Renal Sinus

The renal sinus is a central part of your kidney where things go in (like nerves and arteries) and come out (like pee, veins and lymphatic channels). Like the rest of your kidney, the renal sinus has fat padding around it. It contains:

• Body fat
• Autonomic nerves, which control involuntary actions
• Connective tissue
• Lymphatic channels
• Major and minor calyces, where pee collection starts
• Renal artery and renal vein
• Renal pelvis, which collects pee as your kidneys produce it

Most of your renal sinus is fat that wraps around the other structures. The amount of fat in a kidney’s renal sinus gradually increases with age and weight gain.

What is the function of the renal sinus?

The renal sinus is part of your kidney anatomy. It acts as a compartment that contains fat and other parts of your kidney. This includes your kidneys’ vascular system (arteries, veins and the tiny capillaries that connect them) and nervous system.

It’s the area where things go in and come out. Blood goes in, and it helps filter out waste products and excess fluids. The waste products and excess fluids eventually leave your body as pee.

The renal sinus also has fat padding that protects your kidney.

Where is the renal sinus located in the kidney?

The renal sinus is in the middle part of your kidney. Along its sides is the renal parenchyma. Two major parts of the parenchyma include the renal cortex and renal medulla, which help your kidney function.

What does it look like?

The renal sinus is padded with mostly fat. Fat usually looks white or yellow.

In an ultrasound, it looks hyperechoic compared to the renal parenchyma. “Hyperechoic” means that the ultrasound bounces back lots of echoes, or soundwaves. It usually looks light gray on an ultrasound. It may look round or like an oval.

What are the common conditions that affect the renal sinus?

Conditions and disorders that can affect the renal sinus include:

• Renal sinus cyst: This is a benign (noncancerous), fluid-filled sac. It may grow outside the renal sinus (parapelvic cyst) or inside the renal sinus (peripelvic cyst).
• Renal sinus lipomatosis: This is when there’s too much fat in the renal sinus.
• Benign multilocular cystic nephroma: This is a noncancerous tumor that can grow into the renal sinus.

Other conditions may affect parts in the renal sinus. These include:

• Caliectasis: Pee collection begins in your calyces. Caliectasis causes your calyces to swell with extra fluid. Without treatment, it may cause kidney failure.
• Vascular lesions: A bulge forms on the wall of a renal artery inside the renal sinus. Other names for vascular lesions include renal artery aneurysm, arteriovenous communication or renal vein varix.
• Renal cell carcinoma: This is a cancerous tumor that can grow into the renal sinus.

The amount of fat inside your renal sinus may also affect your blood pressure.

What tests are used to examine the renal sinus?

Imaging tests can show kidney abnormalities or growths. The most common imaging tests include:

• CT scan
• MRI
• Kidney ultrasound
• Nuclear imaging

Other tests that healthcare providers use to check your kidney health include:

• Blood tests
• Kidney biopsy
• Ureteroscopy
• Pee tests

How common are renal sinus cysts?

Lipomatosis and cysts are common types of renal sinus lesions that occur as people age. About 1 out of every 3 people over age 70 has at least one renal cyst. It may be inside or outside of the renal sinus.

Simple renal cysts usually don’t cause symptoms. Many people don’t know they have them. Providers usually diagnose them during an imaging exam for other health reasons. They may want to monitor it closely with regular check-ups and imaging tests.

If a renal sinus cyst bursts, bleeds, gets too big or gets infected, you may need surgery to remove it. This isn’t common.

What is renal sinus invasion?

Renal sinus invasion is when a cancerous tumor spreads into your renal sinus. Renal cell carcinoma is the most common cancer that causes renal sinus invasion. Healthcare providers can usually diagnose renal sinus invasion with a CT scan. 

How is renal sinus lipomatosis diagnosed and treated?

A CT scan can easily identify fatty masses. But renal sinus lipomatosis isn’t easy to officially diagnose without surgery. Healthcare providers usually confirm renal sinus lipomatosis by surgically removing the mass. Then, they’ll examine it under a microscope.

Signs/symptoms that something isn’t working right

Renal sinus conditions may cause symptoms like:

• Pain in your stomach, back or between your ribs and hip
• Fever
• Peeing more than usual (frequent urination)
• Blood in your pee (hematuria)
• Dark pee

Simple lifestyle changes/tips to keep it healthy

The best way to keep your renal sinus healthy and avoid complications is to maintain a healthy weight for you. Gaining weight can increase renal sinus fat.

Other ways to help keep your renal sinus healthy and support overall kidney health include:

• Quit smoking.
• Reduce the amount of salt that you consume.
• Drink plenty of water.
• Get at least 30 minutes of physical activity five days a week.
• Limit how many nonsteroidal anti-inflammatory drugs (NSAIDs) you take. NSAIDs can damage your kidneys if you use them regularly.
• Keep an eye on your blood pressure levels.
• Monitor your blood sugar levels if you have diabetes.

What is the difference between renal pelvis and renal sinus?

The renal pelvis is inside your renal sinus. It’s a large space that collects pee as your kidneys make it. From there, pee flows into your ureters. Ureters are small tubes that connect your kidneys to your urinary bladder.

Is it the same as renal hilum?

The renal hilum is like the door to the renal sinus. Blood vessels, nerves, lymphatic channels, and ureters enter and exit through the renal hilum.