Knowledge of normal variants prevents confusion and a possible incorrect diagnosis. Normal variants are also important to report if they can cause a risk during operative procedures.
Anterior impression in posterior surface of mastoid.
To be avoided during mastoidectomy.
Pseudofractures
Cochlear aqueduct, petromastoid canal.
Be aware of sutures.
Fig. 4.174 Lucent line at the cochlear apex, a so-called cochlear cleft (arrow). This is seen in the majority of young children, and its incidence decreases with advancing age.Fig. 4.175 CT examination for suspected cholesteatoma in an 8-year-old boy. The lucency in the body of the incus (arrow) is a partial volume effect of the space between the short and long process of the incus and not a focal erosion.Fig. 4.176 High signal intensity in the left petrous apex is consistent with fatty bone marrow on a T2 FLAIR sequence in a 13-year-old boy. This could be mistaken for a petrous apex lesion.Fig. 4.177 Bulging sigmoid sinus (arrow); knowledge of this normal variant can prevent accidental laceration at operation.
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