statdx/docs_md/articles/facial-nerve-lesion-temporal-bone_1428754b-a8ee-48a0-98f8-4faeebf8dbab.md

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Facial Nerve Lesion, Temporal Bone	1428754b-a8ee-48a0-98f8-4faeebf8dbab	key value eef2f839-5706-47b9-89c3-60d8315b2b3a Nicholas A. Koontz, MD	name slug treeNodeId Head and Neck head-and-neck ed24ed8c-5d57-4629-879b-447b82d2973d name slug treeNodeId Differential Diagnosis differential-diagnosis 40d68862-8975-4dde-ac2b-ebc43ab0fb5c name slug treeNodeId Temporal Bone temporal-bone 2f7dc690-4970-486f-abb6-ed24d99b7a04 name slug treeNodeId Anatomically Based Differentials anatomically-based-differentials 115faedf-cc6e-41cd-a155-665ce5b062ee name slug treeNodeId Facial Nerve Lesion, Temporal Bone facial-nerve-lesion-temporal-bone null	Head and Neck	5d11bc10-dd61-4bcd-8c3b-ac0d32054bb1	61084d95-357b-49d1-8ce1-5fc8c8732500	23	08/13/18	Facial Nerve Lesion, Temporal Bone	Head and Neck, Differential Diagnosis, Temporal Bone, Anatomically Based Differentials, Facial Nerve Lesion, Temporal Bone	Facial Nerve Lesion, Temporal Bone | STATdx	Facial Nerve Lesion, Temporal Bone	DDX	true	Head and Neck Differential Diagnosis Temporal Bone Anatomically Based Differentials Facial Nerve Lesion, Temporal Bone

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title: "Facial Nerve Lesion, Temporal Bone" docid: "1428754b-a8ee-48a0-98f8-4faeebf8dbab" authors:

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ESSENTIAL INFORMATION

• Key Differential Diagnosis Issues

  • Differential diagnosis considerations - Differential diagnosis built on lesions primary to intratemporal facial nerve - Other lesions included because part of lesion complex is abnormal facial nerve canal
  • Imaging recommendations for Bell palsy - Routine acute-onset Bell palsy not imaged - Image only "atypical" Bell palsy
  • Imaging recommendations for facial nerve lesion group - Temporal bone (T-bone) CT & high-resolution MR are often complementary - Particularly true when larger lesions are discovered with either modality

• Helpful Clues for Common Diagnoses

  • Normal Facial Nerve Enhancement - Key facts - Asymptomatic patient - Normal imaging finding - More prominent on 3T MR - Imaging findings - Bone CT: Normal facial nerve canal - T1 C+ MR: Area of geniculate ganglion, anterior tympanic segment, & posterior genu of facial nerve may normally enhance - Symmetric enhancement typical of normal variation
  • Bell Palsy - Key facts - Acute onset of unilateral peripheral facial nerve paralysis - > 90% recover & do not need imaging - MR imaging for "atypical Bell palsy" - Imaging findings - T-bone CT: Normal facial nerve (CNVII) canal - T1 C+ MR: Intratemporal facial nerve enhances along entire course - T1 C+ MR other: Internal auditory canal (IAC) fundal "tuft" enhancement - Increasing role of 3D-FLAIR - 3D-FLAIR C-: Bright signal along canalicular CNVII - 3D-FLAIR C+: Avid enhancement of canalicular CNVII, particularly fundal "tuft" - High-resolution steady-state free precession T2 should not show mass-like nodular enlargement of CNVII
  • Temporal Bone Fracture Involving Facial Nerve Canal - Key facts - Fracture line crosses facial nerve canal - Fracture line may be difficult to see - Multiplanar reconstructions are essential - High-resolution T-bone CT is criterion standard for imaging but is imperfect tool - Posterior genu & mastoid segment fractures are challenging to identify on CT; easily overlooked - Imaging findings - T-bone CT: Fracture may affect geniculate ganglion, tympanic, or mastoid segment of facial nerve - Transverse fractures affect facial nerve more commonly than longitudinal fractures
  • Intratemporal Facial Nerve Perineural Malignancy - Key facts - If invasive parotid malignancy found on CT or MR, imaging of stylomastoid foramen & mastoid segment facial nerve is critical - Always look for perineural malignancy on intratemporal facial nerve - Imaging findings - T-bone CT: Normal to enlarged mastoid facial nerve canal ± opacification of adjacent mastoid air cells - T1 C+ MR: Enlarged & asymmetrically enhancing facial nerve segment(s) - Regardless of modality, scrutinize stylomastoid foramen & evaluate for loss of normal fat plane - On CT, look for soft tissue replacing normal fat density at stylomastoid foramen - On MR, look for loss of bright precontrast T1 signal at stylomastoid foramen - Caution: Do not fat saturate precontrast T1 MR
  • Facial Nerve Venous Malformation ("Hemangioma") - Key facts - May present with acute onset of peripheral facial nerve paralysis - May be subtle imaging finding early in disease course - Any focal facial nerve enhancement on MR should be investigated with T-bone CT - Imaging findings - Most common location: Geniculate fossa - T-bone CT: "Honeycomb" matrix (50%) - T1 C+ MR: Geniculate ganglion enhancing mass - Other MR findings: When large, spreads anteromedially along greater superficial petrosal nerve course
  • Facial Nerve Schwannoma - Key facts - 50% present with hearing loss - Facial nerve symptoms may be delayed - Imaging findings - Most common location: Geniculate fossa - Often affects multiple contiguous segments of intratemporal facial nerve - T-bone CT: Expanded, tubular facial nerve canal - T1 C+ MR: Enhancing mass along facial nerve - Intramural cystic change possible when large

• Helpful Clues for Less Common Diagnoses

  • Oval Window Atresia W****ith Ectopic Facial Nerve - Key facts - May be seen with external auditory canal (EAC) atresia or as isolated lesion - Presents with conductive hearing loss with normal otoscopic exam - Key diagnosis to make, as facial nerve ectopia may preclude surgery - If ectopic CNVII not recognized on preoperative imaging, may result in iatrogenic facial nerve injury - Imaging findings - T-bone CT: Oval window narrowed with bony atresia plate covering window itself - Tympanic segment facial nerve moves medially from normal location under lateral semicircular canal - Tympanic segment may be found on superior margin, within, or on inferior margin of atresia plate
  • External Auditory Canal Atresia W****ith Ectopic Facial Nerve - Key facts - Severity of external ear microtia directly related to degree of EAC-middle ear malformation - Mastoid segment is most commonly ectopic - Imaging findings - T-bone CT: EAC is dysplastic with mastoid segment facial nerve anterior to normal location - Other CT findings: EAC is stenotic or absent - Small middle ear with ossicle fusion mass ± oval window atresia

• Helpful Clues for Rare Diagnoses

  • Prolapsing Facial Nerve I****nto Middle Ear - Key facts - Intratemporal facial nerve bordering middle ear cavity may have variable bone covering - If dehiscence of facial nerve is accompanied by protrusion of nerve into middle ear, there is high risk of injury during surgery - Imaging findings - T-bone CT: Tympanic segment facial nerve dehiscent ± nerve hanging into middle ear cavity - Other T-bone CT findings: Facial nerve may appear slightly enlarged when not in bony canal
  • Ramsay Hunt Syndrome - Key facts - Herpes zoster oticus affects facial nerve ± vestibulocochlear nerve ± inner ear - EAC vesicles usually precede facial nerve symptoms - When vesicular rash is delayed or mild, clinical confusion about diagnosis may be present - Imaging findings - T-bone CT: Facial nerve canal normal - T1 C+ MR: Enhancing facial nerve in IAC & T-bone - Increasing role of 3D-FLAIR - Bright 3D-FLAIR C- inner ear signal & 3D-FLAIR C+ cochlear nerve enhancement more commonly seen in Ramsay Hunt than Bell Palsy - Enhancement of inner ear structures & cochlear nerve is more variable on T1 C+ MR
  • Lyme Borreliosisof IntratemporalFacial Nerve - Key facts - Bacteria Borrelia is tick-borne systemic infection - May cause acute facial nerve paralysis - Imaging findings - T-bone CT: Normal facial nerve canal - T1 C+ MR: Entire intratemporal CNVII enhances - IAC-CPA CNVII enhancement may also be present

References

Selected References

1. Chen Y et al: Reliability of temporal bone high-resolution CT in patients with facial paralysis in temporal bone fracture. Am J Otolaryngol. 39(2):150-152, 2018
2. Kirsch CFE et al: Practical tips for MR imaging of perineural tumor spread. Magn Reson Imaging Clin N Am. 26(1):85-100, 2018
3. Kuya J et al: Usefulness of high-resolution 3D multi-sequences for peripheral facial palsy: differentiation between Bell's palsy and Ramsay Hunt syndrome. Otol Neurotol. 38(10):1523-1527, 2017
4. Benoit MM et al: Facial nerve hemangiomas: vascular tumors or malformations? Otolaryngol Head Neck Surg. 142(1):108-14, 2010
5. Saraiya PV et al: Temporal bone fractures. Emerg Radiol. 16(4):255-65, 2009
6. Okada K et al: Benign mass lesions deep inside the temporal bone: imaging diagnosis for proper management. Acta Otolaryngol Suppl. (559):71-7, 2007
7. Chan EH et al: Facial palsy from temporal bone lesions. Ann Acad Med Singapore. 34(4):322-9, 2005
8. Kress B et al: Bell palsy: quantitative analysis of MR imaging data as a method of predicting outcome. Radiology. 230(2):504-9, 2004
9. Salzman KL et al: Dumbbell schwannomas of the internal auditory canal. AJNR Am J Neuroradiol. 22(7):1368-76, 2001
10. Caldemeyer KS et al: Imaging features and clinical significance of perineural spread or extension of head and neck tumors. Radiographics. 18(1):97-110; quiz 147, 1998
11. Gebarski SS et al: Enhancement along the normal facial nerve in the facial canal: MR imaging and anatomic correlation. Radiology. 183(2):391-4, 1992
12. Parker GD et al: Clinical-radiologic issues in perineural tumor spread of malignant diseases of the extracranial head and neck. Radiographics. 11(3):383-99, 1991
13. Curtin HD et al: "Ossifying" hemangiomas of the temporal bone: evaluation with CT. Radiology. 164(3):831-5, 1987

Images

Selected Images

Normal Facial Nerve Enhancement Axial T1 C+ FS MR shows the normal enhancement pattern of the facial nerves. Note mild symmetric enhancement of the geniculate ganglia and anterior tympanic segments but absent enhancement of the intracanalicular segments bilaterally.

Normal Facial Nerve Enhancement Axial T1 C+ FS MR shows the normal enhancement pattern of the facial nerves. Note mild symmetric enhancement of the geniculate ganglia and anterior tympanic segments but absent enhancement of the intracanalicular segments bilaterally.

Normal Facial Nerve Enhancement Axial T1 C+ MR reveals prominent but normal enhancement of the geniculate ganglion and anterior tympanic segment of facial nerve .

Normal Facial Nerve Enhancement Axial T1 C+ MR reveals prominent but normal enhancement of the geniculate ganglion and anterior tympanic segment of facial nerve .

Bell Palsy Axial T1 C+ FS MR in a patient with Bell palsy shows a "tuft" of enhancement at the fundus of the internal auditory canal as well as abnormal enhancement along the labyrinthine segment and anterior genu of facial nerve.

Bell Palsy Axial T1 C+ FS MR in a patient with Bell palsy shows a "tuft" of enhancement at the fundus of the internal auditory canal as well as abnormal enhancement along the labyrinthine segment and anterior genu of facial nerve.

Bell Palsy Coronal T1 C+ FS MR in a patient with Bell palsy shows a classic "tuft" of enhancement at the fundus of the internal auditory canal above the crista falciformis . Note additional enhancement of the tympanic segment of facial nerve, which courses below the lateral semicircular canal.

Temporal Bone Fracture Involving Facial Nerve Canal Axial bone CT shows a complex, longitudinally oriented fracture of the right temporal bone, which traverses the anterior genu of the facial nerve canal , resulting in ipsilateral facial paralysis. Note avulsion of the petrous ridge .

Intratemporal Facial Nerve Perineural Malignancy Coronal T1 C+ FS MR shows a small, high, intraparotid adenoid cystic carcinoma centered just below the stylomastoid foramen . Note avid enhancement of the mastoid segment of the facial nerve from perineural tumor spread.

Facial Nerve Venous Malformation ("Hemangioma") Axial bone CT shows a permeative expansile lesion with a "honeycomb" matrix centered at the anterior genu of the facial nerve canal. Note extension into the widened labyrinthine and anterior tympanic segments of the facial nerve canal.

Facial Nerve Schwannoma Axial bone CT demonstrates smooth enlargement of the geniculate fossa and the anterior tympanic segment of the facial nerve canal , which is typical of facial nerve schwannoma. Note that unlike a venous malformation, no internal matrix is seen.

Oval Window Atresia With Ectopic Facial Nerve Axial NECT shows a medialized course of the facial nerve tympanic segment overlying the oval window, which has a prominent bony atresia plate abutting the facial nerve.

Oval Window Atresia With Ectopic Facial Nerve Coronal bone CT in a child with a complex ear malformation shows an atresia plate at the oval window with associated ectopic course of the facial nerve , which is positioned more medial than usual along the atresia plate. Note additional hypoplastic lateral semicircular canal as well as EAC atresia with microtia.

External Auditory Canal Atresia With Ectopic Facial Nerve Coronal bone CT in a child with EAC atresia shows an aberrant course of the facial nerve canal that is positioned inferolateral to its expected course immediately beneath the lateral semicircular canal . A BB marks the expected location of the absent auricle.

Prolapsing Facial Nerve Into Middle Ear Axial bone CT shows a typical case of midtympanic segment facial nerve prolapse into the middle ear cavity . The facial nerve is sagging into the oval window niche.

Ramsay Hunt Syndrome Axial T1 C+ FS MR reveals linear internal auditory canal and intracochlear enhancement, in addition to prominent enhancement of the tympanic segment of the facial nerve. The patient had external ear vesicles at the time of imaging.

Lyme Borreliosis of Intratemporal Facial Nerve Axial T1WI C+ FS MR in a patient with Lyme borreliosis of facial nerve demonstrates intense enhancement of labyrinthine , geniculate , and anterior tympanic segments of the left intratemporal facial nerve. Note that the IAC-CPA segment also enhances faintly.

Additional Images

Normal Facial Nerve Enhancement Axial T1 C+ FS MR shows normal enhancement of anterior tympanic segment and geniculate ganglion portions of intratemporal facial nerve in this asymptomatic patient.

Bell Palsy Axial T1 C+ FS MR reveals an internal auditory canal fundal "tuft" of facial nerve enhancement along with enhancement of the labyrinthine segment and geniculate ganglion in this patient with Bell palsy.

Bell Palsy Axial T1 C+ FS MR shows the midmastoid segment of the facial nerve enhancing avidly . A normal mastoid segment never enhances to this degree.

Temporal Bone Fracture Involving Facial Nerve Canal Axial bone CT demonstrates a transverse fracture through the inner ear. The fracture line passes anteriorly through the labyrinthine segment of the facial nerve canal .

Facial Nerve Venous Malformation ("Hemangioma") Axial bone CT shows a C-shaped venous malformation of the labyrinthine segment and geniculate ganglion segments of the facial nerve. The anterior surface of the petrous apex is also involved.

Oval Window Atresia With Ectopic Facial Nerve Coronal bone CT shows a typical case of oval window atresia with aberrant facial nerve overlying the site of the oval window. Any attempt to repair this atresia will result in injury to CNVII.

Oval Window Atresia With Ectopic Facial Nerve Axial bone CT demonstrates the tympanic segment of the facial nerve overlying the oval window, which has an atresia plate visible .

External Auditory Canal Atresia With Ectopic Facial Nerve Axial bone CT demonstrates that the mastoid segment of the facial nerve is anterior to its normal location as a result of atresia of the EAC.

Lyme Borreliosis of Intratemporal Facial Nerve Axial T1 C+ FS MR shows intense enhancement of the tympanic segment of the facial nerve in this patient with Lyme borreliosis of intratemporal facial nerve.