Rainbow pattern in Kaposi's sarcoma under polarized dermoscopy: a dermoscopic pathological study.

Area of Science:

• Dermatology
• Oncology
• Pathology

Background:

• Kaposi's sarcoma (KS) exhibits distinct dermoscopic features, including a bluish-reddish hue, scaly surface, brown globules, and the characteristic multicoloured 'rainbow pattern'.
• Previous findings highlight the rainbow pattern as a potentially significant diagnostic marker in KS.

Purpose of the Study:

• To ascertain the diagnostic significance of the dermoscopic rainbow pattern in Kaposi's sarcoma.
• To investigate the association between the rainbow pattern and the specific vascular architecture of KS.

Main Methods:

• Polarized light dermoscopy was employed to examine over 100 KS lesions from seven patients and 63 other cutaneous tumours.
• KS lesions with and without the rainbow pattern were excised for comparison of dermoscopic features with histopathology.
• Histological features of other vascular tumours were also analyzed, alongside pre- and post-treatment assessments in one KS patient.

Main Results:

• The rainbow pattern was identified as a highly specific dermoscopic feature for Kaposi's sarcoma.
• Histological analysis revealed a vascular lumen-rich, 'back-to-back' vascular structure in KS lesions exhibiting the rainbow pattern.
• KS lesions lacking the rainbow pattern showed a vascular lumen-poor structure; other vascular tumours did not display the rainbow pattern.

Conclusions:

• The dermoscopic rainbow pattern in Kaposi's sarcoma correlates with the vascular lumen-rich histological subtype.
• This pattern is absent in the vascular lumen-poor subtype and resolves upon complete tumor removal.
• The arrangement of vessels within KS is a key determinant for the presence of the rainbow pattern on polarized dermoscopy.