By: Andy Fortune
Tattoo ink is an exogenous pigment found in skin that has been tattooed but can on occasion be found in associated lymph nodes. (Frieda Carson 2nd edition).
When I was approached to write a blog post, I admit I did not know much about tattoo ink and skin, except that it can be seen on histological sections. So, I referred to the trusted Frieda Carson book from school, and the pathologist I work with at Glenwood Dermatology (a division of Epiphany Dermatology). I asked Dr. Cary Chisholm to explain to me/us more in depth how tattoo ink is differentiated from other pigments found in skin. This was his response.
“To me tattoo ink is pretty easy to spot. The granules are usually black, but we see all colors depending on what color that portion of the tattoo is. The ink is superficial and located in histiocytes or in granulomas. The only pigment that may appear similar is black carbon pigment like from a pencil lead, although that pigment tends to have slightly larger granules and usually extends down into the mid or deep dermis depending on how deeply the foreign body went in. Tattoos are always in superficial dermis due to length of the tattoo needle. Other pigments are easy to differentiate - melanin is brown and finely granular. Fontana Masson will stain this black and does not stain tattoo. Iron is brown and refractile (seen best when the microscope condenser is flipped off) Prussian Blue will stain this blue and does not stain tattoo. Medication pigment tends to be brown and finely granular - usually stains with either Fontana Masson, Prussian Blue, or both. Silver pigment (in patients with Argyria) is sparse, finely granular, and brown/black. It may be seen in the dermis but is best seen around sweat glands.
Processing a specimen such as the specimen pictured above, one does not require anything special. Follow your typical processing procedure for an excision. We run all our specimens (only derm/skin) on a 6-hour processing program. The following pictures are from a case back in 2019 of a 20 something with a tattoo granuloma on his upper leg.