Chapter 44: Biopsy Considerations

INTRODUCTION

Liver transplant is an increasingly widespread therapeutic resource for end-stage and acute liver failure, as well as some metabolic and malignant diseases.

The importance in the evaluation of the allograft biopsy includes the discrimination of:

• Grade and type of steatosis, cholestasis, necrosis, hemorrhagic areas, and necroinflammatory portal and parenchymal activity in the donor liver

• Preservation-reperfusion injury

• Primary nonfunction

• Rejection: hyperacute, acute, antibody mediated, chronic, and late atypical

• Hyperperfusion injury (small-for-size syndrome)

• Technical complications

• Opportunistic infection

• Recurrent disease (Fig. 44-1)

STEATOSIS

Steatosis has been shown to have a high correlation with graft dysfunction after liver transplantation.¹ The assessment of steatosis in the liver biopsy of donor livers is one of the main objectives of the pathologist at the frozen section procedure.

Livers with moderate macrovacuolar steatosis may be used in the absence of other donors, depending on recipient risk factors.^2,3

Types of steatosis:

• Macrovacuolar (fat vacuoles larger than the nuclear size)

• Microvacuolar (fat vacuoles smaller than the nuclear diameter)

• Mixed (macrovacuolar and microvacuolar)

Grade of steatosis:

• Mild (0% to 30%)

• Moderate (30% to 60%)

• Severe (>60%)

General guidelines of the assessment of the fatty liver with the frozen section procedure are as follows:

• The grade of hepatic parenchymal fatty overload is a subjective estimation based on an observer´s experience.

• Despite the limitations, frozen section remains the gold standard for pretransplant donor liver evaluation (Figs. 44-2 and 44-3).^3,4

• The standard stain for frozen section evaluation is hematoxylin and eosin (H&E).

• The percentage of macrovacuolar fat can be determined with a low-power examination (100×).

• Other techniques such as fat stains (Red 0 and Sudan III), as well as computer-based image analysis, although more sensitive to fat detection, are not recommended.⁵

• Livers can also be rejected due to necrosis, prominent portal inflammation, or different grades of parenchymal fibrosis that could be identified on frozen sections.

PRESERVATION-REPERFUSION INJURY

Etiology/Pathogenesis

• Graft preservation and revascularization lead to parenchymal injury.

• Preservation-reperfusion injury (PRI) may be associated with macrovacuolar steatosis.

• The main lesions are sinusoidal endothelial cell damage, Kupffer cell activation, and impaired sinusoidal blood flow.