A spokeswoman for the First Lady declined to offer more details on her condition, but said the 48-year-old is recovering.
According to the a White House spokesperson, the procedure was successful without any complications.
He says "she is in good spirits", and adds, "Thank you to all of the well-wishers!"
While there's no indication whether Mrs. Trump's procedure was an emergency or planned, LaPook said after this kind of procedure, it would not be at all unusual to keep her in the hospital for observation for a number of days.
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.
The president was not present during the procedure.
"Heading over to Walter Reed Medical Center to see our great First Lady, Melania", Trump tweeted.
The East Wing keeping her medical condition private until after the procedure was nothing unusual, the Post said.
The Slovenian-born first lady last week rolled out an agenda for her White House work focused on helping children.
Finally, around 5 p.m., Trump boarded Marine One to visit his wife, who is expected to stay at the hospital "for the duration of the week".
According to Elizabeth Kavaler, a urologist at Lenox Hill Hospital in NY, the first lady may have a common, benign tumor of the kidney called an angiomyolipoma, or AML.
Grisham declined to provide additional information or answer questions about the procedure, saying that the first lady is entitled to privacy.
"The procedure was successful and there were no complications".