Friday's operation could be followed by more surgery, she said.
Police say the boy's stepfather confessed to pushing 42 supposedly "blessed" sewing needles deep into the child because his lover told him to while in trances. The rituals were performed over a period of a month to try to keep the couple together, the stepfather told police.
Roberto Carlos Magalhaes, a 30-year-old bricklayer, told detectives the woman would enter into trances and "command him to stick the needles in the boy's body," police inspector Helder Fernandes Santana told The Associated Press by telephone.
The lover, Angelina Ribeiro dos Santos, paid to have the needles measuring up to 2 inches (5 centimeters) blessed by a woman who practiced the Afro-Brazilian religion Candomble, and convinced Magalhaes that inserting them into the boy would somehow allow them to be together, Santana said.
Police, however, believe Dos Santos was out for revenge on the boy's mother, though they did not say why.
"According to his confession, he acted under influence of the woman, but it was he who stuck the needles in the boy's body," the inspector said.
Magalhaes and dos Santos were both arrested, though no charges have yet been filed.
Dos Santos is not believed to be a member of any religious or occult group, and authorities believe she came up with the idea of the rituals on her own, Santana said.
The two were taken to an undisclosed lockup for their own protection after a mob threw stones at the police station where they were being held. It was not immediately clear whether they had legal representation.
Authorities also detained the woman who blessed the needles so she could be questioned, but Santana said he expects she will be released without charge because she did not know how they were being used.
The boy's mother, a maid, took him to a hospital in the town of Ibotirama on Dec. 10, saying he was complaining of pain.
After X-rays revealed the cause, the mother told police she didn't know how the needles got inside her son, whose name was not released because of his age. The boy was later transferred for more advanced evaluation at a much larger hospital in the coastal city of Salvador.
Police and doctors concluded it would have been impossible for the boy to have ingested the needles -- which have also been found in a lung, in his left leg and spread throughout his abdomen.
Afro-Brazilian religions practiced in Brazil have no ceremonies, rituals or practices involving harm to people, said Nelson Inocencio, director of African-Brazilian studies at the University of Brasilia.
He worried that the incident could hurt the image of the religions, of which Candomble is the most popular, and concentrated most in Bahia state.
"What happened to this boy without a doubt could feed into the prejudice against Afro-Brazilian traditions," he said.
Associated Press writer Alan Clendenning in Sao Paulo contributed to this report.