Menoufia Medical Journal

ORIGINAL ARTICLE
Year
: 2016  |  Volume : 29  |  Issue : 1  |  Page : 147--151

Current role of MRI in cerebellopontine angle lesions


Mohamed A Maaly1, Amr A Sultan2,  
1 Department of Radiodiagnosis, Faculty of Medicine, Menoufia University, Menoufia, Egypt
2 Department of Radiodiagnosis, Chest Hospital, Menoufia, Egypt

Correspondence Address:
Amr A Sultan
MBBCh, Sabry Abo Alam Street, Shebeen El-Kom, 32521 Menoufia
Egypt

Abstract

Objective The aim of our study is to evaluate the current role of MRI in the diagnosis of cerebellopontine angle lesions. Background MRI is considered the gold-standard method for the diagnosis of cerebellopontine angle lesions. This study aimed to explore an appropriate diagnosis to assess the extent and type of the lesion allowing for proper treatment. Patients and methods This study included 25 patients with symptoms suggestive of neurological disorders. Patients were subjected to different MRI sequences such as precontrast, postcontrast, diffusion MR, and MR spectroscopy. Results Of the 25 patients studied, the final diagnosis by MRI showed acoustic schwannoma in 12 (48.0%) patients, which was the most common lesion, followed by meningioma, was noted in seven (28.0%) patients, epidermoid cyst in one (4.0%) patient, prominent anterior inferior cerebellar artery (AICA) in one (4.0%) patient, paraganglioma in one (4.0%) patient, cystic neurofibroma in one (4.0%) patient, neurofibromatosis type 2 in one (4.0%) patient, and an arachnoid cyst in one (4.0%) patient. Conclusion MRI is the gold-standard method to differentiate the lesions by anatomical site of origin, shape, signal intensity, and behavior after an injection of contrast media.



How to cite this article:
Maaly MA, Sultan AA. Current role of MRI in cerebellopontine angle lesions.Menoufia Med J 2016;29:147-151


How to cite this URL:
Maaly MA, Sultan AA. Current role of MRI in cerebellopontine angle lesions. Menoufia Med J [serial online] 2016 [cited 2019 Dec 10 ];29:147-151
Available from: http://www.mmj.eg.net/text.asp?2016/29/1/147/179006


Full Text

 Introduction



Cerebellopontine angle (CPA) cistern is a subarachnoid space containing cranial nerves and vessels bathed in cerebrospinal fluid. The CPA is bounded by the pons, the anterior aspect of the cerebellum, and the petrous temporal bone covered by dura mater. It is centered by internal auditory canal (IAC) and extends caudally from the Vth cranial nerve to the IX-X-XIth cranial nerve complex [1].

The three most common mass lesions of the CPA region are vestibular schwannomas, meningiomas, and epidermoid cysts. Vestibular schwannomas account for 70-80% of all CPA mass lesions, whereas meningiomas and epidermoid cysts account for 10-15 and 5%, respectively [2],[3],[4].

CPA lesions may present with various signs and symptoms including headache, hearing impairment, and hemiplegia. These clinical symptoms cannot differentiate the pathology or the extent of CPA lesions, hence the need for advanced neurological imaging to assess the extent and type of the lesion allowing for proper treatment [5].

Recent reports of MRI of the normal anatomy and of lesions of the CPA and IAC have been most encouraging. The absence of beam-hardening artifacts, multiplanar imaging capability, and greater intrinsic soft-tissue contrast are emphasized as significant advantages of MRI relative to high-resolution computed tomography in the assessment of tumors of the CPA [6].

 Aim



The aim of this study is to evaluate the current role of MRI in the diagnosis of CPA lesions.

 Patients and methods



This study was carried out on 25 patients, six men and 19 women, during the period between July 2012 and June 2014; their ages ranged from 25 to 55 years. These patients were referred to the MRI Unit, Radiodiagnosis Department, Menoufia University Hospital from the ENT, Neurology, and the Neurosurgery Departments.

Ethical considerations

A simple and clear explanation of the research objectives and procedures was provided to each patient and his/her care giver. Informed consent was obtained before interviewing the patients and they weren't obligated to participate. There was no expected hazards to be anticipated from conducting the study.

The patients presented with one or more of the following symptoms: sensoneural hearing loss, tinnitus, headache, vertigo, hemifacial spasm, neuralgia, and wasting of the muscles of mastication.

Patient preparation

Every patient was checked first for any MRI contraindication - for example, cardiac pacemaker, aneurismal clips, ferromagnetic implants, or nail.

Patients who needed anesthesia were required to be in a fasting state 4 h before the scan. An explanation of the procedure was provided to the patients for reassurance.

Equipment

MR brain was performed using a 1.5-T MR scanner (Excelart Vantage; Toshiba Medical Systems, Otawara-shi, Tochigi, Japan).

Technique

The study was carried out with the patients lying supine with their median sagittal plane perpendicular and coinciding with the midline of the scanner table with a standard circularly polarized head coil.

Conventional magnetic resonance imaging

This was performed using sequences such as axial T1 (TR 485 ms, TE 12 ms), axial T2 (TR 4400 ms, TE 105 ms), axial FLAIR (TR 7200 ms, TE 100 ms), coronal T2 (TR 4300 ms, TE 105 ms), and sagittal T1 (TR 540 ms, TE 17 ms) without contrast.

Postcontrast magnetic resonance imaging

Postcontrast MRI was performed after an intravenous administration of Gadolinium-DTP at a dose of 0.1-0.2 mmol/kg body weight to a maximum dose of 20 ml through an intravenous line within 1 min. The examination was performed immediately after the administration of the injection; the duration ranged from 12 to 15 min according to the protocol used. Contrast-enhanced T1-W1 were obtained in axial, sagittal, and coronal planes.

Magnetic resonance diffusion imaging

Three patients were examined by a diffusion-weighted image MRI sequence. In one of these patients, the diagnosis was unclear, between schwannoma and metastases, and the other patient had cystic lesions that may have been an arachnoid or an epidermoid cyst. Axial diffusion weighted (DW) imaging was performed using a single-shot T2-weighted echo planar spin-echo sequence with the following parameters: 1600/107, b values of 500 and 1000 s/mm 2 ; field of view, 24 × 24 cm; matrix size, 128 × 128; section thickness, 7.5 mm; section gap, 0 mm; and one signal acquired.

DW imaging was calculated and performed automatically using the MR instrument.

Spectroscopic data analysis

MR spectroscopy was performed in two patients. The time versus signal intensity was processed to remove residual water signal. Postprocessing of the spectroscopic data consisted of frequency shift, phase, and linear baseline correlation after Fourier transformation. A frequency domain curve was fitted to the Gaussian line shape using the software provided by the manufacturer to define NAA at 2.02 ppm, choline at 3.02 ppm, Cr at 3.01, and lactate at 1.33 ppm; metabolic values were calculated automatically from the area under the metabolic peak using the standard commercial software program provided by the manufacturer.

Peak integral values were normalized to the internal Cr peak. Metabolite ratios of choline/NAA, NAA/Cho, NAA/Cr, NAA/Cr+Cho, and Cho/Cr were calculated.

 Results



The age of the patients studied ranged from 25 to 55 years (mean 39 years). The most frequently involved age group was 25-35 years [10 (40%) patients] [Table 1].{Table 1}

Lesions appeared in MRI with different signals: in the T1-weighted image, isointense in 20 (80.0%) patients, hypointense in four (16.0%) patients, and hyperintense in one (4.0%) patient, whereas in the T2-weighted image, isointense in 14 (56.0%) patients, hyperintense in 10 (40.0%) patients, and hypointense in one (4.0%) patient [Table 2].{Table 2}

Lesions showed different patterns after contrast administration: as a homogenous enhancement in 16 (64.0%) patients, a heterogenous enhancement in six (24.0%) patients, wall enhancement in one (4.0%) patient, and no enhancement in two (8.0%) patients.

Out of the 25 patients studied, the final diagnosis by MRI indicated acoustic schwannoma in 12 (48.0%) patients, which was the most common pathology, followed by meningioma, which was found in seven (28.0%) patients, an epidermoid cyst in one (4.0%) patient, prominent AICA in one (4.0%) patient, paraganglioma in one (4.0%) patient, cystic neurofibroma in one (4.0%) patient, neurofibromatosis type 2 in one (4.0%) patient, and an arachnoid cyst in one (4.0%) patient [Table 3].{Table 3}

A heterogenous enhancement was found by single intensity after administration of contrast between acoustic schwannoma and meningioma in five (41.7%) patients with acoustic schwannoma and no patient with meningioma and a homogenous enhancement in seven (58.3%) patients with acoustic schwannoma, but it was in seven patients of meningioma (100%). The P value was significant (P = 0.047) [Table 4] and [Figure 1],[Figure 2],[Figure 3] and [Figure 4].{Figure 1}{Figure 2}{Figure 3}{Figure 4}{Table 4}

 Discussion



MRI has traditionally been considered the pivotal imaging test for CPA lesions, providing clinically important information on neurological disorders.

The patients in this study represented age groups ranging from 25 to 55 years, mean age 39. Forty percent of the patients were of the age group 25-35 years; this is in agreement with the study of Asaoka et al. [7].

Patients with CPA lesions have many symptoms. The most common presenting symptoms are hearing loss (68%), headache (40%), tinnitus (36%), neuralgia (20%), vertigo (8%), and finally, hemifacial spasm and wasting muscles of mastication (4%); that is in agreement with the study of Walsh et al. [8].

The final diagnosis by MRI of CPA lesions showed that acoustic schwannoma (48.0%) was the most common pathology, followed by meningioma (28.0%), epidermoid cyst (4.0%), prominent AICA (4.0%), paraganglioma (4.0%), cystic neurofibroma (4.0%), neurofibromatosis type 2 (4.0%), and arachnoid cyst (4.0%). The study of Springborg et al. [9] reported that the most common CPA lesions were vestibular schwannomas (80%), followed by meningiomas (10%) and epidermoids (6%).

In our study, schwannomas were shown by T1-weighted images as isointense (91.7%) and hypointense (8.3%) and in T2-weighted images as hyperintense (33.3%), isointense (58.3%), and hypointense (8.3%). Signal intensity after contrast showed heterogenous enhancement (41.7%) and homogenous enhancement (58.3%).

Breuer et al. [10] reported that schwannomas on T1-weighted images appear isointense to hypointense to the brain. On T2-weighted images, they are hyperintense and may be inhomogeneous. The inhomogeneity may reflect cystic degeneration, hemorrhage, or vascularity of the lesion. Often, these lesions are rather round or oval in their cisternal portion, and they taper as they extend into the IAC. The lesions show homogenous enhancement and some show heterogenous after contrast administration.

The current study revealed that comparison between acoustic schwannoma and meningioma by T1-weighted images as hypointense of acoustic schwannoma (8.3%) while meningioma hasn't 0.0%), on the otherhand isointense of acoustic schwannoma was (91.7%) but meningioma was (100%) and hyperintense in no patient of both acoustic schwannoma and meningioma (0.0%).

In T2-weighted images hypointensity was observed in acoustic schwannoma (8.3%) but no patient in meningioma (0.0%) had such changes. other MRI findings were observed e.g. isointense acoustic schwannoma (58.3%) and meningioma (71.4%) and hyperintense of acoustic schwannoma (33.3%) and meningioma (28.6%).

In our study, a comparison between acoustic schwannoma and meningioma was done by signal intensity after contrast administration. Heterogenous enhancement was observed in acoustic schwannoma (41.7%) which wasn't found in patients with meningioma. Homogenous enhancement was observed in acoustic schwannoma (58.3%), but it was predominant in meningioma (100%).

In our study, comparison between acoustic schwannoma and meningioma by associated MRI findings indicated that lesions had a dural base (28.6%) and a dural tail (71.4%) in meningioma, whereas acoustic schwannoma did not (0.0%). Extension into the IAC was observed in acoustic schwannoma, but not in meningioma.

As reported by Lalwani and Jackler [11], differentiation between meningioma and schwannoma on the basis of their radiological appearances is not difficult. As meningiomas rarely expand the IAC, usually have a broad base against petrous bone, and usually have strong homogeneous enhancement that is not found in schwannoma. On the other hand schwannoma expand the IAC with component inside it and heterogenous enhancement is observed after contrast administration.

 Conclusion



MRI can be considered the most useful method to improve the sensitivity of CPA lesions detection.

MRI is the gold-standard method to differentiate the lesions by the anatomical site of origin, shape, signal intensity, and behavior after an injection of contrast media. In some cases, a complementary advanced MRI technique such as diffusion-weighted image and spectroscopy may be needed.

 Acknowledgements



Conflicts of interest

None declared.

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