Absence of Bone over the Geniculate Ganglion

D ANDY recognized that the geniculate ganglion occasionally protrudes through a congenital defect in the roof of the petrous temporal bone. In their book on trigeminal neuralgia, Stookey and Ransohoff 16 noted that in rare instances the petrous bone is defective over the geniculate ganglion. This fact has been considered of such minor significance that it is largely disregarded in descriptions of neurosurgical procedures for treatment of trigeminal neuralgia in which the roof of the petrous temporal bone may be exposed, and it is not among the anatomical variants listed in standard anatomy textbooks, 9,x3 although it has been mentioned in the otological literature. House and Crabtree 1~ reported the incidence of this bony anomaly to be 5 %, presumably on the basis of their clinical material. Batson 3 stated that the geniculate ganglion is not covered by bone in early childhood. This project was undertaken to evaluate the incidence of dehiscence of bone over the geniculate ganglion in the adult and to make available an adequate photographic display of the phenomenon.