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Inverted follicular keratosis
Other Resources UpToDate PubMed

Inverted follicular keratosis

Contributors: Reba Suri MD, Susan Burgin MD
Other Resources UpToDate PubMed

Synopsis

An inverted follicular keratosis (IFK) is a rare, benign neoplasm that typically presents as a single asymptomatic, exophytic, smooth or verrucous papule on the face or neck of a middle-aged or elderly man. It most commonly presents in the seventh decade of life, with a male to female ratio of 2:1. Lesions can be present for anywhere from 6 weeks to 3 years in most cases. An IFK, while benign, can mimic cutaneous malignancies clinically, necessitating further evaluation. Although the etiology is not completely understood, the most widely accepted theory is that an IFK arises from the follicular infundibulum. Others believe that it is a variant of an irritated seborrheic keratosis.

Codes

ICD10CM:
L82.1 – Other seborrheic keratosis

SNOMEDCT:
394728005 – Inverted keratosis

Look For

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Diagnostic Pearls

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Differential Diagnosis & Pitfalls

  • Squamous cell carcinoma (SCC) – IFK can resemble SCC clinically and histologically. Squamous eddies can be confused with keratin pearls seen in SCC; the absence of dysplasia rules out SCC. The well-defined basal palisading seen in IFK also makes this diagnosis less likely.
  • Keratoacanthoma (KA) – A central keratinous plug can be seen histologically in both IFK and KA, but the well-circumscribed borders and absence of atypical cells and infiltrative growth make this diagnosis less likely.
  • Seborrheic keratosis – IFKs can resemble seborrheic keratoses clinically. Histologically, however, seborrheic keratoses are exophytic lesions that do not have a tendency to project inward.
  • Verruca vulgaris – Both IFK and verruca vulgaris are papillomatous lesions. However, squamous eddies are not present in verrucae on histology.
  • Trichilemmoma – Trichilemmoma and IFK share several histologic findings, including basal palisading at the periphery of the lesion. However, squamous eddies are typically absent in trichilemmoma.

Best Tests

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Management Pearls

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Therapy

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References

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Last Reviewed:05/17/2020
Last Updated:05/31/2020
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Inverted follicular keratosis
A medical illustration showing key findings of Inverted follicular keratosis
Copyright © 2022 VisualDx®. All rights reserved.