Trichoadenomas (of Nikolowski) are benign follicular tumours that usually present as slow growing dermal masses. A rare verrucous variant has been described which resembles a benign keratosis clinically.
Histology of trichoadenoma
In trichoadenoma, there is a well defined dermal mass which contains numerous cysts and epithelial strands/islands(figures 1–3). Some of the cysts may rupture and there may be inflammatory changes and calcification. The cysts are lined by a benign infundibulum-like squamous epithelium as seen in an epidermoid cyst (figure 3).
Special studies for trichoadenoma
None are generally needed.
Differential diagnosis of trichoadenoma
This tumour is highly distinctive. A similar cystic component may be seen within other tumours such as trichoepithelioma and basal cell carcinoma, but the degree of cystification is generally much more extensive in trichoadenoma.