Soft Tissue Tumours

Differentiation between tumours is difficult. Characteristics include calcification, bony destruction, fat plane involvement, tissue components. Tumours are classified according to the tissue they recapitulate, even though they probably do not arise from these tissues. Benign:malignant lesions 100:1. Most common malignancies include fibrosarcoma and liposarcoma. ?From mutations in mesenchymal stem cells that are widely distributed in the body. 40% in the lower limbs esp thigh, 20% upper limbs, 10% head and neck, 30% trunk and retroperitoneum. Benign tumous tend to be <50mm, well-defined, no neurovascular encasement. Malignant joint tumours are rare. Superficial tumours (skin, subcutaneous tissue) have better prognosis than deep lesions. Malignant lesions tend to be >50mm, ill-defined, heterogeneous, neurovascular/bone involvement, central necrosis, early rapid peripheral enhancement; any mass deep to the deep fascia and >30mm is a sarcoma until proven otherwise.

  • Subcutaneous lesions – Lipoma, nodular fasciitis, BFH, skin appendage tumour, angiomatous lesion, lymphoma, leimyosarcoma, metastasis, dermatofibrosarcoma protuberans, fibrosarcoma.
  • Intermuscular lesions (split fat sign) – Nodular fasciitis, fibromatosis, ganglion, synovial cyst, bursa, neurogenic tumours, vascular lesion, synovial sarcoma, leiomyosarcoma, lipoma, liposarcoma.
  • Intramuscular lesions (surrounded by muscle) – Lipoma, myxoma, angiomatous lesion, fibrosarcoma, PNET/soft tissue Ewings, other sarcomas.
  • Periarticular lesions – PVNS/GCTTS, synovial chondromatosis, lipoma aborescens, synovial cyst, bursa, ganglion, chondroma, tumoral calcinosis, synovial sarcoma.
  • Multifocal/extensive lesions – Angiomatous lesions, NF1, fibromatosis, lipoma, myxomas, metastases, myeloma, lymphoma.

Homogeneous high T2 – Neural tumours, synovial sarcoma.

Primarily Fibrous

Superficial Fibromatosis

Nodular or broad fascicles of fibroblasts and myofibroblasts surrounded by collagen. Unknown aetiology, but different from deep fibromatosis. M>F.

  • Palmar fibromatosis (Dupuytren contracture) – Irregular nodular thickening of palmar fascia, fibrotic bands tethering flexor tendons with contractures (esp ring and little fingers). Typically elderly, 50% bilateral. May coexist with plantar fibromatosis.
  • Plantar fibromatosis – Similar changes to plantar fascia, but flexion contractures and bilaterality are uncommon. Middle age.
  • Penile fibromatosis (Peyronie disease) – Usually dorsolateral aspect of penis causing abnormal curvature of the shaft, urethral stricture.
  • Infantile dermal/digital fibromatosis – Extensor surfaces of digits with nodules on skin/tendons/fascia/periosteum, occasionally bony erosion. Usually 1-2yo, frequent recurrence.
  • Juvenile aponeurotic fibroma – Children and adolescents, slowly infiltrating usually volar/plantar aponeurotic tissue of hands, wrists and feet, may calcify (esp interosseous membrane distal forearm).

Deep-Seated Fibromatosis

(Desmoid tumour, aggressive fibromatosis, fibrosarcoma grade I desmoid type). Group of borderline benign fibrous tumours or low grade fibrosarcomas. Sheets of well-differentiated fibroblasts in herringbone pattern without mitoses. Most in soft tissues. Slow-growing, tends to be large at presentation with local infiltration through compartments, grows along fascial planes, no visible capsule, occasionally multicentric. When bone is involved (by direct extension) there is benign periostitis with thick spicules/’spikes’. Usually multilocular with thick bony septa. Margins difficult to assess due to being infiltrative and unencapsulated (wide excision margin required). Don’t metastasize but may have extensive local extension and recurrence. Usually low T1 and T2 (hypocelullar), occasionally intermediate/high T1/T2, variable enhancement (may be intense).

  • Extra-abdominal fibromatosis – M=F. Typically shoulder, chest wall, back, thigh musculature.
  • Abdominal fibromatosis – Generally anterior abdominal wall in women during or after pregnancy.
  • Intra-abdominal fibromatosis – Mesentery or pelvic walls. May be associated with Gardner syndrome.
  • Congenital generalised fibromatosis – Extensive developing in utero, usually fatal within a few months.
  • Desmopastic fibroma – Rare bone fibromatosis. Most teens with geographic cortical expansion, endosteal erosion, central in metaphysis in long bones, pelvis, mandible. May have aggressive zone of transition, no matrix, no host response.

Fibrosarcoma

Anywhere in body, mostly deep tissees of extremities, may occur in bone. Many now reclassified as fibromatoses/desmoid tumours, MPNSTs or synovial sarcomas. Typically infiltrative, areas of haemorrhage and necrosis, occasional peripheral dystrophic cuvilinear/punctate calcification. Recurrence in 50%, metastases in 25%. T1 isointense to muscle, heterogeneous high T2 (myxoid variant central low T1 high T2 with nodular peripheral enhancement). May have reactive pseudocapsule (but is still aggressive). May cause smooth adjacent bony cortical pressure erosion. Bony involvement primary (most) or secondary (20%) where it is continous; from underlying underlying Paget’s, radiotherapy, chondrosarcoma, NOF, fibrous dysplasia, enchondroma, chronic osteomyelitis or osteonecrosis. Usually lytic with wide zone of transition, may be well-defined, permeative, moth-eaten. May have dystrophic calcification (15%) or bony sequestrum. Low T1, heterogeneous high T2. Most high-grade with poor prognosis. Metastases to lung, bone, LN, liver. Common local recurrence.

Fibrohistiocytic Tumours

Cellular elements resembling fibroblasts and histiocytes (macrophages), but do not necessariy arise from fibroblasts.

  • Benign fibrous histiocytoma (BFH, derma tofibroma) – Common, usually dermis and subcutaneous tissues. Painless, slow-growing, <10mm.
  • ‘Malignant fibrous histiocytoma (MFH)’ – This term has now been dropped, now reclassified as variants of fibrosarcoma or other tumour types. Initially thought to be the most common sarcoma, with extensive pleomorphism. Neoplastic cell now recongised as fibroblastic.

Primarily Fatty

Lipoma

80% subcutaneous, most others intermuscular/intramuscular. Subclassified into conventional lipoma, fibrolipoma, angiolipoma (may be painful), spindle cell lipoma, myelolipoma, pleomorphic lipoma. May be extensively infiltrating. Asymptomatic, soft, compressible, mobile. Sharply defined, fat signal. May have dystrophic calcification or ossification from trauma; dense central calcification, dense ring calcification, or occasionally chondroid tissue. May have few thin enhancing septae, otherwise doesn’t enhance. Any nodules, thickened margins, irregular/nodular enhancement raises the possibility of low-grade liposarcoma.

  • Atypical lipomas – Locally recur, but don’t metastasize.
  • Lipomatosis – Congenital multiple lipomas, random or symmetrical over body. Local lipomatosis may occur after local corticosteroid injection.
  • Macrodystrophia lipomatosa – Localised gigantism with overgrowth of fat and vascular elements (hence overgrowth of soft tissues and bone), usually hand/foot. DDx neurofibromatosis, vascular lesions.
  • Lipoblastoma – Benign, young children (typically <3yo). Enhancing nonadipose tissue at the periphery, also simulates liposarcoma on histology. Liposarcomas almost exclusively occurs in adults.
  • Intraosseous lipoma – Rare, lytic lesion with sclerotic margin, no matrix or reaction. May have central nidus of dystrophic calcification. Usually metaphysis of long bone or calcaneus (in triangular region between major trabecular arcs), occasionally parosteal (may elicit periosteal reaction with hyperostosis or radiating bony spicules).
  • Lipoma arborescens – Rare, monoarticular, usually knee. Hypertrophic synovial frond-like villi distended with fat, large joint effusion. Occasional subsynovial fat deposits. Occasionally erodes adjacent bone.

Liposarcoma

Second most common malignant primary soft tissue tumour in adults (after fibrosarcoma), most 40-60yo. Commonly deep tissues in buttock, thigh, leg, retroperitoneum. Typically develops into large tumours. Low grade well-differentiated lesions have fat signal/density, may have nonfat nodularity at margins, thick/enhancing septa. Myxoid/round cell liposarcoma (intermediate differentiation) have cyst-like areas of myxoid material (intense T2), very little fat signal. Pleomorphic variant is highly undifferentiated with little/no visible fat. Metastases to lung, liver, other solid organs.

Primarily Muscular

Skeletal muscle neoplasms are almost all malignant (benign rhabdomyoma is rare).

Rhabdomyosarcoma

From skeletal muscle. Most common soft tisse sarcoma of childhood and adolescence, usually <20yo. Any location, mostly head and neck or genitourinary where there is little normal skeletal muscle.

  • Embryonal rhabdomyosarcoma (60%) – <10yo, typically nasal cavity, orbit, middle ear, prostate or paratesticular. Sarcoma botryoides subtype develops in nasopharynx, CBD, bladder, vagina.
  • Alveolar rhabdomyosarcoma (20%) – Adolescents, typically deep muscles of extremities.
  • Pleomorphic rhabdomyosarcoma (rare) – Typically deep tissues in adults, may resemble other pleomorphic sarcomas.

Leiomyoma

Benign smooth muscle tumour. Commonly in uterus, skin, nipples, scrotum, labia, less commonly GIT. Multiple cutaneous leiomyomas may be AD, associated with uterine leiomyomas and RCC.

Leiomyosarcoma

Adults, F>M. Most in skin and deep soft tissues of extremities and retroperitoneum. May be large and bulky.

[[General Vascular#Vascular Tumours|Vascular Tumours]]

Primarily Neural

Peripheral Nerve Sheath Tumours (PNST)

Classically fusiform with entering and exiting nerves.

Benign PNSTs usually 20-30yo. Initial slow growth. Can be very painful when large.

  • Neurofibromas – Composed of Schwann cells, fibroblasts and collagen surounding nerve fibres. Localised/solitary (90%, not associated with NF1), plexiform or diffuse. Most superficial cutaneous nerves, if superficial may not have typical fusiform shape. Invades nerve fascicles which become separated. Near water density, low T1, heterogeneous high T2. Fascicular sign – nerve fascicles visible within tumour. Target sign – low central T2 (fibrocollagenous core) with ring of high signal (peripheral myxomatous tissue). Split fat sign – fat separating tumour from adjacent muscles, esp tapering parts ot tumour. Split fat and target signs may also be seen in schwannomas and MPNSTs. Very low malignant potential.
  • Schwannoma (neurilemoma, neurinoma, perineural fibroblastoma, peripheral glioma) – Composed of Schwann cells and variable myxoid material and collagen, positive for S-100 protein. Don’t engulf nerve, hence can be ‘peeled-off’. Most commonly spinal and sympathetic nerve roots, flexor surfaces of extremities (esp ulnar and peroneal nerves). Usually solitary, if multiple generally cuteneous and small associated of NF1. Variable target sign. Schwannomatosis – rare multiple peripheral schwannomas. Ancient schwannoma – cystic degeneration.

Malignant PNST (neurofibrosarcoma, malignant schwannoma) – 20-50o, M>>F. 50% associated with NF1. Some arise from preexisting neurofibroma. Usually deep eg sciatic nerve, brachial plexus, sacral plexus. Large, irregular, heterogeneous signal. Variable target sign.

Morton’s Neuroma

Perineural fibrosis (not a neoplasm) and nerve degeneration in interditigal space of foot between metatarsal heads/necks (most 2nd/3rd or 3rd/4th). ?From repetitive trauma with abrasion of digital nerve by intermetatarsal ligaments. Associated with high-heeled shoes with F>>M. Dumbell-shaped mass between MT heads with low T1, occasionally high T2, usually intense enhancement and vascularity.

Neural Fibrolipoma

(Fibrolipomatous hamartoma). Harmartomatous overgrowth of mesodermal and epidermal elements causing nerve enlargement with interposed fattty tissue. Children or young adults. Esp median nerve. High T1 and T2 surrounding thickened nerve bundles. May be associated with macrodactyly and macrodystrophia lipomatosa.

Miscellaneous and Tumour-Like Lesions

Synovial Sarcoma

(Synovioma). More common in younger patients. Cells resemble synovioblastic cells (but don’t arise from the synovium). Most are in the deep soft tissues, 60-70% lower limbs esp around the knee and thigh. <10% are intra-articular. Most 20-50yo. Typically mass present for several years. Dystrophic calcification in 20-30% (less common in other sarcomas). Nonspecific isointense T1, heterogeneous high T2, may have fluid-fluid levels and internal haemorrhage. Most well-defined without surrounding oedema (but most have microinvasion beyond the pseudocapsule). May be very high T2 resembling ganglion cyst, but it does enhance. Common metastases to lung, bones and LN, local recurrence in 1/4. 5-yr survival 25-60%.

[[Arthritis#Tenosynovial Giant Cell Tumour|Tenosynovial Giant Cell Tumour]]

[[Arthritis#Synovial Chondromatosis|Synovial Chondromatosis]]

Reactive Pseudosarcomatous Proliferations

Reactive fibroblasts proliferate after local trauma (blunt trauma, burns, neurologic disorders) or idiopathic. May develop suddenly and grow rapidly. Histologically mimics sarcoma, hence avoid biopsy.

  • Nodular fasciitis (infiltrative/pseudosarcomatous fasciitis) – Most common, in deep dermis, subcutaneous or muscle. Ill-defined, fibroblasts and myofibroblasts. Commonly volar forearm, chest, back. Reported preceding trauma only in 10-15%.
  • Myositis ossificans – Heterotopic formation of bone and cartilage in soft tissue, typically atheletic adolescents esp proximal upper limbs. Preceding trauma in >50%. Myositis ossificans is within skeletal muscle, heterotopic ossification is general. In 1st 4/52 pseudosarcomatous soft tissue mass (may be painful, warm, doughy) being isointense T1 high/heterogeneous T2, surrounding oedema, periosteal reaction and bone marrow oedema. 4-8/52 centripetal maturation with amorphous osteoid -> peripheral mature compact bone. Peripheral calcification can be faint best on CT or delayed XR in 1-2/52. Later completely ossifies with central bone marrow. DDx parosteal osteosarcoma (denser calcification centrally), juxtacortical chondroma which may scallop underlying cortex, osteochondroma, tumoral calcinosis.

Myositis ossificans progressiva – Autosomal dominant progressive ossification of ?intersittial tissues of striated muscles, tendons and ligaments. Secondary muscle pressure atrophy. Commonly acute torticollis with painful mass of SCM, proggressing to shoulder girdle, rib cage, upper arms, spine, pelvis. Bone formation may bridge adjacent bones.

Tumoral Calcinosis

Periarticular calcified soft tissue masses esp hip, shoulder, elbow. Typically in renal failure. Calcifications tend to be amorphous, often fluid-fluid levels.

Ganglion and Synovial Cysts

Cyst-like mass common around wrist, knee (meniscal cysts), shoulder (paralabral cysts) or other joints. Intraosseous ganglia common in carpus. Connection to joint (neck) needs to be resected for sucessful treatment.

  • Ganglion – 10-15mm pea sized cyst near joint capsule or tendon sheath, from cystic or myxoid degeneration of connective tissue, lacks true cell lining. Fluid is similar to synovial fluid, but there is no communication with the joint space. Common around joints of wrist.
  • Synovial cyst – Herniation of synovium through joint capsule, from increased pressure in tight joint or degeneration of ligament/tendon etc. Most commonly small capsular/meniscal/labral defect acting as one-way valve with joint space. Includes Baker cyst (esp RA). Might not appear cystic on CT, often septated.
  • Digital mucous cyst – ?Myxoid degeneration of connective tissue adjacent to and usually communicating with degenerative joint. Usually DIPJ or under nail fold of hands.

Elastofibroma Dorsi

More common in older women, mean 65-70yo. Classically infrascapular deep to serratus anterior and latissimus dorsi, most bilateral. 50% assymptomatic. Alternating fibrous and fatty components seen on US and MRI.