Which of the following is an example of a testicular factor affecting male infertility?

Varicocele is indeed an example of a testicular factor affecting male infertility. It refers to an enlargement of the veins within the scrotum, which can lead to increased testicular temperature and impair sperm production and quality. This condition is relatively common and is known to be associated with fertility issues in men, as it can affect the testicles' ability to produce healthy sperm.

Hypogonadotrophic hypogonadism, while it does impact testosterone levels and sperm production, is primarily classified as a hypothalamic or pituitary disorder rather than a direct testicular issue. Obstructive sleep apnea is a sleep disorder that can affect hormonal balance and, indirectly, fertility but does not act as a direct testicular factor. Gynecomastia (the enlargement of breast tissue in men) is often related to hormonal imbalances and does not directly affect testicular function.

Thus, varicocele stands out because it directly relates to the anatomy and function of the testes, making it a clear example of a testicular factor influencing male infertility.