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Malignant Otitis Externa (MOE)/Skull base osteomyelitis

Introduction

Malignant otitis externa (MOE), also known as necrotizing otitis externa, is a rare and severe infection of the external ear canal. It is typically caused by the bacterium Pseudomonas aeruginosa. MOE primarily affects individuals with compromised immune systems, such as the elderly or those with diabetes. The infection starts in the ear canal and can spread to surrounding tissues, including the skull base.

The clinical presentation of MOE is characterized by severe ear pain, foul-smelling discharge, hearing loss, and swelling in the affected area. Left untreated, MOE can lead to serious complications, such as bone erosion, cranial nerve involvement, and even spread to nearby structures like the brain.

MRI plays a crucial role in diagnosing and staging MOE. On MRI, findings consistent with MOE include soft tissue inflammation and edema in the external ear canal, extending to the adjacent temporal bone and skull base. The involved structures may demonstrate enhancement following the administration of contrast material. MRI can also help identify complications such as abscess formation, osteomyelitis, and involvement of the cranial nerves or nearby blood vessels.

Additionally, MRI can aid in monitoring the response to treatment and assessing disease progression. It provides detailed anatomical information and helps guide clinicians in determining the extent of the infection, planning surgical interventions if necessary, and evaluating the overall response to therapy.

Malignant otitis externa (skull base osteomyelitis ) MRI images

Indications for MOE/Skull base MRI scan

Contraindications

Patient preparation MOE/Skull base MRI scan

Positioning for MOE/Skull base MRI scan

MALIGNANT OTITIS EXTERNA (MOE) or SKULL BASE OSTEOMYELITIS MRI positioning photo

MRI Malignant Otitis Externa (MOE) protocols and planning

MOE/Skull base MRI scan localiser

A three-plane localizer must be taken at the beginning to localize and plan the sequences. Localizers are usually less than 25 seconds and are T1-weighted low-resolution scans.

T2 stir axial 3mm SFOV

Plan the axial slices on the coronal plane and angle the planning block parallel to the right and left internal auditory meatus. Check the planning block in the other two planes. An appropriate angle must be given in the sagittal plane, parallel to the hard palate. The slices must sufficiently cover the skull base and should extend from the glabella down to the upper lip.

Malignant otitis externa (MOE) MRI protocols and planning of axial scans

Parameters

TR

4000-5000

TE

110

FLIP

150

NEX

3

SLICE

3 MM

MATRIX

256X256

FOV

180-200

PHASE

R>L

GAP

10%

TI

150

T1 tse axial 3mm SFOV

Plan the axial slices on the coronal plane and angle the planning block parallel to the right and left internal auditory meatus. Check the planning block in the other two planes. An appropriate angle must be given in the sagittal plane, parallel to the hard palate. The slices must sufficiently cover the skull base and should extend from the glabella down to the upper lip.

Malignant otitis externa (MOE) MRI protocols and planning of axial scans

Parameters

TR

400-600

TE

15-25

SLICE

3 MM

FLIP

140

PHASE

R>L

MATRIX

256X256

FOV

180-200

GAP

10%

NEX(AVRAGE)

2

RESOLVE DWI axial 3mm

Plan the axial slices on the coronal plane and angle the planning block parallel to the right and left internal auditory meatus. Check the planning block in the other two planes. An appropriate angle must be given in the sagittal plane, parallel to the hard palate. The slices must sufficiently cover the skull base and should extend from the glabella down to the upper lip.

Malignant otitis externa (MOE) MRI protocols and planning of axial scans

Parameters

TR

7000-9000

TE

70
115

FLIP

130

NXA

1    2

SLICE

3MM

MATRIX

192X192

FOV

200-230

PHASE

R>L

GAP

10%

B VALUE

0
1000

T2 STIR coronal 3mm SFOV

Plan the coronal slices on the axial plane and angle the planning block parallel to the right and left internal auditory meatus. Check the planning block in the other two planes. An appropriate angle must be given in the sagittal plane, perpendicular to the hard palate. The slices should be sufficient to cover the skull base from the zygomatic arch to the posterior border of the temporal bone.

Parameters

TR

4000-5000

TE

110

FLIP

150

NEX

3

SLICE

3 MM

MATRIX

256X256

FOV

160-180

PHASE

R>L

GAP

10%

TI

150

T1 tse coronal 3mm small FOV

Plan the coronal slices on the axial plane and angle the planning block parallel to the right and left internal auditory meatus. Check the planning block in the other two planes. An appropriate angle must be given in the sagittal plane, perpendicular to the hard palate. The slices should be sufficient to cover the skull base from the zygomatic arch to the posterior border of the temporal bone.

Parameters

TR

400-600

TE

15-25

SLICE

3 MM

FLIP

140

PHASE

R>L

MATRIX

256X256

FOV

170-180

GAP

10%

NEX(AVRAGE)

2

MRV skull base 3D phase-contrast (PC) sagittal

Plan the sagittal 3D block on the axial plane and position the block parallel to the midline of the brain. Verify the planning block in the coronal plane, ensuring it is parallel to the line along the midline and 3rd ventricle. Place the saturation band at the bottom of the block in the sagittal planes to avoid capturing arterial signals. Ensure that the number of slices is sufficient to cover the entire brain from one temporal lobe to the other.

MRV of the brain is an important sequence in the MOE protocol because the infection can cause jugular vein and cavernous sinus thrombosis. If phase-contrast scanning is not available, dynamic contrast-enhanced venography of the skull base should be performed.

Malignant otitis externa (MOE) MRI protocols and planning of jugular vein and cavernous sinus

Parameters

TR

68-75

TE

8-9

FLIP

15

NEX

2

SLICE

1MM

MATRIX

256X256

FOV

280

PHASE

A>P

GAP

20%

velocity

10

For contrast enhanced scans

For post-contrast Malignant Otitis Externa (MOE) imaging, please use T1 SE fat-saturated axial and coronal small FOV sequences after the administration of IV gadolinium DTPA injection (copy the planning outlined above). The document below provides access to the recommended dosage of gadolinium DTPA injection, as advised by the manufacturer.

Optional Scans

T1 VIBE DIXON 3D axial .7 mm isotropic SFOV post contrast

Plan the axial slices on the sagittal plane and angle the planning block parallel to the hard palate. Check the planning block in the other two planes. An appropriate angle must be provided in the coronal plane, perpendicular to the nasal septum. The slices should sufficiently cover the face from the glabella down to the body of the mandible. Slice and phase oversampling should be applied to avoid wrap-around artifacts.

planning of MRI face axial 3D scans

TR

6.9

TE

2.39   4.77

FLIP

12

NEX

2

SLICE

.7 MM

MATRIX

256X256

FOV

170-180

PHASE

R>L

SLICES

200

OVERSAMPLE

10% and100%

T2 space stir 3D axial 1mm isotropic SFOV

Plan the axial slices on the sagittal plane and angle the planning block parallel to the hard palate. Check the planningg block in the other two planes. An appropriate angle must be provided in the coronal plane, perpendicular to the nasal septum. The slices should sufficiently cover the face from the glabella down to the body of the mandible. Slice and phase oversampling should be applied to avoid wrap-around artifacts.

planning of MRI face axial 3D scans

Parameters

TR

2000-2600

TE

200-250

FLIP

35

NEX

1.5

SLICE

1 MM

MATRIX

256X256

FOV

180-200

PHASE

R>L

GAP

10%

TI

130