Surgical anatomy and pathology of the middle ear

Abstract

Middle ear surgery is strongly influenced by anatomical and functional characteristics of the middle ear. The complex anatomy means a challenge for the otosurgeon who moves between preservation or improvement of highly important functions (hearing, balance, facial motion) and eradication of diseases. Of these, perforations of the tympanic membrane, chronic otitis media, tympanosclerosis and cholesteatoma are encountered most often in clinical practice. Modern techniques for reconstruction of the ossicular chain aim for best possible hearing improvement using delicate alloplastic titanium prostheses, but a number of prosthesis-unrelated factors work against this intent. Surgery is always individualized to the case and there is no one-fits-all strategy. Above all, both middle ear diseases and surgery can be associated with a number of complications; the most important ones being hearing deterioration or deafness, dizziness, facial palsy and life-threatening intracranial complications. To minimize risks, a solid knowledge of and respect for neurootologic structures is essential for an otosurgeon who must train him- or herself intensively on temporal bones before performing surgery on a patient.

Keywords: Surgical anatomy; facial nerve; middle ear; otitis media; tympanic membrane.

Figure 1

A perforation in the tympanic membrane is closed with a perichondrium transplant in underlay technique, with the transplant being stabilized on the bony ear canal to prevent dislocation.

Figure 2

Development of a cholesteatoma: keratinizing squamous epithelium advancing from the superior TM into the epitympanic recess of the middle ear (schematic drawing without TM).

Figure 3

A defect of the of the long incus process is bridged with an angular titanium prosthesis. Some surgeons also use a drop of bone cement, but long‐term stability, especially at its contact zone at the incus necrotic bone, is obscure.

Figure 4

If the incus is defect, a partial ossicular replacement prosthesis (PORP) is inserted between TM (with or without contact to the malleus) and stapes.

Figure 5

If the stapes suprastructure is defect, a total ossicular replacement prosthesis (TORP) connects the malleus handle/TM with the stapes footplate.

Figure 6

In patients suffering from high grade sensorineural hearing loss or complete deafness, a cochlear implant electrode is inserted into the cochlea to directly stimulate the acoustic nerve. Prior to insertion of the electrode via the round window into the scala tympani, the bony lip of the round window has to be drilled away to fully expose the round window membrane.

Figure 7

In otosclerosis, the ankylosed stapes is replaced by a piston prosthesis which is attached to the incus long process and its piston inserted into the inner ear perilymph through a perforation in the stapes footplate.

Figure 8

Picture of a temporal bone. A posterior tympanotomy (PT) is drilled as a triangular passage from the mastoid to the tympanic cavity, bordered by the facial nerve (FN) and the chorda tympani (arrow). I, Incus; LSC, lateral semicircular canal; JB, jugular bulb, TM, tympanic membrane.