The SSC is located just beneath the middle cranial fossa plate. The superior end of the PSC joins the superior semicircular canal (SSC), forming the common crus. Its ampulla is located at its inferior end, just medial to the facial nerve. The PSC courses nearly in parallel with the posterior fossa dura. The posterior semicircular canal (PSC) lies just posterior to the LSC, and the posterior edge of the LSC points almost the center of the PSC. Other two semicircular canals are sited nearly perpendicularly to the LSC. The ampulla is located in the medial wall of the posterior attic. At the anterior end of the LSC is the ampulla that accommodates sensory cells and opens to the utricles. However, due to its proximity to the antrum, the LSC is the most vulnerable labyrinth to pathologies that erodes the medial wall of the antrum such as cholesteatoma. The bony capsule of the labyrinth is compact and hard, and more resistant to bone erosion. The prominence of the LSC in the medial wall of the antrum is sloping about 30 degrees, running from anterosuperior to posteroinferior. Medial to the pars flaccida and lateral to the neck of the malleus is the Prussak’s space, where epitympanic cholesteatoma starts to invaginate medially from the pars flaccida. The pars flaccida is located superiorly to the lateral process of the malleus, and delineated superiorly by a bony notch in the superior canal wall called the Rivinus notch. The tympanic annulus is attached to a groove on the bony canal called the tympanic sulcus. The lamina propria thickens in the periphery of the pars tensa to form tympanic annulus. The pars tensa, located inferiorly to the lateral process of the malleus and the anterior and the posterior malleal folds, occupies majority of the tympanic membrane. The tympanic membrane is divided into two parts. The lamina propria may be lost in an atrophic tympanic membrane, and may be thickened by a tympanosclerotic plaque. Between these two layers, a fibrous layer, the lamina propria exists. Laterally, it is covered with an epidermal layer, and medially with a mucosal layer. The tympanic membrane is composed of three layers.
Sufficient visualization of this angle is the key for successful tympanic membrane reconstruction.
The anterior angle is often hindered by a bony protrusion of the anterior wall. Because of this dimension, the anteroinferior bony wall is longer than the posterosuperior one, and the anterior tympanomeatal angle is more acute than the posterior. The conically shaped tympanic membrane is tilted anteroinferiorly.
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