Pilar sheath acanthoma – pathology

Pilar sheath acanthoma falls within the group of benign follicular tumours and represents a proliferation arising from follicular infundibulum and isthmus regions.

Histology of pilar sheath acanthoma

Scanning power view of the histology of pilar sheath acanthoma demonstrates a small invaginating epidermal process (figure 1). A widened follicular infundibulum ends in acanthotic bulbous protrusions into the adjacent and underlying dermis (figure 2). The outer root sheath proliferation has infundibular differentiation superficially with keratohyaline granule formation (figure 2). Inferiorly the tumour shows follicular isthmus differentiation where the corneocytes take on a deeper red-pink colour (figure 3).

Pilar sheath acanthoma – pathology

Figure 1

Figure 2

Figure 3

Differential diagnosis of pilar sheath acanthoma

Dilated pore of Winer: in this tumour there is only a minor degree of radiating hyperplastic epithelium.

Trichofolliculoma: radiating hair follicles in variable states of maturity are seen to extend from the central dilated pore or cystic structure.

Draft 15 November 2010