Interest Group Acoustic Neuroma

Acoustic neuroma - Internet portal on acoustic neuroma brain tumours.

Guidelines

(Provisional guidelines)
(also see LL of DGNC 008/013 v. 01/1999)

Imaging diagnostics:
The task of modern, imaging diagnostics of sensorineural hearing loss consists in proving or excluding, as well as the type of diagnostic classification of space-occupying processes in the inner ear region, the meatus acusticus internus (MAI) and cerebellopontine angle. Processes, which can be symptomatic within the labyrinth even when it is only the size of a few millimetres, put particularly high demands on sectional image diagnostics. Its early detection is desirable, as with a smaller tumour size it is possible for operative treatment preserving functional integrity of cranial nerves VII and VIII.

The MRT is the method of first choice for imaging diagnostics of an acoustic neuroma (1,3,5,8,9,10,12,14,15,16,17,20,21).

The following examination protocol is recommended:
A. Magnetic Resonance Tomography: (also see BÄK guidelines on the quality assurance of a Magnetic Resonance Tomography of 29. 9.2000 and guidelines on the criteria for quality assessment in nuclear spin tomographies of 16.10.2000, cerebellopontine angle position, petrous bone, skull base)

By means of the Scout image, the settings of the section planes must be as symmetrical as possible to facilitate the comparison with the contralateral side.

1. Orienting overview axial T2-weighted images to assess the brain, brainstem, cerebellopontine angle and petrous bone to rule out:

  • Brainstem lesions (e.g. MS groups, glioma, bleedings, etc.)
  • Cerebellopontine angle tumours (e.g. Neurinoma, epidermoide, metastases, angioma, meningeoma, etc.)
  • Petrous bone disease (e.g. Inflammation of the pneumatisation areas; tumours such as glomus tumours, chordoma, chondroma, cholesteatoma; deformities)
A possible pathological process in which these appropriate modes must be explained (e.g. T1-weighted MRT with and without IV contrast agent, CT if necessary, angiography, etc.).

2. High resolution 2D/3D T1-weighted sequences (e.g. T1W SE, SD 1-3 mm; 3D MP RAGE, SD </= 1 mm; or similar) with and without intravenously administered contrast agent (0.2ml/kg KG Gadolinium DTPA) in the axial and coronary incisions, and if necessary in the sagittal or anatomically adapted (e.g. vertical or parallel to the MAI) sections.
Acoustic neuroma/vestibular Schwannoma show a clear increased signal with the administration of IV contrast agents.

The differential diagnosis includes:
Meningeoma, facialis neurinoma, lipoma, lymphoma, hamartoma, hemangioma, AV malformation, bleeding, arachnoiditis, Ramsey Hunt syndrome, labyrinthitis, neuritis, cochlear otospongiosis, neurovascular compression syndrome.

False positive findings with contrast agent enhancement, similar to an intracanalicular acoustic neuroma, can be produced, e.g. through neuritis, AVM, arachnoiditis, Ramsey Hunt syndrome (2,10). The results are to be assessed together with the clinical image, and in case of doubt it is necessary to carry out an additional neurological clarification or an MRT follow-up after 6 months to detect a reduction in inflammatory conditions through contrast enhancements.

In addition to the contrast agent supported T1-weighted sequences, the exact position and space-occupying effect of a pathological process can be displayed, with regard to the nerves in the inner ear canal, the cochlea and arches, using high resolution 3D T2-weighted thin film sequences. These sequences are also applied increasingly to operation planning for small acoustic neuromas.

3. High resolution 3D T2-weighted sequences (e.g. 3DFT CISS, 3D FASE, ZIP 3D FRFASE, 3D TSE) of the petrous bone with a film thickness of </= 1mm isotrope.
Image of the inner ear with the cochlea and labyrinth, meatus acusticus internus, with the individual cranial nerves, and the immediate vicinity, with axial and coronary reconstructions, as well as possible anatomically adapted further reconstructions for:
a. proving/excluding an abnormality
b. the precise localisation and classification of the tumour on the affected cranial nerves and the relationship to the fundus
c. proving neurovascular contact

With good quality images that allow a detailed representation of the structures of the middle and inner ear (cochlea, labyrinth, facialis canal) and separate assessment of the meatus acusticus internus (MAI) nerves, where no abnormality is detected, can be evaluated as ruling out an acoustic neuroma, according to Soulie D. et al.(17) and Annesley-Williams D.J. et al. (3). Under this condition this sequence can serve as an alternative to T1W + contrast agent (CA), in the event of CA incompatibility.

False positive findings can be clarified with high resolution T1W images by administering CA (Nakashima 2002; Hermans 1997: 9/38 false positives in T2W)
False negative findings (Hermans 1997: 2/38: 1 miniscule, intralabyrinth tumour, 1
miniscule intracanalicular tumour with similar findings to the opposite side; Nakashima 2002:
for labyrinthitis or neuritis (e.g. Bell´s palsy) very rarely present a false positive without the use of contrast agent); for a possible tumour that is still very small in size and with the slow growth of an acoustic neuroma (see below) a follow-up can be carried out without risk of missing a favourable date for treatment.

Stereotactic measures: If MR images are used for calculating target coordinates in stereotactic measures, it must be considered that the geometric precision of MRT images can be affected by deformation of the magnetic fields, e.g. by susceptibility induced artefacts.

Follow-up:
Essential tasks of a follow-up include the observation of the growth with conservative management for procedures requiring space, and the post-operative follow up of possible growth recurrence. One requirement for a reliable comparison of chronologically separate examination findings is to implement them with identical examination parameters and most likely in the same institution.

For determining the size of tumours the so-called "voxel count" methods together with high resolution 3D T2-weighted sequences, e.g. 3D CISS (in flat resolution 0.4 mm x 0.4 mm, 0.7 mm thickness, 0.1 mm3 voxel), are especially precise and reliable (20). Measurements should be taken in all three projections. Measurement errors increase the bigger the voxels.

The growth of acoustic neuromas is very slow in the vast majority of cases. (Perry et al. 2001: observation of 41 patients over 6 mths – 9 years: growth 0 – 1.2 cm/year; 21 patients showed an average growth of 0.322 cm /year, only 5 required additional measures. There was no correlation between initial tumour size and growth rate.)

Examination protocol: First follow-up after 6mths, if no growth is detected, a further check up at 1 year intervals.
A definitive statement about the frequency of follow-ups and the length of observation periods cannot currently be made due to a lack of appropriate long-term studies, given that there are tumours with different growth behaviour (a. continuous, b. not reliably visible, c. others grow after respite period, d. tendency to regress, e. irregular growth (5).

B. Computer Tomography: (also see BÄK guidelines on quality assurance in the Computer Tomography of 10.4.1994)

The Computer Tomography is the second examination procedure of choice. It is used:

  • when patients cannot be examined with an MRT ( e.g. magnetisable metallic implants, pacemakers and other active (electronic/magnetic) control devices, claustrophobia, etc.), and
  • for images
a. of the petrous bone structure
(e.g. Enlargement of the MAI, proof of anomalies, malformations (atresia, mondini malformation), fractures, etc.)
(cave: double-sided enlargement of the MAI can be caused by an ectasia of the dura (7)
b. of destroyed bone processes (e.g. cholesteatoma, osteomyelitis, maligne otitis, etc.)
c. of calcification (e.g. tumour calcifications, otosclerosis, etc.)

CT protocol:
1. Only for patients who cannot be examined by MRT:
Overview examination of the whole brain with 4mm film thickness in the posterior fossa region and 8 mm supratentorial.

2. High resolution images of the petrous bone with film thicknesses of 1 – 1.5 mm in the bone window and 2 – 3 mm in the soft tissue window before and after intravenous administration of a contrast agent containing iodine. Reconstructions in the orthograde, in slantwise and anatomically adapted projections. With modern multidetector devices it is possible for further increases in spatial resolution (18).

The modern CT is able to prove extra-canalicular neuroma from an average size of 5 mm after the administration of contrast agent, because this is mostly iodine for brain tissue in the original CT. By using bigger film thicknesses it has considerably lower sensitivity to estimate tumours under an average of 10 – 15 mm in size.
Intra-canalicular tumours are not clearly shown in a CT without an air cisternography; this procedure comes into question more for patients who cannot be examined by MRT under any conditions. However, J. Vogl (19) reports that out of 10 operatively assured results, there were over 2 false negative air cisternography results.
Instead of the air cisternography, a CT cisternography can also be carried out using an intrathecal approved contrast agent (6).

Literature:

1. Allen R.W., H.R. Harnsberger, C. Shelton, et al.:
Low-Cost High Resolution Fast-Spin-Echo MR of Acoustic Schwannoma: An Alternative of Enhanced Conventional Spin-Echo MR ? AJNR 17: 1205-10, 1996

2. Anderson R.E., J.M. Laskoff:
Ramsay-Hunt syndrome mimicking intracanalicular acoustic neuroma on contrast-enhanced MR. AJNR 11, 409, 1990

3. Annesley-Williams D.J., R.D. Laitt, J.P.R. Jankins, et al. :
Magnetic resonance imaging in the investigation of sensorineural hearing loss: is contrast enhancement still necessary?
The Journal of Laryngology & Otology 115 :14-21, 2001

4. Carmody R.F.:
The Temporal Bone. In: Zimmerman R.A., W.A. Gibby, R.F. Carmody (Hrg.) Neuroimaging. Clinical and Physical Principles. Springer, pp 1159-1194,

5. Charabi S., J. Thomsen, M. Mantoni, et al.:
Acoustic neuroma (vestibular schwannoma): growth and surgical and non-surgical consequences of the wait-and-see policy. Otolaryngol Head Neck Surg 113: 5-14, 1995

6. Dubois P.J., B.P. Drayer O.W. Bank, et al.:
An evaluation of current diagnostic radiologic modalities in the investigation of acoustic neurilemmomas. Radiology 126: 173-9, 1978

7. Gibby W.A.: CT:
Clinical Applications and Contrast Agents. In: Zimmerman R.A., W.A. Gibby, R.F. Carmody (Hrg.) Neuroimaging. Clinical and Physical Principles. Springer, pp 25-62, 2000

8. Glastonbury Christine M., Chr. Davidson, H.R. Harnsberge, et al.:
Imaging Findings of Cochlear Nerve Deficiency. AJNR 23: 635-643, 2002

9. Held P., C. Fellner, J. Seitz, et el.:
The value of T2(*)-weighted MR images for the diagnosis of acoustic neuromas. European Journal of Radiology 30: 237-244, 1999

10. Hermans R., A. Van der Goten, B. De Foer, et al.:
MRI screening for acoustic neuroma without gadolinium: value of 3DFT-CISS sequence. Neuroradiology 39: 593-598, 1997

11. Jackler R.K.:
Acoustic Neuroma (Vestibular Schwannoma).In: R.K. Jackler, D.E. Brackmann (Hrg.) Neurotology. Mosby, pp 729-785, 1994

12. Krombach G.A., T. Schmitz-Rode, J. Tacke, et al.:
Magnetic resonance tomography imaging of the inner ear of patients with sensorineural hearing loss or vertigo. Laryngorhinootology 80 (Apr.) (4), 177-81, 2001

13. Modugno G.C., A. Pirodda, G.G. Ferri, et al.:
Small acoustic neuromas: Monitoring the growth rate by MRI Acta Neurochir (Vienna) 141: 1063-7, 1999

14. Nakamura T., S. Naganawa, T. Koshikawa, et al.: High-spatial-resolution MR cisternography of the cerebellopontine angle in 90 seconds with a zero-fill interpolated fast recovery 3D fast asymmetric spin-echo sequence. AJNR 23:1407-1412, 2002

15. Nakashima K., M. Morikawa, H. Ishimaru, et al.:
Three-dimensional fast recovery fast spin-echo imaging of the inner ear and the vestibulocochlear nerve. Eur Radiol 12: 2776-2780, 2002

16. Perry B.P., B.J. Gantz, J.T. Rubinstein:
Acoustic neuromas in the elderly. Otol Neurotol 22(3): 389-91, 2001

17. Soulie D., Y.-S. Cordoliani, J. Vignaud, et al.:
MR imaging of acoustic neuroma with high resolution fast spin echo T2-weighted sequence. European Journal of Radiology 24, 61-65, 1997

18. Tomandl B.F., P. Hastreiter, K.E.W. Eberhardt, et al.:
Virtual Labyrinthoscopy: Visualization of the Inner Ear with Interactive Direct Volume Rendering. RadioGraphics 20: 547-558, 2000

19. Vogl Th. J., M.G. Mack:
Bildgebende Diagnostik von Tumoren der mittleren Schädelbasis, der Felsenbeine und des Kleinhirnbrückenwinkels [Imaging diagnostics of tumours of the upper skull base, petrous bone and cerebellopontine angle] . In: J. Vogl Th. J., Mäurer, R. Felix (Hrg.) Bildgebende Diagnostik bei Tumoren der Kopf-Hals-Region. Schnetztor-Verlag GmbH, Konstanz, pp 32-57, 1996
[Imaging diagnostics for tumours of the head-throat region.]

20. Yamada I., A. Tsunoda, Y. Noguchi, et al.:
Tumor Volume Measurements of Acoustic Neuromas With Three- Dimensonal Constructive Interference in Steady State and Conventional Spin-Echo MR Imaging. J of Magnetic Resonance Imaging 12: 826-32, 2000

21. Zealley I.A., R.C. Cooper, K.M.A. Clifford, et al.:
MRI screening for acoustic neuroma: a comparison of fast spin echo and contrast enhanced imaging in 1233 patients. The British Journal of Radiology 73: 242-247, 2000

The guidelines were created by the "Quality assurance" committee of the German Society for Neuroradiology.
Members of the committee: Prof. Dr.W.J.Huk (Chair), PD Dr. J. Berkefeld, Dr. U. Grzyska,
Prof. Dr. O. Jansen, PD Dr. M. Mull, Prof. Dr. P. Stoeter

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