Chronic Venous Insufficiency: This condition is characterized by the veins' inability to send blood back to the heart from the legs, leading to fluid accumulation and swelling. It's a common cause of bilateral lower leg swelling, especially in older adults or those with a history of venous problems.

Heart Failure: Swelling in the legs can be a sign of heart failure, where the heart is not pumping efficiently, causing fluid buildup.
Kidney Disease: Conditions like nephrotic syndrome can lead to significant protein loss in the urine, resulting in low albumin levels, which in turn causes fluid to leak out of blood vessels and into tissues, leading to swelling.
Liver Cirrhosis: Cirrhosis can lead to a decrease in albumin production and an increase in venous pressure, both of which can cause fluid to accumulate in the legs.
Hypothyroidism: Although less common, hypothyroidism can cause swelling due to the accumulation of mucopolysaccharides in the skin and other tissues.

Deep Vein Thrombosis (DVT): Although DVT typically presents unilaterally, it's crucial not to miss it, as it can be life-threatening if it leads to a pulmonary embolism. Bilateral DVT, though less common, can occur.
Lymphoma or Other Malignancies: Certain cancers can cause swelling by obstructing lymphatic or venous return.
Inferior Vena Cava Obstruction: This is a rare but potentially life-threatening condition that can cause bilateral leg swelling due to the obstruction of blood flow back to the heart.

Lipedema: A chronic condition characterized by the abnormal growth of fat cells in the legs, leading to swelling and pain.
Fabry Disease: A genetic disorder that can lead to the accumulation of a particular type of fat in the body's cells, affecting many parts of the body and potentially causing swelling among other symptoms.
Sarcoidosis: An inflammatory disease that can affect multiple organs in the body and, in rare cases, cause leg swelling due to granulomatous infiltration of lymph nodes or other tissues.