Radiology of the petromastoid canal

The petromastoid canal is a thin structure that connects the mastoid antrum with the posterior cranial fossa and houses subarcuate blood vessels and prolongation of the dura. The current retrospective study was designed to investigate radiology of the petromastoid canal in different age groups and to determine whether increasing the scanner's resolution could enhance the detection capability of this structure.

Axial sections of 504 high-resolution computed tomographic images obtained with 0.6-, 1.1-, or 1.3-mm-thick slices through the petrous bones were reviewed. Sixteen asymmetric images were excluded from the statistical analysis. Type I petromastoid canal was invisible; Type II and Type III appeared as thin channels less than 0.5 and 0.5 to 1 mm in width, respectively, and Type IV was greater than 1 mm wide.

The petromastoid canal Type II was detected more frequently in patients older than 5 years (p<0.0001) and Type IV was demonstrated more often in children up to age 5 years (p<0.0001). The occurrence of a Type I petromastoid canal was not dependent on the age of the patients or the resolution of the images (p=0.82). Increasing the resolution failed to improve the visibility of the petromastoid canal or the ability to detect it. A wide petromastoid canal (>2 mm) was significantly more common in younger patients (22.2% versus 2.4% in the older group) (p<0.0001). A petromastoid canal beginning medially directly from the internal auditory canal was detected in 4 of 488 (0.8%) images. The lateral opening of the petromastoid canal can be found posteriorly to the medial orifice, anteriorly to it, or at the same level. The posterior lateral opening was demonstrated to be more common than the other two types in patients younger than 5 years, and the anterior opening was detected more frequently in older patients (p=0.0006).

The shape and width of the petromastoid canal differ radiologically between populations younger and older than 5 years of age. The findings of the current study may be important for otolaryngologists engaged in cochlear implantation or involved in treating otogenic intracranial complications, especially in young children.