POSTERIOR FOSSA ANEURYSMS PRESENTING AS MASS LESIONS

¹ From the Departments of Radiology (Neuroradiology) and Neurology, College of Medicine, University of Iowa, Iowa City, Iowa.

Aneurysms of the posterior fossa represent approximately 8 per cent of all intracranial aneurysms. These aneurysms may rupture to produce the familiar picture of subarachnoid hemorrhage, may be asymptomatic or may enlarge without rupturing to produce a multitude of neurologic symptoms. The diffuse ectasias of the vertebro-basilar system rarely rupture but may be indistinguishable clinically from a large aneurysm.

Posterior fossa aneurysms or ectasias may mimic cerebellopontine angle tumor, especially acoustic neuroma or pontine glioma and "posterior fossa mass." Less frequently, such an aneurysm or ectasia may precipitate a psychosis, trigeminal or glossopharyngeal neuralgia, or a spinal cord lesion.

The most characteristic clinical picture of a patient with a large unruptured posterior fossa aneurysm or ectasia is a prolonged, episodic and progressive course of cerebellar, pontine or medullary symptoms and signs. Headaches, disturbances of equilibrium, nystagmus, lower cranial nerve involvement and pyramidal signs with little sensory impairment should suggest the possibility of a posterior fossa aneurysm.

Vertebral arteriography should be performed in any patient in whom the clinical or roentgenologic findings suggest the possibility of a basilar artery aneurysm.

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