Magnetic Resonance Imaging Evaluation of Extra Axial Cerebellopontine Angle Tumours

Author(s): Ramanna H.C.1 , Mohan S.2 , Shobhalakshmi C.S.3

BACKGROUND Cerebello-Pontine Angle (CPA) tumours are classified into extra-axial, intra-axial, extradural and petrous axis tumours and are usually benign. Depending on the origin of tumour and neurovascular structures displacement, CPA tumours can be asymptomatic or may present with tinnitus, vertigo or unilateral hearing loss. We wanted to study the magnetic resonance imaging (MRI) characteristics of extra axial CPA tumours and assess the incidence of extra axial CPA tumours. METHODS Patientswith signs and symptoms of CPA tumours and diagnosed with CPA tumour on computed tomography were analysed and MRI was performed with contrast study. RESULTS Tumours of CPA are not uncommon and represent 6 - 10 % of intracranial tumours. In extra axial CPA tumours, schwannoma (50 %), meningioma (30 %) are the most common; less common are arachnoid cyst (12.5 %) and epidermoid cyst (7.5 %). Schwannomas are the most common extra axial CPA tumours followed by meningioma. Schwannomas are enhancing masses most commonly arising from the vestibular nerve, usually round in shape with associated extension into internal auditory canal showing intense heterogeneous enhancement; meningiomas are hemispherical or oval shaped lesions with a broad attachment to the tentorium or dura mater usually shows intense homogeneous enhancement. Epidermoid cysts and arachnoid cysts appear with CSF signal intensity on all the MRI sequences; epidermoid cyst shows restriction on DWI but arachnoid cyst does not show restriction on DWI and is suppressed on FLAIR sequences. CISS image clearly demonstrates the epidermoid cyst. CONCLUSIONS MRI is the most sensitive non-invasive modality to evaluate extra axial CPA tumours. MRI helps to detect the location and describes the extension of the lesions based on their signal characteristics and contrast enhancement patterns.