I was sitting on the beach in front of the clear blue water of the Mediterranean Sea in the amazing Almaza Bay, North Coast, Egypt when I was thinking about a topic to write in this blog. The magnificent color of the sea triggered me to think about things presenting with blue color in dermatopathology practice. I thought of recollecting them in this blog.

The first thing that I remembered was sea blue histiocytosis, a condition that I have never seen!! where the histiocytes are increased in size with sea blue colored cytoplasm with many tiny vacuoles best perceived by May-Giemsa stain. A lovely grey blue color is also seen in the large keratinocytes of EDV which always have fascinated me with their characteristic color.

Mucinous deposits in the skin with all its various forms presents with a bluish color in H&E sections. Calcium deposits and calcified elastic fibers also appear blue. Moreover, foreign materials such as fillers, particularly hyaluronic acid, appear as blue deposits in the dermis. Also light blue is the color of solar elastosis. Hematoxylin precipitates are also a cause of blue deposits that might be seen during H&E slide examination.

In addition to all basaloid cell tumors which appear blue, the designation as blue cell colored tumors goes to a very important group of tumors which are the small blue cell tumors mainly including lymphomas, melanomas, MCC and neuroendocrine tumors.

Some bacterial structures and fungal structures may also appear blue.

[center] Did I miss any other blue things in our practice??!![/center]