Years published: 2023
NORD gratefully acknowledges Gregory Cichon and Zachary LeMense, MD candidates at Creighton School of Medicine and Joan Delto, MD, Assistant Professor of Urology at Creighton University School of Medicine, for the preparation of this report.
Renal oncocytoma, also known as oncocytoma of the kidney, is a rare type of benign kidney tumor. It is composed of oncocytes, which are cells that have an abnormally large number of mitochondria, the organelles that produce energy for the cell. Renal oncocytomas are usually slow-growing and do not spread beyond the kidney, but in rare cases they can become cancerous.
Symptoms of renal oncocytoma may include abdominal pain, blood in the urine and a mass in the abdomen. These tumors are often discovered incidentally during imaging tests for other reasons. Diagnosis is typically confirmed through biopsy, which involves removing a small sample of tissue for examination under a microscope.
Treatment of renal oncocytoma typically involves surgical removal of the tumor. In some cases, only the part of the kidney containing the tumor is removed, while in others the entire kidney may need to be removed. In cases where the tumor is large or has grown into nearby structures, additional treatments such as radiation, chemotherapy or immunotherapy may be necessary.
Renal oncocytomas are rare, with an estimated incidence of 0.5-1.5 cases per million people per year, and they account for about 3-7% of all kidney tumors. They occur most commonly in middle-aged to older adults, with a peak incidence in the sixth and seventh decades of life. Men are more likely to develop renal oncocytoma than women.
There is limited research on renal oncocytoma, as it is a rare condition. However, studies have shown that these tumors tend to have a good prognosis, with a low risk of recurrence after surgical removal. In most cases, patients can return to normal activities within a few weeks of surgery.
The exact cause of renal oncocytoma is not well understood, but there are several factors that may increase a person’s risk of developing this condition. One possible cause of renal oncocytoma is genetic mutations. Some people may have inherited genetic mutations that increase their risk of developing this type of tumor. Other genetic mutations that may lead to the development of renal oncocytomas occur in tuberous sclerosis complex (TSC) and Birt-Hogg-Dubé syndrome.
Another possible cause of renal oncocytoma is chronic kidney disease. People with chronic kidney disease may be more likely to develop renal oncocytoma due to the long-term damage to the kidneys.
Obesity is also a potential risk factor for renal oncocytoma. People who are obese may be more likely to develop this type of tumor due to the extra strain on their kidneys.
Other kidney cancers, particularly clear cell carcinoma and chromophobe renal cell carcinoma, may also be associated with renal oncocytomas, either growing alongside oncocytomas or appearing similar to them clinically. Part of the diagnostic and follow-up process may involve ruling out the possibility of these malignant growths from a benign diagnosis such as renal oncocytoma.
Overall, the exact causes of renal oncocytoma are not well understood, and more research is needed to better understand this condition. However, genetic mutations, chronic kidney disease and obesity are all potential risk factors for renal oncocytoma.
In most cases, renal oncocytoma is found incidentally during imaging tests performed for other reasons. It is more common in older individuals, with the average age at diagnosis being around 60 years old. It is also more common in men than in women.
Renal oncocytomas that are found as a single mass and on one side of the body tend to be sporadic or random in incidence. However, when multiple tumors are discovered or when both kidneys are affected, it may be a sign that there is an underlying disease process occurring. This situation has been described in diseases such as tuberous sclerosis complex and Birt-Hogg-Dubé syndrome.
The diagnosis of a renal oncocytoma typically begins with a physical examination, during which the doctor may feel a mass in the abdomen or flank area. The doctor may also order imaging tests, such as an ultrasound, CT scan, MRI or Sestamibi scan to confirm the presence of a tumor and to determine its size, location and activity.
If the imaging tests suggest that the tumor may be a renal oncocytoma, the doctor will likely recommend a biopsy to confirm the diagnosis. Features on CT scan or MRI that may indicate the presence of an oncocytoma are a homogenous, well-circumscribed solid mass, sometimes with a central scar. During a biopsy, a small sample of tissue is removed from the tumor and examined under a microscope. The presence of oncocytes, which are abnormal cells with an unusually large number of mitochondria, can help confirm the diagnosis of a renal oncocytoma. When the tumor is removed, the overall appearance can further confirm the diagnosis. Renal oncocytomas are described as being “mahogany brown” or “dark red” in color due to the large quantity of mitochondria in the tumor cells.
To provide a more detailed workup for the diagnosis of a renal oncocytoma, the doctor may also order blood and urine tests to assess the function of the kidneys and to look for any abnormalities. These tests may include a complete blood count (CBC), blood chemistry panel, urine analysis and creatinine clearance test.
Once the diagnosis of a renal oncocytoma is confirmed, the doctor will discuss the treatment options with the patient. Surgical removal of the tumor is the most common treatment, but it may not be necessary if the tumor is small and not causing any symptoms. The type of surgery will depend on the size and location of the tumor and may include partial or total nephrectomy, removal of the kidney. If surgery is not an option, a clinician may instead use cryoablation.
Treatment for renal oncocytoma may include active surveillance or monitoring with imaging tests (CT, MRI or ultrasound) if the mass is very small, thermal ablation (applying heat or freezing the tumor) or surgery. The type of surgical procedure used will depend on the size and location of the tumor. In some cases, a partial nephrectomy, which involves removing the part of the kidney containing the tumor, may be performed. In other cases, a radical nephrectomy, which involves removing the entire affected kidney, may be necessary.
After surgery, the patient will typically be monitored for any signs of recurrence or the development of other tumors. This may involve regular imaging tests such as CT or MRI scans, to check for any changes in the kidneys.
It is important for patients with renal oncocytoma to receive regular follow-up care after their initial treatment. This can help ensure that any changes in the kidneys are detected and treated promptly. In addition, maintaining a healthy lifestyle, including following a healthy diet and exercising regularly, can help reduce the risk of recurrence and other health problems.
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Renal oncocytoma. Genetic and Rare Diseases Information Center (GARD). Updated Feb. 2023. https://rarediseases.info.nih.gov/diseases/8477/renal-oncocytoma Accessed March 28, 2023.
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