Magnetic resonance elastography of the liver in patients status-post fontan procedure: feasibility and preliminary results

Abstract

Objective: The purpose of this study was to evaluate the feasibility of performing magnetic resonance elastography (MRE) as a screening tool for elevated liver stiffness in patients' status-post Fontan procedure.

Background: With greater numbers of Fontan patients surviving far into adulthood, a factor increasingly affecting long-term prognosis is the presence of hepatic congestion and fibrosis. If detected early, steps can be taken to potentially slow or halt the progression of fibrosis. MRE is a relatively new, noninvasive imaging technique, which can quantitatively measure liver stiffness and provide an estimate of the extent of fibrosis.

Methods: A retrospective study was conducted using MRE to evaluate liver stiffness in patients with a history of Fontan procedure. An MRE was performed in the same session as a clinical cardiac MRI. The liver was interrogated at four slice locations, and a mean liver stiffness value was calculated for each patient using postprocessing software. The medical records were reviewed for demographic and clinical characteristics.

Results: During the time frame of this investigation, 17 MRE exams were performed on 16 patients. All patients had elevated liver stiffness values as defined by MRE standards. The median of the individual mean liver stiffness values was 5.1 kPa (range: 3.4-8.2 kPa). This range of liver stiffness elevation would suggest the presence of mild to severe fibrosis in a patient with standard cardiovascular anatomy. We found a significant trend toward higher liver stiffness values with greater duration of Fontan circulation (rs = 0.55, P = .02).

Conclusion: Our preliminary findings suggest that MRE is a feasible method for evaluating the liver in Fontan patients who are undergoing surveillance cardiac MRI. Further investigation with histologic correlation is needed to determine the contributions of hepatic congestion and fibrosis to the liver stiffness in this population.

Keywords: Elastography; Fontan; MRE; Pediatric; liver biopsy.

Figure 1

A schematic diagram of patient set-up with the MRE hardware. The active driver is placed in the MR computer room and the passive driver, connected via a hollow plastic tube through a wave-guide, is positioned on the anterior body approximately over the liver region [14]. MRE techniques modified and adapted for pediatric imaging.

Figure 2

(a) 18 year old female with a history of hypoplastic left heart syndrome post Fontan procedure performed 17 years ago. MRE exam was performed as part of a clinical cardiac MR study. Patient had no visible Fontan baffle fenestration. (b) MRE slice selection on the patient: The Torso coil is positioned such that the anterior portion of the coil can be used for cardiac imaging and the posterior region can be used for liver imaging. The four axial slices are prescribed so that the liver is imaged in its widest portion, inferior to the heart.

Figure 3

13 year old female with a history of tetralogy of Fallot with pulmonary atresia and hypoplastic right ventricle. Patient had an extracardiac fenestrated Fontan surgery at age 4. MRE was performed as part of the follow up cardiac MR exam. MRE images show increased liver stiffness (5.0 kPa), represented by the red, orange, and yellow areas. The sternotomy wires in the patient cause susceptibility artifact through the left lobe of the liver, but did not affect the ability to obtain liver stiffness values in the right lobe of the liver. The red structure in the left upper quadrant is the spleen.

Figure 4

(a) 31 year old female with a history of pulmonary atresia with tricuspid stenosis, hypoplastic right ventricle, and normally related great vessels, status post neonatal Waterston shunt followed by classic Fontan procedure at age 5 years. A follow-up cardiac MRI was performed to evaluate her Fontan pathway, cardiac chamber sizes, and ventricular function and liver MRE was performed as part of this exam. Mean liver stiffness was 4.0 kPa, well above the accepted normal mean for an adult of 2.3 kPa. (b) Coronal post-contrast MRI image obtained in the portal venous phase shows diffuse heterogeneous “cloud-like” enhancement of the liver parenchyma, a finding that is seen with liver fibrosis [21].

Figure 5

A graph of MRE liver stiffness versus years status post Fontan procedure (n=17). There is a trend towards increasing liver stiffness with increasing duration of Fontan physiology (correlation coefficient of 0.5 and p < 0.05).