Following an extended radical mastoidectomy, exenteration of the inferior wall of the tympanic bone and the hypotympanic cells. Generally, at the end of this approach, abdominal fat is put into the cavity and a “blind sac” closure of the external auditory canal is carried out; however, it is also possible to leave the cavity open by performing a large meatoplasty.

It is mainly performed in cases of extensive cholesteatoma, such as petrous cholesteatoma and in cases with posttraumatic or postoperative cerebrospinal fluid leakage. The other indication is cochlear implantation or active middle ear device implantation where an open cavity procedure has previously been carried out. It is also an intermediate stage in neurotologic procedures such as infratemporal fossa “types A, B, or C” approaches or the transotic approach.

Dissection continues on the same bone on which an extended radical mastoidectomy has already been carried out. Superiorly the dural plate of the middle cranial fossa, posteriorly the dural plate of the sigmoid sinus, and inferiorly the digastic ridge have been exposed. The solid bone of the facial canal and of the three semicircular canals has also been revealed.

DR: Digastric ridge

MCF: Middle cranial fossa (dural plate)

SS: Sigmoid sinus (dural plate)

TB: Tympanic bone

The subsequent stages are specific to the subtotal petrosectomy procedure. Using a medium-sized cutting burr, the anterior and inferior walls of the tympanic bone, indicated in the previous illustration, are drilled. The burr should be revolving away from the facial nerve.

II: 3–4mm cutting and diamond burrs

MIL: Mastoid facial nerve

The tympanic bone has been drilled; the inferior wall lowered and the anterior wall thinned. Care should be taken not to enter the temporomandibular joint during this stage. A white discoloration on the temporal bone and a bluish-pink discoloration in the operation indicates the temporomandibular joint.