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A 29-year-old woman presented with blurred vision of 2 week’s duration. She had consulted an optometrist to have her eyeglass prescription checked and was told that she should visit a doctor.

She had a six-month history of intermittent headaches and diminished hearing on the right. She had been to a doctor on two prior occasions for the headache and was prescribed a mild analgesic with some relief. She had mentioned the hearing loss to the doctor, but no further work up was done.

On examination, she was a healthy appearing woman in no distress. There was markedly diminished hearing on the right. The Weber test localized to the left. Pupillary response and extraocular motion were intact, with slight rotary nystagmus in all directions. There was diminished sensation on the right side of the face. The right corneal reflex was diminished. The gag reflex was also diminished on the right. The tongue was midline. Visual acuity with corrective lenses was 20/25 right eye, 20/30 left eye. Funduscopic examination revealed bilateral papilledema and no hemorrhages.

  • What is this patient’s diagnosis?

Her head CT is shown in Figure 1.

The clinical presentation of this patient is classic for an acoustic schwannoma (formerly called acoustic neuroma) or other cerebello-pontine angle tumor. Unfortunately, diagnosis of this disease is occasionally delayed because of its gradual onset and a failure to appreciate the significance of unilateral hearing loss. In this patient, the tumor had grown to a large size causing obstructive hydrocephalus and papilledema.

Tumors (and abscesses) can often be detected on noncontrast CT because the lesions are hypo- or hyperattenuating (appear darker or lighter) relative to normal brain tissue. In addition, surrounding edema and mass effect distorts other anatomical structures. Lesions in the posterior fossa are, however, often difficult to detect by CT. This is because adjacent thick cortical bone creates beam-hardening artifacts, which diminish the ability of CT to visualize anatomical detail and to detect slight differences in tissue density (Figure 1, images 10 and 11).

In this patient, the right side of the cerebellum has slightly lower attenuation (appears darker) than the left (Figure 1, images 8 and 9). More importantly, the fourth ventricle is compressed and displaced toward the left, which indicates that the tumor is on the right and compressing the cerebellum and brainstem. In addition, the temporal horns of the lateral ventricles and the third ventricle ...

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