Recent advances in clinical practice
AN APPRAISAL OF THE
OF LIVER FIBROSIS
R A Standish, E Cholongitas, A Dhillon, A K Burroughs,
A P Dhillon
Gut 2006;55:569–578. doi: 10.1136/gut.2005.084475
See end of article for authors’
Professor A P Dhillon,
Academic Department of
Histopathology, Royal Free
Campus, Royal Free and
University College Medical
School, Rowland Hill St,
London NW3 2PF, UK;
One of the most important aspects of the histopathological assessment of liver biopsies in the
setting of chronic liver disease is determination of the degree of fibrosis and architectural change.
Most of the work in this regard has been concerned with chronic viral hepatitis. This article
attempts to assess critically our current and historical biopsy practice, from subjective fibrosis
scoring systems to biopsy sample size; and the appropriate use of the data that scoring systems
generate in the research and clinical setting. An understanding of the limitations of each of the
components of the fibrosis assessment process can help to devise appropriate protocols to ensure
that the information obtained is optimised, and its degree of reliability appreciated. It is only from
this starting point that recently promulgated antifibrotic medications and ‘‘non-invasive’’ liver
fibrosis assessment techniques can be evaluated properly.
The degree of liver fibrosis is one of the most important diagnostic and prognostic assessments in
chronic liver disease. Histological assessment of fibrosis is regarded as the ‘‘gold standard’’ in this
respect. Clinical manifestations of liver disease and liver dysfunction accompany architectural
changes of the liver parenchyma that are a result of advanced stages of liver fibrosis. Previously, it
was thought that liver fibrosis and end stage liver disease (cirrhosis) were irreversible, and
therefore crude determinations of liver fibrosis were acceptable because the therapeutic impact of
this assessment was relatively minor. Recent work suggests that liver fibrosis may be modified by
treatment1–4and so critical re-evaluation of the histopathological methods used to assess liver
fibrosis is necessary. Liver biopsy assessment of fibrosis is not only the end point for the
development of antifibrotic treatments but also forms the benchmark for validation of serum
‘‘surrogate markers’’ of liver fibrosis and other non-invasive techniques that purport to measure
liver fibrosis and stage of liver disease.
There are several important issues which make interpretation of the current literature difficult.
c Firstly, the bulk of the literature published recently regarding the adequacy of liver biopsies is
based on studies of chronic viral hepatitis. This literature suggests that the majority of liver
biopsy samples are too small to be representative and therefore are inadequate for a reliable
assessment of histological stage or grade.
c Secondly, that the histopathological scoring of the stage of liver disease is largely an
assessment of architectural change and not a measurement of amount or degree of fibrosis.
c Thirdly, that stage scores are often mistaken for measurements, and inappropriate statistical
techniques are then applied.
c Lastly, although recognised but often forgotten, that the scores generated are prone to
considerable intraobserver and interobserver error.
Thus histopathological liver fibrosis assessment has become a tarnished ‘‘gold standard’’ and it
needs to be improved. Progress will depend on recognition of the problem, a better understanding
of the need for an adequate sample, and a much better understanding of the nature of ‘‘staging
scores’’—including the use of more appropriate statistical tools and strategies to minimise
observer variation. For proper quantification of liver collagen, image analysis (IA) of appropriately
stained liver sections or biochemical assay might be necessary.
SCORING SYSTEMS AND VARIABILITY
Before going on to address the important issue of biopsy size and adequacy, we would like first to
consider analysis of the biopsy. Currently, most centres carry out descriptive reporting when
assessing diagnostic biopsies from an individual patient. However, in the trial and research
setting, evaluation of biopsies is carried out using subjective scoring systems that produce
shorthand values for various categories of inflammation (grade), and fibrosis and architectural
disruption (stage). There are many such systems2 5 6but
essentially they ‘‘score’’ (that is, categorise) similar features.
The history of these scoring systems dates back to 1981
when the histological features of chronic hepatitis were
evaluated for potential importance in determining the
prognosis according to the understanding at the time of the
pathophysiology of chronic hepatitis B virus (HBV) infection,
and organised into a scoring system by Knodell and
colleagues.5Evaluations were based on review of 14 biopsies
from five patients: one with chronic HBV and four with
presumed chronic non-A-non-B infection—at that time,
hepatitis C virus (HCV) had not been identified. In the
Knodell ‘‘histological activity index’’ system (HAI), each of
four histopathological features (periportal ¡ bridging necro-
sis, intralobular degeneration/focal necrosis, portal inflam-
mation, and fibrosis) are assessed separately and assigned a
score. In order to exaggerate the difference between mild and
serious disease, Knodell and colleagues5eliminated the
number 2 from their scoring system for each of these
features. Some consider this a drawback of this system, as it
makes the scores discontinuous, but by omitting the 2, the
Knodell system conveniently and simply allows the four key
histopathological aspects of chronic liver disease (noted
above) to be assigned to categories of: normal or minor
change and two degrees of major change for each of the axes
of assessment apart from periportal ¡ bridging necrosis
(which is weighted further in the presence of bridging
necrosis because of its perceived pathophysiological impor-
The currently most widely used system is the Ishak, or
‘‘revised Knodell’’, system6which attempts to correct the
criticism of numerical discontinuity by reintroducing the
number 2. The criticism is itself erroneous when it is
understood that the ‘‘numbers’’ associated with any histo-
pathological scoring system represent a numerical shorthand
for a descriptive categorical assignment, and are neither
integers nor numerical measurements along a continuum in
a mathematical sense (see below).
The first three axes of the Knodell HAI relate to the
necroinflammatory grade of the disease. The fourth feature
Stage component of the Ishak system.6*Proportion (%) of area of illustrated section showing Sirius red staining for collagen (collagen
Ishak stage category
been plotted against their individually measured collagen proportionate
area (CPA). Clearly, the measured amount of fibrosis, and the
corresponding Ishak category, are different evaluations. The increase in
fibrosis with Ishak disease stage category is not a straight line.
Relationship between Ishak stage scores and measured
HISTOPATHOLOGICAL ASSESSMENT OF LIVER FIBROSIS
assesses the stage of disease by evaluating the degree of
fibrous portal tract expansion, fibrous portal-portal linking,
portal-central fibrous bridges, and the formation of fibrous
septa and parenchymal nodules.
The Ishak system6assesses fibrosis in seven categories,
ranging from normal to cirrhosis (see fig 1) and so has
potentially more discriminant descriptive power. All scoring
systems basically use the same principles to record liver
disease stage. It is obvious that the ‘‘stage’’ or ‘‘fibrosis’’ score
is composed of a mixture of features, none of which
specifically depends on the amount of fibrous tissue in a
liver biopsy sample. The higher Ishak scores particularly
depend more on architectural changes and degree of
nodularity rather than amount of fibrous tissue. Even the
lower scores (for example, ‘‘portal tract expansion’’) are only
partly dependent on the amount of portal tract collagen
because portal tracts can be considerably expanded by
inflammatory infiltrates as well (fig 2).
Although in the original Knodell publication HAI was
stated to be ‘‘numerical, objective, and reproducible’’,5it has,
strictly speaking, never been any of these things. The
considerable observer variation in the subjective interpreta-
tion of the categorical assignments has been often under-
estimated or ignored as a source of variability, despite the fact
that both inter- and intraobserver variability have been well
documented with respect to the various scoring systems.7–9
Indeed, Knodell and colleagues recommended that a change
of four points in the aggregate score was required before
there was a high probability of a real or significant change,
rather than merely representing a shift attributable to
reinterpretation or mistaken interpretation of the biopsy
features.5Not surprisingly, studies have shown that this
variability is reduced if there are fewer categories to choose
from within each axis of assessment, but this approach
reduces the descriptive power of the more abbreviated scoring
systems that have been proposed.
The METAVIR scoring system was designed for the
assessment of HCV chronic hepatitis specifically and repro-
ducibly. In its current formulation,10HCV hepatitis activity is
based on evaluation of piecemeal necrosis and lobular
METAVIR algorithm ‘‘because this feature is a prerequisite
for the definition of chronic hepatitis even without activity.’’
Nevertheless, the recent study by Rousselet and colleagues,11
using the METAVIR system to examine 254 liver biopsies
from patients with chronic viral hepatitis, found that: ‘‘the
level of experience (specialisation, duration, and location of
practice) had more influence on agreement than the
characteristics of the specimen (length, fibrosis class number,
miscellaneous factors). Agreement can be improved by
experienced pathologist or consensus reading’’.11The experi-
ence of the histopathologist is an important variable that
must be considered and optimised.
Procedures to minimise observer variation are required
when any scoring system is used in studies of liver fibrosis:
pre-trial consensus meetings should be held by the histo-
pathologists involved who should have sufficient experience
of the disease to be studied to debate and decide the precise
fibrosis assignment categories and the borders between them.
Then the entire study series should be assessed by at least
two hepatopathologists independently, followed by consen-
sus sessions to discuss significant disagreements; and the
assessments should be conducted within as short a period as
is practical (that is, the assessment should not be of single
biopsies weeks or months apart).12An additional component
that can be included in study protocols to improve detection
of subtle changes is the comparative review of each subject’s
paired biopsies, from the beginning and end of a trial, after
the initial blinded histological scoring has been performed.
This should be performed with limited unblinding only (that
is, comparison of biopsy pairs without knowledge of
intervention versus control, or time point of biopsy).
However, the subtler the change that is detected in this
way, the greater the risk of over-interpretation if the samples
In reality, few studies are structured in such a way. Routine
scoring of liver biopsies is not appropriate for sporadic
assessments in daily diagnostic practice because of the
likelihood of inter- and intraobserver errors, and promotion
of the spurious idea that something quantitative has been
achieved. Routine scoring is done with increasing frequency
under the impression that the UK National Institute for
Health and Clinical Excellence (formerly known as the
National Institute for Clinical Excellence) HCV treatment
guidelines require this: the guidelines state that ‘‘Interferon
alpha and ribavirin as combination therapy is recommended
for the treatment of moderate to severe hepatitis C (defined
as histological evidence of significant scarring (fibrosis) and/
or significant necrotic inflammation), at standard doses for
patients over the age of 18 years’’.13The original guidelines
(Appraisal 14, 2000) suggested in a more detailed discussion
(than is present in the 2003 revision) that ‘‘Liver biopsy is
undertaken, if there are no increased risks, in order to assess
liver scarring and necro-inflammation according to an
accepted severity scale such as the Knodell’’. A later
document (Appraisal 75, 2004) eliminates reference to the
Knodell system. Wisely, there is neither reference to any
particular scoring system nor is any score specified that
mandates treatment in the 2004 guidelines. The decision of
how much histological fibrosis, necrosis, and/or inflamma-
tion is ‘‘significant’’ should be a matter for discussion
between the patient and their hepatologist, taking into
account the potential risks and benefits of treatment versus
no treatment in any individual case. Furthermore, recent
studies suggest that in non-genotype 1 HCV, the benefit/risk
Strategies to minimise interobserver and
intraobserver scoring variability.
c At least two pathologists with appropriate experience
should be involved in studies involving histopathological
scoring of chronic liver disease stage.
c Pre-trial consensus meetings should define precisely the
interpretation of the categorical definitions of the scoring
system to be used, and clarify the boundaries between the
c Independent blinded assessment of the complete study
series should be performed by each of the pathologists.
c Further consensus meetings to discuss scoring discrepan-
cies should take place.
c Assessments should be carried out in as short a time as
c Partially unblinded (without knowledge of time sequence
or treatment group) qualitative comparison of biopsies
from individual subjects after the initial scoring may be
HISTOPATHOLOGICAL ASSESSMENT OF LIVER FIBROSIS
balance currently favours treatment in even histologically
mild disease, so that there may no longer be the need for
therapeutic decisions to be biopsy driven at all.14
HISTOPATHOLOGICAL SCORES AND NUMBERS
The central dictum of Pythagoras’ followers was ‘‘all is
number’’. Unfortunately, where histological scoring systems
are concerned, all is not number (fig 3). Failure to appreciate
this essential point has led to misinterpretation of the
histological scores and application of inappropriate statistical
techniques. Consequently, the conclusions of most of the
relevant literature are questionable.
Histological scores are at best ordered categorical data and
not numbers. Any statistical analysis must be carried out
with this in mind. One would no more consider these scores
to be treatable numerically than one would add, subtract, and
divide different categories under the heading of "colour", or to
mix and match apples and oranges. Appropriate statistical
treatment of categorical data includes the use of contingency
tables to convert categorical data into frequency data, which
can then be numerically manipulated.8This important aspect
of the nature of scoring has eluded many investigators, and
little of the available literature on the subject has converted
categorical data into frequency data.
Clinicians, including those who work with drug regulatory
authorities (in contrast with hepatopathologists), are less
familiar perhaps with the nature of the scores and the
underlying definitions which lead to their assignment. For
example, the French METAVIR group analysed scores of
stage in biopsies from patients with chronic hepatitis C virus
infection to produce an ‘‘annual fibrosis progression rate’’.15
Not only does this assume a linear progression of fibrosis in
HCV infection (which has not been demonstrated), but the
work produced annual fibrosis progression rates with
bewildering score fractions. One accepts that any histopatho-
logical fibrosis scoring scale consists of rather arbitrary points
on a continuum between normality and cirrhosis, but when
those points have been strictly defined at the start of a study,
because the in-between points lack any histological descrip-
tive definition, the sense of the subsequently invented
fractions also lacks meaning. Despite this, the ‘‘annual
fibrosis progression rate’’ has become popular in some
similar studies, and this ‘‘measure’’ is in danger of becoming
as entrenched as the aggregated HAI score.
The same issues are pertinent when considering other
histopathological scoring systems. A scoring system suitable
for a particular disease process is unlikely to be suitable for a
different process. For example, a scheme designed for the
assessment of steatohepatitis such as that devised by Brunt
and colleagues16would be inappropriate for the assessment of
chronic viral hepatitis, for which we should use scoring
systems such as the Knodell or Ishak, because fibrosis
develops and progresses in different ways in these diseases.
Such misunderstandings can be confusing until one realises
that all scoring systems are based on our understanding of
the pathophysiology of the disease in question and the
histopathologist is only trying to describe what is seen. The
Two liver biopsies, each of which is stained with Sirius red for collagen.
Both biopsies show parenchymal nodules surrounded by fibrous tissue,
fulfilling the histological diagnostic criteria of cirrhosis. Therefore, each
biopsy can also be described as ‘‘Ishak stage 6’’ (which is merely a
symbol for the histological definition of cirrhosis). The overall area of
one of the biopsies consists of 27% collagen, and 12% of the other
biopsy is collagenous (collagen proportionate area (CPA)). Obviously,
the histopathological diagnosis of cirrhosis (and assignment of ‘‘Ishak
stage 6’’), and the measured amount of fibrosis are entirely different
Ishak stage scores are neither numbers nor measurements.
Histopathological scoring of chronic liver
disease stage guidelines.
c Scoring is not recommended for routine daily diagnostic
c Diagnostic evaluation of longitudinal changes of disease
stage in individual patients should be performed by direct
comparison and review of all biopsies, and not by
comparison of recorded scores.
c Stage scoring is not a measurement, but a categorical
assignment (based largely on architectural changes), and
any statistical analysis should take this into account.
c Numerical manipulation of scores (for example, calcula-
tion of average and aggregate numbers) is statistically
invalid, and may lead to erroneous conclusions.
c There remains an important role for stage scoring in the
research setting, perhaps alongside other methods of
c The scoring system used should be appropriate to the
disease process that is being studied according to an
understanding of the pathophysiology of the condition.
c Strategies should be used to minimise interobserver and
intraobserver scoring variability.
HISTOPATHOLOGICAL ASSESSMENT OF LIVER FIBROSIS
misuse of histopathological scoring systems confounds
efforts to understand the natural history of disease which
should be based on long term longitudinal follow up and
outcome. The danger of misleading others with inappropriate
manipulations of histopathological scores is clear and
present, and the ease with which one can fool colleagues,
and oneself, is alarming.
Several years ago it was stated rather arbitrarily, and
probably dictated by clinical pragmatism and a compromise
with reality, that ‘‘a liver biopsy containing six portal tracts
satisfies most hepatopathologists’’.17Now it is timely to move
forward from the laudable desire to achieve histopathological
happiness to a more scientific approach with regard to liver
biopsy adequacy. In the case of liver fibrosis assessment, to
determine the size of an adequate (representative) liver
biopsy we must know the variability of distribution of liver
fibrosis within the liver for the particular disease under
consideration, which is likely to change with the stage of
disease. An assessment when there is a less than adequate
biopsy sample needs to be considered in the light of the
degree to which that analysis is reliable or unreliable (that is,
the confidence interval).
Sampling error usually results in underestimation of the
feature being assessed but, for example, inclusion of
capsular/subcapsular tissue overestimates both histological
activity and fibrosis, and inclusion of the connective tissue
normally seen in large (septal) portal tracts will overestimate
chronic viral hepatitis related fibrosis (see fig 4). Colloredo
and colleagues18showed that reduction of the size of the
biopsy available for histological review (both the length and
diameter of the needle core) influences histological inter-
pretation, with shorter cores more likely to be scored with
lower grade and stage—interpreted as ‘‘underestimation’’ of
overall disease activity. Following this study they recom-
mended a biopsy length of 20 mm or greater—with more
than 11 complete portal tracts—in order to reliably grade and
stage a biopsy for chronic viral hepatitis.18When these liver
biopsy characteristics are compared with the average biopsy
(even in specialised centres), then efforts to improve sample
adequacy are clearly necessary.
Biopsy size is also one of the variables that impact on the
reliability of scoring (both grade and stage). Two similar
studies of pairs of synchronous liver biopsies from patients
with HCV infection have been performed in efforts to assess
the reliability of disease stage and grade assessments in
chronic HCV infection. In the first study, by Siddique and
colleagues,19pairs of right lobe biopsies from 29 patients were
evaluated. Each biopsy contained 4–5 portal tracts (around
half the currently recommended number). Using the Knodell
HAI, Siddique et al showed that in approximately 20% of
cases the stage score differed between the synchronous
biopsy pairs by two categories or more.19Persico et al
compared Ishak stage scores of synchronous left and right
lobe biopsies.20The left and right lobe biopsies had mean
lengths of 2.5 (¡0.9) cm and 2.8 (¡1.1) cm, respectively.
There was minimal variation of stage score between the
paired biopsies.20These two studies together show the need
for adequate biopsies to minimise variation in stage assess-
ment due to sampling error. The studies demonstrate that
inadequate samples give unreliable results and adequate
samples give reproducible results.
Bedossa and colleagues21studied large liver tissue sections
of resections from patients with chronic HCV infection
(including both liver resections and livers removed at the
time of transplantation), which were given a METAVIR stage
score. Internal variation within each tissue section was not
directly addressed in this part of the study, and a single stage
score was ascribed to each large section. Picro Sirius Red
F3BA (Sirius red) staining and IA—measuring the area of
Sirius red staining per unit area of liver tissue (see discussion
of IA below)—were used to determine the ‘‘virtual’’ biopsy
size that adequately reflected the overall stage of liver disease.
‘‘Virtual’’ biopsies of 25 mm length (1 mm diameter, which
approximately corresponds to a needle of internal diameter
1.2 mm) ‘‘correctly’’ staged 75% of cases. Considering that
the same data set was used both to construct the IA range for
each stage score and to test it, this is perhaps a little
disappointing. This could be because this attempt to use IA to
validate the stage score ignores the disparate nature of the
techniques—scoring being to a large extent a subjective
architectural assessment and IA being a measurement of
fibrosis. Variation attributable to sample size decreased
progressively up to a (1 mm diameter) biopsy length of
40 mm but intrinsic variability of liver fibrosis persisted in
virtual biopsies of greater than 40 mm.21
Given these recent revelations with regard to liver biopsy
adequacy, there has been concern regarding the feasibility of
safely obtaining adequate samples for reliable grading and
staging of chronic liver disease. Sample size is probably
related to operator experience and efforts should be made to
improve operator performance. Percutaneous (PLB) and
transjugular (TJLB) liver biopsies are the two main techni-
ques used to obtain liver specimens. Reviewing the literature,
11 studies were identified that have information about both
the length and number of complete portal tracts (CP) in PLB
19 22–31. In order to adjust for the different cohort sizes, mean
length and number of CP were summated relative to the
number of biopsies in each study (n, that is, overall mean
length =S [n 6mean length]/Sn). The mean number of CP
in all of the studies was evaluated similarly (that is, overall
mean CP =S [n6mean CP]/Sn). The raw CP data were not
available from the studies to enable calculation of an overall
median, which would have been more appropriate for
assessment of complete portal tracts (table 1). Overall mean
length was 13.5 mm, and overall mean number of CP was
6.58. Some studies did not specify the type of needle used.
Where specified, Menghini-type PLB were significantly
longer compared with Tru-cut type PLB (16.2 v 12.1 mm),
but with almost the same mean number of CP (6.09 v 6.35).
Adequacy of liver biopsy
c Adequate samples must be obtained which are represen-
tative of the disease process that is being evaluated.
c The current recommendation for chronic viral hepatitis is
that the biopsy should be at least 20 mm length (1.4 mm
diameter) and should contain at least 11 complete portal
c Smaller biopsies are likely to be unrepresentative.
c Small inadequate biopsies tend to underestimate both
disease grade and stage.
c Variability increases with smaller samples.
c Recognition of the limitations of interpretation of small
biopsies is essential in the management of patients and in
the therapeutic trial setting.
HISTOPATHOLOGICAL ASSESSMENT OF LIVER FIBROSIS
Insufficient information was included in these papers
regarding the number of needle passes, which is a significant
omission, as it has been shown that the complication rate
correlates with the number of passes.32Fewer studies had
information for both the length and number of CP obtained
with TJLB using Tru-cut and/or Menghini-type needles.25 33–35
Based on the data given by these four studies and following
the same methodology as above, these show that with an
average of 2.9 passes, the total mean length and CP were
20.9 mm and 8.09, respectively (table 2).
The implication of these findings is that, in well
documented series of PLB and TJLB, the average length
and mean number of portal tracts for over half the patients
are well below the current recommendations for reliable
grading and staging of biopsies taken for the assessment of
chronic viral hepatitis.36Thus in order to obtain an adequate
sample, a standard percutaneous approach will require two
passes on average, increasing the risk of complications.32Via
a transjugular route, several passes can be made without
increasing complications. In a series of 326 TJLB from our
centre, using three passes as standard, a median length of
22 mm and a median number of 8 CP was achieved without
complications.35It seems reasonable to suppose that an
adequate number of CP (>11) could be achieved safely by
performing four or more passes.
As the clinical importance of liver fibrosis assessment grows,
the limitations of biopsy scoring systems are becoming more
apparent. The changes described in the scoring categories are
largely architectural, with little reference to the actual
amount of collagen (fibrosis) in the liver sample. Routine
(diagnostic) fibrosis assessment is usually carried out on a
trichrome or reticulin stain. These are not specific collagen
stains, and no measurement is made. If, after due considera-
tion, it is felt to be desirable to determine precisely how much
liver fibrosis there is (if liver collagen is what is meant), to
validate studies of surrogate markers of fibrosis for example,
or changes with antifibrotic treatment, then proper measure-
ment of liver collagen is unavoidable. This will require time,
effort, adequate sampling, and appropriate methodology. We
cannot continue to pretend that subjective scoring has
measured something when it has not.
Lord Kelvin said ‘‘In physical science the first essential step
in the direction of learning any subject is to find principles of
numerical reckoning and practicable methods for measuring
some quality connected with it. I often say that when you can
measure what you are speaking about, and express it in
numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers,
your knowledge is of a meagre and unsatisfactory kind; it
may be the beginning of knowledge, but you have scarcely in
your thoughts advanced to the state of Science, whatever the
matter may be’’.37
His reference to suitable ‘‘principles of numerical reckon-
ing’’ alludes to the use of appropriate statistical analysis,
which we have already touched on. As the value of routine
histopathology demonstrates, clinically relevant data do not
have to be numerical to be useful, but to pretend that they are
numerical (when they are not) is wrong. It may be
informative to measure what is seen, but to imagine it has
been measured without doing so is self-delusion.
This brings us to the finding of a ‘‘practicable method for
measuring’’ liver fibrosis. It is possible to use biochemical
methods to measure the amount of collagen in tissue
homogenates, but this requires the destruction of the tissue,
so no further information can be gathered, which is
unsatisfactory in the assessment of a diagnostic liver biopsy
(in which context most human study material is gathered).
In a recent study, Lee et al took multiple biopsies from the
same livers (each of 12 livers sampled after transplantation,
resection, or autopsy), and showed that hydroxyproline
measurements of the biopsies from each liver had a
coefficient of variance between 13% and 36% (mean 23%),
and that this variation was present at all stages of liver
disease.38In this study, 16 gauge Tru-cut needle biopsies with
biopsy lengths of 10–15 mm were used and ‘‘obviously
identifiable large vessels on the biopsy samples were excised
and excluded from hydroxyproline measurements’’. Because
of the nature of the biochemical assay, we cannot know the
number of complete portal tracts in the samples but this
study illustrates that even biochemical approaches to the
quantification of liver biopsy fibrosis will be subject to
appreciable sampling variability, and dependent on sample
Computer assisted IA of histochemically stained sections is
a method for measuring fibrosis morphologically, it does not
hinder the other necessary diagnostic evaluations, and
collagenous structures irrelevant to the disease process (and
which contribute to the variability between samples) can be
excluded precisely (fig 4). Broadly speaking, IA uses
segmentation of digital images to measure the area of
collagen and the area of tissue, producing a ‘‘fibrosis ratio’’
or collagen proportionate area (CPA).
To quantify hepatic collagen histologically, it is necessary
first to stain it specifically. Sirius red has an affinity for most
in which both biopsy length and number of complete portal tracts were reported
Systematic review of studies reporting the quality of percutaneous liver biopsies
1675 13.516.212.1 6.586.09 6.35
CP, complete portal tracts.
quality of transjugular liver biopsies in which both biopsy
length and number of complete portal tracts were
Systematic review of studies reporting the
CP, complete portal tracts.
HISTOPATHOLOGICAL ASSESSMENT OF LIVER FIBROSIS
hepatic collagens, including types I and III (the major
components of liver collagen)39 40and this binding correlates
with chemical hydroxyproline assay under standardised
laboratory conditions.41Although the nature of the binding
of the dye is not fully understood, staining of liver sections
appears to be reliable and reproducible. Thus Sirius red
staining is the preferred histochemical method when
quantifying liver fibrosis, even though the staining may not
be stoichiometric.42Some groups interested in IA have used
reticulin or trichrome stains, and others have suggested the
use of immunohistochemistry, but due to variability in
staining and difficulty in accurate thresholding, these
techniques can suffer from poor reproducibility.
Normal human liver is estimated to contain approximately
5.5 mg/g of collagen, and cirrhotic liver contains of the order
of 30 mg/g.39Other estimates of normal liver collagen
concentration suggest 2–8 mg/g wet weight of liver.43We
must also consider that different disease processes probably
lead to different amounts of collagen deposition at different
stages of disease. Even the same disease process at the same
stage is likely to produce different amounts of collagen in
different individual patients. This aspect of collagen deposi-
tion has not yet been fully evaluated.44
IA studies have looked at fibrosis in many conditions,
producing overall similar results ranging from 1–4% fibrous
tissue in normal liver to 15–35% fibrous tissue in cirrho-
sis.21 45–50However, the differences in the technology and
methodology used in these studies means that the results are
not directly comparable.
Many of these studies have also attempted to correlate the
image analysis measurements of fibrosis with the categorical
stage scores. Manabe et al found that CPA did not correlate
well with the components of the Knodell scoring system.50
Pilette et al used the Knodell and a modified METAVIR
scoring system and found that these correlated with liver
biopsy percentage area of fibrosis.48Kage et al found that CPA
correlated with their modified staging system based on the
Desmet and Scheuer staging systems.46This collection of
inconsistent results can be explained by the notion that IA
and histopathological stage scores assess quite different
things, and in different ways. In assigning histological stage
score categories, much depends on architectural changes. It
may be in some (or many) cases that the amount of fibrous
tissue increases with these architectural derangements, but
that is not specifically addressed in any of the scoring
systems. No heed is paid to the width of a fibrous septum or
the size of a nodule, for example, so two cirrhotic livers
scoring 6 on Ishak staging might contain vastly different
amounts of collagen, and thus have different IA measure-
ments (fig 3). Despite this argument, O’Brien et al showed
that IA measurements correlated well with Ishak stage
scores, but only in the higher stages.45Results such as these
may be chance occurrences, or only applicable to the limited
framework of the individual study.
than in the small portal tracts which are usually affected by chronic viral
hepatitis. This is a section of normal liver stained with Sirius red for
collagen. The section includes normal liver capsule (top) and a large
portal tract (middle left). In studies of chronic viral hepatitis, these areas
should be excluded from measurements of liver fibrosis because chronic
viral hepatitis affects small portal tracts primarily. Otherwise, subtle
changes due to disease or treatment will be obscured. Uncritical
inclusion of structural collagen components confounds attempts to
measure disease related collagen accurately, so that editing is
necessary of structures (for example, large portal tracts, capsular
collagen), and technical staining artefacts that are irrelevant to the
pathological process being studied.
Normal liver contains more collagen in normal structures
1 10 19 28 37 46 55
Measured area (mm2)
64 73 82 91
Area of collagen (% of tissue area)
Normal liver unedited mean
Normal liver edited mean
liver stained with Sirius red (unedited versus editing of structural
collagen). A smaller sample is adequate and representative if collagen
that is not relevant to the disease process being studied is removed from
the measurement. A traditional morphometric method of determining
representative sample size is by measuring the feature of interest (in this
case, liver fibrosis) in consecutive microscopic fields, and calculating
the ‘‘cumulative mean’’. When a stable cumulative mean is achieved,
the overall area measured can be regarded as an adequate
(representative) sample. Editing (exclusion) of large portal tracts
(.0.5 mm diameter), capsule, and technical artefacts in this
experiment (measurement of collagen proportionate area) achieves a
stable cumulative mean with a much smaller sample size. Without
editing, fluctuations of the cumulative mean persist at sample sizes
equivalent to quite large liver biopsies. The graph also illustrates the
dominant proportion of collagen that resides in normal structures in
normal liver, and the relatively small amount of fibrous tissue that is
normally present in small (,0.5 mm diameter) portal tracts.
Cumulative mean of collagen proportionate area of normal
HISTOPATHOLOGICAL ASSESSMENT OF LIVER FIBROSIS
We are in the early days of elucidating the best way of
using IA reliably, and the clinical utility or otherwise of IA
has yet to be established. At present, a range of computer and
camera hardware, software, and experimental procedures
(and liver sample sizes) are being used, and so it is not
surprising that some of the results are contradictory and
confusing. When some of the methodological aspects have
been resolved, IA may find a useful place in the armamen-
tarium available to assess liver biopsy fibrosis.51 52Just as in
biopsy scoring, there are elements of study design that can be
put in place to minimise variability (see above), so with IA it
is important to pay attention to various aspects of the
methodology (including section thickness and staining, light
source stability, camera characteristics, and accurate thresh-
olding53of the image) to ensure stability and reproducibility
of measurements. In addition, just as a mental note is made
of capsular collagen, large septal portal tracts, and blood
vessels when assessing fibrosis by scoring (so that these
normal collagenous structures can be excluded from the
disease stage scoring because they do not represent disease
related collagen), so too in IA these structures need to be
edited out of the measurement, particularly in the analysis of
biopsy specimens, so as not to overshadow small disease or
treatment related changes in the measured amount of
fibrosis (figs 4, 5).
It is important to remember that IA in its simplest form is a
measurement of area, and is unable to evaluate architectural
changes such as nodularity, fibrous portal linking, and
portal-central fibrous bridging, which are the histological
features of architectural change included in stage scoring
systems. Thus IA and stage scoring are different assessments
(although they may in some circumstances be linked) and
should be understood as complementary aspects of liver
biopsy assessment (figs 2, 3).
NON-INVASIVE ASSESSMENT OF FIBROSIS
The procedure of obtaining a liver biopsy is not without its
attendant risk of morbidity and even mortality. The risk of
complications is of the order of 1%, and the risk of mortality
has been put at between 0.1% and 0.01%. The advent of the
transjugular approach may reduce these further, particularly
in high risk patients, and may allow multiple samples to be
taken without the increased risk that is seen with multiple
percutaneous passes in standard liver biopsies.54 55With this
small but significant danger in mind and taking into account
intra/interobserver error as well as sample variability, non-
invasive methods of liver fibrosis assessment have been
developed. These include using various imaging techniques
and serological markers—‘‘surrogate’’ markers of fibrosis.
Imaging techniques such as ultrasound, computed tomo-
graphy, and magnetic resonance scanning as yet cannot
detect small changes in fibrosis in an individual patient
although some studies have shown good correlation with
stage scoring. Newer techniques may be more sensitive but
are still experimental. Sandrin et al have shown good
correlation between a non-invasive ‘‘liver stiffness’’ measure-
ment (based on transient elastography of the liver) with the
METAVIR stage score, a correlation which was shown by Ziol
et al to improve with larger biopsy specimens.56–58
Traditional serological markers of liver function—‘‘liver
function tests’’—give little indication of the various underlying
pathological processes, including fibrosis. More complex panels
of markers have been evaluated to examine the possibility of
non-invasive fibrosis assessment.59 60The panel of markers
developed by Rosenberg et al has limited application because it
was only reliable for estimating the absence of fibrosis and not
its extent.61Poynard et al have developed a patented algorithm
(the ‘‘Fibrotest’’)whichtheyhaveshowncanpredict significant
fibrosis in chronic HCV infected patients according to the
curve’’ of 0.73–0.87 and a negative predictive value (excluding
significant fibrosis) of 91%.60However, we must consider what
these calculations mean biologically, and how they have been
validated. We have already mentioned that the use of stage
the METAVIR system—has well recognised limitations, and we
Rosenberg et al, a liver biopsy length of >12 mm length or
content of >5 portal tracts (it is not specified if the portal tracts
were complete or incomplete) was necessary for inclusion of the
specimen in the study.59Generally, the performance of non-
invasive testsof liverfibrosishasbeenevaluatedusingreference
histological samples which were biopsies of suboptimal size by
current standards (,20–25 mm length and/or containing ,11
complete portal tracts) or the quality of which was not
mentioned.58 62–65In a recent editorial, Thuluvath and Krok
remind us that the validity of non-invasive serum marker
assessments is yet to be established in longitudinal (as opposed
to cross sectional) studies, and the results of already published
studies need to be replicated in different laboratories before
these assessments can play an accepted part in the clinical
management of patients.66
The utility of each of the new ‘‘non-invasive’’ analytical
approaches must be validated against long term patient
follow up and precisely measured end points. If one of the
end points is liver fibrosis, this must be measured specifically,
reliably, reproducibly, accurately, and using adequate sam-
ples. Until this has been done, surrogate markers of liver
fibrosis must be regarded as qualitative approximations, and
not quantitative assessments.
With the emergence of potentially efficacious antiviral and
antifibrotic agents, much depends on making sure that
assessment of liver fibrosis is reliable. The present method of
subjective assessment of liver fibrosis and architecture by a
single histopathologist is reasonable in the daily diagnostic
situation, but application of grading and staging scoring
systems is inappropriate routinely. Adequate samples accord-
ing to current standards for the disease in question must be
obtained to avoid error, and if these are not available, the
limitations of suboptimal samples must be recognised,
acknowledged, and stated clearly.
Histopathological stage scoring is sufficient for many
clinical trials, and is the correct approach for observational
studies. However, better design, improved organisation, and
more appropriate statistical evaluation than has generally
been the case up to now is needed in studies involving liver
biopsy analysis. The use of fibrosis stage scores as numerical
data is an unacceptable statistical technique in studies using
subjective histopathological categories as an end point.
Reviewers, researchers, and readers require education with
regard to this matter, not only with respect to the design and
interpretation of current and future studies, but also in the
interpretation of studies already published. Formal quantifi-
cation of liver collagen may be necessary in some studies.
There are great dangers attendant upon a failure to
recognise the pitfalls in our current liver fibrosis assessment
HISTOPATHOLOGICAL ASSESSMENT OF LIVER FIBROSIS
practice and if on recognition of such we do not make the
required improvements. There are dangers from the point of
view of future patients, who may be inappropriately treated
or denied treatment that has been mistakenly discarded
because of ignorance of the histopathological process. The
‘‘golden standard’’ of liver biopsy assessment of fibrosis has
become tarnished with age, but with effort it can be polished
to regain its rightful place as a more worthy gold standard.67
R A Standish, A Dhillon, A P Dhillon, Academic Department of
Histopathology, Royal Free and University College Medical School,
E Cholongitas, A K Burroughs, Academic Department of Liver
Transplantation and Hepatobiliary Medicine, Royal Free and University
College Medical School, London, UK
. . . . . . . . . . . . . . . . . .
Dr Cholongitas and Professor Burroughs are involved in a trial supported
by Astellas looking at immunosuppression of patients following liver
transplant for HCV. Dr Standish was a research fellow supported by
GlaxoSmithKline for two years, finishing September 2002.
Conflict of interest: None declared.
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