The liver regrows lost mass, but not its original shape

The human liver can regrow lost tissue: a healthy liver can lose more than 75 percent of its mass to surgery or injury and the remainder will grow back toward its original size, making it the only solid organ in the body that regenerates this way. Most other organs patch damage with scar tissue instead.

Does the liver grow back completely?

Not quite: popular accounts say it regenerates “completely” within weeks, but measurements in people are more modest. The A2ALL study followed 350 living donors and 353 recipients at U.S. transplant centers and imaged their livers three months after surgery. Donors had regrown an average of about 676 grams of tissue, reaching roughly 80 percent of their original volume; recipients’ grafts reached about 93 percent of the expected size. The authors called this “rapid yet incomplete” restoration, and earlier studies had found that many donors still had not regained their full liver volume a year later.

Nor does the liver rebuild the piece that was removed. In studies of partial liver removal, the surviving lobes enlarge until their combined mass is restored, but the regenerated organ has a different shape, with fewer lobes; the lobes that were cut away never return.

How does regrowth make living-donor transplants possible?

Both pieces grow: a healthy adult gives part of their liver, and both the remnant and the transplanted portion grow to meet their owners’ needs. That capacity is what makes living-donor liver transplants possible. Surgeons size the donation carefully: donors left with the smallest remnants grew fastest but also showed more signs of strain on liver function in the first month.

Why the liver can do this when the heart or kidneys cannot is still unexplained. As MIT biologist Kristin Knouse, who studies liver regeneration, puts it:

“We still don’t understand why the liver can regenerate but other organs cannot.”