Skin nonmelanocytic tumor

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Contributed by Monika Bhatt, M.D.

• Hypertrophic scar:
  • Does not grow outside of wound margins
  • Can regress on its own
  • Does not contain keloid type collagen bundles on histological exam (Weidner: Modern Surgical Pathology, 2nd Edition, 2009)
    • Lacks hyalinized collagen fibers
    • More delicate fibrillar collagen
• Dermatofibroma:
  • Positive dimple sign on physical exam; lesion develops a central depression when lateral pressure is applied
    • Coloration includes a central patch and surrounding delicate pigment network
  • More common on the lower legs
  • No history of preceding trauma
  • Greater cellularity compared to keloid
• Dermatofibrosarcoma protuberans:
  • No history of trauma
  • Harbors translocation t(17;22)(q22;q13) that results in a COL1A1::PDGFB fusion gene
  • Most commonly found on the chest, shoulders and limbs
  • Greater cellularity and more irregular borders, compared to keloid (StatPearls: Keloid [Accessed 31 May 2024])
  • Rare and locally aggressive spindle cell tumor
  • Keloidal variants (morphea and scleroderma); progression of disease, no history of trauma and may show signs of connective tissue disease
• Xanthoma disseminatum (StatPearls: Keloid [Accessed 31 May 2024]):
  • Rare, histiocytic proliferation showing lesions that resemble keloid
  • Lesions show a diffuse symmetric pattern
  • May result in development of diabetes insipidus
• Lobomycosis:
  • Fungal infection caused by Lacazia loboi
  • Usually found on the distal extremities
  • History of exposure to dolphins or rural soil in Central and South America
  • Microscopically granulomatous inflammation with giant cell reaction is seen
  • PAS and silver stain highlight the fungal organisms

A mass forming nodule is excised from a patient's ear. Histological findings are shown in the image above. What is the diagnosis?

1. Dermatofibroma
2. Dermatofibrosarcoma protuberans
3. Hypertrophic scar
4. Keloid

D. Keloid. The image above shows a nodular bundle of keloidal collagen within the reticular dermis. The collagen bundles are thick eosinophilic bands arranged in a nodular or haphazard pattern, a characteristic finding in keloids. Also, the ear is the most common site for keloid formation. Answer C is incorrect because hypertrophic scars would have fewer thick collagen fibers. Answer A is incorrect because dermatofibromas are more common on the lower extremities and would show greater cellularity. Answer B is incorrect because dermatofibrosarcoma protuberans are most commonly found on the chest, shoulders and limbs and would demonstrate greater cellularity and irregular borders.

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Reference: Keloid

Which of the following commonly occurs after excision of a keloid?

1. Complete resolution
2. Increase in propensity for development of squamous cell carcinoma
3. Melanoma in situ
4. Recurrence

D. Recurrence. Keloids are a benign entity that are known to have the potential to recur after surgical excision. Therefore, intralesional steroids or radiotherapy in conjunction with surgical management is usually the treatment of choice to prevent recurrence. Answers B and C are incorrect because keloids are not known to have malignant transformation or an increased propensity for cancer. Answer A is incorrect because recurrence is common despite treatment.

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Reference: Keloid

Which of the following is a key difference between keloids and hypertrophic scars?

1. Keloids grow beyond the wound site
2. Keloids have an increased propensity for malignant transformation
3. Keloids never recur after treatment
4. Keloids occur exclusively in pigmented skin

A. Keloids grow beyond the wound site. On gross examination, keloids grow beyond the site of initial injury, while hypertrophic scars remain confined to the wound margins. Answer D is incorrect because keloids can occur in all skin types although individuals with darker pigmented skin are more prone to keloid formation after skin trauma. Answer C is incorrect because keloids can recur after treatment. Answer B is incorrect because keloids are benign skin lesions and do not have a propensity for malignant transformation.

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Reference: Keloid