Why does kidney atrophy lead to an increase in volume?

       In patients with renal atrophy, an apparent increase in kidney size may be associated with impaired renal function, increased vascular permeability, and other factors. A definitive diagnosis requires a comprehensive series of diagnostic tests. Specific causes are outlined below:

       1. Impaired Renal Function

       Renal atrophy—whether due to physiological or pathological causes—can severely compromise overall kidney function and glomerular filtration. When excess body fluid cannot be adequately excreted via the kidneys, it accumulates within the kidneys and other organ tissues, leading to fluid retention. This retention may result in paradoxical enlargement of the atrophic kidney.

       2. Increased Vascular Permeability

       Pathological renal atrophy may arise from conditions such as acute pyelonephritis or renal failure. Inflammatory processes or functional deterioration within the kidney can damage, detach, or cause atrophy of vascular endothelial cells, thereby increasing vascular permeability. Consequently, excessive fluid extravasation from the vasculature accumulates within the renal parenchyma, eventually leading to secondary renal edema and consequent enlargement of the kidney.