Magnetic resonance tomography aids in neuro diagnoses

NUREMBERG, Germany — Magnetic resonance tomography can be a helpful test for definitive diagnosis in neuro-ophthalmic conditions where functional tests alone are not enough, according to a speaker here.

"There is no doubt that that magnetic resonance tomography (MRT) has extended our 'field of vision' so to speak," said Prof. Dr. med. Guntram Kommerell. "But you must also understand the limitations of this new technique."

Prof. Kommerell, a neuro-ophthalmologist from Freiburg, Germany, delivered the Ridley Lecture here at the German Ophthalmic Surgeons meeting, on the topic of on neuro-ophthalmology in the age of MRT.

Prof. Armin Scharrer introduced the speaker with mock disbelief.

"A Ridley Lecture to be read by a neuro-ophthalmologist?" Prof. Scharrer said. "This is a wide span, between microsurgery and a scientist who works in a field which seems strangely a bit off.”

But Prof. Kommerell noted that Prof. Harold Ridley, for whom the lecture is named, understood that ophthalmic surgery is only part of ophthalmology.

Prof. Kommerell explained that MRT can help to arrive at a diagnosis when functional tests do not tell the whole story.

He describe the case of a patient with pituitary adenoma with typical preoperative defects on perimetry. Postoperatively the left eye was blind, but the right eye was relatively unaffected; function was fully preserved, Prof. Kommerell said. Ophthalmologists continued to see the patient during the follow-up period, and because there was preserved function no one saw any reason for neuroradiological diagnosis.

"But when a computer tomogram was made after some time, it was seen that a recurrence of the pituitary adenoma had in fact occurred," Prof. Kommerell said. "Was this a surprise? Not really, because one thing is for sure; in a position where the optic nerve is already atrophic and when no functioning fibers exist, a recurrence won't be detected."

A relapse can be identified by further deterioration of visual function, Prof. Kommerell said. He concluded that visual field is a sensitive indicator only during initial diagnosis, not later during follow-up. That is when MRT is needed, he said.

However, there are limitations to even this technology, and MRT coupled with functional tests still may not be enough. He presented another case example confirming the limitations of MRT.

A female patient that was referred to a neurologist with bilateral loss of visual field. The neurosurgeon was ready to operate for pituitary adenoma, but Prof. Kommerell said he saw that the temporal defects in this patient also affected the nasal segments, which is typical of refractive scotoma.

"Perimetry was not mapped correctly because of ectasia of the bulb," Prof. Kommerell said. "For necessary examination you need to examine from the direction where you see the losses. We found that you needed -7 D in order to get a clear image of the fundus."

Prof. Kommerell said he told the neurologist about his findings and the neurologist agreed that it does happen every now and again, that the pituitary was as large as he had found it, but without the presence of adenoma. But this patient, according to the neurologist, had been referred for temporal visual defects. "So this was an ophthalmologic misinterpretation, and this actually led the neurologist on the wrong track," Prof. Kommerell said. "The compression of vision, part of it can only be diagnosed with the help of a corresponding MRT plus characteristic impairments of function. These two really belong together."

The benefit of MRT, Prof. Kommerell said, is that MRT can show a tumor recurrence even in “silent” areas of the visual pathway. "However, it cannot tell us if the optic nerve is under compression," he said. "MRT can show the cause or motility disturbances, but only if you ask adequate questions. It will not supply any information in the case of functional disturbances."