Crystal structure of Auer rods in acute myeloblastic leukaemia (AMyL).

Ultrathin sections containing Auer rods from cases of acute myeloblastic leukaemia (AMyL) were tilted in the goniometer stage of the electron microscope and the resulting series of electronmicrographs analysed in an optical diffractometer illuminated by laser. The results showed that Auer rods of AMyL show a truly three dimensional crystal structure. Measurements from the optical diffraction patterns were consistent with a monoclinic unit cell, the unit cell edge lengths a, b, and c being 6.6 [SD) 0.5) nm, 8.6 (0.2) nm, and 9.6 (1.0) nm, respectively; the angle between a and c being 120 (7) degrees. This structure was quite distinct from the "tubular" substructure reported by others in the Auer rods of acute promyelocytic leukaemia (APL), although it was consistent with periodicities measured by others in Auer rods of AMyL. A complete understanding of the three dimensional structures of Auer rods in the different types of acute myeloid leukaemia (AML) could well prove to be of considerable diagnostic importance.