Types of Liver
Liver transplantation refers to
the surgical replacement of a diseased liver with a donor-grafted
organ. This is most commonly orthotopic (complete
removal and replacement), but occasionally heterotopic,
where the native organ is left in situ. The transplant may be whole
liver, a reduced-size liver, or a liver segment, the latter as means
of overcoming donor organ scarcity, particularly for pediatric recipients
(Figure 29–1). Reduced-size liver
grafts, such as a left-lateral segment or hemireduction graft,
can be derived from either cadaver or living donors, or from split-liver transplantation, where
two grafts are created from a single donor organ for two recipients,
usually an adult and an infant.1
Surgical techniques for liver transplantation in children.
Orthotopic whole-organ replacement, and reduced-size techniques.
Donors are matched for size and blood type.
The United Network for Organ Sharing in the United States has
devised the Model for End-stage Liver Disease (MELD)
and Pediatric End-stage Liver Disease (PELD),
which are numerical scales that are currently used for liver allocation.2 Similar
systems exist in other countries. These scores are based on a patient’s
risk of dying while waiting for a liver transplant, derived from
objective and verifiable medical outcomes data. The MELD score,
used for patients aged 12 years and older, is based on bilirubin,
international normalized ratio (INR), and creatinine. The PELD score
is based on bilirubin, INR, albumin, growth failure, and age, factors
which better predict mortality in children. These scores do not
alone determine the likelihood of getting a transplant. Other factors
include matched (blood group and size) organ availability, the occurrence
of higher priority exceptions (e.g., those with fulminant hepatic
failure), and the distribution of MELD/PELD scores for
other patients in a local area or region, and consideration for
living donation. The PELD/MELD system also has designated exception
scores assigned to specific liver conditions that have preserved
liver synthetic function and thus corresponding low allocation scores,
such as those children with metabolic liver diseases (e.g., urea
cycle disorders) and hepatoblastoma. In addition, a program can
request a higher exception score if the calculated score does not
truly represent the patient’s condition. This is done by
submitting an exception score request to their UNOS regional review
board for consideration.
The annualized incidence of liver transplantation in the United
States is 10–12 per million total population, that is,
50–60 cases per million children/year (1/16,000
children), or about 600 children, one-third of these being infants.
Approximately 55% of these transplants are for end-stage chronic
liver disease, the majority of these due to biliary atresia (BA);
about 25% are for metabolic liver diseases, 10% for
acute liver failure, and 5% for liver tumors (Figure 29–2).3,4...