The following case of trichofolliculoma was presented in a 3.5-year-old male neutered guinea pig.
The lesion was a long-standing subcutaneous mass from the right flank and consisted of a raised, firm skin lump with a pre-incised deep border measuring 45 x 42mm (Figure 1). The guinea pig was otherwise in good health and did not exhibit any other clinical signs.
When examined histologically the lesion consisted of a discrete expansile nodular mass located in the hypodermis below intact haired skin and mildly inflamed dermis. The mass had a cystic centre bordered by squamous epithelium and contained small amounts of eosinophilic secretory material (Figure 2). The bulk of the mass was composed of rudimentary proliferating follicular structures (Figure 3A), which were haphazardly arranged around primary follicles or cysts (Figure 3B).
The supporting stroma was thin and consisted of loose fibrovascular connective tissue with low numbers of inflammatory cells. The lesion compressed the surrounding connective tissue. It did not infiltrate through the panniculus muscle, and it had clear margins around it in the submitted sections.
Diagnosis and treatment
Trichofolliculoma is a very common and distinct skin tumour in the guinea pig, but it is less commonly seen in other domestic species. It can affect either sex or any age of the species. Tumours can be single or multiple and can grow up to between 4 and 5cm. They can develop anywhere on the body, although the dorsum and caudal hip area are common locations. The tumours sometimes have a central pore through which inspissated white and grey cellular debris may be expressed.
They [trichofolliculomas] can develop anywhere on the body, although the dorsum and caudal hip area are common locations.
The mass exhibits benign biological behaviour and may be regarded as a hamartoma rather than a true neoplasm. Hamartomas are regarded as malformations of tissue that retain their normal anatomical relationships, rather than an uncontrolled proliferation of a single cell line following genetic mutation. This usually results in a well-demarcated, slow-growing lesion. However, the guinea pig may overgroom these areas leading to superficial ulceration, haemorrhage and crusting with possible secondary infection; therefore, surgical excision is advised and is expected to be curative.