3rd Year MBBS
MSK Module
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Topic 11 — Soft-Tissue and Muscle Tumours
A rapid connection of tumour differentiation, morphology, biological behaviour, clinical presentation and major complications.
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1. THE TOPIC IN ONE CONNECTED FLOW
Soft-tissue tumours are named according to the tissue they resemble, such as fat, fibrous tissue, skeletal muscle or smooth muscle. Their morphology shows the direction of differentiation, while cellular atypia, mitotic activity, necrosis, invasion and metastasis determine whether the lesion behaves as benign, locally aggressive or malignant.
Adipocytic, fibroblastic, skeletal-muscle or smooth-muscle pattern
Controlled, rapidly proliferative, infiltrative or frankly malignant
Mature fat, spindle fascicles, lipoblasts, rhabdomyoblasts or cigar-shaped cells
Circumscribed, locally infiltrative or destructive with metastatic potential
Superficial mobile swelling or deep progressively enlarging mass
Histology connects cell type, architecture, atypia, mitoses and necrosis
Cure, local recurrence, compression, tissue destruction or distant metastasis
2. KEY CLINICAL CONNECTIONS
Adipocytic Tumours
Soft, superficial and freely mobile mass
→ uniform mature adipocytes without atypia
→ lipoma.
Deep thigh or retroperitoneal mass
→ adipocyte size variation, atypical stromal cells or lipoblasts
→ liposarcoma with recurrence or metastatic risk.
Fibroblastic Lesions
Rapid superficial growth with typical mitoses
→ benign myofibroblastic proliferation
→ nodular fasciitis, not automatically sarcoma.
Bland collagenous spindle cells with muscle infiltration
→ poorly defined extensions
→ fibromatosis with difficult excision and local recurrence.
Skeletal-Muscle Tumours
Childhood mass with primitive cells and rhabdomyoblasts
→ skeletal-muscle differentiation
→ rhabdomyosarcoma.
Submucosal grape-like mass
→ botryoid embryonal pattern; alveolar nests with central discohesion
→ alveolar subtype.
Spindle-Cell Malignancy
Whorled uterine mass with uniform cigar-shaped nuclei
→ low mitoses and no tumour-cell necrosis
→ leiomyoma.
Atypia, high mitotic activity and necrosis
→ leiomyosarcoma; herringbone malignant fibroblasts
→ fibrosarcoma with haematogenous spread.
3. AIM HIGH-YIELD INTEGRATION REVIEW
→ soft, yellow, mobile superficial mass
→ benign behaviour.
→ deep enlarging mass
→ local recurrence and possible metastasis.
→ may mimic sarcoma
→ absence of marked atypia supports benignity.
→ difficult complete excision
→ repeated local recurrence without metastasis.
→ childhood soft-tissue mass
→ local destruction and metastatic potential.
→ embryonal type; fibrous septa with central discohesion
→ alveolar type.
→ benign; atypia, mitoses and tumour-cell necrosis
→ malignant.
→ local invasion
→ haematogenous spread, especially to lungs.
Rapid growth or frequent mitoses alone do not prove malignancy. Nodular fasciitis grows rapidly and may have many mitoses, but the mitoses are typical and marked pleomorphism is absent.