Learning objectives
Anomalies of the course of the tympanic portion of the CN7 (VII-2) are the most common.
An anterior displacement of the mastoid portion of the CN7 (VII-3) is important to specify before cochlear implantation.
The CN7canal may be dehiscent,
with or without inferior herniation of the corresponding nerve.
The CN7 must always be analyzed on temporal bone CT / MRI.
Background
•The facial nerve’s course is known to be quite a complex one.
•One must analyse it’s course and it’s position,
especially on CT,
before any surgical exploration of the middle ear,
particularly in a malformative context.
•A congenital malformation of the facial nerve cannot be an surprise anymore for the surgeon during an operating procedure.
Protocols for the study of the congenital anomalies of the facial nerve
CT :
-Study box placed above the orbits (red line)
-0,3-0,4 mm axial reconstructions, parallel to the lateral...
Findings and procedure details
1) Agenesia or hypoplasia of the CN7
Agenesia
Hypoplasia of the facial nerve
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)
2.2 Open angle between VII-1 and VII-2
Congenital anomaly frequently found in Geyser ear and BOR syndrom.
2.3 Absence of VII-2
2.4 Lateralized VII-2 in the tympanic cavity
2.5...
Conclusion
Anomalies of the course of the tympanic portion of the CN7 (VII-2) are the most common.
An anterior displacement of the mastoid portion of the CN7 (VII-3) is important to specify before cochlear implantation.
The CN7 canal may be dehiscent,
with or without inferior herniation of the corresponding nerve.
The CN7 must always be analyzed on temporal bone CT / MRI.
All these modifications must be specified to the surgeon before any operating procedure.
Personal information
Ms Aïna Venkatasamy,
Radiology resident,
Strasbourg University Hospital,
Strasbourg - FRANCE
[email protected]
Professor Francis Veillon,
Professor of Radiology,
Departement of Radiology 1,
Hôpital de Hautepierre,
Strasbourg University Hospital,
Strasbourg - FRANCE
[email protected]
References
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Lang J.
Cerebellopontine angle,
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Clinical anatomy of the posterior cranial fossa and its foramina.
New York-Stuttgart,
Thieme,
1991 : 83-91.
2.
Wadin K.
The radioanatomy of the high jugular fossa and the labyrinthine portion of the facial canal.
A radioanatomic and clinical investigation (doctorat thesis).
Uppsala University Sweden 1986.
3.
May M.
Anatomy for the clinician.
In : M May,
B.
Schaitkin.
The facial nerve.
New York-Stuttgart,
Thieme,
2000 : 19-56.
4.
Schuknecht H,
Gulya...