**Core Concept**
Fluid movement between the intravascular and interstitial compartments is a dynamic process governed by hydrostatic and oncotic pressures. Increased fluid accumulation in the interstitial space indicates an imbalance in these forces, favoring fluid extravasation.

**Why the Correct Answer is Right**
In conditions like heart failure or liver cirrhosis, the reduced oncotic pressure due to hypoalbuminemia or decreased intravascular volume leads to increased hydrostatic pressure in the capillaries. This elevated pressure forces fluid out of the capillaries and into the interstitial space, causing edema. The accumulation of fluid in the interstitial space can be further exacerbated by increased capillary permeability, often seen in conditions like inflammation or infection.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is not directly related to the pathophysiology of fluid accumulation in the interstitial space.
**Option B:** This option is incorrect as it describes the opposite process, where fluid is being retained within the intravascular compartment.
**Option C:** This option is not relevant to the description of fluid accumulation in the interstitial space.

**Clinical Pearl / High-Yield Fact**
Remember that the pathophysiology of edema involves an imbalance between hydrostatic and oncotic pressures, often due to decreased oncotic pressure or increased hydrostatic pressure. This can be seen in various clinical conditions, including heart failure, liver cirrhosis, and nephrotic syndrome.

**Correct Answer: D. Edema.