Case examples of posterior fossa lesions, not obvious on clinical examination

Timothy C. Hain, MD •. Page last modified: November 16, 2009

Case 1: Posterior Fossa Stroke

A 79 year old woman with diabetes and hypertension, came to medical attention because of an acute ataxia. She had not been taking her medications regularly. A CT scan in the emergency room was read as normal. On examination, she presented with inability to walk, and a direction changing positional nystagmus. There were no cerebellar signs in her limbs, no rebound nystagmus, and no ocular dysmetria. She was started on exercises for lateral canal BPPV, and sent for an MRI scan.

Axial image shows subacute stroke of cerebellum involving vermis Saggital shows lower subtle high signal of lower half of cerebellar vermis

The MRI scan was read as showing a subacute stroke of the cerebellar vermis.

Comment: This patient with multiple risk factors, presented with a mild positional nystagmus and ataxia. In retrospect, the clue that this was a stroke rather than an otologic disturbance was the disproproportion of her symptoms (ataxia) to her signs (mild positional nystagmus), in a context where vascular risk factors were very high.

Case 2: Cerebellar Hemangioblastoma

Axial cerebellar hemangioblastoma. Saggital cerebellar hemangioblastoma

The patient whose MRI is shown above presented with dizziness, unsteadiness and headaches. His examination showed a modest positional nystagmus, as well as papilloedema. There was no saccadic dysmetria. Without examination of the fundus, the diagnosis could not be made.

After the papilloedema was noticed, he had an MRI done and was admitted immediately for neurosurgery. The tumor was not locally invasive, but rather was separable from the cerebellum, and the patient had very little residual.

This case provides a clear example of why neurology participation is desirable in dizziness evaluation centers. If this man had gone to a practice where ophthalmoscopy was not routinely performed, the diagnosis might have been fatally delayed.