Soft tissue lesions

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

WHO classification of soft tissue 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.

Adipocytic tumours

Hibernoma

General

  • Consists of brown fat (present in the infants to generate heat).[3]
  • Benign.
  • Usually asymptomatic.[4]

Epidemiology

  • Young adults.

Gross

  • Well-circumscribed.
  • Lobulated and light-brown on sectioning.

Microscopic

Features:[5]

  • Large polygonal/oval cells:
    • Nucleus - central & small.[6]
      • Nucleoli typically prominent.[7]
    • Cytoplasm - multivacuolated, oval, eosinophilic, granular.

Image:

Liposarcoma

  • Most common malignant sarcoma in the retroperitoneum.

Microscopy

Features:

  • Lipoblasts:
    • Large sharply demarcated vacuole.
    • Nucleus:
      • Hyperchromatic (dark staining) nucleus.
      • Eccentric location.
      • Nuclear indentation.

Images:

IHC

  • IHC is of limited value.
  • S-100 +ve ~1/3 of the time.
  • Reticulin ???.

Smooth muscle tumours

Leiomyosarcoma

See gyne notes.

Microscopy

Features:

  • Nuclear atypia.
  • Necrosis.
  • Mitoses.

Fibroblastic/myofibroblastic tumours

Proliferative fasciitis

  • Need to write something here.

Hemangiopericytoma

General

  • Grouped with solitary fibrous tumour in the WHO classification; possibly the same tumour (?).[8]
  • 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.[9]
  • Oncogenic osteomalacia - assoc. with hemangiopericytoma.[10]

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.[11]

Location

  • Usually extremities - femur or prox. tibial.[12]

Histology

Features:[13]

  • Hypervascular lesion - key diagnostic feature.[14]
    • 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:[15][14]

  • 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.

DDx

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

Desmoplastic fibroblastoma

  • AKA collagenous fibroma.[16]
  • Benign lesion.
  • Classically found in shoulder region.

IHC

  • Beta-catenin -ve.[17]
    • Significance ???

Vascular tumours

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:[18]

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

Microscopic

Features:[19]

  • Vascular channels that anastomose.
  • +/-Nuclear atypia.
  • Hyaline globules - pale pink globs (that are paler than RBCs) - key feature.
  • +/-Hemosiderin deposits.

DDx:

  • Angiosarcoma (have many mitoses).

IHC

  • CD31 +ve, CD34 +ve, HHV-8 +ve.

Angiosarcoma

  • Malignant tumour.

Microscopic

Features:

  • Very many small capillaries or irregular shape lined with:
    • Atypical nuclei, pleomorphic nuclei.
  • Mitoses.
  • Cytoplasmic vacuoles.
    • Cells trying to form lumina - embryologic.

Hemangioendothelioma

  • Usually benign.

Microscopic

Features:[20]

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

IHC

  • Factor VIII +ve.

Other

Neurofibromatosis

Comes in two flavours:

  1. NF1 (peripheral).
  2. NF2 (central).

NF1

Features (need 2/7 to diagnose):[21]

  • Two or more neurofibromas or one plexiform neurofibroma.
  • Café-au-lait spots.
  • Freckles in axilla or inguinal area.
  • Optic nerve glioma.
  • Iris hamartomas (Lisch nodules).
  • Sphenoid dysplasia or typical long-bone abnormalities (e.g. bowing).
  • First-degree relative with NF1.

NF2

Features (need 1/3 to diagnose):[22]

  1. Bilateral CNVIII masses on imaging.
  2. Unilateral CNVIII mass + first-degree relative with NF2.
  3. First-degree relative with NF2 and 2/4 of the following:
    1. Meningioma.
    2. Glioma.
    3. Schwannoma.
    4. Juvenile cataract.

Small round blue cell tumours (SRBCT)

A group of tumours that has a similar histologic appearance. It is a group of tumours that is seen more often in childhood than adulthood.

DDx

  • Neuroblastoma.
  • Wilm's tumour.
  • Alveolar rhabdomyosarcoma.
  • Ewing sarcoma/PNET - this entity is dealt with in the bone article.
  • Lymphoma (diffuse large B cell lymphoma).
  • Retinoblastoma.
  • Hepatoblastoma.
  • Desmoplastic small round cell tumour.

Microscopic

Features:

  • Sheets of cells, very cellular.
  • Small cells ~ 2X RBC diameter.
  • Scant cytoplasm.
  • Coarse chromatin.
  • Nucleolus (???).
  • +/-Vascular.

Rhabdomyosarcoma

  • Often abbreviated RMS.
  • Most common paediatric sarcoma.
  • ~6% of all childhood cancer.

Histological subdivision:

  1. Alveolar rhabdomyosarcoma.
    • Usually young adults/adolescents.
    • Early mets common.
  2. Embryonal rhabdomyosarcoma.
    • Usual <10 years old.
    • Typically locally invasive.

Molecular and histologic subdivision:

  1. Translocation-positive alveolar RMS.
  2. Translocation-negative alveolar RMS.
  3. Embryonal RMS.

Notes:

  • Translocation-negative alveolar RMS shares characteristics with embryonal RMS.

Microscopy

Alveolar rhabdomyosarcoma:

  • Alveolus-like pattern:
    • Fibrous septae lined by tumour cells.
      • Space between fibrous sepate may be filled with tumour: solid variant of alveolar rhabdomyosarcoma.
  • Eccentric nucleus (???).
  • Cytoplasm - dense pink staining on H&E (if well differentiated).
  • Usu. nuclear pleomorphism +++.
  • Mitoses common.

Molecular diagnostics

Alveolar rhabdomyosarcoma

Common translocations (~80%):

  • t(1,13).
    • PAX3/FKHR fusion gene.
  • t(2,13).
    • PAX7/FKHR fusion gene.

Several uncommon translocations exist.

IHC

  • Desmin (best marker).
  • Actin.

Tumours of uncertain differentiation

Clear cell sarcoma

  • Known among pathologists as "soft-tissue melanoma" and "melanoma of the soft parts", as it has a strong morphological resemblance.[23]
    • 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.[24]

Microscopy

Features:[23]

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

Image:

IHC

Features:[23]

  • S100 +ve.
  • HMB-45 +ve.
  • Melan A (MART-1) +ve; sometimes -ve.
  • bcl-2 +ve.
  • CD57 +ve (usually).

Keratins:

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

Molecular studies

  • Chromosomal translocation t(12;22)(q13;q12).[23]
    • Fusion transcripts:
      • EWSR1-ATF1.
      • EWSR1-CREB1 (GI tract associated).

See also

References

  1. ↑ WMSP PP.601-3.
  2. ↑ WMSP PP.598-604.
  3. ↑ WMSP P.605.
  4. ↑ Ahmed SA, Schuller I (December 2008). "Pediatric hibernoma: a case review". J. Pediatr. Hematol. Oncol. 30 (12): 900–1. doi:10.1097/MPH.0b013e318184e6dd. PMID 19131775.
  5. ↑ Chen DY, Wang CM, Chan HL (March 1998). "Hibernoma. Case report and literature review". Dermatol Surg 24 (3): 393–5. PMID 9537018.
  6. ↑ http://www.pathconsultddx.com/pathCon/diagnosis?pii=S1559-8675(06)70271-6
  7. ↑ http://surgpathcriteria.stanford.edu/softfat/hibernoma/
  8. ↑ WMSP P.609.
  9. ↑ URL: http://emedicine.medscape.com/article/1255879-overview. Accessed on: 2 May 2010.
  10. ↑ URL: http://emedicine.medscape.com/article/1255879-overview. Accessed on: 2 May 2010.
  11. ↑ URL: http://emedicine.medscape.com/article/1255879-diagnosis. Accessed on: 2 May 2010.
  12. ↑ URL: http://emedicine.medscape.com/article/1255879-overview. Accessed on: 2 May 2010.
  13. ↑ URL: http://emedicine.medscape.com/article/1255879-diagnosis. Accessed on: 2 May 2010.
  14. ↑ 14.0 14.1 Enzinger & Weiss's Soft Tissue Tumors. 4th Ed. PP.1007-13. ISBN 0-323-01200-0.
  15. ↑ WMSP P.609.
  16. ↑ PMID 18271804.
  17. ↑ PMID 18544056.
  18. ↑ URL: http://www.histopathology-india.net/KS.htm. Accessed on: 31 January 2010.
  19. ↑ Klatt. AOP P.23.
  20. ↑ Klatt. AOP P.23.
  21. ↑ URL: http://emedicine.medscape.com/article/1177266-overview. Accessed on: 3 May 2010.
  22. ↑ URL: http://emedicine.medscape.com/article/1178283-overview. Accessed on: 3 May 2010.
  23. ↑ 23.0 23.1 23.2 23.3 Hisaoka M, Ishida T, Kuo TT, et al. (March 2008). "Clear cell sarcoma of soft tissue: a clinicopathologic, immunohistochemical, and molecular analysis of 33 cases". Am. J. Surg. Pathol. 32 (3): 452–60. doi:10.1097/PAS.0b013e31814b18fb. PMID 18300804.
  24. ↑ URL: http://www.informaworld.com/smpp/723576818-750600/ftinterface~db=all~content=a789166263~fulltext=713240928. Accessed on: 5 May 2010.
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