The subarcuate, or petromastoid, canal is a thin channel connecting the posterior cranial fossa with the mastoid antrum. It contains the subarcuate artery and prolongation of the dura mater [1] and travels horizontally in the mastoid bone, parallel to the internal auditory canal and through the loop of the superior semicircular canal (Fig. 1). The narrow, elongated adult appearance is attained by 5 years of age [1]. A wide subarcuate canal (>2 mm) in a child is a normal variant and should not be mistaken for pathology. It can be clinically significant because it can be a route for spreading middle ear infections intracranially or a site of postsurgical or post-traumatic bleeding or CSF leak [1, 2].

Fig. 1
figure 1

An axial temporal bone CT in a 21-day-old child shows prominent subarcuate canals (arrows) measuring 4 mm, which pass through the superior semicircular canals (arrowheads)

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