Skin masses

Question 1

Differentials?

Answer 1

• Penetrating wound causing infection/inflammation/cellulitis
• Insect bite with inflammation
• Mast cell tumour (MCT)
• Histiocytoma

Question 2

Differentials are:

• Infection/inflammation/cellulitis
• Insect bite with inflammation
• Mast cell tumour
• Histiocytoma

Which do you think is likely and why? What are your next steps.

Answer 2

Mast cell tumour

• Metastatic potential so need to screen local lymph node ± liver and spleen
• Wide excision required at this site - could be difficult so consult oncologist
• Histology required for grading

Question 3

Differentials?

Answer 3

• Injection reaction
• Microchip reaction
• Tumour e.g. spindle cell tumour, MCT
• Cyst

Question 4

Thoughts?

Answer 4

• Mixed inflammation within adipose tissue = panniculitis
• No evidence of infection but can’t say for certain
• Classical appearance of injection reaction
• Usually resolves spontaneously

Question 5

Thoughts?

Answer 5

• Mixed inflammation within adipose tissue = panniculitis
• No evidence of infection but can’t say for certain
• Classical appearance of injection reaction
• Usually resolves spontaneously

Question 6

Differentials

Answer 6

• Lipoma
• Benign cyst
• MCT
• Low grade other neoplasm e.g. spindle cell tumour, adnexal tumour

Question 7

Thoughts?

Answer 7

• Subcutaneous fat appears identical
• If fat is aspirated but the lesion looks aggressive, you may have an unrepresentative sample. If in doubt, repeat the aspirate.
• Fat is commonly aspirated when attempting pre scapular and popliteal lymph node aspirates.

Question 8

Differentials?

Answer 8

• Abscess/cellulitis
• Sarcoma e.g. haemangiosarcoma, osteosarcoma, injection site sarcoma
• Mast cell tumour

Question 9

Thoughts?

Answer 9

Septic inflammation

• Many neutrophils
• These do not appear significantly degenerate but there are intracellular bacteria indicating infection
• This is consistent with an abscess/area of cellulitis e.g. cat bite abscess

Question 10

Differentials?

Answer 10

• Inflammatory mass
• Neoplasm esp. spindle cell tumour

Question 11

Thoughts?

Answer 11

• FNA consistent with spindle cell (mesenchymal) tumour
• Biopsy required for histopathological diagnosis
  
  • Haemangiopericytoma confirmed on incisional biopsy → locally invasive but infrequent metastasis
  • Complete surgical excision if pos ± radiotherapy needed