Table 4.

Histologic differential diagnoses for fibroadnexal hamartoma.

Differential diagnosis	Similar features	Different features
Keratoacanthoma (“Infundibular Keratinizing Acanthoma”	Follicular origin cystic or crateriform features	Lacks sebaceous component
		Lacks mesenchymal component
Squamous papilloma	Exophytic presentation	Lacks cystic follicular presentation
		Lacks mesenchymal component
		Lacks cystic follicular presentation
Sebaceous adenoma	Presence of multiple large lobules of sebaceous cells	Lacks exuberant mesenchymal component
		Lacks cystic follicular presentation
Sebaceous hyperplasia	Mature sebaceous component	Lacks mesenchymal component
		Lacks cystic follicular presentation
Basal cell tumor, benign	Dense fibrous stroma may be present	Basal cells predominate
		Lacks sebaceous epithelial component
		Lacks cystic follicular presentation
Trichoepithelioma	Follicular origin	Lacks sebaceous epithelial component
		Formation of rudimentary hair follicles (+/−)
Fibroma	Proliferative fibroblastic component	Lacks sebaceous epithelial component
		Lacks cystic follicular presentation
Sebaceous trichofolliculoma	Cystic follicular presentation	Depressed lesion with surface opening
	Sebaceous component	Lacks exuberant mesenchymal component typically well-demarcated
		Collagenous stroma of low cellularity
		Hair shafts have cystic follicular lumen rudimentary hair follicles (+/−)
Pilomatricoma	Follicular origin	“Ghost” cells
		Lacks mesenchymal component
		Lacks sebaceous epithelial component
Tricholemmoma	Follicular origin	Lacks mesenchymal component
		Lacks sebaceous epithelial component