Soft tissue lesions

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Soft tissue lesions strike fear in many pathologists as they are uncommon and may be difficult to diagnose.

WHO classification of soft tissue lesions/tumours

Morphologic grouping[1]

  1. Adipocytic tumours.
  2. Fibroblastic/myofibroblastic tumours.
  3. "Fibrohistiocytic" tumours.
  4. Smooth muscle tumours.
  5. Skeletal muscle tumours.
  6. Vascular tumours.
  7. Perivascular (pericytic) tumours.
  8. Chondro-osseous tumours.
  9. Tumours of uncertain differentiation.

Biologic potential grouping[2]

  1. Benign.
  2. Intermediate (locally aggressive).
  3. Intermediate (rarely metastasizing).
  4. Malignant.

Prevalence

  • All sarcomas are rare buggers.
    • As the classification has been changing over the past years (with more subtypes being recognized/identified) numbers are variable from study-to-study.
  • Once upon a time almost everything was called malignant fibrous histiocytoma; thus, it is listed as a common entity in some publications.

Most common:[3]

  • Liposarcoma.
  • Leiomyosarcoma.

Molecular testing

  • Molecular testing plays an important role in soft tissue pathology.
  • It is generally seen as an adjunct test that:[4]
    • Often is used to confirm the histomorphologic impression/quality control.
    • Frequently has some prognostic significance.
    • May directly affect treatment.

Translocations

Patterns

Name Description DDx Image Other
Storiform, AKA patternless pattern[5] whorled, cartwheel-like arrangement Undifferentiated pleomorphic sarcoma image ? other ?
Herring bone like herring bone (technique) for climbing a hill in cross country skiing; books on a shelf, where they have partially fallen over -- on the one shelf to the left and the one below to the right fibrosarcoma, synovial sarcoma, MPNST image ? other ?
Fasicular description leiomyoma image ? other ?
Biphasic nests of cells and stroma synovial sarcoma, DSRCT, alveolar RMS image ? other ?

Adipocytic tumours

This category includes:

  • Lipoma.
  • Liposarcoma.
  • Hibernoma.

Smooth muscle tumours

Leiomyosarcoma

See gyne notes.

Microscopy

Features:

Fibrohistiocytic tumours

Undifferentiated pleomorphic sarcoma

  • Abbreviated UPS.
  • Previously known as malignant fibrous histiocytoma.[6]

General

  • Common sarcoma.
  • Usu. deep tissue of the trunk and extremities.

Microscopic

Features:[7]

  • Storiform pattern (AKA patternless pattern - key feature.
  • Marked nuclear pleomorphism key feature.
    • Variation is nuclear size, nuclear shape and nuclear staining (esp. hyperchromasia).
  • Mitoses - abundant; atypical mitoses common.
  • Necrosis (common).
  • Mix of spindle cells and epithelioid cells.

Other findings:

  • +/-Giant cells (see subclassification).
  • +/-Inflammation (see subclassification).
    • Neutrophils.
    • Eosinophils.

Subclassification

UPS is subclassified the following way:[8]

  • UPS with giant cells.
  • UPS with inflammation.
  • UPS not otherwise specified (NOS) - wastebasket diagnosis; if neither of the above two apply.

Fibroblastic/myofibroblastic tumours

Proliferative fasciitis

  • Need to write something here.

Solitary fibrous tumour

General

  • Grouped with hemangiopericytoma in the WHO classification; possibly the same tumour (?).[9]
  • May be benign or malignant; more commonly benign.[10][11]

Microscopic

Features:

  • Well-circumscribed.
  • Fibroblast-like cells (spindle cells).
  • Hemangiopericytoma-like area (staghorn vessels) - not seen on image.
  • Keloid-like collagen bundles.

Images:

Hemangiopericytoma

General

  • Grouped with solitary fibrous tumour in the WHO classification; possibly the same tumour (?).[9]
  • Arises from the pericyte, a connective tissue cell of small vessels that is thought to be involved in flow regulation.
  • Hematologic spread most common - to lungs.[12]
  • Oncogenic osteomalacia - assoc. with hemangiopericytoma.[13]

Presentation

  • Usually painless mass, slow enlargement.

Radiology

  • Intramedullary lytic mass.
  • May be well-circumscribed.
  • +/-Periosteal reaction.
  • +/-Sclerotic border.

May be worked-up with angiography to distinguish from a vascular malformation.[14]

Location

  • Usually extremities - femur or prox. tibial.[15]

Histology

Features:[16]

  • Hypervascular lesion - key diagnostic feature.[17]
    • Abundant thin-walled branching small vessels of variable size.
      • May be described as "staghorn vessels" or "antler-like" vasculature.
      • Cells may "onion-skin" around thin blood vessels.
  • Spindle or ovoid shaped cells in nests or sheets.

IHC

Features:[9][17]

  • Vimentin +ve (usually).
  • Desmin -ve (typical).
  • Factor VIII -ve (marks endothelium).
  • CD34 +ve.
    • CD34 usu. -ve in synovial sarcoma.
  • CD31 -ve (marks benign endothelium).
  • vWF (von Willebrand factor) -ve.

May be in the DDx for meningioma:[18]

  • EMA -ve.
  • S100 -ve.

DDx

  • Other vascular tumours.
  • Vascular malformations.
  • Synovial sarcoma.

Desmoplastic fibroblastoma

  • AKA collagenous fibroma.[19]
  • Benign lesion.
  • Classically found in shoulder region.

IHC

  • Beta-catenin -ve.[20]
    • Significance ???

Low-grade fibromyxoid sarcoma

  • AKA hyalinizing spindle cell tumour.

General

  • Deep soft tissue.

Microscopic

Features:[21]

  • Myoid stroma - key feature.
  • Low cellularity.
  • Spindle cells.

Notes:

  • Few/absent mitoses.

Molecular pathology

t(7;16)(q33;p11)[22]

Vascular lesions

Vascular lesions are "too red"; they have too many RBCs.

Hemangioma

General

Comes is various flavours:[23]

  • Tufted.
    • Small clusters of blood vessels.
  • Microvenular hemangioma.
  • Glomeruloid hemangioma.
  • Epithelioid hemangioma.
  • Targetoid hemosideric hemangioma.

Microscopic

Features:

  • Abundance of benign small blood vessels. (???)

Kaposi sarcoma

General

  • Not really a sarcoma.
  • Caused by HHV-8.
  • Associated with immunodeficiency, e.g. HIV/AIDS.

Stages

It is seen in different stages:[24]

  1. Patch stage.
  2. Plaque stage.
  3. Nodular stage.
  4. Lymphangioma-like. (???)

Microscopic

Features:[25]- key feature.

  • +/-Nuclear atypia.
  • Hyaline globules (intracytoplasmic)[26] - pale pink globs (that are paler than RBCs) - important feature.
  • +/-Hemosiderin deposits.

DDx:

  • Angiosarcoma (have many mitoses, nuclear atypia).
  • Masson's hemangioma (Intravascular papillary endothelial hyperplasia).

Notes:

Images:

IHC

  • CD31 +ve.
  • CD34 +ve.
  • HHV-8 +ve.

Masson hemangioma

General

  • Benign non-neoplastic lesion - a vessel that has thrombosed and recanalized.
  • AKA intravascular papillary endothelial hyperplasia.[29]
  • Histomorphologically may be confused with low-grade angiosarcoma or other soft tissue sarcomas.[29]

Microscopic

Features:

  • Well-circumscribed - key (low power) feature.
  • Abundant small vascular channels with benign endothelium.

Notes:

  • Looks like Kaposi sarcoma at high power.

Angiosarcoma

General

  • Malignant tumour - with a horrible prognosis.[30]
  • Classically on the scalp or head & neck.
  • May arise secondary to therapeutic radiation or chronic lymphoedema related to breast carcinoma.

Microscopic

Features:

  • Very many small capillaries of irregular shape lined with:
    • Pleomorphic nuclei.
      • May have hobnail morphology.
  • Mitoses.
  • Cytoplasmic vacuoles.
    • Cells trying to form lumina - embryologic.

Notes:

IHC

  • CD34 +ve.
  • D2-40 +ve. (???)
  • CD31 +ve.

Hemangioendothelioma

General

  • Usually benign.

Microscopic

Features:[25]

  • Well-formed thin vascular channels on a fibrous stroma - key feature.
  • +/-Thrombosis.
  • +/-Calcification.
  • +/-Fibrosis.
  • +/-Myxoid change.

IHC

  • Factor VIII +ve.

Skeletal muscle tumours

Rhabdomyoma

Rhabdomyosarcoma

  • Abbreviated RMS.

Comes it two main flavours:

  • Alveolar rhabdomyosarcoma.
  • Embryonal rhabdomyosarcoma.

The histology may be that of a small round cell tumour.

Chondro-osseous tumours

This grouping includes tumours derived from cartilage and bone.

Tumours of uncertain differentiation

Desmoplastic small round cell tumour

  • Abbreviated DSRCT.

General

  • Males > females.
  • Usu. affects young adults.
  • Typically retroperitoneal.
  • Poor prognosis.

Microscopic

Features:[31]

  1. Broad bands of paucicellular fibrous stroma with:
  2. Small round cells in nests with an undulating sharp border.

Notes:

  • Usu. abundant mitoses.
  • +/-Necrosis.

Images:

DDx:

IHC

Features:

  • AE1/AE3 +ve.
  • Desmin +ve.
  • EMA +ve.

Molecular

Clear cell sarcoma

  • Known among pathologists as "soft-tissue melanoma" and "melanoma of the soft parts", as it has a strong morphological resemblance.[34]
    • Molecular changes and origin distinct from melanoma.
  • Incidence: rare soft tissue tumour.

Clinical

  • Usually - deep soft tissue or extremities.
  • Guarded prognosis.
  • First described in 1965.[35]

Microscopy

Features:[34]

  • Architecture: sheets or fascicular (bundles) arrangement.
  • Cells: Spindle cells or epithelioid cells.
  • Prominent nucleoli - basophilic.
  • Fibrous septae.
  • Uniform

Image:

IHC

Features:[34]

  • S100 +ve.
  • HMB-45 +ve.
  • Melan A (MART-1) +ve; sometimes -ve.
  • BCL2 +ve.
  • CD57 +ve (usually).

Keratins:

  • EMA may be +ve.
  • CAM5.2 -ve.
  • AE1/AE3 -ve.

Molecular studies

  • Chromosomal translocation t(12;22)(q13;q12).[34]
    • Fusion transcripts:
      • EWSR1-ATF1.
      • EWSR1-CREB1 (GI tract associated).

Synovial sarcoma

General

  • Does not arise from cartilage.[36]
  • Young adults or adolescents.

Microscopic

Comes in three flavours:[36][37]

  1. Spindle cell sarcoma with features of hemangiopericytoma, i.e. staghorn vessels.
  2. Biphasic synovial sarcoma:
    1. Spindle cells with features of hemangiopericytoma.
    2. Epitheliod glands or nests.
  3. Primative round cell type.

Images:

IHC

Features:[36]

  • Vimentin +ve + cytokeratin and/or EMA +ve.
  • CD99 +ve.

Others:

Molecular pathology

Unique translocation:

  • t(X;18)(p11.2;q11.2).[40]

See also

References

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