Differential Diagnosis for Cutaneous Masses

Question 1

Benefits of FNA/FNCS

Answer 1

Quick
Simple
Cheap
Possible to do in-house
Helpful in establishing diagnosis

Question 2

Possible outcomes of cytological findings

Answer 2

Arrive at definitive diagnosis
Investigate further
Leave mass alone

Question 3

What can cytology tell us about a mass?

Answer 3

Inflammatory
○ Septic
○ Sterile
Non-inflammatory
○ Cystic
○ Hyperplastic/dysplastic
○ Neoplastic
* Round
* Epithelial
*Mesenchymal

Question 4

Process of assessing cytology

Answer 4

1. Is there a significant amount of immune cells?
2. What tissue cell type is present?
3. Is there neoplasia present?

Question 5

1. Is there a significant amount of immune cells?

Answer 5

Neutrophilic (suppurative or acute) inflammation
Includes “abscess”
Pyogranulomatous inflammation
Granulomatous (macrophagic or chronic) inflammation
Eosinophilic inflammation
“Septic” vs “no organisms seen”

Question 6

2. What tissue cell type is present?

Answer 6

Epithelial?
Round?
Mesenchymal?

Question 7

Epithelial skin tumours

Answer 7

Adherent together
White line between cells
Some order to structure

Question 8

Epithelial skin tumour examples

Answer 8

Trichoblastoma
Basal cell tumour
Trichoepithelioma
Hair follicle tumour
Squamous cell carcinoma
Seen in white cats (UV light)
Sebaceous cell tumours
Adenoma
Carcinoma
Epithelioma
Anal sac apocrine adenocarcinoma
Perianal gland (hepatoid) adenoma

Question 9

Mesenchymal skin tumours

Answer 9

• Arise from:
  ○ Connective tissue
  ○ Muscle
  ○ Bone & cartilage
  ○ Nerve cells
  ○ Endothelial cells
• Cells in non-cohesive aggregates or individually
• Cell borders are variably defined and often indistinct
• Embedded in matrix
• Spindle shaped cells with cytoplasmic tails common
• Cells can be oval or plump
• Often won’t make definitive characterisation of mesenchymal proliferation by cytology

Question 10

Mesenchymal skin tumour examples

Answer 10

Fibroma and fibrosarcoma
Lipoma and liposarcoma
Perivascular wall tumours
Haemangiopericytoma
Myopericytoma
Anaplastic sarcoma with giant cells
(malignant fibrous histiocytoma)
Haemangioma/haemangiosarcoma
Peripheral nerve sheath tumour
Myxoma/myxosarcoma
Melanoma
Granulation/healing

Question 11

Lipoma

Answer 11

• Adipocytes with small nucleus and abundant cytoplasm
  ○ Same size nucleus just less magnification needed to view cell
• Free fatty droplets
• Cells may fall off slides during staining/fixation
  ○ Avoid methanol fixation
  ○ Consider drop rather than drip
• Subcutaneous fat appears identical to lipomas

Question 12

Round cell tumours

Answer 12

Individual cells
Round/roundish
High cell harvest
Look at nucleus:
○ Cytoplasmic ratio
Look at position of nucleus to determine cell type
Look in cytoplasm

Question 13

Round cell tumour examples

Answer 13

Mast cell tumour
Lymphoma
Plasmacytoma
Histiocytic tumours
Transmissible venereal tumours (TVT)

Question 14

Plasmacytoma

Answer 14

Discrete cells
More eccentric nuclei - pushed up against walls
Chromatin clumping
Perinuclear clear zones - pale areas near nucleus

Question 15

3. Is there neoplasia present

Answer 15

Are there cells present that shouldn’t be in this tissue?
Is it benign or malignant?

Question 16

Benign Mass cytology

Answer 16

Minimal - mild anisocytosis
Normal - reduced nuclear:cytoplasmic ratio
Minimal - mild anisokaryosis
Low mitotic count

Question 17

Malignant Mass cytology

Answer 17

Marked anisocytosis
Increased nuclear:cytoplasmic ratio
Marked anisokaryosis with frequent binucelation
High mitotic count