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Address for correspondence: Dr Nicholas Jufas, Kolling Deafness Research Centre, Kolling Building, Royal North Shore Hospital, St Leonards, NSW 2065, Australia E-mail: [email protected]
Dr N Jufas takes responsibility for the integrity of the content of the paper
Introduction
The protympanum is a middle-ear space anterior to the mesotympanum. It is also known as the bony portion of the Eustachian tube, and merges with the junctional then cartilaginous portions anteriorly. It joins into the epitympanum superiorly, with the superior border of the tensor tympani canal or supratubal recess (if present) marking the transition. It is confluent with the hypotympanum inferiorly with the junction marked by the protiniculum, a consistent bony ridge from the promontory to the lateral wall. The posteromedial and posterolateral borders are the tympanic branch of the glossopharyngeal (Jacobson's) nerve and the anterior annulus of the tympanic membrane respectively.1
Although the protympanum is a key anatomical region in a number of otological pathologies and operative procedures, detailed anatomy of the protympanum has often been ignored because of difficulties encountered in its complete visualisation. The increased popularity of endoscopic ear surgery has allowed objective lenses with angulation to be introduced into the middle-ear space, enabling the visualisation of regions such as the entire protympanum. In fact, quantitative analysis of the protympanum using three-dimensional modelling has demonstrated that over 90 per cent visibility is possible with endoscopes compared with 14 per cent for microscopes.2 This improved visualisation has meant that the anatomy of and anatomical features within the protympanum can now be described and categorised in detail.
The overall protympanum conformation can be quadrangular or triangular in a two-dimensional plane perpendicular to the Eustachian tube long axis.3 The demarcation between the two is based on whether the inferior wall is more or less than half of the equivalent superior wall length respectively. The lateral wall of the protympanum – from the annulus of the anterior tympanic membrane to the junctional portion of the Eustachian tube – can either be convex or concave in orientation. The protiniculum (from the Latin protinus, meaning ‘farther on’) follows from the previously described promontorial ridges of the middle ear: the ponticulus, subiculum and finiculus.4 It has three conformations: A = ridge, B = bridge and...