**Core Concept**
In infants, a hydrocele is a common condition characterized by the accumulation of serous fluid in the tunica vaginalis testis or along the spermatic cord. This occurs due to the patency of the processus vaginalis, a peritoneal extension that allows for the free movement of fluid between the abdominal cavity and the scrotum.

**Why the Correct Answer is Right**
The correct answer is related to the anatomical structure and developmental physiology of the infant. The processus vaginalis is a peritoneal extension that normally closes during fetal development, but in some cases, it may remain patent, leading to the accumulation of fluid in the scrotum. This is more common in males due to the longer length of the processus vaginalis.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect as it does not relate to the underlying cause of hydrocele in infants.
* **Option B:** This option is incorrect as it is associated with a different condition, varicocele, which involves the enlargement of the pampiniform plexus of veins in the scrotum.
* **Option C:** This option is incorrect as it is associated with a different condition, testicular torsion, which involves the twisting of the spermatic cord and testis, leading to ischemia.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that hydrocele in infants is often a transient condition that resolves spontaneously as the processus vaginalis closes, and surgical intervention is rarely necessary.

**Correct Answer: C. Patent processus vaginalis.**