Seborrheic keratosis

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Author: Mikael Häggström [note 1]

Gross processing of skin excisions

Gross pathologic processing of skin excisions[1][notes 1]
Lesion size
<4 mm 4 - 8 mm 9 - 15 mm
Benign appearance

Tissue selection from skin excision with lesion less than 4 mm with benign appearance.png

Tissue selection from skin excision with lesion 4-8 mm with benign appearance.png

Tissue selection from skin excision with lesion 9-15 mm with benign appearance.png

Suspected malignancy Tissue selection from skin excision with less than 4 mm suspected malignant lesion.png Tissue selection from skin excision with 4-8 mm suspected malignant lesion.png Tissue selection from skin excision with 9-15 mm suspected malignant lesion.png

In table above, each top image shows recommended lines for cutting out slices to be submitted for further processing. Bottom image shows which side of the slice that should be put to microtomy. Dashed lines here mean that either side could be used. Further information: Gross processing of skin excisions

Microscopic evaluation

Seborrheic keratosis

Typical microscopic findings in seborrheic keratosis:

  • A localized epidermal proliferation of basaloid and squamoid cells (mostly round and basaloid).[2]
  • Most commonly a dome-shaped exophytic epidermal growth, containing multiple cornified cysts.[2]
  • Melanin pigment deposition can occur.[2]

Squamous cell-like skin proliferations: Differential diagnosis

Main differential diagnoses and their characteristics:[3]

Clinically, seborrheic keratosis generally occurs in elderly patients.


The most important component is generally whether there is any evidence of malignancy. Example:

Seborrheic keratosis, low magnification.
Microscopically, squamous epithelium with hyper- and parakeratosis as well as acanthosis and multiple horn cysts. Picture is consistent with seborrhoic keratosis. No atypia. The dermis shows inflammatory infiltrates. No evidence of malignancy. The lesion is totally removed.

  See also: General notes on reporting


  1. The excision examples show a normal mole (upper row, benign appearance) and a superficial basal cell carcinoma (lower row, suspected malignancy).
  1. For a full list of contributors, see article history. Creators of images are attributed at the image description pages, seen by clicking on the images. See Patholines:Authorship for details.
  2. - Buschke–Löwenstein tumor is an alternative name for verrucous squamous cell carcinoma in the ano-genital region.
    - Carcinoma cuniculatum is a characteristic form of verrucous squamous cell carcinoma on the sole.
  3. Inverted follicular keratosis is generally thought to be a rare variant of seborrheic keratosis, but this position is not universally accepted.
    - Karadag, AyseSerap; Ozlu, Emin; Uzuncakmak, TugbaKevser; Akdeniz, Necmettin; Cobanoglu, Bengu; Oman, Berkant (2016). "Inverted follicular keratosis successfully treated with imiquimod ". Indian Dermatology Online Journal 7 (3): 177. doi:10.4103/2229-5178.182354. ISSN 2229-5178. 

Main page


  1. There are many variants for the processing of skin excisions. These examples use aspects from the following sources: ". Ochsner J 5 (2): 22–33. 2003. PMID 22826680. PMC: 3399331. Archived from the original. . 
    - With a "standard histologic examination" that, in addition to the lesion, only includes one section from each side along the longest diameter of the specimen.
    - It also shows an example of circular coverage, with equal coverage distance in all four directions.
    - The entire specimen may be submitted if the risk of malignancy is high.
  2. 2.0 2.1 2.2 Weidner, Noel (2009). Modern surgical pathology . Philadelphia, PA: Saunders/Elsevier. ISBN 978-1-4160-3966-2. OCLC 460883320. 
  3. Initially copied from: Paolino, Giovanni; Donati, Michele; Didona, Dario; Mercuri, Santo; Cantisani, Carmen (2017). "Histology of Non-Melanoma Skin Cancers: An Update ". Biomedicines 5 (4): 71. doi:10.3390/biomedicines5040071. ISSN 2227-9059. 
    "This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ("

Image sources