Page 89 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

VetBooks.ir 8 Epithelial Tumours

Cutaneous epithelial neoplasms can originate from any of the epithelial structures present in the
skin and are classified based on the cell of origin and presence or absence of squamous or adnexal
differentiation. The subcutaneous tissue lacks epithelial structures. Hence, there are no primary
epithelial tumours arising in the subcutis. Cutaneous epithelial tumours can be broadly classified
as follows:

• Epithelial tumours without squamous or adnexal differentiation:
• Basal cell tumour.
• Tumours of the epidermis:
• Papilloma.
• Squamous cell carcinoma.
• Adnexal tumours:
• Follicular tumours: different types of follicular tumours can be observed in dogs and
cats, some of which cannot be differentiated on cytology. The follicular tumours that
will be described in the specific sections of this book include: trichoblastoma, trichoep-
ithelioma, pilomatricoma, and infundibular keratinizing acanthoma. These tumours,
besides being the most frequent, may show some cytological features that facilitate
their recognition on cytology.
• Sebaceous and modified sebaceous glands tumours: sebaceous adenoma, epithelioma
and carcinoma, and perianal gland adenoma, epithelioma and carcinoma.
• Apocrine and modified apocrine glands tumours: sweat gland adenoma and carcin-
oma, anal sac adenocarcinoma, and ceruminous adenoma and carcinoma.
• Adnexal tumours without further differentiation: clear cell adnexal carcinoma.
Merkel cell tumour will also be described in this section, although this is not strictly an epithelial
tumour but a neuroendocrine neoplasm originating from mechanoreceptors present in the epi-
dermis and follicular epithelium.
Cytological diagnosis of cutaneous epithelial lesions
A practical approach to the cytological diagnosis of skin lesions (tumours or non- neoplastic epi-
thelial lesions) should try to answer to the following questions:

• From what type of structure does the lesion originate (e.g. epidermis, sebaceous or sweat
glands, hair follicle)?
• Is the lesion benign or malignant?
• Less frequently, is it a primary cutaneous neoplasm or a cutaneous metastasis of another
malignancy?

76 © Francesco Cian and Paola Monti 2019. Differential Diagnosis in Small Animal Cytology
(F. Cian and P. Monti)