What are the typical presentation and treatment options for Keratoacanthoma (KA)?

Keratoacanthoma: Presentation and Treatment Options

Keratoacanthoma (KA) is a rapidly growing, well-differentiated squamoid lesion that should be surgically excised due to its clinical and histological similarities to squamous cell carcinoma and potential for aggressive behavior.

Clinical Presentation

Typical Features

• Morphology: Dome-shaped nodule with a central keratin-filled crater (crateriform architecture)
• Growth pattern: Rapid onset (typically 2-4 weeks) 1
• Size: Usually 1-2 cm, though can reach >5 cm (giant keratoacanthoma) 2
• Distribution: Predominantly on sun-exposed areas:
  • Face, scalp, ears, neck
  • Dorsal aspects of arms and hands
  • Lower extremities 3
• Demographics: Most common in elderly, fair-skinned individuals 4

Variants

• Giant keratoacanthoma: >2-3 cm in diameter, can cause destruction of underlying tissues 2
• KA en plaque/nodule: Rare variant without central crater, presenting as verrucous plaque or nodule 5
• Keratoacanthoma-type squamous cell carcinoma: Term used when histological features overlap with SCC 3

Pathophysiology and Risk Factors

Etiology

• Primary: Ultraviolet radiation exposure 4
• Other factors:
  • Chemical carcinogens
  • Trauma
  • Thermal burns
  • HPV infection (possible co-carcinogenic effect) 2
  • Immunosuppression 3

Natural History

• Typical course: Rapid growth phase followed by spontaneous regression within months 4
• Concerning features: Perineural invasion, intravascular invasion, infiltrative growth pattern 2, 4

Diagnosis

Clinical Evaluation

• Characteristic appearance: Dome-shaped nodule with central keratin plug
• Rapid growth history (weeks rather than months)
• Location on sun-damaged skin

Histopathology

• Well-differentiated squamous epithelium
• Central keratin-filled crater
• Symmetrical architecture
• Glassy eosinophilic cytoplasm
• May show concerning features like perineural invasion 2

Treatment Options

First-Line Treatment

• Surgical excision: Recommended for most KAs due to:
  • Difficulty distinguishing from SCC histologically
  • Potential for aggressive behavior
  • Provides definitive histological diagnosis 4, 1

Alternative Treatments

• Intralesional methotrexate:

  • Effective for KAs in cosmetically sensitive areas
  • Protocol: Initial debulking followed by 12.5-25 mg injections weekly
  • Complete resolution in approximately 89% of cases
  • Typically requires 2-4 injections 6

• Cryosurgery:

  • Effective for smaller lesions
  • Double freeze-thaw cycle recommended for better efficacy 3

• Curettage and electrodesiccation:

  • Suitable for smaller, well-defined lesions
  • May require multiple cycles for thicker lesions 3

Treatment Selection Considerations

1. Location:

   • Cosmetically sensitive areas (face, ears): Consider intralesional methotrexate 6
   • Periocular: Use cryosurgery with contact probe 3
   • Hands/extremities: Consider intralesional therapy 6

2. Size and depth:

   • Large or infiltrative lesions: Surgical excision preferred
   • Smaller, superficial lesions: Cryotherapy or curettage may be sufficient

3. Patient factors:

   • Elderly patients with comorbidities: Consider less invasive options 6
   • Immunosuppressed patients: More aggressive management recommended 3

Follow-up and Monitoring

• Regular skin examinations for recurrence or new lesions
• Histological evaluation of any lesion that fails to respond to treatment
• Sun protection education to prevent new lesions

Important Considerations

• KAs that fail to respond to treatment require further evaluation, including possible re-biopsy 3
• Though KAs typically regress spontaneously, treatment is recommended due to:
  • Inability to reliably distinguish from SCC clinically
  • Reports of aggressive behavior including perineural invasion
  • Potential for local tissue destruction during growth phase 1