Which of the following is characterized by swollen tissues due to fluid accumulation?

Edema is specifically characterized by the accumulation of fluid in the interstitial spaces of tissues, leading to swelling. This condition can occur due to various reasons, such as increased capillary permeability, reduced oncotic pressure, or impeded lymphatic drainage. It results in a visible and palpable swelling of the affected areas, which can occur in localized regions, like a sprained ankle, or throughout the body, such as in cases of heart failure or kidney disease.

Inflammation, while it may also cause some swelling, is primarily identified by its broader context involving the body's response to injury or infection, which includes redness, heat, pain, and often a functional impairment of the affected area. Necrosis refers to the death of cells and tissues due to lack of blood flow or injury, which does not necessarily cause swelling. Atrophy is the reduction in size or wasting away of an organ or tissue and does not involve fluid accumulation or swelling. Therefore, edema is the correct choice as it directly relates to fluid buildup in tissues.