Benign Soft Tissue Tumours

Lipoma

Epidemiology

  • Adults
  • Men > women

Aetiology

  • Tumour of adipose tissue (white fat)
  • Tumours of brown fat are called Hibernomas – occur in hibernating animals or relatively inactive young children
  • Multiple lipomatosis – Decrum’s disease

Clinical Features

  • Subcutaneous usually
  • Painless
  • Usually <5 cm but can be very large
  • Subtypes:
    • Intramuscular – must be sure this is not a low-grade liposarcoma
    • Pleomorphic
    • Spindle cell lipoma
      • Both are benign but may be confused with malignant lesions
    • Angiolipoma – the only painful lipoma – still benign

Imaging Features

  • Lipoma should look the same as fat on every MRI sequence

Management/Outcomes

  • Marginal excision
  • Recurrence rate <5%

Haemangioma/Intramuscular Haemangioma

Epidemiology

  • <30 years old and more common in children

Clinical Features

  • If superficial, bluish compressible mass that fills with gravity
  • May have a bruit but not usually pulsatile
  • Is a venous problem normally
  • May be deep in muscle (intramuscular haemangioma)
  • Painless normally

Imaging Features

  • High signal on T1 and T2

Management/Outcomes

  • NSAIDs and compression bandages first line
  • Surgical excision has a high recurrence rate
  • Sclerotherapy or embolization are often useful alone or with surgery

Neurilemoma (Schwannoma)

Epidemiology

  • Young adults
  • More common than neurofibroma

Aetiology

  • Benign tumour of Schwann cells
  • Associated with the NF2 gene

Clinical Features

  • Slow-growing painless mass
  • May cause neurologic symptoms or pain on stretch but uncommon

Imaging Features

  • Low signal on T1, High signal on T2
  • Lesion is eccentric to the nerve but in continuity with it
  • May have a positive Tinel’s sign

Pathology

  • Different cellular areas split into Antoni A and B regions
  • Verocay bodies are pathognomonic
  • Stains positive for S100 antibody

Management

  • Marginal excision if symptomatic
    • Shells out like a pea from the nerve
  • Observe otherwise
  • Preserve nerve fibres if excising

Neurofibroma & Neurofibromatosis

Epidemiology

  • Young adults or children

Aetiology

  • A benign nerve tumour
  • May arise from any nerve
  • May be superficial or plexiform (infiltrative)
  • Occurs de novo or as part of neurofibromatosis 1 or 2

NF1

  • 1/4000 births
  • Von Recklinghausen’s disease
  • Chromosome 17 translocation
  • Autosomal dominant

NF2

  • 1/40,000 births
  • Chromosome 22 translocation (Remember NF2 – Ch 22)

Diagnostic Criteria for Neurofibromatosis Type 1

At least two of the following criteria (ROLANCO): 1. Relative with NF1 2. Osseus abnormality - Cortical scalloping, pseudoarthrosis, NOF, scoliosis 3. Lisch nodule (hamartoma of melanocytes in the iris) 4. Axillary freckling 5. Neurofibromas x2 or one plexiform neurofibroma 6. Café au lait spots – 6 or more 7. Optic glioma

Clinical Features

  • Usually superficial but may be deep and very large
  • Generally asymptomatic
  • Slow-growing (beware rapid growth)
  • Tinel positive rarely
  • <5% risk of malignant change to neurofibrosarcoma
    • Almost always in NF1 rather than solitary lesions
    • Usually in plexiform (infiltrative) neurofibroma

Imaging Features

  • Low signal T1, high signal T2
  • Fusiform rather than eccentric (schwannoma) on the nerve
  • May be dumbbell-shaped
  • Look for skeletal signs:
    • Pseudoarthrosis, NOF, cortical scalloping, scoliosis
    • Scoliosis is most common

Pathology

  • Interlacing bundles of elongated cells with dark staining nuclei

Management

  • Observe if asymptomatic
  • Excise if symptomatic – nerve defect possible
  • Treat osseous problems accordingly

Nodular Fasciitis

Epidemiology

  • Most common fibrous tumour

Aetiology

  • Completely benign but mistaken for malignant

Clinical Features

  • Usually on volar aspect of upper limb, neck, back
  • Usually superficial
  • Rapidly grows over 2 weeks then stabilizes
  • Quite small in size
  • 50% painful
  • Solitary
  • No risk of malignant transformation

Imaging Features

  • Low signal T1 but enhances highly with gadolinium
  • Superficial, deep or along fascia planes

Pathology

  • Normal fibroblasts in clumps

Management

  • Excision has a very low recurrence rate

Intramuscular Myxoma

Epidemiology

  • Older adults

Aetiology

  • Mucoid lesion within muscles

Associated Conditions

  • Mazabraud Syndrome:
    • Multiple myxomas and fibrous dysplasia (Remember M for Mazabrauds and Multiple Myxomas)

Clinical Features

  • Slow-growing mass
  • Painful in 20%
  • May cause mass effect on nerves
  • Solitary unless part of a syndrome - Mazabrauds
  • Buttocks and thighs usually

Imaging Features

  • Lie within muscle compartments

Management

  • Marginal excision – low recurrence rate

Desmoid Tumour

Epidemiology

  • Young adults

Aetiology

  • Part of the fibromatosis family of tumours (e.g., Dupuytren’s, Lederhosen’s)

Clinical Features

  • The most common locally aggressive benign soft tissue tumour
  • Infiltrates surrounding tissues
  • 50% are intra-abdominal, 50% extra-abdominal
    • Shoulder, chest wall, back, thigh
  • Grow slowly, are usually pain-free and feel ‘rock hard’ and fixed
  • Unpredictable natural history

Imaging Features

  • Low T1 and T2 signal - Enhance with gadolinium

Pathology

  • Fibroblasts, spindle cells, and collagen

Management/Outcomes

  • Treat like a sarcoma – Wide excision
  • Consider adjuvant radiotherapy or post-operative radiotherapy
  • Recurrence rate is high

Elastofibroma

  • Rare reactive benign lesion
  • Occurs exclusively between scapula and chest wall
  • Causes snapping scapula syndrome which may cause pain
  • MRI has heterogeneous signal on T1 and T2
  • No chance of malignancy
  • Treatment is by excision which is successful
  • Histology stains for Elastin

Synovial Chondromatosis

Epidemiology

  • Young adults

Aetiology

  • Metaplastic proliferation of hyaline cartilage in the synovium
  • Initially not visible on XR
  • Cartilage fragments undergo endochondral ossification to become calcified and visible

Clinical Features

  • Affects hip, knee, shoulder, elbow, ankle in that order
  • Hundreds of intra-articular loose bodies
  • Cause pain and erode articular surfaces

Management

  • Synovectomy and removal of all loose bodies
  • High recurrence if synovectomy is not complete

Myositis Ossificans

Epidemiology

  • Young adults

Aetiology

  • Post-traumatic almost exclusively
  • Almost always within muscle

Clinical Features

  • Usually in quads, gluteals, or brachialis
  • Grows in size over several months
  • Then stabilizes but becomes hard
  • Usually mature by one year
  • Often regresses after this
  • Causes pain with muscle activity or restricted joint motion

Pathology

  • Zonal pattern:
    • Periphery: Mature lamellar bone
    • Middle: Osteoblasts, fibroblasts, and calcification
    • Centre: Fibrous tissue – more lucent on XR

Differential Diagnosis

  • Soft tissue sarcoma – histology is completely different
  • CT scan and MRI will usually differentiate

Management

  • Observe
  • NSAIDs
  • Do not excise until mature and only if symptomatic
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