CT findings in the different surgical procedures performed in chronic middle ear disease including cholesteatoma have been well illustrated by Mukherji et al.; diagrams of the procedures are shown below, courtesy of the author (Mukherji et al. 1994). Surgical procedures for cholesteatoma can be broadly classified as closed cavity or canal-wall-up (CWU) mastoidectomy/tympanoplasty or open cavity or canal-wall-down (CWD) mastoidectomy depending on whether the posterior wall of the external auditory canal (EAC) is preserved. The choice of technique is usually determined by the extent of the disease and the experience and personal preferences of the surgeon (Majithia et al. 2012; Ayache et al. 2012). Defining the true extent of cholesteatoma and staging disease using non-EPI DWI can help the surgeon with his choice of surgery and surgical approach (Majithia et al. 2012). Both types of procedure have their advantages and disadvantages (Khemani et al. 2011). When possible, CWU is the procedure of choice for the treatment of cholesteatoma for most otologic surgeons (Brackmann 1993). CWU techniques preserve the anatomy of the posterior canal wall, eliminating the need for periodic bowl cleaning and avoiding the risk of recurrent bowl infections. The mastoid air cells including Koerner’s septum are removed. In this manner, communication of the surgically created cavity (mastoid bowl) with the antrum and epitympanum is established (Fig. 2). A major disadvantage of CWU procedures is less wide surgical exposure with a subsequent higher rate of residual (35 %) and recurrent (18 %) cholesteatomas (Stasolla et al. 2004). In children, these percentages may be even higher as a more aggressive behaviour of cholesteatomas is observed. Another disadvantage of CWU mastoidectomy is the limited possibility of clinical and otoscopical evaluation. This is why some institutions promote a more rigorous follow-up and a rapid second-look surgery (Plouin-Gaudon et al. 2010a). In case of CWD mastoidectomy, the posterosuperior wall of the EAC is removed, allowing communication between the mastoid cavity and the EAC. Further access to the middle ear cavity is created, depending on the extent of disease encountered. If disease is limited to the epitympanum, only the scutum needs to be resected and the ossicular chain can be preserved (Fig. 3). When the ossicular chain is involved in the disease process, a radical mastoidectomy is performed. The tympanic membrane is detached from its annulus and the mastoid segment of the facial nerve canal is skeletonised allowing wide access to the middle ear cavity (Fig. 4). However, the stapes superstructure is left in place whenever possible. Complete posterior canal wall removal provides exposure of the entire attic and middle ear, helping to ensure complete disease eradication. This approach can reduce the residual and recurrence rate to as low as 2 %. The CWD procedure is nowadays preserved for repeatedly recurrent disease with difficult to treat cholesteatoma and for patients with high risk of getting lost in follow-up. A major disadvantage of the CWD technique is the accumulation of debris in the exteriorised mastoid cavity, requiring periodic cleaning and, on occasion, water restrictions to prevent bowel infections. The CWD technique also provides for removal of the nitrogen-absorbing mucosa of the mastoid. After surgery, the new epithelial lining of the mastoid bowl is a stratified keratinizing epithelium. In the CWU procedure, the mastoid retains its native cuboidal nitrogen-absorbing epithelium. Eustachian tube dysfunction could result in reaccumulation of secretory middle ear effusion and retraction of the posterior superior quadrant of the tympanic membrane, causing recurrent cholesteatoma (Gantz et al. 2005). In order to avoid this problem, a bony obliteration technique has been advocated. The advantages of the procedure include providing increased intraoperative exposure (similar to a CWD technique), removal and obliteration of the nitrogen absorbing mastoid epithelium with bone pâté, and reconstruction of the posterior canal wall. The procedure is designed to prevent development of post-operative retraction pockets and recurrences by obliterating the mastoid cavity and isolating the tympanum from the attic and mastoid using bone chips and bone pâté (Mercke 1987). Although primary bony obliteration provides excellent results with low recurrence rates, it also carries with it the risk of obliterating and obscuring residual cholesteatomas. Follow-up by means of imaging using non-EPI DWI MRI is mandatory to prevent late complications after possible obliteration of residual cholesteatomas (De Foer et al. 2007, 2010).

Tympanoplasty is a technique to reconstruct the conductive hearing system, i.e. the tympanic membrane and/or the ossicles. Five types of tympanoplasty have been defined by Wullstein (Swartz and Harnsberger 1998). Routine post-operative imaging studies are not required after simple myringoplasty (type I tympanoplasty). However, when imaging is performed within the first weeks after the procedure, a thickening of the tympanic membrane can be noticed, as well as a middle ear effusion. In type II tympanoplasty the malleus is bypassed and the graft connects directly to the body of the incus. In type III tympanoplasty the graft attaches to the capitulum of the stapes, in type IV tympanoplasty to the footplate of the stapes and in type V tympanoplasty the graft attaches to the oval window.

Ossicular reconstructions are commonly performed in patients with extensive cholesteatoma with involvement of the ossicular chain, as well as in patients with tympanosclerosis, otosclerosis or congenital ossicular malformations. Initially, cartilage and temporalis fascia have been used, before the introduction of allografts. Allografts gained wide acceptance, especially in Europe. The main reason for using allografts is their excellent biocompatibility. However, they require time and skill for sculpting and availability may be a problem. Moreover, they may harbour foci of cholesteatoma and a growing risk of transmitting infectious diseases, such as Creutzfeld-Jacob and AIDS, have been mentioned (Stone et al. 2000). For all these reasons, synthetic prostheses have been developed. Prostheses most commonly used for ossicular reconstructions include stapes prostheses for otosclerosis (Fig. 5), incus interposition auto- or homografts (Fig. 6), partial ossicular replacement prostheses (PORP) and total ossicular replacement prostheses (TORP) (Fig. 7).

Otological evaluation of patients who have undergone ossicular reconstruction is often difficult. CT can be helpful in demonstrating prosthetic failure (recurrent cholesteatoma, granulation tissue, adhesions or mechanical problems) that may cause post-operative CHL and identify patients in whom revision surgery must be considered (Stone et al. 2000).

Many diseases and dysplasias can affect the osseous components of the temporal bone. Some diseases such as otosclerosis are limited to the temporal bone and do not occur elsewhere in the body (Hasso et al. 1996). The term ‘otosclerosis’ was introduced by Adam Politzer, who described the histopathological findings in 1894 (Declau et al. 2001). Otosclerosis occurs in two phases: an early, active phase, during which bone resorption occurs (otospongiotic stage) and a later, inactive phase (sclerotic stage). Diagnosis of otosclerosis is based on clinical findings, audiometric testing and family history, but medical imaging is often demanded to confirm the diagnosis (Nowé et al. 2004). The typical clinical features of otosclerosis are gradually increasing hearing loss (HL), most frequently occurring between the third and fifth decades. Although usually both ears are affected, often there is an asymmetry in HL with one ear showing a greater conductive impairment. Tinnitus is a common symptom and it may become louder as the HL progresses. The origin of the tinnitus is not clear but it may be the result of cochlear degeneration or an abnormal degree of vascularity within the labyrinthine capsule. Vertigo is rare and is probably the effect of toxic enzymes on the vestibular labyrinth (de Bruijn 2000). In otosclerosis, three major patterns of involvement are discerned: fenestral, retrofenestral and mixed. First, a purely fenestral type, which involves the oval window, most commonly the anterior aspect in the approximate location of the embryologic fissula ante fenestram. The second type is a retrofenestral (cochlear) form, primarily involving the cochlea, with SNHL as a result. Both types of otosclerosis may coexist in one patient, resulting in mixed hearing loss (d’Archambeau et al. 1990).