The following content was adapted from the 2012 USCAP short course: Pattern-based algorithms in diagnostic liver pathology presented by Dr. Romil Saxena and Dr. Neil D. Theise.
Assessment of liver architecture
Normal architecture:
Sheets of hepatocytes interrupted at uniform intervals by portal tract branches and hepatic venous tributaries of various sizes
Scarce fibrous tissue (if present, should surround the portal tracts and central veins)
Clues to alteration of architecture:
Portal tracts and central veins are not seen in the biopsy
Architecture is distorted by fibrous tissue.
Evaluate portal tracts & lobules to determine pattern of injury present
Following assessment of parenchymal architecture, examination of portal tracts and lobules usually leads one to identify the dominant pattern of injury.
The major patterns of liver injury include:
Portal infiltrates
Ductular reaction
Steatosis
Lobular injury
Fibrosis.
The algorithm below can be utilized to help determine which pattern is present.
Portal Cellular Infiltrates
"The BLUE portal tract"
The infiltrate may be limited to the portal tracts or extend beyond it to involve the limiting plate of hepatocytes at the interface with portal tracts (interface hepatitis, formerly referred to as piecemeal necrosis). There may be associated lobular inflammation with variable degrees of hepatocyte necrosis.
The old term is “ductular proliferation,” but this term focused too much on the epithelial, ductule-like cells in the reactions, excluding the equally important stromal, vascular, and inflammatory components that accompany them. The combination of these elements is what helps to define the disease states characterized by prominent ductular reactions.
Common Causes:
Inflammatory hepatitis (chronic viral hepatitis, autoimmune hepatitis, drug induced hepatitis)
Chronic biliary diseases (primary biliary cirrhosis, chronic biliary strictures)
Metabolic diseases (Wilson disease, alpha-1 antitrypsin deficiency)
Sarcoidosis
Neoplastic conditions (lymphomas/leukemias).
The character of the infiltrate, the pattern of involvement and associated findings (such as ductular reaction in chronic biliary diseases, intracytoplasmic globules in alpha-1 antitrypsin deficiency) provide clues to the diagnosis.
Ductular Reaction/Proliferation
"THE BILIOUS PORTAL TRACT"
Ductular reactions (DRs) are a mixed tissue reaction at the interface of portal tract or septal stroma and the hepatic parenchyma. The hepatobiliary epithelial cells in DRs are now recognized as most often representing a stem/progenitor cell response to bile duct or hepatocyte injury and derive from the most important stem cell niche for the liver, the canal of Hering, where the hepatocyte canalicular system meets the smallest branches of the biliary tree. However, in some cases, less frequently, there may also be biliary metaplasia of hepatocytes at the interface as well, and thus represent a degenerative rather than a regenerative process.
If DRs are prominent at low power the differential diagnosis is usually simple, particularly if there is appropriate clinical history to go along with the biopsy, surgical or autopsy liver tissue being examined. These may be divided into acute vs. chronic injuries and biliary vs. hepatocellular tract injuries.
Biliary Tract Disorders presenting with DR
Obstruction (stricture, biliary atresia)
Primary biliary cirrhosis (PBC)
Primary sclerosing cholangitis (PSC)
PFIC
Alagille
Ascending cholangitis
Non-biliary disorders presenting with DR:
Neonatal hepatitis
Viral hepatitis
Alpha-1 antitrypsin
Budd-Chiari
Sepsis
Alcohol induced liver disease
Drug induced hepatitis
Lobular Injury
"THE DISTRESSED LOBULE"
When the lower power view of a biopsy specimen shows portal tracts in normal distribution, but a “busy lobule,” the causes are diverse and an eye for subtlety is required. There is usually an amazing amount of diagnostic data contained in the fine detail that will require significant time analyzing the high power view of the tissue, the rare times when it is the high power examination that is the most telling for evaluating liver disease.
Common causes of lobular injury:
Inflammation :Acute hepatitis
Metabolic processes: Fatty change, Steatosis, Storage material
Vascular diseases: Sickle cell disease, Veno-occlusive, Cardiac decompensation, Budd-Chiari
Infiltrative processes: Malignant/neoplastic, Amyloid
Pigment deposition: Hemosiderosis, Dubin-Johnson, Cholestasis (drug induced, graft vs. host, chronic rejection)
Steatosis
"THE BUBBLY LIVER"
Steatosis or accumulation of fat is commonly seen in liver biopsies. Since fat dissolves out during paraffin processing of tissues, its presence is seen as empty vacuoles of various sizes.
The fat vacuoles may appear as:
Large intracytoplasmic lipid vacuoles that enlarges the hepatocyte in which they reside and push the nucleus against the cell membrane (Macrovesicular steatosis).
Multiple small vacuoles that indent but do not displace the nucleus (microvesicular steatosis).
Medium sized vacuoles which are similar to those of macrovesicular steatosis except that they are smaller and do not enlarge the cell. These are referred to variably medium droplet fat or small-droplet fat; the latter term may cause confusion with microvesicular steatosis.
The pattern of fat accumulation and accompanying histological findings provide clue to the differential diagnosis.
The commonest conditions which display a steatotic pattern of liver injury are:
NAFLD
Alcohol-induced liver disease (ALD)
Wilson disease
Drug-induced liver injury (amiodarone, methotrexate, anti-HIV agents)
Viral infections (hepatitis C virus, human immunodeficiency virus)
Metabolic diseases can cause fat accumulation due to defective fat utilization or protein/caloric deprivation due to malabsorption of dietary avoidance. Accumulation of fat occurs easily in children and infants in temporary states of caloric deprivation. Metabolic diseases most often associated with fat accumulation are:
Cystic fibrosis
Galactosemia
Hereditary fructose intolerance
Glycogen storage disease I and III
Urea cycle defects
Fatty oxidation defects
Mitochondriopathies
Near-Normal Appearance
"THE CALM (but not quiet) LIVER"
Etiologies associated with no changes:
OTC (Ornithine Transcarbamylase deficiency)
Primary hyperoxaluria
Urea cycle defects
Etiologies causing subtle changes:
Gaucher's
Resolving hepatitis
Wilson's disease
Canalicular cholestasis
Veno-occlusive disease
Sickle cell disease
Compression from adjacent mass
Nodular regenerative hyperplasia
Hepatocellular adenoma
Fibrosis
"THE SCARRED LIVER"
Fibrosis is the end result of most chronic liver diseases and is therefore not a primary pattern of injury. However, when a liver biopsy demonstrates fibrosis as the predominant finding, one has to work backwards to elucidate the primary underlying liver disease. In these instances, the pattern of fibrosis and associated histological findings may provide valuable clues.
Commonly encountered issues for pathologists:
Overestimation of fibrosis: Normal fibrous tissue may sometimes be mistaken for pathological fibrosis. Pitfalls include overestimation of fibrous tissue in subcapsular parenchyma which normally contains more fibrous tissue within 5 mm of the capsule – this includes more fibrous tissue in the portal tracts and around central veins as well as fibrous bridges between adjacent portal tracts, adjacent central veins or between portal tracts and central veins.
The amount of fibrous tissue in a portal tract depends on its size, so that large portal tracts contain a significant amount of fibrous tissue. The size of the constituent structures within a portal tract is useful in determining the size of the portal tract itself; large portal tracts contain large vessels and bile ducts and correspondingly more fibrous tissue. Sometimes large and/ or branching may be sampled in a biopsy and these may be mistaken for portal fibrosis or even bridging fibrosis. At other times, portal tracts may be cut longitudinally so that they run across the entire width of the biopsy; these should not be mistaken as bridging fibrous septa.
Fragmented Biopsy Specimen: The presence of bridging fibrous septa and nodules (as in advanced fibrosis or cirrhosis) may cause fragmentation of a liver biopsy. Fragmentation may also occur in the absence of advanced fibrosis. The distinction between these two possibilities is not always easy but is assisted by assessing the borders of the fragments (rounded versus frayed) and the hepatic plate architecture on a reticulin stain.
Bridging Necrosis/ Multiacinar Collapse: Collapse of the connective tissue framework in areas of contiguous cell loss is often mistaken for fibrosis. Careful evaluation of the H&E stain and the reticulin stain helps in elucidating the true nature of this lesion. Trichrome stain will be most helpful, showing little in the way of mature collagen deposition and highlighting the presence of ductular reactions within the zone of necrosis rather than at the interface with intact hepatic parenchyma typical when there is a true fibrous septum.
Focal Nodular Hyperplasia In a needle biopsy: The fibrous septa and nodules that characterize this mass lesion may give a false impression of cirrhosis. The presence of abnormal eccentrically thickened vessels, when present, provides a diagnostic clue.
Mass Lesion
"THE PUSHY/MEAN LIVER"
The diagnosis of mass and cysts of the liver depends, first and foremost, on identification of the predominant cell type, in the former, and the predominant cyst lining cells (or the absence of such) in the latter.
Immunohistochemical staining is now the indispensable tool for diagnosing tumors and cysts; routine histochemical stains are simply insufficient in a majority of cases. But, as always in liver pathology, full knowledge of the clinical history and understanding of the status of the nontumoral liver are both essential in the diagnostic pathway – thus, diagnosis of liver masses and cysts is most often an interdisciplinary process.
Conditions that cause mass lesions:
Primary hepatocellularhepatocellular adenoma, focal nodular hyperplasia, hepatoblastoma, hepatocellular carcinoma)
Primary biliaryadenoma, cholangiocarcinoma
Mesenchymal lesionsmesenchymal hamartoma, infantile hemangioma, angiomyolipoma
Cystic lesionsmucinous cystic neoplasm, biliary intraductal papillary neoplasm, ciliated hepatic foregut cyst, abscess, hydatid cyst
Hematopoietic primary lymphoma, disseminated malignancy
Metastatic tumor
Caveats in Liver Biopsy Diagnosis
There is considerable overlap in morphological patterns of injury among various liver disease
Example: various hepatitides (viral, autoimmune, drug-induced) show portal inflammatory infiltrates and distinction between them often requires clinical and serological data
More than one pattern of injury may be present in a liver biopsy.
Thus although ductular reaction intuitively indicates a biliary disease, mild ductular reaction may be present in chronic viral hepatitis. Similarly, portal inflammatory infiltrates may be present in biopsies with a pattern of lobular injury.
Liver injury due to drugs may mimic almost any liver disease and is therefore always a diagnostic consideration
Drugs are also the most frequent culprit of a mixed or atypical pattern of liver injury. Diagnosis of drug induced injury relies on 1) establishing a temporal relationship between injury and drug use (including disappearance of symptoms on withdrawal of drug and reappearance on re-challenge; and 2) excluding competing causes of the observed findings.
Pathognomic features of certain diseases may be very focal and not always represented in a liver biopsy.
Example: Granulomatous cholangio-destruction of primary biliary cirrhosis or the occluded central veins of veno-occlusive disease/ sinusoidal obstruction syndrome. In such cases, other “soft” findings may be helpful in establishing the diagnosis against the right clinical context.
Some diseases demonstrate a diverse pattern of liver injury
Example: Wilson disease may present with a pattern of chronic hepatitis or steatohepatitis. Another example includes alpha-1 antitrypsin deficiency
With some lesions, the pattern observed in a liver biopsy depends upon what part of the lesion was obtained by the biopsy.
Example: Focal nodular hyperplasia may be mistaken for cirrhosis or for hepatocellular adenoma, depending on where the needle biopsy entered the lesion.