Page 107 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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Infundibular keratinizing acanthoma (IKA) (dog)
VetBooks.ir Benign keratinized tumour arising from the squamous epithelium of the

infundibulum and isthmus of the hair follicle.

Clinical features

• Common benign tumour in dogs. It has not been described in cats.
• Age: 4–10 years old, but younger animals can be affected.
• Usually solitary lesions, but multiple neoplasms can occur.
• This tumour generally has a large central cyst filled with keratin that opens on the sur-
face of the skin with a central pore. The neoplastic cells are located at the periphery of the
mass and usually represent a small portion of the entire lesion. Multiple secondary cys-
tic lesions may develop over time.
• It most frequently occurs on the dorsum, neck, tail and legs.
• It is a benign lesion and carries a good prognosis.
• Over-represented canine breeds: Norwegian Elkhound, Tibetan Terrier, Pekingese.

Cytological features
• Cellularity is variable.
• Background: lightly basophilic and variably haemodiluted.
• Fine-needle aspirates sampled from the large central cyst yielding a large amount of variably
degenerating keratinized material, composed of polygonal anucleated squamous epithelial
cells, amorphous keratin and cholesterol crystals. Nucleated neoplastic cells are often absent
in the aspirates.
• If the needle is redirected in the areas composed of neoplastic cells, variable numbers of
squamous epithelial cells at different maturation stages may be found.
• The nucleated cells, when present, may vary from basaloid epithelial cells to intermediate
and mature squamous epithelial cells. An orderly progression throughout these stages can
often be observed.
• A concurrent pyogranulomatous inflammation is common, especially when the wall of the cyst
is compromised, leading to the exposure of the keratin to the surrounding tissues.

Differential diagnoses
• Follicular cyst (infundibular cyst and isthmus cyst)
• Trichoepithelioma