Gross Processing of Liver Specimens

Roger K. Moreira, MD

2.1 GROSS ANATOMY

Weight

The normal human liver varies significantly in size, with an average weight of approximately 1,500 g (ranging between 838 and 2,584 g in a recent large autopsy study of normal healthy adults postaccidental death). The liver weight tends to be higher with increasing body weight and body mass index, but the overall correlation is poor.¹

Surface anatomy

The normal surface of the liver is smooth, glistening, and uniform. The relatively translucent normal Glisson’s capsule allows visualiziation of the normal, homogeneous tan-brown color of the underlying parenchyma. The liver edge (anteroinferiorly) normally forms a somewhat acute angle (which can become rounded in pathologic states leading to hepatomegaly). Anteriorly, four ligaments are present—the coronary, triangular, falciform, and round. Of these, the falciform ligament is of greater pathologic importance because it represents the landmark between the anatomic right and left lobes (discussed below). Posteroinferiorly, an area of peritoneal reflexion—the bare (i.e., not covered by the Glisson’s capsule) area of the liver is visible within the triangular ligament, adjacent to which the inferior vena cava enters the liver. The hepatic hilum, gallbladder, round ligament, and part of the falciform ligament are also seen (Figs. 2.1, 2.2, and 2.3).

Hepatic lobes and segmental anatomy

Anatomically, the liver is divided into right and left lobes by the falciform ligament (Fig. 2.1). The right lobe is further divided in its medial portion into the caudate lobe (posteriorly) and quadrate lobe (anteriorly). This anatomic approach is the most commonly used by pathologists on routine examination of the liver (tumors, focal lesions, etc). Functionally, however, the liver is divided into right and left lobes (and eight segments) based on vascular supply, with the plane dividing the right and left lobes passing along a line between the gallbladder and the inferior vena cava (Fig. 2.4).
This functional segmentation is widely used by surgeons and radiologists, so it is important for pathologists to be able to recognize the pertinent anatomic landmarks for the purposes of surgical/radilogic-pathologic correlation.

Figure 2.1 Gross appearance of a normal liver (postfixation), anterior view.

Figure 2.2 Gross appearance of a normal liver (postfixation), posteroinferior view.

Figure 2.3 Gross image of hepatic hilar structures.

Figure 2.4 Segmental anatomy of the liver. The liver is subdivided into eight segments (further subdivided into subsegments) based on the vascular supply.

2.2 INITIAL SPECIMEN HANDLING

Regardless of the type of liver specimen received (see discussion about specific specimen types below), the initial step in the gross evaluation is to assure proper specimen identification, labeling, and fixation. Review of the available medical records should also be done routinely in order to obtain data about the indication of the procedure and identify potential need for especial processing techniques. Radiologic correlation is also extremely helpful during specimen grossing, especially in complex focal lesions and multifocal tumors because valuable information about the number and location of lesions as well as their relationship with adjacent structures can be obtained. For routine histopathologic examination, the tissue must be placed in the appropriate fixative (most commonly, formalin), but in cases in which a metabolic disease or lymphoma are suspected, a portion of fresh tissue should be placed in glutaraldehyde (for possible electron microscopy) or saline/RPMI medium (for possible flow cytometry). For larger specimens such as large wedges, lobectomies, and total hepatectomies, there should be a sufficient volume of fixative (ideally 25 to 50× the volume of the specimen, but 10× at a minimum),² and tissue should be allowed to fix for an appropriate amount of time in order to penetrate into the middle of the specimen. Tissue penetration rate varies depending on the type of tissue, fixative used, temperature, among other factors, and can be calculated using the following equation: d = K t, where d is the penetration distance (mm), K is the diffusion constant (according to the type of fixative), and t is time (hours). For 10% formalin solution, tissue penetration is less than 1 mm/hour, and approximately 25 hours are needed to completely fix a 1-cm-thick specimen (i.e., 5 mm of penetration from each side) (Fig. 2.5). Specimen sectioning prior to fixation (sliced
at 1-cm intervals) and perfusion with fixative solution are alternatives for large liver specimens in order to expedite tissue fixation. Finally, gross photographs are becoming a routine practice in most laboratories (Fig. 2.6), and gross images of the fresh, whole specimen as well as postfixation sections should be obtained. These images can be very useful diagnostically (i.e., gross correlation during slide review) and represent an invaluable educational resource.

Figure 2.5 Formalin fixation of liver tissue. This panel shows a 2.5-cm cube of liver tissue sectioned at various times during the fixation process. (A) one hour, (B) 3 hours, (C) 12 hours, and (D) 20 hours. The fixation process was not complete for over 24 hours.

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