Page 68 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

VetBooks.ir 7 Cysts, Tumour-like Lesions
and Response to Tissue Injury

To this category belong all those lesions that may arise in the skin or subcutis and that are not
strictly inflammatory or neoplastic. These include follicular or adnexal cysts, developmental
anomalies, response to tissue trauma, altered deposition of minerals, necrosis and tumour-like
proliferations. Most of these processes can be identified on cytology; however, sometimes
definitive diagnosis relies on histopathological examination.

7.1 Follicular Cysts

Non-neoplastic, sac-like cavities arising in the hair follicle and lined by stratified squamous epithelium.

Clinical features
• Relatively common in dogs, less frequent in cats.
• Age: most commonly seen in adult animals.
• They can occur in any location, but most commonly arise on the head and trunk.
• Usually occur as single masses, less frequently as multiple (e.g. German Shepherd Dog
and Pekingese). A small pore can occasionally be found on the surface of the lesion.
Masses can be ulcerated.
• Usually confined to the dermis. Larger cysts may extend into the subcutaneous adipose tissue.
• They are benign lesions; however, rupture of the cystic wall and exposure of the keratin
to the surrounding tissues can elicit an endogenous foreign body reaction character-
ized by a neutrophilic to pyogranulomatous inflammation.

Cytological features

• Aspirates usually exfoliate a moderate to large amount of specimen.
• Background: clear or pale basophilic. It may contain cholesterol crystals and hair shafts.
• High numbers of anucleated squamous epithelial cells exfoliate singly or in large groups.
Amorphous dense keratin can also be observed.
• Neutrophils, macrophages and/or multinucleated giant inflammatory cells can be seen in
inflamed cysts.
Variants
• Follicular cysts can be classified as infundibular, isthmic, matrical and hybrid, based on the
type of lining epithelium of the cystic wall. However, this classification does not have any
clinical implication and the general term of follicular cyst is most frequently used.

© Francesco Cian and Paola Monti 2019. Differential Diagnosis in Small Animal Cytology 55
(F. Cian and P. Monti)