Skin - nonmelanocytic tumors
Adnexal tumors - hair follicles
Inverted follicular keratosis

Author: Andrew L.J. Dunn, M.D. (see Authors page)
Editor: Sara C. Shalin, M.D., Ph.D.

Revised: 18 October 2017, last major update September 2017

Copyright: (c) 2002-2017, PathologyOutlines.com, Inc.

PubMed Search: Inverted follicular keratosis [title]

Cite this page: Dunn, A. L. J. Inverted follicular keratosis. PathologyOutlines.com website. http://pathologyoutlines.com/topic/skintumornonmelanocyticinvertedfollicularkeratosis.html. Accessed October 18th, 2017.
Definition / general
  • Found on the head and neck
  • Usually affects older males
Essential features
  • Benign, usually endophytic proliferation of follicular infundibulum with squamous eddies
Terminology
  • IFK
Epidemiology
  • Older men
Sites
  • Predominantly head and neck
Etiology
  • May be irritated seborrheic keratosis, irritated verruca vulgaris or keratotic lesion that involves the infundibular region of hair follicle
Case reports
Treatment
  • Not necessary; biopsy is usually curative
Clinical images

Images hosted on other servers:

8 - 12 mm pedunculated nodule

Gross description
  • Solitary skin colored papule with or without filiform growth measuring less than 1 cm
Microscopic (histologic) description
  • Patterns include:
    • Wart-like variant
    • Keratoacanthoma-like pattern
    • Solid nodular
  • Well circumscribed endophytic growth of squamous cells with lobular extension into the dermis; exophytic lesions with a keratoacanthoma-like appearance have been described
  • Variable number of squamous eddies; may be increased secondary to irritation
  • Peripheral basaloid cells with occasional mitotic activfty
Microscopic (histologic) images

Images hosted on PathOut server:

Images contributed by Andrew L. J. Dunn

Various magnifications

Warty-like variant



Images hosted on other servers:

Various images

Positive stains
Board review question #1
Which of the following is true about inverted follicular keratosis?

  1. BCL2 is downregulated in dendritic cells
  2. Squamous eddies are an atypical finding in inverted follicular keratosis
  3. These lesions are more commonly found on the head and neck
  4. These lesions are more common in young women
Board review answer #1
C. These lesions are more commonly found on the head and neck

Bcl-2 has been found to be upregulated in the dendritic cells of IFKs but not seborrhea keratosis. IFKs are typically found on the head and neck of older males. Squamous eddies are a usual finding in IFKs.