The Temporal Bone: Normal Variants


The Temporal Bone: Normal Variants

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.

Table 4.54 Normal variants




Cochlear cleft

Fig. 4.174

Especially in children. Lucency lateral to apical turn.

Lucent periotic zone in infants

No retrofenestral otosclerosis.

Incudal “hole”

Fig. 4.175, p. 402

Lucency in incus body.

Partial volume effect.

High jugular bulb

Jugular bulb above the caudal level of the posterior semicircular canal.

Frequently a diverticulum of the jugular bulb.

Fatty marrow in petrous apex

Fig. 4.176, p. 402

High signal intensity on T1 and T2 turbo spin echo.

Can be misinterpreted as a lesion, especially when unilateral. Compare signal intensity with subcutaneous fat.

Bulging sigmoid sinus

Fig. 4.177, p. 402

Anterior impression in posterior surface of mastoid.

To be avoided during mastoidectomy.


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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Jul 12, 2020 | Posted by in PEDIATRIC IMAGING | Comments Off on The Temporal Bone: Normal Variants
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