[Diagnostic contribution of the new imaging systems in arterial and nerve disorders of the posterior fossa].

Giant aneurysms of the vertebrobasilar system are rare, representing only 5% of intracranial aneurysms and are the cause of severe pseudo-tumoral of hemorrhagic syndromes. Their endovascular or surgical treatment is always very dangerous. The basilar megadolicho-artery, of congenital origin, is frequently expressed by a hemispasm or facial neuralgias. The diagnosis is made easily by TDM and angiography. Abstaining from therapy is the rule. The much debated vascular rings are often held responsible for the microvascular compression syndrome, leading to facial neuralgias, hemispasm, Ménièrie-form or pseudo-tumoral cochleo-vestibular syndrome, neuralgia of the IXth or spasmodic torticollis. The radiological diagnosis is very difficult and mainly depends on MRI. However, quite often, only surgical exploration enables the diagnosis and treatment of the neurovascular compressive syndrome.