Musculoskeletal PathologyPart III

Soft Tissue Tumours

Soft tissue tumors

non-skeletal mesodermal tissues: adipose tissue, fibrous tissue, muscle, blood vessels and peripheral nerves (despite 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 differentiation lines (e.g. liposarcoma is not a tumor arising from adipose tissue but exhibiting lipoblastic differentiation)

Classification of soft tissue tumors

Lipomatous tumorsLipomaLiposarcomaSmooth muscle tumorsLeiomyomaLeiomyosarcomaSkeletal muscle tumorsRhabdomyomaRhabdomyosarcomaFibroblastic tumorsNodular fasciitisFibromatosesFibrosarcoma

Fibrohistiocytic tumorsBenign fibrous histiocytomaMalignant fibrous histiocytomaVascular tumorsHemangiomaAngiosarcomaTumors of peripheral nervesSchwannomaNeurofibromaMalignant peripheral nerve sheath

tumorTumors of uncertain originSynovial sarcoma

Lipomathe most common soft tissue tumor in adultsmiddle-aged and elderly peoplesubcutaneous tissue of the trunk and limbs (superficial lipoma)deep soft tissue (deep lipoma)synovial membrane (lipoma arborescens)soft, slowly growing masswell circumscribed, lobular arrangement, yellow cut surfacewell-defined lobules of mature adipose tissuenumerous histologic subtypes (angiolipoma, myolipoma, chondroid lipoma, pleomorphic/spindle cel lipoma)

Liposarcoma

most common malignant soft tissue tumoradults (peak incidence 40-60 years)lower limb and retroperitoneal spacekey diagnostic feature: multivacuolated lipoblast (two or more lipid droplets within the cytoplasm)

well-differentiated lipoma-like liposarcoma (atypical lipomatous tumor): closely resemble lipoma, but a few spindle or stellate cells with hyperchromatic atypical nuclei, high recurrence rate, no meastases (intermediate behaviour)

myxoid liposarcoma: small undifferentiated mesenchymal cells and 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

Leiomyoma

skin, subcutaneous tissue, uterus, gastrointestinal tract

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

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: infancy, fatal by the age of 5 years, association with tuberous sclerosis (50%)usually multiple rounded nodules involving heart ventricleslarge polygonal cells with central mass of eosinophilic cytoplasm, abundant glycogen and narrow processes extending to the periphery (“spider cells“)

Rhabdomyosarcoma

most common malignant soft tissue tumour in infants and young children

rhabdomyoblasts (round, elongated or oval cells with excentric eosinophilic cytoplasm – “tadpole cells, strap cells, racket cells“)

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 matrixbothryoid rhabdomyosarcoma (grape-like): embryonal rhabdomyosarcoma with polypoid configuration and myxoid consistency, occurs in mucosa-lined organs

alveolar rhabdomyosarcoma: 10 - 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

Nodular fasciitis

benign fibroblastic proliferationadolescents and young adultsrapidly growing nodule within subcutaneous tissue, forearm is the most common site

plump immature fibroblasts arranged in short bundles, numerous mitoses, cellular pleomorphism not present

Superficial fibromatoses

palmar fibromatosis (Dupuytren’s contracture): middle-aged men, nodular thickening of palmar aponeurosis leading later to flexion deformities of fingers

plantar fibromatosis (Ledderhose’s disease): nodular thickening of plantar aponeurosis

penile fibromatosis (Peyronie’s disease): abnormal curvature of penis

nodules of well-differentiated fibroblasts arranged in long sweeping bundles

Deep fibromatoses (desmoid tumors)

abdominal: abdominal wall, young adults, particularly women, often in peripartum or postpartum period, sometimes in surgical scars

intra-abdominal: young adults, mesentery, association with Gardner’s syndrome (intestinal polyposis)

extra-abdominal: the most aggressive, adults in the third and fourth decades, pectoral and pelvic girdles

deep intramuscular location, large size (up to 10-15cm), infiltrative growth pattern, high risk of recurrence after excision

Fibrosarcoma

uncommon malignant neoplasmmiddle aged adultsdeep soft tissues of lower limbs and trunk

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

Benign fibrous histiocytoma (dermatofibroma)

common lesion, most frequently on the skin of lower leg

papule or nodule, often deeply pigmented

situated within the mid-dermis

spindle cells arranged in curious whorled pattern (storiform pattern)

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)

Haemangioma

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

Angiosarcoma

irregular anastomosing vascular spaces lined by endothelial cells with large hyperchromatic nucleihighly aggressive tumor with poor prognosis

Kaposi’s sarcomavariant of angiosarcomaoften patients with AIDSmultiple bluish plaques and nodules on the skin of lower extremitiesspindle-shaped cells with the presence of red cells containing slits and haemosiderin deposition

Schwannoma (neurilemmoma)

smooth lobulated lesion usually attached to a nerve

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

Neurofibroma

not infrequently multiplesometimes part of neurofibromatosisfusiform expansion of affected nerve

spindle-shaped cells with elongated wavy nuclei set in myxoid stroma

Malignant peripheral nerve sheath tumor (MPNST)

adultsmost common locations: neck, forearm, lower leg, buttocklarge mass producing fusiform enlargement of a major nerverelatively uniform spindle-shaped cells with hyperchromatic nuclei and high mitotic activity

Synovial sarcoma

neither derived from nor differentiates to synovial lining cells (historical name has been retained)young adults (15-40 years)extraarticular soft tissues, often near joint capsules and tendons

two cell types:epithelial (forming nests and gland-like spaces – resembles carcinoma)spindle (arranged in sheets – resembles fibrosarcoma)

biphasic (both cell types)monophasic (spindle or epithelial cells only)

frequent reccurences, metastases in lymph nodes and lungs