A three-year-old girl with her head weighing 20 kg due to hydrocephalus, is recovering steadily after a 3D-printed titanium alloy skull was implanted, doctors said.

The girl, nicknamed Han Han, underwent the surgery for more than 17 hours on Wednesday morning at the No. 2 People's Hospital of central China's Hunan Province and is under observation, said neurosurgeon Kuang Weiping, who is in charge of her treatment.

Born with hydrocephalus, Han Han was admitted to the hospital two months ago. Since September 2014, she has become bedridden as her head grew four times the normal size, taking up more than half of her total weight.

Due to the heavy weight, parts of her brain suffered serious infections and she lost sight because her optic nerve was affected.

Kuang said they believed her skull was likely to rupture as infected parts became thinner and only the "brain-shrinking" operation could save her life.

During the process, neurosurgeon peeled her scalp and skull, then drained the fluid in her head. After the swollen structures in her brain returned to the normal size, they implanted the donated artificial skull and covered it with her scalp.

"We were very, very careful, because brain tissue without a skull is like a peeled egg. Fortunately, it went smoothly," Kuang said.