These benign lesions affect older patient than nodular fasciitis (rarely
occurs in children).
The lesions may occur either in superficial soft tissue (proliferative
fasciitis) or in skeletal muscle (proliferative myosiitis).
Proliferative fasciitis is common in the extremities, specially in the
lower limb. Proliferative myositis is common in shoulder girdle and upper
trunk.
Grossly, proliferative fasciitis resembles
nodular fasciitis
. Proliferative myositis is a poorly defined scar-like lesion involving
muscle and overlying fascia.
In both conditions, there are clusters of rounded basophilic
fibroblasts with prominent nuclei and nucleoli (ganglion-like) which
blend with areas showing usual features of nodular fasciitis. However, the
stroma is more myxoid and fibrinoid areas may be present.
In proliferatiive myositis an additional feature is poorly demarcated
fibroblastic proliferation involving the epimysium, perimysium and
endomysium in a checkerboard-like fashion.
Immunohistochemistry reveals that the ganglion- like cells express
vimentin and lack actin or desmin.
Immunohistochemistry and electron microscopy confirm the mixed
fibroblastic and myofibroblastic nature of these lesions.
Differential diagnosis:
Carcinoma, melanoma or large cell lymphoma in adults .
Rhabdomyosarcoma
and even
ganglioneuroblastoma in children.
These entities are separated by clinical appearance and by
immunohistochemistry.
Acral myxoinflammatory fibroblastic sarcoma is a low grade sarcoma of
extremities which can involve joints and tendon sheaths. This multinodular
tumour consists of fibrous areas with marked inflammation, vacuolated
cells and mononuclear or binucleated Reed-Sternberg-like cells.
Ischemic fasciitis was first
described by Montgomery et al (PUBMED
) in 1992 as atypical
decubital fibroplasia and was subsequently termed ischemic fasciitis by
Perosio and Weiss (PUBMED).
Ischemic fasciitis predominantly occurs in elderly patients who are
physically debilitated or immobilised.
The common sites include soft tissues of the shoulder, posterior chest
wall, sacrum, greater trochanter, buttock, thigh and arm. The patient
usually has a short history of 3 weeks to six months.
Lesions are located
in the deep subcuti and occasionally extended into the muscle. Extensive
epidermal epidermal ulceration is absent.
Microscopically, there is a lobular arrangement of zones of of fibrinoid
and coagulative necrosis with fibrin thrombi and spindle cells in a
prominent myxoid stroma rimmed by ingrowing ectatic thin walled vessels.
The spindle cells are focally atypical with large hyperchromatic nuclei,
prominent nucleoli and basophilic cytoplasm resembling those of
proliferative fasciitis. Fat necrosis is seen at the periphery.
Immunohistochemistry : Two thirds are actin positive, and half are CD34
positive. Desmin is negative.
Differential diagnosis:
1.
Decubitus ulcer
has more extensive ulceration overlying granulation tissue without zones
of necrosis, a myxoid stroma or atypia.
2. Proliferative fasciitis
lacks the zonal architecture , vascular features and peripheral
granulation tissue.
3.
Epithelioid sarcoma
is subcutaneous with central necrosis but in more discrete nodules and
cytologically bland and epithelial markers are positive.
4.
Myxoid malignant fibrous
histiocytoma
lacks the zones and is more pleomorphic
and cellular with a typical vascular pattern.
5.
Acral myxoinflammatory
fibroblastic sarcoma has
inflammation, large polygonal cells with prominent nucleoli and myxoid
nodules with vacuolated fibroblasts.
6.
Myxoid chondrosarcoma
is multilobular and has more uniform
bland cells , often in a lace-like pattern, a hyaluronidase-resistant,
more myxoid and less necrotic stroma with haemorrhage ,glycogen in cells
and S100 protein positivity.
7.
Myxoid liposarcomahas a striking vascular pattern
with lipoblasts and is extremely rare in the subcutis.
