Author: Stacey Newton BVSc FRCPath CertEM (Int Med) PhD MRCVS
A 7-year-old male neutered Labrador presented with a 2 cm raised firm mass present at the base of the right ear. It appeared not to be attached underneath and was quite mobile. Fine-needle aspirates for cytology were performed.
Cytology: This demonstrated mainly several varying sized often compressed clusters of uniform cuboidal shaped epithelial cells. They demonstrated round to oval nuclei with indistinct or occasionally small prominent nucleoli. They had low amounts of pale basophilic cytoplasm. Some of the cells showed some palisading and occasional acinar type arrangement. There was some eosinophilic amorphous material present amongst the cells. Occasional more individual spindle to polygonal shaped cells were observed as well as a few well-differentiated squamous epithelial cells. A small amount of keratin was present.
17.7x
34.5x
48.5x
Interpretation: Basilar epithelial neoplasm most likely trichoblastoma.
Further investigation: Just over 3 months later the mass was excised. It was at that time 4.4 cm in diameter. The lab received a piece of skin and tissue measuring 6.5 cm with a firm raised white mass measuring 4.6 cm.
Histology: Sections were prepared showing large expansile and discrete nodular mass located below compressed haired skin. There were interconnecting tortuous cords and nests of uniform neoplastic basal epithelial cells. The cells showed palisading along the basement membrane. The cells were uniform and arranged in cords and aggregates with some fibrovascular stroma. The mass was excised with a minimal margin of 0.5 to 1 mm at the narrowest point. Rare mitotic figures were observed.
0.3x
7.8x
29.7x
Interpretation: cutaneous trichoblastoma.
Comment
Trichoblastoma are part of a group of follicular tumours. This is a benign lesion that derives or shows differentiation to the primitive hair germ cells. This is a common tumour in dogs as well as fairly common in cats. It is most commonly seen in dogs of 4-10 years of age. Most frequent sites in the dog are head, neck and at the base of the ears. In the cat it frequently occurs on the head and the cranial half of the trunk.
Grossly they appear as solitary firm and alopecic masses which are polypoid or dome-shaped in the dog. In the cat they are usually solitary and dome-shaped.
There are different variants of this tumour including ribbon and medusoid, granular cell, solid or cystic, trabecular and spindle cell variant.
Other differentials for these types of lesions would include sweat gland adenomas, sebaceous epitheliomas, melanocytomas when they are pigmented and granular cell tumour. This last tumour is however very rare in dogs and cats.
Trichoblastomas carry a good prognosis with complete excision usually curative.
The malignant form of trichoblastoma has never been described in dogs and cats but is rarely reported in people.