At a glance

Described by: William House (1961)
Targets: IAC, labyrinthine facial nerve, tegmen, petrous apex
Position: Supine, head turned; surgeon at the head
Key landmarks: Middle meningeal artery, GSPN, arcuate eminence
Main risks: Facial nerve, temporal lobe retraction, hearing

Overview and history

William House described exposure of the internal auditory canal through the middle cranial fossa in 1961^[1]. Through a small temporal craniotomy the dura is elevated from the floor of the middle fossa and the roof of the IAC is drilled, allowing removal of intracanalicular tumours without entering the labyrinth.

Indications

Small vestibular schwannomas confined to the IAC or with minimal CPA extension, in patients with good hearing.
Facial-nerve decompression and facial-nerve schwannomas of the labyrinthine and geniculate segments.
Repair of tegmen defects with encephalocele or CSF leak, and superior semicircular canal dehiscence.
As the first part of an extended (Kawase) middle fossa approach^[2].

Surgical anatomy

On the middle fossa floor, the middle meningeal artery enters through the foramen spinosum; medial and posterior to it the GSPN runs forward from the facial hiatus. The arcuate eminence marks approximately the superior semicircular canal. The IAC lies along the line bisecting the angle between the GSPN and the arcuate eminence. At the lateral end of the IAC the facial nerve lies anterosuperior, separated from the superior vestibular nerve by the vertical crest (Bill's bar), and the cochlea is just anterior to the fundus^[3].

Operative steps

Temporal craniotomy, about 4–5 cm, centred over the root of the zygoma and two-thirds in front of the external auditory canal.
Elevate the dura from posterior to anterior; identify the middle meningeal artery, the GSPN and the arcuate eminence.
Find the IAC medially, where it is furthest from the cochlea and the labyrinth, and drill its roof laterally toward the fundus.
Open the dura of the IAC along its posterior part, identify the facial nerve and remove the tumour from the vestibular nerves.
Close with a muscle or fat plug over the opened canal; seal opened air cells.

Complications and how to avoid them

Facial weakness: the facial nerve lies on top of the tumour in this exposure; handle it as little as possible.
Hearing loss from cochlear or labyrinthine injury or from loss of the cochlear blood supply.
Temporal-lobe retraction injury, aphasia (dominant side) or seizures.
CSF leak through opened air cells.

Take-home

Surgical pearls

Lift the dura from back to front to protect the geniculate ganglion.
Locate the IAC medially, where the margins of safety are widest.
Best for small intracanalicular tumours and good hearing; not for large CPA tumours.

References

General education for medical professionals. It summarises published literature and is not advice for any individual patient or a substitute for supervised surgical training.

Middle Fossa