Benign tumors are noncancerous. Most are asymptomatic, are discovered incidentally, and are not immediately life threatening.
Renal adenomas are the most common form of benign, solid kidney tumor, and are typically small, low-grade growths. Their cause is unknown. Because they usually are asymptomatic, their incidence is unknown, although one study found them present in 7% to 22% of autopsy cadavers. In rare cases, when they have grown large enough to affect kidney function or adjacent vessels, symptoms similar to those of RCC may occur.
Adenoma cells look much like low-grade RCC cells under a microscope. In fact, while they are considered benign, there is presently no known cellular classification to differentiate them from RCCs. Many researchers and physicians regard them as early stage precancers, to be treated accordingly.
Oncocytoma is a benign, usually asymptomatic tumor that can grow quite large. They can develop throughout the body and are not unique to the kidneys. Their cause is unknown, and they appear with greater frequency in men than in women. Typically, they are discovered incidentally by ultrasound, IVP, CT, or MRI scan for an unrelated health problem.
Under a microscope, many oncocytomas resemble early-stage RCCs. Many physicians regard them as precancerous growths to be surgically removed unless the patient's age or overall health condition dictates otherwise.
Also known as renal hamartoma, angiomyolipomas are rare benign tumors usually caused by an inherited genetic mutation. They can occur on an isolated, individual basis, but most often are associated with a rare genetic disease called tuberous sclerosis, which can cause tumors in the skin, kidneys, brain, and other organ systems. About 80% of persons diagnosed with tuberous sclerosis also have angiomyolipoma.
In patients without tuberous sclerosis, these tumors most often occur in middle-aged women. Most cases are discovered when the patient undergoes a CT scan for an unrelated abdominal problem, suffers gastrointestinal discomfort, or suffers a sudden hemorrhage caused by the rupture of a large tumor.
Management of the condition depends on the size of the tumors and the severity of the symptoms they produce. Asymptomatic patients and those with small tumors usually are not treated; instead, they are observed periodically with an eye toward surgery if the tumors grow or produce symptoms. Because of the potential for spontaneous rupture and life-threatening hemorrhage, patients with large tumors usually are considered candidates for some form of surgical treatment, ranging from partial nephrectomy to arterial embolization.
Fibromas are tumors of the fibrous tissue on, in, or surrounding the kidney. They are rare and are more common in women. Their cause is unknown and most do not cause symptoms. Usually they grow on the periphery of the kidney and can become large before becoming clinically obvious. While generally benign, these tumors have no special characteristics to differentiate them from malignant tumors of the kidney. Because of this uncertainty of diagnosis, partial or radical nephrectomy is the standard treatment.
Lipomas are rare renal tumors that originate in the fat cells within the renal capsule or surrounding tissue. They typically occur in middle-aged women, can grow very large, and produce pain and hematuria. Like many benign tumors, they may become cancerous and usually are treated with total nephrectomy.