1) Agenesia or hypoplasia of the CN7
Agenesia
Fig. 3: Agenesia of the facial nerve axial HRT2 wi MRI (red) compared to normal image (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 4: Agenesia of the facial nerve, High Resolution (HR) T2 3D MRI, sagittal plane of the internal auditory meatus (red) compared to normal image(green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Hypoplasia of the facial nerve
Fig. 5: Hypoplasia of the facial nerve, HR T2 3D MRI, sagittal plane of the internal auditory canal (red) compared to normal (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
2) Anatomical anomalies of the course of the facial nerve and/or canal
2.1 Above the internal auditory meatus
Elevation of the course of the facial nerve in the cerebellopontine angle.
The nerve runs in an own canal above the internal auditory meatus (IAM)
Fig. 6: VII 1 above the internal auditory meatus HR T2 MRI axial slightly oblique plane (red) compared to a normal one (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 7: VII 1 above the internal auditory meatus, axial non enhanced CT, slices at two different level, same patient (red) compared to a normal one (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 8: VII1 above the internal auditory meatus, Sagittal non enhanced CT, same patient as before (red) compared to normal image (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 9: VII1 above the internal auditory meatus, coronal non enhanced CT
(same patient) (red) versus normal image at the same level of section (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
2.2 Open angle between VII-1 and VII-2
Congenital anomaly frequently found in Geyser ear and BOR syndrom.
Fig. 10: Open angle between VII1 and VII2, CT axial plane through the labyrinthine portion of the facial nerve (red) compared to normal image at the same level (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
2.3 Absence of VII-2
Fig. 11: Absence of normal VII2= anteriorized VII3 right after VII1, no VII2, coronal non enhanced CT (red) compared to normal VII 2 (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
2.4 Lateralized VII-2 in the tympanic cavity
Fig. 12: Lateralized VII2 in the tympanic cavity, coronal CT through the tympanic facial nerve canal and the oval window (red) compared to normal VII 2 (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
2.5 Inferior herniation of the nerve in a dehiscent bony canal
Fig. 13: Inferior herniation of the facial nerve in a dehiscent canal (VII2 in most of the cases), coronal CT (red) compared to normal VII 2 (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
2.6 Lowered facial nerve in,
close or not to the stapes,
or below the oval window
A line,
parallel to the floor of the facial nerve canal is below the oval window if the VII 2 is lowered.
Fig. 14: Lowered VII2 on the footplate, coronal CT (red) compared to normal VII 2 (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 15: Lowered VII2 on non enhanced coronal CT (red) compared to normal VII 3 (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
2.7 Medialized VII-3 canal in or close to the jugular bulb
Fig. 16: Medialized and anteriorized VII3 close to the jugular bulb, coronal CT (red) versus normal VII 3 (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
2.8 Anteriorized VII-3
An anteriorized VII 3 is visible on a coronal plane through the oval window.
A normal VII 3 must always be behind the level of the round and oval windows.
Fig. 17: Anteriorized VII3, coronal CT (red) versus normal VII 3
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
3) Anomalies of size of the facial nerve canal
The normal CN7 canal size has numerous normal variants: geniculate ganglion fossa ranging from 1.8 to 4.5 mm,
VII-2 from 1.3 to 2.9mm.
Fig. 18: Enlarged labyrinthine portion of the facial nerve, axial CT (red) compared to normal VII 1 (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 19: Enlarged labyrinthine portion of the facial nerve MRI T1 wi after Gadolinium injection (same patient as previous slide) (red) compared to normal VII 1 (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 20: Enlarged tympanic portion of the facial nerve, axial non enhanced CT (2 sections the first one above the other) (red) compared to normal VII 2 (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 21: Enlarged mastoid portion of the facial nerve, axial CT (red) compared to normal VII 3 (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
MRI HR T2 images are necessary for the detection of CSF in the geniculate ganglion fossa,
which is a normal variant.
The T1 postcontrast images eliminate a tumor.
Fig. 22: Cerebrospinal fluid (CSF) in the geniculate ganglion fossa, normal variant, axial CT (red) compared to normal geniculate ganglion fossa (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 23: Cerebrospinal fluid (CSF) in the geniculate ganglion fossa (same patient), axial HR T2 wi MRI (red) compared to a normal geniculate ganglion fossa (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
The enlarged geniculate ganglion fossa may also be due to a meningocele.
Fig. 24: Meningoencephalocele of the geniculate ganglion fossa, coronal CT (red) compared to a normal geniculate ganglion fossa (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 25: Meningoencephalocele of the geniculate ganglion fossa (same patient)
HR T2 MRI, coronal plane through the geniculate ganglion fossa (red) compared to a normal image (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
4) Nerve duplication
Duplication of VII-1 is most commmon.
Fig. 26: Duplication of the VII1, axial CT (2 sections the first one above the other) , same patient : two canals one on top of the other (red) compared to a normal image (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Fig. 27: Duplication of VII 1 coronal CT (same patient) : 2 canals one above the other (red) versus normal image (green)
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Duplication of VII-2 is rare.
Fig. 28: Duplication of VII 2, coronal CT (red) compared to normal VII 2
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015
Duplications of VII-3 are theorically possible but remain extremely rare.
In most cases,
when a canal is visible next to the VII3 it belongs to the stapes muscle.
Fig. 29: Normal VII 3 and stapes muscle canal, on coronal CT
References: Department of Radiology 1, Strasbourg University Hospital, Strasbourg University, France 2015