Chronic Venous Insufficiency: This condition is the most common cause of unilateral or bilateral lower extremity edema due to the incompetence of venous valves, leading to blood pooling in the legs.

Cellulitis: A bacterial infection of the skin and subcutaneous tissue that can cause localized edema, redness, and warmth.
Deep Vein Thrombosis (DVT): A blood clot in the deep veins of the legs, which can cause swelling, pain, and discoloration.
Lymphedema: A condition characterized by the abnormal collection of protein-rich fluid in the interstitial tissue, leading to swelling of the affected limb.
Orthostatic Edema: Edema caused by standing for long periods, which can lead to fluid accumulation in the legs due to gravity.

Compartment Syndrome: A serious condition resulting from increased pressure within a muscle compartment, which can lead to nerve and muscle damage if not promptly treated.
Necrotizing Fasciitis: A life-threatening infection that affects the tissue beneath the skin and surrounding muscles and organs, requiring immediate medical attention.
Phlegmasia Cerulea Dolens: A severe form of DVT that can cause significant swelling, pain, and cyanosis of the affected limb, potentially leading to gangrene.

Fabry Disease: A genetic disorder that can cause edema, pain, and other systemic symptoms due to the accumulation of a particular type of fat in the body's cells.
Lipedema: A chronic condition characterized by the abnormal growth of fat cells in the legs, leading to swelling and pain.
Klippel-Trenaunay Syndrome: A rare congenital condition that affects blood and lymph vessels, leading to edema, varicose veins, and other vascular anomalies.