Reinke crystals are rod-like cytoplasmic inclusions which can be found in Leydig cells of the testes. Occurring only in adult humans and wild bush rats, their function is unknown.
They are large enough to be seen in an optical microscope and can be visualized using Giemsa, trichrome, Gram, and PAS stains. Reinke crystals are rare in normal testes, but are found in approximately 1/3 of all Leydig cell tumours.
These crystals are named after the German anatomist Friedrich Berthold Reinke.
References
Reinke crystals Wikipedia(Text) CC BY-SA