The Rio de Janeiro State Health Department said that the husband of Elisangela Borborema Rosa was cleaning his spear gun when it went off, firing a harpoon that hit her cervical spine.
She was taken to the Regional Hospital of Araruama in Rio de Janeiro state and underwent emergency surgery after the incident, which happened on Monday in the coastal city of Arraial do Cabo in Brazil.
Doctors treating the woman at the hospital said that the harpoon came within an inch of killing her.
"We had to be very careful when we took it out because of the possibility of injury caused by the removal," said Dr Kleber Medeiros.
He said they were especially concerned when extracting the harpoon in case it was blocking an essential artery."If we took it out she could haemorrhage, which would require an immediate intervention."
In a similar incident, a Brazilian man escaped brain damage last month after accidentally shooting himself in the head with a harpoon.
Bruno Barcellos de Souza Coutinho was cleaning fishing equipment at his house, in the small town of Petropolis in the state of Rio de Janeiro when the accident happened.