**Question:** A 3-month-old boy is brought to the physician because his parents cannot find one of his testicles. Physical examination confirms the parents' observation. Which of the following is the most likely diagnosis?

A. Cryptorchidism
B. Hydrocele
C. Testicular torsion
D. Obstructed descent

**Correct Answer:** A. Cryptorchidism

**Core Concept:** Testicular descent is a process that occurs during fetal development, ensuring that both testes descend into the scrotum. In some cases, one or both testes fail to descend into the scrotum, leading to conditions like cryptorchidism, hydrocele, torsion, or obstructed descent.

**Why the Correct Answer is Right:** Cryptorchidism refers to the condition where one or both testes fail to descend into the scrotum. In a 3-month-old boy, the testes should already have descended. Thus, cryptorchidism is the most probable diagnosis in this case, as the testicle is undescended and the physical examination confirms the parents' observation.

**Why Each Wrong Option is Incorrect:**

**A. Hydrocele:** A hydrocele is a collection of fluid within the tunica vaginalis (the outer layer of the scrotum) surrounding the testicle, typically caused by herniation or injury. Hydrocele would not explain the undescended testicle in this scenario, as the testicle is still in the inguinal canal.

**B. Testicular Torsion:** Testicular torsion occurs when the spermatic cord twists around the testicle, leading to impaired blood supply and testicular dysfunction. This answer is incorrect because the presented case is more likely due to an undescended testicle rather than twisted one.

**C. Obstructed descent:** Obstructed descent refers to a testis that fails to descend into the scrotum due to an anatomical abnormality. This answer is incorrect because the issue in this case is the testicle being undescended, not obstructed descent.

**Clinical Pearl:** Understanding the correct diagnosis (cryptorchidism) is crucial for appropriate management and treatment, including surgical intervention if necessary, to prevent long-term complications such as infertility and testicular cancer risk. Inguinal hernias can also occur in cryptorchidism, which should be evaluated and repaired to prevent potential complications.