Foramen singulare

The foramen singulare, also known as the singular foramen or singular canal, is a thin channel within the petrous temporal bone that carries the singular nerve from the internal auditory canal. It is a normal structure that may be mistaken for a temporal bone fracture (i.e., it is a pseudofracture) ^4,6.

Gross anatomy

The foramen arises from the posteroinferior aspect of the fundus of the internal auditory canal, i.e., medial to the inferior vestibular area (one of the four quadrants of the internal auditory canal fundus). The opening is approximately 2 mm medial to the transverse or falciform crest ^2,3. Its total length is around 4 mm ⁵. The canal ends at the ampulla of the posterior semicircular canal.

It carries the singular nerve, which is also known as the posterior ampullary nerve and is a branch of the inferior vestibular nerve that carries afferent information from the posterior semicircular canal ².

It is a surgical landmark during the retrosigmoid approach to the internal auditory canal, in which the posterior wall is removed up to the point of the singular canal but no further to avoid fenestration of the labyrinth ⁷.