Acoustic neuromas (vestibular schwannomas) comprise more than 90 per cent of all cerebello-pontine angle (CPA) lesions. We present a rare case of a giant vertebro-basilar aneurysm presenting as a CPA lesion. The general condition of the patient precluded the completion of the magnetic resonance (MR) sequences. The clinical and limited radiological results (T2 images alone, the features of which were not specific) initially did not lead to a specific diagnosis. To obtain further radiological information a computed tomography (CT) scan with contrast was performed and this revealed the lesion to be an aneurysm. The diagnostic difficulties and the treatment dilemmas of such a lesion are discussed. The importance of fine, axial, post-contrast CT arteriography with three-dimensional reconstruction, MR angiography and digital subtraction angiography are highlighted. The limitations of MR imaging in patients with CPA lesions are discussed.

A case report of a six-year-old child is presented, who had had a unilateral sensorineural hearing loss for several years. Because of impairment in the ABR as well as in the caloric testing a MRI and CT scan were performed. A 17 mm tumour in the cerebellopontine angle (CPA) was detected, which after suboccipital surgery proved to be a rhabdomyoma. This tumour has not been described before in the CPA. Unilateral sensorineural hearing loss should, at all ages, be an indication for further (radiodiagnostic) investigations.

Fifty-nine unusual cerebello-pontine angle tumours have been studied. These lesions represent 19.3 per cent or 1 in 5 of a series of 305 cerebello-pontine angle tumours of which the rest, 246 (80.7 per cent), were acoustic neuromas. An analysis of the relative incidence, histology and presenting clinical features has been carried out. The various radiographical features and imaging techniques used to diagnose these fascinating tumours have been described and also the otoneurosurgical procedures necessary to excise them.