“It’s like literally an outpatient procedure,” said Dr. Eleanor D. Lederer, a professor at the University of Louisville School of Medicine and past president of the American Society of Nephrology. “You go in, you have it done, you lie in bed for a while to keep the blood vessel from bleeding and then you go home.”

Another doctor, however, said Mrs. Trump was probably being kept in the hospital longer because of her position. “That’s because she is the first lady,” said Dr. Jeffrey Cadeddu, a professor of urology and radiology at the University of Texas Southwestern Medical Center in Dallas. “If it was you, you’d be in and out in a day, I promise.”

Still, embolization kills some surrounding healthy kidney tissue, which causes swelling and pain as a patient recovers, so a longer stay could be helpful or necessary, doctors said.

The White House did not explain what led Mrs. Trump to seek treatment or whether the “benign kidney condition” meant she had a benign tumor or something else. Specialists said it could be that doctors had been monitoring a mass for a while and decided to act on it now because it had grown. Or they said it could be that she experienced symptoms of some sort, like noticing blood in the urine or experiencing back pain or stomach pain.

Doctors may also have discovered bleeding while conducting routine tests for other reasons.

Dr. Joseph A. Vassalotti, the chief medical officer at the National Kidney Foundation, said his guess was that Mrs. Trump had either a benign tumor known as an angiomyolipoma or a bleeding cyst. “It sounds like it was a benign tumor,” he said.

Dr. David G. Warnock, an emeritus professor of medicine at the University of Alabama at Birmingham and a past president of the kidney foundation, said doctors frequently perform an embolization if a biopsy or other diagnostic procedure causes bleeding.

“My list of benign conditions that you’d embolize is pretty short,” he said. “Ninety percent of them are to stop bleeding after some procedure like a kidney biopsy.”