18 – Cytology of Skin and Subcutaneous Tissue

Question 1

What are some non-neoplastic skin lesions?

Answer 1

• Keratin-containing cyst (follicular cyst)
• Apocrine cyst (and apocrine cystomatosis)
• Sebaceous hyperplasia
• Inflammation
  o Non-infectious inflammation (foreign body; insect bite)
  o Infectious inflammation (bacterial, fungal)

Question 2

Follicular cysts

Answer 2

• Single or multiple, nodular lesions, may be pigmented
• Rupture can release keratin into the dermis, resulting in severe foreign-body type (pyogranulomatous) reaction
• Dense, laminated keratin deposits
• Cyst wall: usually does NOT exfoliate

Question 3

Apocrine cysts

Answer 3

• Single or multiple
• Secondary to ductal obstruction
• Variably sized nodules covered by atrophic or alopecic skin
• FNA: colourless fluid (occasionally dark)
• Few vacuolated macrophages
• May contain coarse deep blue material (iron)

Question 4

Sebaceous hyperplasia

Answer 4

• Very common in older dogs (Cocker, Mini Poodle)
• Single or multiple nodules with cauliflower like appearance
• Can be pigmented
• Need histo to differentiate b/w: normal, hyperplasia and adenoma
• Usually are benign

Question 5

Inflammatory skin lesions

Answer 5

• Classified by predominant cell population
• May or may not see inciting cause
  o Infectious organisms
  o Foreign material

Question 6

Foreign-body type reactions

Answer 6

• Penetration of plant, animal or inorganic material into the skin
• May progress to a nodular response that drains fluid
• Mixed inflammation: macrophages > neutrophils, lymphocytes
• Might see
  o Multinucleated or epitheloid macrophages
  o Fibroplasia (spindle cells)
  o Secondary bacterial infections
• *don’t always see the foreign material

Question 7

Neoplastic lesions

Answer 7

• Epithelial
• Round cell
• Spindle cell (mesenchymal)
• ‘neuroendocrine’ appearance

Question 8

What are the most common cutaneous epithelial tumours?

Answer 8

• Hair follicle tumours
• Tumors of skin glands
  o Sebaceous gland tumors
  o Apocrine gland tumors
• Fibroadnexal dysplasia or hamartoma
• SCC

Question 9

Hair follicle tumors

Answer 9

• Can have both solid and cystic areas
• Many have different variants depending on cell of origin and type of keratinization
• Majority are BENIGN with good prognosis
• TRICHOBLASTOMA most common in dogs

Question 10

Trichoblastoma

Answer 10

• Most common in dogs (hair follicle tumor)
• Rows of small cuboidal basal cells

Question 11

Tumors of skin glands

Answer 11

• Can have solid and cystic areas
• Sebaceous gland
• Apocrine gland
  o Many different variants, mostly benign
  o Apocrine adenoma: very common in cats!

Question 12

Fibroadnexal dysplasia or hamartoma

Answer 12

• NOT a tumor: may be congenital or acquired
• Benign malformations of connective tissues, +/- follicles, +/- sebaceous glands, +/- apocrine glands
• Need histo to diagnose

Question 13

SCC

Answer 13

• Ulcerated nodules and plaques in the skin/hairless areas
• Well differentiated: individual squamous cells with atypia
• Poorly differentiated: more cohesive, less “squamous” features
• Often associated with neutrophilic inflammation

Question 14

What are some examples of round cell tumors?

Answer 14

• Mast cell tumor
• Histocytoma
• Plasma cell tumor
• Lymphoma
• Transmissible venereal tumor

Question 15

Mast cell tumors

Answer 15

• Dome-shaped, alopecic, erythematous to ulcerated nodules
• **DOGS»cats
• Degranulation can lead to sudden change in size
• Often see eosinophils in dogs (not cats)
• Prognosis depends on stage and histological grade
• Cytolocial grading: less reliable, based on cellular and nuclear atypia
• All mast cell tumor should be considered potentially malignant
• *Diff-Quik: does not stain mast cells that well

Question 16

Canine histiocytoma

Answer 16

• Dome or button-shaped alopecic mass
• Grows rapidly
• Often on limbs, head or pina
• Common in dogs <3 years
• Usually regress within 3 months (T-cell infiltrate)
• “fried egg appearance”

Question 17

Cutaneous plasma cell tumors (plasmacytoma)

Answer 17

• Relatively uncommon
• Can be well differentiated (plasma cell appearance) to poorly differentiate or pleomorphic
• Benign, <1% associated with multiple myeloma
• Oral tumors can be aggressive and infiltrative

Question 18

What are the common spindle (mesenchymal) cell tumors?

Answer 18

• Soft tissue sarcoma
• Hemangioma/hemangiosarcoma
• Melanoma
• *not all are spindle shaped

Question 19

Soft tissue sarcoma

Answer 19

• Umbrella category: need histo to differentiate
  o Perivascular wall tumors
  o Peripheral nerve sheath tumors
  o Fibroma/fibrosarcoma
• Slow growing, infiltrative, firm masses, with low rate of metastasis
• May be pedunculated; may grow very large
• Important to submit to histo for grading and evaluation of margins

Question 20

Hemangioma/hemangiosarcoma

Answer 20

• Hemangioma: may only see blood on FNA
• Hemangiosarcoma: tend to be more cellular
• Cytology may not be definitive (need histo)
• May see cells attempr to form atypical vascular structures (with RBCs in center)

Question 21

*Melanoma

Answer 21

• Most cutaneous melanomas are benign
• Oral and digital/nail melanomas tend to be malignant
  o Locally invasive (bone), metastasize to lymph nodes and lungs
• Cells may be pleomorphic (spindle, round and/or epitheloid) in same tumor
• Contain dark blue to brown-black granules (melanin)
  o Amelanotic forms occur
• Must differentiate from melanophages (macrophages with phagocytosed melanin)

Question 22

What are some examples of tumors of secretory epithelial or neuroectoderm origin?

Answer 22

• Pancreatic islet cells (ex. insulinoma)
• Thyroid/parathyroid tumors
• Adrenal gland tumors
• Apocrine gland anal sac adenocarcinoma

Question 23

What are “naked nuclei” neoplasms?

Answer 23

• Fragile cells that often rupture
• Bare nuclei in a sea of cytoplasm
• Often very bland appearing, even when malignant

Question 24

Apocrine gland anal sac adenocarcinoma (AGASACA)

Answer 24

• Highly invasive metastatic tumor (sublumbar LNs, then to liver, lungs)
• 20-50% paraneoplastic hypercalcemia from PTHrp (see PU/PD)
• Acinar-like arrangement