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Musculoskeletal Pathology Part III Soft Tissue
Tumours
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Soft tissue tumors Arising in non-skeletal
mesodermal tissues such as adipose tissue,
fibrous tissue, muscle, blood vessels and
peripheral nerves (despite their neuroectodermal
origin) Benign, malignant and intermediate
(low-grade malignant locally aggressive, can
recur, no metastatic potential) Originate from
primitive mesenchymal stem cells Classification
according to their differentiation lines (e.g.
liposarcoma is not a tumor arising from lipoblast
but exhibiting lipoblastic differentiation)
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Classification of soft tissue tumors

• Lipomatous tumors
• Lipoma
• Liposarcoma
• Smooth muscle tumors
• Leiomyoma
• Leiomyosarcoma
• Skeletal muscle tumors
• Rhabdomyoma
• Rhabdomyosarcoma
• Fibroblastic tumors
• Nodular fasciitis
• Fibromatoses
• Fibrosarcoma

• Fibrohistiocytic tumors
• Benign fibrous histiocytoma
• Malignant fibrous histiocytoma
• Vascular tumors
• Hemangioma
• Angiosarcoma
• Tumors of peripheral nerves
• Schwannoma
• Neurofibroma
• Malignant peripheral nerve sheath tumor
• Tumors of uncertain origin
• Synovial sarcoma

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Lipoma Very common benign tumor Subcutaneous
tissue of the trunk and limbs in the middle-aged
and elderly Soft, slowly growing
mass Microscopic features well-defined lobules
of mature adipose tissue Lipoma
variants Angiolipoma thin-walled small blood
vessels occupy significant portion of the
lesion Spindle-cell lipoma mixture of mature
adipocytes, short bundles of collagen and small
uniform spindle cells
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Liposarcoma The most common malignant soft tissue
tumor Adults (peak incidence 40-60 years) Site
lower limb and retroperitoneal space Key
diagnostic feature multivacuolated lipoblast
(two or more lipid droplets within the
cytoplasm) Subtypes Well-differentiated
lipoma-like liposarcoma (atypical lipomatous
tumor) closely resemble lipoma, but a few
spindle or stellate cells with hyperchromatic
atypical nuclei, high reccurence rate, no
meastases Myxoid liposarcoma small
undifferentiated mesenchymal cells ad lipoblast
set in a myxoid stroma, plexiform chicken-wire
network of capillaries, good prognosis, rare
metastases Pleomorphic liposarcoma mixed cell
population (spindle cells, tumor giant cells and
small number of lipoblasts), poor prognosis,
frequent metastases
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Leiomyoma Skin, subcutaneous tissue, uterus,
gastrointestinal tract Microscopic features
interlacing bundles of well-differentiated smooth
muscle cells with bright eosinophilic cytoplasm
and blunt-ended nuclei Leiomyosarcoma Mesentery,
retroperitoneal space, wall of large veins,
skin, subcutaneous tissue, deep soft tissues of
limbs Signs of malignancy large size, high
mitotic rate, areas of necrosis, marked cellular
pleomorphism
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Rhabdomyoma Extremely rare lesions Adult type
head and neck of middle aged individuals, large
round or polygonal cells with eosinophilic
cytoplasm and abundant cytoplasmatic
glycogen Genital type polypoid growth of the
cervix, vagina or vulva in middle age, large
rhabdomyoblasts with cross-striations Fetal
type boys younger than 3 years, head and neck,
mixture of immature skeletal muscle and loose,
rather myxoid stroma Cardiac rhabdomyoma occurs
in infancy, regularly fatal by the age of 5
years, association with tuberous sclerosis in
about 50 usually multiple rounded nodules
involving heart ventricles Large polygonal cells
with central mass of eosinophilic cytoplasm,
abundant glycogen and narrow processes extending
to the periphery (spider cells)
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Rhabdomyosarcoma The most common malignant soft
tissue tumour in infants and young
children Diagnosis depends on the demonstration
of rhabdomyoblasts (round, elongated or oval
cells with excentric eosinophilic cytoplasm, in
which fibrillated appearance may be noted
tadpole cells, strap cells, racket cells)
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Subtypes of rhabdomyosarcoma Embryonal
rhabdomyosarcoma most common, early childhood,
head and neck region (orbit, nasopharynx, middle
ear) and genitourinary system, small rounded or
spindle-shaped cells within a myxoid
matrix Bothryoid rhabdomyosarcoma (grape-like)
embryonal rhabdomyosarcoma with polypoid
configuration and myxoid consistency, occur in
mucosa-lined organs Alveolar rhabdomyosarcoma
between the ages of 10 to 20 years, muscles of
limbs and trunk, honecomb-like spaces bounded by
fibrous septa, spaces lined by small round or
oval undiffernentiated cells, loss of cohesion
towards the centre of spaces Pleomorphic
rhabdomyosarcoma limbs of adults, large cells
with eosinophilic cytoplasm and either single or
multiple highly atypical nuclei
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Nodular fasciitis Benign fibroblastic
proliferation Adolescents and young
adults Rapidly growing nodule within
subcutaneous tissue, forearm is the most common
site Microscopic features plump immature
fibroblasts arranged in short bundles, numerous
mitoses, cellular pleomorphism not present
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Superficial fibromatoses Palmar fibromatosis
(Dupuytrens contracture) middle-aged men,
nodular thickening of palmar aponeurosis leading
later to flexion deformities of fingers Plantar
fibromatosis (Ledderhoses disease) nodular
thickening of plantar aponeurosis Penile
fibromatosis (Peyronies disease) abnormal
curvature of penis Microscopic features
nodules of well-differentiated fibroblasts
arranged in long sweeping bundles
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Deep fibromatoses (desmoid tumors) Abdominal
abdominal wall, young adults, particularly women
who have borne children, often detected in
peripartum or postpartum period, sometimes in
surgical scars Intra-abdominal young adults,
mesentery, association with Gardners syndrome
(intestinal polyposis) Extra-abdominal the most
aggressive, adults in the third and fourth
decades, pectoral and pelvic girdles General
features deep intramuscular location, large size
(up to 10-15cm), infiltrative growth pattern,
high risk of recurrence after excision
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Fibrosarcoma Relatively uncommon malignant
neoplasm Middle aged adults Deep soft tissues of
lower limbs and trunk Microscopic features
bundles of spindle shaped cells arranged at
angles to one another (herring-bone pattern),
frequent mitoses Infantile fibrosarcoma within
the first two years of life, much better prognosis
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Benign fibrous histiocytoma (dermatofibroma) Comm
on lesion, most frequently on the skin of lower
leg Papule or nodule, often deeply
pigmented Microscopic features situated within
the mid-dermis, spindle cells arranged in curious
whorled pattern (storiform pattern)
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Malignant fibrous histiocytoma (MFH) Deep soft
tissues of limbs, retroperitoneum Irregularly
arranged plump, eosinophilic, spindle-shaped
cells with darkly staining and often bizarre
nuclei, numerous mitoses, interspersed
macrophage-like cells, storiform pattern in some
areas MFH represents merely a morphological
pattern shared by wide variety of poorly
differentiated malignant neoplasms, it is a
heterogeneous group of unrelated lesions
(pleomorphic sarcomas, dedifferentiated
carcinomas, high-grade lymhomas etc.) MFH
(synonymous designation undifferentiated
pleomorphic sarcoma) diagnosis of exclusion
following thorough sampling and judicious use of
ancillary techniques (immunohistochemistry,
electron microscopy)
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Haemangioma Many of them are hamartomas rather
than true neoplasms Capillary haemangioma
skin, mass of proliferated capillaries Pyogenic
granuloma rapidly developing polypoid nodule,
many small capillaries similar to those seen in
granulation tissue, myxoid stroma, surface often
eroded Cavernous haemangioma skin, liver,
aggregates of large dilated thin-walled vessels
lined by flattened endothelium
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Angiosarcoma Irregular anastomosing vascular
spaces lined by endothelial cells with large
hyperchromatic nuclei, highly aggressive tumor
with poor prognosis Kaposis sarcoma Variant of
angiosarcoma, often patients with AIDS, multiple
bluish plaques and nodules on the skin of lower
extremities, spindle-shaped cells with the
presence of red cells containing slits and
haemosiderin deposition
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Schwannoma (neurilemmoma) Smooth lobulated
lesion usually attached to a nerve Microscopic
features two patterns recognized Antoni A
compact areas formed by regular interlacing
bundles of uniform spindle-shaped cells, often
foci of nuclear palisading Antoni B looser open
areas, small cells with rounded nuclei
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Neurofibroma Not infrequently multiple,
sometimes part of neurofibromatosis Infiltrates
and expands the affected nerve Microscopic
features spindle-shaped cells with elongated
wavy nuclei set in myxoid stroma
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Malignant peripheral nerve sheath tumor
(MPNST) Adults, most common locations neck,
forearm, lower leg, buttock Large mass producing
fusiform enlargement of a major
nerve Microscopic features relatively uniform
spindle-shaped cells with hyperchromatic nuclei
and high mitotic activity
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Synovial sarcoma Term synovial sarcoma is a
misnomer (the tumour is neither derived from nor
differentiates to synovial lining cells
historical name has been retained) Young adults
(15-40 years) Originates from extraarticular soft
tissues, often near joint capsules and
tendons Microscopic features tumour consists of
two cell types Epithelial (forming nests and
gland-like spaces resembles carcinoma) Spindle
(arranged in sheets resembles
fibrosarcoma) Due to presence of epithelial and
spindle cell types, it can be classified
as Biphasic (both cell types) Monophasic
(spindle or epithelial cells only) frequent
reccurences, metastases in lymph nodes and lungs