Perirenal fat is a type of fatty tissue located around the kidneys. It envelops the fibrous capsule of the kidney and extends into the renal sinus, the central cavity of the kidney where blood vessels and nerves enter and exit. Its anatomical position places it in close proximity to the kidney.
What is Perirenal Fat
Perirenal fat is primarily adipose tissue, a specialized connective tissue that stores energy. It resides within the retroperitoneal space, behind the abdominal cavity, and is encased by the renal fascia, also known as Gerota’s fascia, holding it tightly around the kidneys and adrenal glands. This fascia also separates perirenal fat from pararenal fat, an adjacent fat depot.
While largely considered white adipose tissue, perirenal fat can exhibit characteristics similar to brown fat. In adults, it can still contain brown and highly activated beige cells, white adipose cells that have undergone a “browning” process. This unique composition suggests a more active role than simple energy storage.
Roles of Perirenal Fat
Perirenal fat performs several physiological roles beyond energy storage due to its location and composition. One primary function is mechanical protection, as it acts as a cushion, shielding the kidneys from external physical shocks and providing structural support to stabilize their position within the abdominal cavity. This helps prevent kidney displacement, a condition known as nephroptosis.
Beyond mechanical support, perirenal fat also contributes to thermal insulation, helping to maintain a stable temperature around the kidneys. It generates heat through non-shivering thermogenesis, a process facilitated by its rich vascular supply and the presence of brown fat-like characteristics.
Furthermore, perirenal fat functions as an endocrine organ, secreting various signaling molecules known as adipokines. These adipokines can influence kidney function and systemic metabolism, playing a role in glucose and lipid homeostasis, as well as inflammatory responses. This endocrine activity highlights its active participation in biological processes.
Perirenal Fat and Health Outcomes
Dysfunctional or excessive perirenal fat has been increasingly linked to various adverse health outcomes, demonstrating its role in metabolic and cardiovascular health. Its proximity to the kidneys allows it to directly influence renal function through mechanical pressure and the secretion of bioactive substances. Excessive accumulation of perirenal fat can exert mechanical pressure on the kidneys, potentially leading to increased renal vascular resistance and impaired glomerular filtration.
The endocrine activity of perirenal fat also plays a significant role in disease development. It secretes pro-inflammatory adipokines and other signaling molecules that can drive oxidative stress and disrupt the microenvironment of the kidneys, contributing to damage to renal tubules and glomeruli. This mechanism contributes to the progression of chronic kidney disease (CKD), with studies showing a significant association between perirenal fat thickness and CKD, including diabetic nephropathy and nephropathy caused by abnormal cardiac function.
Perirenal fat accumulation is also associated with hypertension, and studies indicate a positive correlation between its thickness and blood pressure. Its involvement extends to metabolic syndrome, a cluster of conditions including high blood pressure, high blood sugar, excess body fat around the waist, and abnormal cholesterol levels. Elevated perirenal fat volume has been positively associated with an increased risk of metabolic syndrome.
Moreover, excess perirenal fat has been identified as a risk factor for cardiovascular disease, independently of other metabolic parameters. The mechanisms involve the secretion of adipokines that influence glucose and lipid metabolism, contributing to systemic inflammation and insulin resistance, which are known precursors to cardiovascular complications.