If hypospadias is also present, this evaluation becomes an even higher priority.

• Bilateral non-palpable testicle in a newborn: endocrine evaluation without delay
• If hypospadias is also present: pediatric urology, endocrinology, and genetics together
• Whether testicles are present: hormone testing; exact location: laparoscopy

• Whether the testicles are present can largely be determined through hormone testing (baseline and stimulated hormone levels); this distinguishes anorchia (complete absence of both testicles) from testicles located within the abdomen. If testicular tissue is present, diagnostic laparoscopy is used to locate it and plan its descent.

During adolescence, testicular size and development are monitored in both groups; in bilateral cases, hormone levels are also evaluated, and a sperm analysis is recommended in adulthood. In a unilateral history, follow-up focuses more on whether the testicle has stayed in place and maintained its size.

• Testicular cancer risk is elevated compared with the general population in both groups; orchiopexy performed before puberty reduces this risk but does not eliminate it. This is why self-examination is taught from puberty onward. Being able to have fertility questions answered by the same team during the transition from childhood to adulthood, with pediatric urology and adult urology working together, is especially valuable in bilateral cases.