Are body surface area based estimates of liver volume applicable to children with overweight or obesity? An in vivo validation study

Abstract

The liver is the primary organ responsible for clearing most drugs from the body and thus determines systemic drug concentrations over time. Drug clearance by the liver appears to be directly related to organ size. In children, organ size changes as children age and grow. Liver volume has been correlated with body surface area (BSA) in healthy children and adults and has been estimated by functions of BSA. However, these relationships were derived from "typical" populations and it is unknown whether they extend to estimations of liver volumes for population "outliers," such as children with overweight or obesity, who today represent one-third of the pediatric population. Using computerized tomography or magnetic resonance imaging, this study measured liver volumes in 99 children (2-21 years) with normal weight, overweight, or obesity and compared organ measurements with estimates calculated using an established liver volume equation. A previously developed equation relating BSA to liver volume adequately estimates liver volumes in children, regardless of weight status.

FIGURE 1

(a) Axial T2 magnetic resonance (MR) images through the level of the mid liver from a from a 15 year old girl with obesity. (b) Axial MR images from the same patient with an overlay showing an example of the manually drawn contours that were used to calculate liver volumes. (c) Axial t1 fat saturated MR images from the same patient at the same level showing the automated contours (white) that were also used to calculate liver volumes. Note the similarity between the contours on images in (b) and (c). In a subset of patients who had both automated and manually contoured liver volumes available (n = 22), the volumes were within 1% of each other.

FIGURE 2

Flow of the data available after liver volumes were collected in the retrospective study (dataset 1) and the prospective study (dataset 2). BSA, body surface area

FIGURE 3

Age distribution of datasets 1 (black bars) and 2 (grey bars)

FIGURE 4

Measured liver volume versus Johnson estimation of liver volume with twofold error

FIGURE 5

Liver volumes versus body surface area (BSA). Dataset 1 (panel a) and dataset 2 (panel b). BSA was calculated using the method described by Johnson et al. Regression lines are fit to weight class (normal, overweight, or obese) using LV = A*BSA^B. The solid line shows the estimates of liver volume as a function of BSA as published by Johnson et al.