Chronic Venous Insufficiency: This condition is a common cause of unilateral leg edema, especially if the patient has a history of deep vein thrombosis (DVT), varicose veins, or has undergone surgeries that might have compromised venous return.

Deep Vein Thrombosis (DVT): A blood clot in the deep veins of the leg can cause swelling, pain, and discoloration, typically affecting one leg.
Cellulitis: A bacterial infection of the skin and subcutaneous tissues that can cause swelling, redness, and warmth, often confined to one leg.
Lymphedema: Swelling caused by impaired lymph drainage, which can be primary (inherited) or secondary (due to surgery, infection, or trauma), and may affect one leg.

Compartment Syndrome: A condition where increased pressure within a muscle compartment leads to inadequate blood supply, which is a medical emergency requiring prompt intervention.
Phlegmasia Cerulea Dolens: A severe form of DVT that causes significant swelling and cyanosis of the affected limb, which can lead to gangrene if not treated promptly.
Malignancy (e.g., Lymphoma or Soft Tissue Sarcoma): Although less common, malignancies can cause unilateral leg edema due to obstruction of lymphatic or venous return.

Filariasis: A parasitic infection that can cause lymphedema, typically seen in tropical regions.
Klippel-Trenaunay Syndrome: A rare congenital condition characterized by vascular malformations, which can lead to unilateral leg edema.
Fabry Disease: A genetic disorder that can cause peripheral edema among other systemic symptoms, due to the accumulation of a particular type of fat in the body's cells.