Inverted Follicular Keratosis
Senait W. Dyson, MD
David Cassarino, MD, PhD
Key Facts
Terminology
Inverted follicular keratosis (IFK)
Benign tumor of follicular infundibulum
Clinical Issues
Common benign tumor found mostly in men
90% on head and neck
Microscopic Pathology
Hyperkeratosis and parakeratosis
Endophytic papillomatous proliferation of epithelium
Numerous squamous eddies are typically present and are characteristic feature
Mitotic figures present in basaloid cells
No significant cytologic atypia or pleomorphism
Top Differential Diagnoses
Irritated seborrheic keratosis
Well-differentiated squamous cell carcinoma
 Inverted follicular keratosis (IFK) is a well-circumscribed, endophytic epithelial proliferation. This tumor shows multiple connections to the epidermis  , and multiple folliculocystic structures (similar to milia) are present  . |
 High magnification of the center of this lesion shows bland squamoid cells surrounding small follicular lumina and smaller, peripheral, more basaloid-appearing cells  . |
TERMINOLOGY
Abbreviations
Inverted follicular keratosis (IFK)
Synonyms
Irritated seborrheic keratosis variant
Definitions
Benign tumor of follicular infundibulum considered by many to be identical to irritated seborrheic keratosis
ETIOLOGY/PATHOGENESIS
Etiology
Lesions arise from follicular infundibula, which explains the downward proliferation of these lesions
IFK is considered to be identical to seborrheic keratosis derived from follicular infundibulum instead of surface epidermis
Epithelium of follicular infundibulum has the same histology and keratinization as surface epidermis
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