Skin nonmelanocytic tumor

Benign (nonmelanotic) epidermal tumors or tumor-like lesions

Inverted follicular keratosis


Editorial Board Member: Kiran Motaparthi, M.D.
Said Albahra, M.D.
Gregory A. Hosler, M.D., Ph.D.

Last author update: 27 July 2022
Last staff update: 24 January 2023

Copyright: 2002-2023, PathologyOutlines.com, Inc.

PubMed Search: Inverted follicular keratosis

Said Albahra, M.D.
Gregory A. Hosler, M.D., Ph.D.
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Cite this page: Albahra S, Hosler GA. Inverted follicular keratosis. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/skintumornonmelanocyticinvertedfollicularkeratosis.html. Accessed January 29th, 2023.
Definition / general
  • Benign tumor of the follicular infundibulum
Essential features
  • Benign, endophytic follicular tumor with characteristic presence of squamous eddies
Terminology
  • Inverted follicular keratosis (IFK)
ICD coding
  • ICD-9: 216 - benign neoplasm of skin
  • ICD-10: L82.1 - other seborrheic keratosis
Epidemiology
Sites
Pathophysiology
  • Unknown at this time
Etiology
Clinical features
Diagnosis
  • Can be made on biopsy
Case reports
Treatment
  • Biopsy is usually curative
  • Larger lesions treated by complete excision
Clinical images

Images hosted on other servers:
Pedunculated nodule in the upper cutaneous lip

Pedunculated nodule in the upper cutaneous lip

Microscopic (histologic) description
  • Well circumscribed, endophytic tumor with large lobules or finger-like extensions that resemble expanded follicles
  • Variable number of squamous eddies
  • Occasional mitoses within peripheral basaloid cells
  • Histologic variants have been described (J Cutan Pathol 1984;11:387):
    • Papillomatous wart-like: exophytic with overlying hyperkeratosis and parakeratosis
    • Keratoacanthoma-like: central exoendophytic mass
    • Cystic type: irregular clefts within tumor and formation of small cysts
Microscopic (histologic) images

Contributed by Gregory A. Hosler, M.D., Ph.D.

Silhouette

Squamous eddies

Desmoplastic features

Mucin deposition

Pseudoviral features

Positive stains
  • BCL2: positive dendritic cells are present in increased numbers in the suprabasal areas, compared to seborrheic keratosis (J Cutan Pathol 2006;33:498)
Videos

Inverted follicular keratosis:
5 minute pathology pearls

Inverted follicular keratosis with great squamous eddies

Sample pathology report
  • Skin, upper cutaneous lip, shave biopsy:
    • Inverted follicular keratosis
Differential diagnosis
  • Irritated seborrheic keratosis:
    • Presence of squamous eddies; however, lacks endophytic growth
  • Tricholemmoma:
    • Similar lobulated, endophytic architecture
    • Clear glycogenated cells, palisaded basilar layer and thickened basement membrane
  • Verruca vulgaris:
    • More exophytic than endophytic with inward curving papillomatosis, coarse hypergranulosis and koilocytes
    • Associated with human papillomavirus
Board review style question #1

Which of the following is true about inverted follicular keratosis (IFK)?

  1. BCL2 is downregulated in dendritic cells
  2. Squamous eddies are an atypical finding in IFK
  3. These lesions are more common in young women
  4. These lesions are more commonly found on the head and neck
Board review style answer #1
D. These lesions are more commonly found on the head and neck. BCL2 has been found to be upregulated in the dendritic cells of IFK but not seborrheic keratosis. IFK is typically found on the head and neck of older men. Squamous eddies are a usual finding in IFK.

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Reference: Inverted follicular keratosis
Board review style question #2

This image comes from the head of an elderly patient. What is the most likely diagnosis?

  1. Inverted follicular keratosis
  2. Poroma
  3. Squamous cell carcinoma
  4. Trichilemmoma
  5. Verruca vulgaris
Board review style answer #2
A. Inverted follicular keratosis

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Reference: Inverted follicular keratosis
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