History
2 1/2 - year-old boy complaining of pain in the left buttock.
The mother felt a mass which was rapidly growing. A complete
excision was attempted.
Pathology
A large fragment of fatty tissue measuring 8 x 3.3 x 3 cm was
received. On section, a relatively well demarcated lesion measuring
3.5 x 2 x 2 cm was found. The mass was bulging from the surrounding
fatty tissue, multilobulated, of homogeneous tan and translucent
colour with few yellowish areas. On histology, the lesion was
made of a proliferation of plump, elongated cells with a variety
of patterns. More centrally, the lesion had a myxoid stroma,
surrounded by clusters of cells with whorling or fascicular
appearance. Many vessels were found with small, round, clefted
or slit like spaces reminiscent of staghorn formations. Sparse
mononuclear inflammation with or without multinucleated giant
cells was visualized. The cellularity varied from one field
to the
other and nuclear polymorphism was negligible. Many extravasated
erythrocytes were found as well as areas reminiscent of fibroblast
cell culture.
Discussion
Nodular fasciitis is a frequent lesion that may occur in childhood
or adolescence in 20% of
cases. It has a slight male preponderance with most of the cases
occurring in the second
decade. Presentation in neonates or infancy is reported. According
to Stout, it is often located in the upper extremity, especially
the forearm, but head and neck are frequently involved in children.
The mass grows rapidly (10-12 weeks) and may not reach more than
3.5 cm. The nodule is tender or painful and usually found in
the subcutaneous (80%) or deep soft tissue (muscle or periosteum).
Solitary lesions are more frequently seen but multiple nodules
may appear simultaneously or at intervals. There is no history
of trauma.
On gross examination, a non encapsulated nodule,
round or ovoid, grey or tan and firm is
found with a rubbery, myxoid or gelatinous appearance on cut
surface. 10% of the cases have an irregular infiltrative or arborizing
growth pattern.
On histology, a characteristic zonal pattern
is found with a hypocellular myxoid central
portion with abundant vessels, a tissue culture-like arrangement
of myofibroblasts surrounded by a peripheral proliferation of
spindle fibroblasts in fascicles, sparse mononuclear inflammatory
cells and extravasated erythrocytes. Other constituents may be
keloid bands of collagen, cartilaginous metaplasia, calcification,
osteoid or heterotopic ossification. Mitotic figures may be abundant
but never atypical. A variety of these histological elements,
myxomatous, fibromatous or osteoid, found in the lesion are helpful
for the diagnosis of this benign mass. The time of duration may
influence the predominant histological pattern. It may be more
myxoid in the early phase to cellular and fibrous later on.
In the myxoid phase, the proliferation assumes a feathery
appearance with fibroblasts
scattered in a highly vascular myxoid stroma with extravasated
red blood cells and necrosis. In the cellular or intermediate phase,
fibroblasts become more plump and large with vesicular nuclei
in a less myxoid matrix. Multinucleated cells are at their peak.
In the fibrous phase, the lesion is mainly composed of bundles
of spindled fibroblasts with pycnotic or hyperchromatic nuclei
and increased collagen in interlacing strands.
The immunohistochemistry reveals a myofibroblastic
phenotype and histiocytes. The cells
are vimentin, muscle specific actin and smooth muscle actin positive,
with some CD 68
positive ones. Desmin, cytokeratin and S-100 protein are negative.
Flow cytometry always
reveals a diploid DNA and the proliferative activity from low
to moderate. P53 is absent or
found in less than 1% of the cases. There is no characteristic
chromosomal anomaly, apart
from 2 cases with chromosomal aberrations which were described
in the literature.
The differential diagnosis varies according
to the duration of the lesion and the predominant histological
pattern. It may include a fibromatosis, a benign fibrous histiocytoma,
myositis ossificans or even a sarcoma.
The fibromatosis is more infiltrating, non uniformly
fascicular with more collagenous stroma and contains few or no
inflammatory cells.
Benign fibrous histiocytoma is made of more polymorphic
elements, more storiform or curvilinear growth and on immunohistochemistry,
the markers for actin are negative. Myositis ossificans in
its early phase could have a similar histological presentation
as during the myxoid phase presentation of nodular fasciitis.
The presence of a loose, immature, vascular and fibroblastic
proliferation with mild to moderate polymorphism, mitotic figures
and chronic inflammation with multinucleated giant cells could
be similar, but in myositis ossificans, new bone or plump osteoblasts
are already located at the periphery of the lesion.
In sarcoma, the growth is not as rapid, but
more polymorphic and necrotic. The treatment consists in a local
excision with margins of uninvolved tissue. The process is self-limiting
and local recurrence represents 2%, mainly in incomplete resection
or in piecemeal presentation during the active growth phase.
