At a glance

Exposes: Sigmoid sinus, tegmen, presigmoid dura, facial nerve
Key landmarks: Mastoid antrum, lateral canal, digastric ridge
Hearing: Preserved (labyrinth intact)
Uses: Tegmen repair, presigmoid access, jugular bulb
Main risks: Facial nerve, labyrinth, sigmoid sinus

Overview

A cortical mastoidectomy removes the air cells of the mastoid process to expose the middle fossa dura (tegmen) above, the sigmoid sinus behind, and the presigmoid posterior-fossa dura (Trautmann's triangle) medially, while leaving the otic capsule intact. On its own, it is used to repair tegmen defects and to drain or reach lesions of the mastoid; as part of larger approaches, it is the first stage of retrolabyrinthine, translabyrinthine, transcochlear and infratemporal fossa approaches^[1].

Indications

Repair of tegmen mastoideum and tegmen tympani defects with CSF otorrhoea or encephalocele, often combined with a middle-fossa craniotomy^[2].
Retrolabyrinthine presigmoid exposure for CPA and petroclival lesions with hearing preservation, and for some MVDs.
Exposure of the sigmoid sinus and jugular bulb for venous pathology and paragangliomas.
Infections of the mastoid with intracranial extension.

Surgical anatomy

MacEwen's (suprameatal) triangle on the lateral surface overlies the mastoid antrum. The lateral semicircular canal in the floor of the antrum is the key landmark for the second (tympanic–mastoid) genu of the facial nerve, which lies just anterior and inferior to it. The digastric ridge points to the stylomastoid foramen. Trautmann's triangle, the presigmoid dura between the superior petrosal sinus, the sigmoid sinus and the labyrinth, is the window into the posterior fossa used in presigmoid approaches.

Operative steps

Postauricular incision; expose the mastoid cortex, the spine of Henle and the temporal line.
Drill with large cutting burrs and continuous irrigation, saucerising the edges.
Identify the tegmen, the sigmoid sinus and the antrum; find the lateral semicircular canal.
Follow the digastric ridge to the stylomastoid foramen and outline the course of the facial nerve.
For presigmoid exposure, skeletonise the sigmoid sinus and open the dura of Trautmann's triangle.
Close with fat and fascia when the dura has been opened; plug the aditus if the middle ear is to be isolated.

Complications

Facial-nerve injury, avoided by early identification of the lateral canal and digastric ridge and use of monitoring.
Sensorineural hearing loss and vertigo from opening the labyrinth.
Sigmoid sinus tear or thrombosis.
CSF leak and wound complications.

Take-home

Surgical pearls

The lateral semicircular canal is the compass of the mastoid.
Use the largest burr that fits and saucerise to keep the view open.
A small, thin-walled tegmen defect is often associated with intracranial hypertension.

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.

Transmastoid