Reinke crystals are rod-like cytoplasmic inclusions which can be found in Leydig cells of the testes.
Luteinized thecomas and stromal Leydig cell tumors are indistinguishable except for the presence of crystalloids of Reinke in the latter.
[3][4][5] Another ovarian tumor where Reinke crystalloids were noted is the Brenner tumour, an epithelial-stromal ovarian tumor distinguishable by nests of transitional epithelial cells (urothelial) with longitudinal nuclear grooves (coffee bean nuclei) in abundant fibrous stroma.
[8] They are large enough to be seen in an optical microscope and can be visualized using Giemsa, trichrome, Gram, and PAS stains.
[9] Reinke crystals are rare in normal testes, but are found in approximately one third of all Leydig cell tumours.