Solitary fibrous tumour and haemangiopericytoma: evolution
of a concept
C Gengler & L Guillou
University Institute of Pathology, Lausanne, Switzerland
Gengler C & Guillou L
(2006) Histopathology 48, 63–74
Solitary fibrous tumour and haemangiopericytoma: evolution of a concept
Haemangiopericytoma (HPC) was described in 1942
by Stout and Murray as a distinctive soft tissue
neoplasm, presumably of pericytic origin, exhibiting a
characteristic well-developed ‘staghorn’ branching vas-
cular pattern. Over the years, it appeared that this
growth pattern was a non-specific one, shared by
numerous, unrelated benign and malignant lesions,
and that HPC was better considered as a diagnosis of
exclusion. Three categories of lesion may now be
individualized within the heterogeneous group of HPC-
like neoplasms. The first category corresponds to those
non-HPC neoplasms that occasionally display HPC-like
features (e.g. synovial sarcoma). Lesions belonging to
the second category show clear evidence of myoid ⁄
pericytic differentiation and correspond to true HPCs.
They generally show a benign clinical course, and
include glomangiopericytoma ⁄ myopericytoma, infan-
tile myofibromatosis (previously called infantile HPC),
and a subset of sinonasal HPCs. The third category is
the solitary fibrous tumour (SFT) lesional group, which
includes fibrous-to-cellular SFTs, and related lesions
such as giant cell angiofibromas and lipomatous HPCs.
In practice, any HPC-like lesion can be allocated to one
of these categories, leaving the ill-defined ‘haemangio-
pericytoma’ category empty.
Keywords: giant cell angiofibroma, haemangiopericytoma, haemangiopericytoma of sinonasal tract, infantile
haemangiopericytoma, lipomatous haemangiopericytoma, myofibromatosis, myopericytoma, solitary fibrous
Abbreviations: EMA, epithelial membrane antigen; GCA, giant cell angiofibroma; HPC, haemangiopericytoma;
SFT, solitary fibrous tumour; SMA, smooth muscle actin
Since being coined more than 60 years ago, the term
haemangiopericytoma (HPC) has over the years been
used fairly loosely, to describe a wide variety of
neoplasms which have certain morphological charac-
teristics in common: a monotonous appearance at
low-power examination, moderate to high cellularity,
and the presence of numerous, variably thick-walled,
branching ‘staghorn’ vessels. Great confusion has
arisen regarding this ‘HPC tumour category’ as a
result, leading to difficulties in predicting clinical beha-
viour for a given neoplasm, and thus in establishing
specific treatment modalities. Roughly speaking, up to
15% of soft tissue neoplasms show HPC-like features, at
least focally. HPC is currently no longer considered a
specific entity but rather as a growth pattern, shared by
many, often unrelated neoplasms. Many entities have
progressively escaped from the ill-defined ‘haemangio-
pericytoma’ tumour category over the past 10 years,
and those which remain tend now to be recognized as
cellular or malignant forms of solitary fibrous tumour
(SFT). In this review, the origins of the controversy are
Address for correspondence: Louis Guillou MD, Institut Universitaire
de Pathologie, Rue du Bugnon 25, CH-1011 Lausanne, Switzerland.
? 2006 Blackwell Publishing Limited.
Histopathology 2006, 48, 63–74. DOI: 10.1111/j.1365-2559.2005.02290.x
discussed, and current concepts of HPC and SFT are
Haemangiopericytoma: an historical
In 1942, Stout and Murray1described nine tumours
which were ‘composed of capillary blood vessels with
one or more layers of rounded cells arranged about
them, which cannot be called glomus tumours (….),
yet differs from simple capillary haemangiomata
because of the presence of their perivascular cells’.
The authors believed ‘that these tumours should be
distinguished by a specific name [and suggested]
‘‘haemangiopericytoma’’ as properly descriptive’, based
on certain cytological similarities with pericytes. Peri-
cytes were first described in 1923 by Zimmermann, a
Swiss histologist, as specialized cells normally present
around amphibian and vertebrate capillaries; they were
thought to be modified smooth-muscle cells.2
In their seminal paper on HPC, Stout and Murray1
separated their tumours into four groups. In the first
group, the perivascular cells had a rounded appearance
resembling conventional ‘epithelioid’ glomus cells. In
the second group, the perivascular cells were both
rounded and spindle-shaped, enmeshed in an abundant
reticulin network. The latter cell type, illustrated in
Figure 2 of Stout and Murray’s paper,1had the
appearance of smooth muscle cells but lacked myo-
fibrils, bearing some resemblance to lesions called
nowadays myofibroma ⁄ myofibromatosis and myo-
pericytoma (see below). The last two groups, which
included one lesion each, were composed of a locally
aggressive and a metastasizing neoplasm with an HPC-
like appearance. Of interest, for the lesion which had
metastasized to the liver, the authors’ description was
as follows: ‘where the tumour is older, the endothelia
are surrounded by thick compacted collagen sheaths of
a hyaline aspect in ordinary stains and the tumour cells
are outside of these’, a description and also an
illustration (Figure 4 of Ref. 1) which fits quite neatly
with what we now call solitary fibrous tumour.
In 1949, examining a series of 25 additional cases of
HPC, Stout3enlarged upon his first observations,
demonstrating that HPC could be found anywhere in
the body and, furthermore, that morphology was not
predictive of behaviour for all lesions. Histologically,
tumour cells could vary greatly in size and shape (from
rounded to spindled) and the amount of intercellular
connective tissue was also very variable. Stout himself
acknowledged the marked morphological variability
of HPC: ‘When one first undertakes to unravel the
complex histological pictures exhibited by this tumour,
the task seems hopeless, for the variations appear
endless’.3He also noted that a common denominator in
HPC was the ‘profuse proliferation of obvious or occult
capillaries, each one surrounded by a thin or thick
connective-tissue sheath’, a feature which turned out
to be, years later, in combination with the branching
vascular pattern, a diagnostic marker of the entity. In
his article on HPC published in 1949, Stout acknow-
ledged the fact that the term ‘haemangiopericytoma’
was given in reference to Zimmermann’s pericytes
‘without any real scientific basis in support’.3
The concept of haemangiopericytoma raises
more issues than it solves....
As experience accumulated, it became apparent that
the HPC concept gave rise to three types of problems.
First, many pathologists realized that the characteris-
tic morphological features of HPC were actually not
specific for a given entity, inasmuch as many other
benign and malignant, well-characterized tumours
display HPC-like areas in varying proportions.4,5A
non-exhaustive list of these tumours is provided in
Table 1. The diagnosis of HPC is a diagnosis of
exclusion, as pointed out by Stout himself in 1953:6
‘our general attitude in regard to haemangiopericyt-
oma is to reject it as a diagnosis if we can think of any
other reasonable explanation for the tumour’. Thus,
when confronted with an HPC-like tumour, the
pathologist should first rule out all HPC mimics that
might benefit from specific therapy or management
(e.g. infantile fibrosarcoma, synovial sarcoma, phos-
phaturic mesenchymal tumour, etc.…).
Second, an HPC may be expected to consist of vessels
and of cells showing features of pericytic differentiation,
as its name implies. Whereas vessels are easily recog-
nized on microscopic examination, this is not the case
with so-called pericytic differentiation. Prior to the
era of immunohistochemistry, recognition of pericytic
differentiation was based essentially on electron micro-
scopic examination and cell culture studies. Ultrastruc-
turally, normal pericytes are cellular elements showing
elongated cell processes, pericellular basal lamina,
plasmalemmal pinocytosis and variable numbers of
microfilaments.7,8Immunohistochemically, they usu-
ally express muscle-specific actin (HHF-35), smooth
muscle actin and tropomyosin, but are mostly negative
for desmin and h-caldesmon,8–10an immunoprofile
which fits that of modified ⁄ specialized vascular smooth
muscle cells. A non-exhaustive review of the literature
shows that about 30% of HPCs show evidence of
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