Musculoskeletal Pathology Part 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 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

Lipoma the most common soft tissue tumor in adults middle-aged and elderly people subcutaneous tissue of the trunk and limbs (superficial lipoma) deep soft tissue (deep lipoma) synovial membrane (lipoma arborescens) soft, slowly growing mass well circumscribed, lobular arrangement, yellow cut surface well-defined lobules of mature adipose tissue numerous histologic subtypes (angiolipoma, myolipoma, chondroid lipoma, pleomorphic/spindle cel lipoma)

Liposarcoma most common malignant soft tissue tumor adults (peak incidence 40-60 years) lower limb and retroperitoneal space key 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 ventricles large 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 matrix bothryoid 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 proliferation adolescents and young adults rapidly 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 neoplasm middle aged adults deep 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 nuclei highly aggressive tumor with poor prognosis Kaposi’s 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

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 multiple sometimes part of neurofibromatosis fusiform expansion of affected nerve spindle-shaped cells with elongated wavy nuclei set in myxoid stroma

Malignant peripheral nerve sheath tumor (MPNST) adults most common locations: neck, forearm, lower leg, buttock large mass producing fusiform enlargement of a major nerve relatively 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