Benign Renal Neoplasm
A benign kidney tumor is a growth in the kidney that does not spread to other parts of the body and is not usually life-threatening, though it can sometimes cause symptoms that need treatment.
Table of contents
- What is a benign renal neoplasm?
- Types of benign kidney tumors
- Symptoms
- Causes and risk factors
- How are benign kidney tumors diagnosed?
- Treatment options
- Non-cancerous kidney cysts
What is a benign renal neoplasm?
A benign renal neoplasm is a growth or tumor in the kidney made up of abnormal cells that do not behave like cancer. The word “benign” means that these growths do not spread (metastasize) to other parts of the body[1]. Most growths that develop in the kidneys are not cancerous, and up to 20 percent of small kidney tumors are benign[6].
Benign kidney tumors are not usually life-threatening. They are typically removed with surgery and do not usually come back (recur)[1]. However, even though these tumors are not cancerous, they can sometimes cause health problems or symptoms that require medical attention[6].
Types of benign kidney tumors
There are several different types of benign kidney tumors. Each type has different characteristics and may require different approaches to treatment.
Papillary renal adenoma
Papillary renal adenoma is the most common type of benign kidney tumor[1][6]. These tumors are small and grow slowly. They usually do not cause any symptoms and are often discovered during imaging tests done for other reasons[1].
Oncocytoma
An oncocytoma starts in the cells of the collecting ducts of the kidney. These are the small tubes inside the kidney that help move urine toward the bladder. Oncocytomas can grow quite large, and there can be several of them in one or both kidneys[1]. They often appear as well-defined solid masses that grow slowly and typically do not spread[4]. Sometimes oncocytomas are found at the same time as a cancerous tumor[1].
Angiomyolipoma
An angiomyolipoma is a kidney tumor made up of three types of tissue: fat, blood vessels, and smooth muscle[1][2]. This is the most common kind of benign kidney tumor overall, affecting less than 1 in 100 people in the general population[2]. Most angiomyolipomas are small and do not cause problems[4].
These tumors often develop in people with tuberous sclerosis, a genetic condition that causes non-cancerous tumors to form in many organs, including the eyes, skin, brain, lungs, heart, and kidneys[1]. In most cases, an angiomyolipoma is golden yellow because of its fat content and can range in size from about half an inch to about 8 inches[2].
Even though these tumors are non-cancerous, they can spread into and destroy surrounding tissue. Tumors larger than 4 cm (about 1-1/2 inches) can also cause sudden bleeding from the kidney into the abdomen[1][2].
Symptoms
Many benign kidney tumors do not cause symptoms, especially when they are small. A doctor may only discover them when treating another condition[6]. When symptoms do occur, they can include the following.
Blood in the urine (hematuria) is one of the most common symptoms. It is important to get medical help right away if you notice blood in your urine or have pain when urinating. However, sometimes blood may only be visible under a microscope[6][7].
A kidney tumor may cause pain in the lower back or between the ribs and hips. This area is called the flank[6][7]. You may also experience a lump that you can feel, loss of appetite, unexplained weight loss, fever, nausea and vomiting, or a urinary tract infection[2][6].
Anemia, which means having low levels of red blood cells, can also occur. Healthy kidneys help the body make more red blood cells by producing a hormone called erythropoietin. If a tumor affects the amount of this hormone released or causes you to lose red blood cells in your urine, you may develop anemia[6].
Causes and risk factors
The cause of many benign kidney tumors is unknown[6]. Doctors and medical researchers do not know the exact causes of kidney tumors[7].
However, some things may increase your chance of developing benign kidney tumors. You may be more likely to have a kidney tumor if you use tobacco products, regularly have more than seven alcoholic drinks per week, have obesity, have a family history of high blood pressure, have a family history of kidney tumors, or are regularly around chemicals that contain chlorine[7].
Certain health conditions can also increase your risk. These include lymphangioleiomyomatosis (LAM), tuberous sclerosis complex, neurofibromatosis type 1, and von Hippel-Lindau disease[2]. If you have any of these conditions, you should get regular imaging tests to try to catch kidney tumors early[2].
Some research suggests that certain genetic changes to the TSC1 or TSC2 genes may play a role in the development of angiomyolipomas. These genes are responsible for producing a protein called tuberin that helps control the size and growth of cells. When these genes change, it affects the production of tuberin, and cells may grow out of control[2].
How are benign kidney tumors diagnosed?
Because kidney tumors usually do not have symptoms, healthcare providers often discover them during tests for other conditions[7]. Many small tumors are found during imaging such as a CT scan or MRI that was ordered for unrelated reasons like back pain or abdominal pain[4].
If you have symptoms, a healthcare provider will conduct a complete physical examination and ask if you have a personal or family history of kidney tumors or cancer[7].
Several tests may be ordered to help diagnose kidney tumors:
- Imaging tests are painless tests that help your provider take a closer look at your kidneys. These may include a CT scan (computed tomography), which is considered the gold standard for detecting kidney masses, MRI (magnetic resonance imaging), or ultrasound[4][7].
- Urinalysis involves providing a urine sample that will be tested at a lab to see if it contains microscopic amounts of blood that are not visible to the naked eye[7].
- Blood tests may be done to check kidney function and count blood cells[7].
- In some cases, a biopsy may be done, especially if you already have cancer elsewhere, surgery would be risky, or there is concern for a rare tumor type[4].
One important tool used to evaluate kidney cysts is the Bosniak Classification System, developed in 1986. This system helps doctors assess the risk that a kidney cyst might be cancerous based on how it appears on a CT or MRI scan[4].
Treatment options
The treatment for benign kidney tumors depends on several factors, including the size of the tumor, whether it is causing symptoms, and your overall health.
Surgery
Surgery is the main treatment for benign kidney tumors[1]. About 75 percent of kidney tumors are cancerous, so even when a tumor appears benign, doctors often recommend removing it[7]. However, not all kidney tumors need surgery. For many people, especially if the mass is small (less than 3 cm), growing slowly, and not causing symptoms, the best approach may be “active surveillance” or close monitoring with scans[4].
There are two main types of surgery for kidney tumors. One option is removing the entire kidney (nephrectomy). The other is removing the cancer but leaving as much of the kidney as possible (partial nephrectomy). You may also need to have some lymph nodes removed, which are part of the body’s drainage system[1].
Active surveillance
For small renal masses, which are usually about 4 cm (about 1.5 inches) or smaller, active surveillance may be an option[4]. Research shows that many of these small lesions do not become aggressive. Studies have shown that patients under active surveillance can have excellent outcomes, with very low rates of cancer spreading[4].
Other treatment options
For angiomyolipomas specifically, arterial embolization may be used. This procedure blocks the blood supply to the tumor[1]. It can help shrink the cancer and control symptoms if you are not well enough to have surgery[1].
Non-cancerous kidney cysts
Simple kidney cysts are the most common non-cancerous condition of the kidney. A simple cyst is a round or oval fluid-filled sac. One or more cysts can develop in a kidney, and simple kidney cysts are very common in people over the age of 50[1].
Most simple kidney cysts are found when an imaging test is done for other medical reasons. When seen on an imaging test, simple kidney cysts have smooth, well-defined, and rounded edges. This helps doctors tell them apart from kidney tumors[1].
If simple kidney cysts are not causing any symptoms, they do not need any treatment. If they start causing problems like pain, infection, or bleeding, the doctor will drain the cysts using a long needle or have them removed by surgery[1].
