By DARLENE SUPERVILLE
Associated Press

WASHINGTON - First lady Melania Trump underwent a "successful" procedure Monday to treat a benign kidney condition and was expected to remain hospitalized for the rest of the week, her staff said. President Donald Trump took a helicopter to Walter Reed National Military Medical Center to visit her and tweeted that his wife was in "good spirits."

Mrs. Trump, 48, had the embolization procedure Monday morning. The president spoke with Mrs. Trump before the procedure and with her doctor afterward, the first lady's office said.

The president tweeted shortly before arriving at Walter Reed outside Washington, saying it was a "successful procedure," describing his wife as being "in good spirits" and offering his thanks "to all of the well-wishers!" He spent over an hour at the hospital before departing, without addressing waiting reporters, via motorcade under stormy skies.

The White House did not offer any additional details on Mrs. Trump's condition, though Vice President Mike Pence described the procedure as "long planned" as he opened a speech at an evening event celebrating Israel's independence. "Melania is already on the mend," Pence said.

In the Senate, Minority Leader Chuck Schumer, D-N.Y., sent well wishes for "a speedy recovery to the first lady."

She was last seen in public on Wednesday at a White House event where she and the president honored military mothers and spouses for Mother's Day.

Two urologists who have no personal knowledge of Mrs. Trump's condition said the most likely explanation for the procedure is a kind of noncancerous kidney tumor called an angiomyolipoma.

They're not common but tend to occur in middle-aged women and can cause problematic bleeding if they become large enough, said Dr. Keith Kowalczyk of MedStar Georgetown University Hospital.

"The treatment of choice" is to cut off the blood supply so the growth shrinks, added Dr. Lambros Stamatakis of MedStar Washington Hospital Center. Doctors do that with an embolization, meaning a catheter is snaked into the blood vessels of the kidney to find the right one and block it.

Most of the time, these benign tumors are found when people undergo medical scans for another reason, but sometimes people have pain or other symptoms, Kowalczyk said. Many times, embolization patients go home the same day or the next.

The president had no official public appearances Monday and declined to answer shouted questions from reporters about his wife as he departed the White House for Walter Reed.

The former model from Slovenia is Trump's third wife and the couple has been married for 13 years. They have a 12-year-old son named Barron.

Mrs. Trump, who has been gradually raising her profile as first lady, recently hosted her first state dinner and launched a public awareness campaign to help children.

With the president watching, Mrs. Trump last week unveiled the "Be Best" campaign, which she said will focus on childhood well-being, social media use and opioid abuse.

Mrs. Trump joined her husband last month to host the prime minister of Japan for a two-day summit at the Trumps' Florida estate, and the Trumps hosted the president of France at the White House on a three-day state visit, including a lavish state dinner. Mrs. Trump also represented the administration at the April funeral of former first lady Barbara Bush.

The Trumps and their marriage have been under scrutiny in recent months after revelations that a porn actress was paid $130,000 in hush money to keep quiet about claims she had sex with Trump in 2006. Trump has acknowledged reimbursing his lawyer for the payment to porn star Stormy Daniels but denies her allegations. Separately, a former Playboy model has revived her allegations of a 10-month affair with Trump in 2006. Trump also denies the allegations from Karen McDougal.

Mrs. Trump has, at times, has been noticeably absent from her husband's side. But both made a point of displaying affection during last week's Rose Garden event where she announced the "Be Best" initiative.

The first lady lived full time in New York during the administration's opening months so Barron would not have to change schools midyear. She and Barron moved to the White House last June.
 
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AP Medical Writer Lauran Neergaard and AP writer Jill Colvin contributed to this report.