Phlebitis or Thrombophlebitis: This condition involves inflammation of a vein, which can cause it to become hardened. It is a common issue that can occur in any vein, including those around the penis, often due to infection, injury, or a blood clot.

Varicocele: This is an enlargement of the veins within the scrotum, similar to varicose veins. While it primarily affects the scrotum, it can sometimes be felt as hardened veins around the penis due to the close anatomical proximity.
Sclerotherapy Complications: If sclerotherapy (a procedure used to treat varicose veins) has been performed in the area, there could be complications leading to hardened veins, such as inflammation or scarring.

Penile Cancer: Although rare, penile cancer can cause changes in the skin and tissues of the penis, including the formation of hardened areas that might be mistaken for hardened veins. Early detection is crucial for effective treatment.
Lymphogranuloma Venereum (LGV): This is a sexually transmitted infection that can cause lymphadenopathy (swollen lymph nodes) and other systemic symptoms. In rare cases, it might cause localized inflammation that could be mistaken for hardened veins.

Behçet's Disease: A rare disorder that causes blood vessel inflammation throughout the body, which can lead to a variety of symptoms including skin lesions, genital sores, and potentially hardened veins due to phlebitis.
Mondor's Disease: A rare condition characterized by thrombophlebitis of the superficial veins of the penis or breast, leading to a hardened, cord-like structure under the skin. It is often associated with trauma or injury to the area.