Hypogonadism: Elevated FSH levels are often indicative of primary hypogonadism, where the testes do not produce enough testosterone, leading to an increase in FSH secretion by the pituitary gland in an attempt to stimulate the testes. A bilateral varicocele could potentially cause hypogonadism due to increased temperature and oxidative stress affecting testicular function.

Varicocele: As mentioned, a bilateral varicocele could indeed contribute to elevated FSH levels by impairing testicular function. Varicoceles are known to affect sperm quality and testosterone production.
Testicular Dysfunction: Conditions affecting the testes, such as orchitis or testicular trauma, can lead to elevated FSH levels due to impaired testicular function.
Idiopathic Hypogonadotropic Hypogonadism: Although less common, this condition involves a problem with the pituitary gland or hypothalamus leading to low testosterone and potentially elevated FSH if the issue is with the testes' response to gonadotropins.

Testicular Cancer: Although rare, testicular cancer can cause hormonal imbalances, including changes in FSH levels. It's crucial to rule out testicular cancer due to its potential severity and the importance of early detection.
Pituitary Tumors: Tumors affecting the pituitary gland can disrupt normal hormonal balances, leading to elevated FSH levels. These tumors can be benign or malignant and require prompt medical attention.

Klinefelter Syndrome: A genetic condition (47,XXY) that affects male development and is associated with primary hypogonadism, which could explain elevated FSH levels.
Myotonic Dystrophy: A rare genetic disorder that can affect testicular function and lead to hormonal imbalances, including elevated FSH.
Autoimmune Disorders: Certain autoimmune conditions can target the testes or the pituitary gland, leading to hormonal imbalances. These are rare but important to consider in the differential diagnosis.