Melanosome macrocomplex: an ultrastructural component of patterned and nonpatterned seborrheic keratoses

Area of Science:

• Dermatopathology
• Cell Biology
• Melanogenesis

Background:

• Seborrheic keratoses (SKs) are common benign skin tumors.
• Their pathogenesis, particularly the nature of melanin structures within them, remains incompletely understood.
• Previous studies have debated whether SKs possess nevoid characteristics.

Purpose of the Study:

• To investigate the ultrastructural characteristics of melanosomes in both patterned and randomly distributed seborrheic keratoses.
• To determine if seborrheic keratoses exhibit nevoid features at the ultrastructural level.

Main Methods:

• Ultrastructural analysis using electron microscopy.
• Examination of five patterned seborrheic keratoses from two patients.
• Examination of fifteen pigmented, randomly distributed seborrheic keratoses from five patients.

Main Results:

• Melanosome macrocomplexes, measuring 2-5 microns, were identified in all examined seborrheic keratoses.
• These macrocomplexes, consisting of clustered discrete melanosomes within membrane-bound phagosomes, were found in melanocytes, keratinocytes, Langerhans cells, and dermal macrophages.
• No melanin macroglobules (giant melanosomes) were observed.

Conclusions:

• The presence of melanosome macrocomplexes is a consistent ultrastructural finding in seborrheic keratoses.
• The absence of melanin macroglobules supports the conclusion that seborrheic keratoses, regardless of distribution pattern, are not nevoid in nature.
• These findings contribute to understanding the cellular mechanisms of melanin handling in seborrheic keratoses.