Retinotopic organization of the visual cortex before and after decompression of the optic chiasm in a patient with pituitary macroadenoma

Case report

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Compression induced by a pituitary tumor on the optic chiasm can generate visual field deficits, yet it is unknown how this compression affects the retinotopic organization of the visual cortex. It is also not known how the effect of the tumor on the retinotopic organization of the visual cortex changes after decompression. The authors used functional MRI (fMRI) to map the retinotopic organization of the visual cortex in a 68-year-old right-handed woman before and 3 months after surgery for a recurrent pituitary macroadenoma. The authors demonstrated that longitudinal changes in visual field perimetry, as assessed by the automated Humphrey visual field test, correlated with longitudinal changes in fMRI activation in a retinotopic manner. In other words, after decompression of the optic chiasm, fMRI charted the recruitment of the visual cortex in a way that matched gains in visual field perimetry. On the basis of this case, the authors propose that fMRI can chart neural plasticity of the visual cortex on an individual basis and that it can also serve as a complementary tool in decision making with respect to management of patients with chiasmal compression.

Abbreviations used in this paper:fMRI = functional MRI; V1 = primary visual cortex.

Article Information

Address correspondence to: Neil Duggal, M.D., M.Sc., F.R.C.S.C., Division of Neurosurgery, Clinical Neurological Sciences, University Hospital, London Health Sciences Centre, 339 Windermere Road, London, Ontario N6A 5A5, Canada. email: neil.duggal@lhsc.on.ca.

Please include this information when citing this paper: published online June 8, 2012; DOI: 10.3171/2012.4.JNS112158.

© AANS, except where prohibited by US copyright law.

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Figures

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    Pattern deviations for the automated Humphrey perimetry 30-2. Numeric values represent the difference in luminance (in dB) between the patient's ability to detect a light and the expected age-corrected normal values at each test point in the visual field (while also adjusting for any shifts in overall sensitivity) for the left eye before the second operation (A), the right eye before the second operation (B), the left eye after the second operation (C), and the right eye after the second operation (D). Up to 30° in visual angle was tested, corresponding roughly to what was examined with fMRI (28°). Numbers in the gray and black squares represent points in the visual field that fall in the lower 5% and 1% ranges, respectively, for what is expected for the patient's age. Note that this patient showed a profound visual defect in her left lower visual field before the surgery. Raw measurements (in dB) are also shown in Fig. 3 after data interpolation was made with a cubic spline.

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    Preoperative and postoperative T1-weighted MRI studies. Examination of the patient's T1-weighted MRI studies reveal compression of the left optic nerve and the left portion of the optic chiasm (both indicated by the yellow arrows) before the patient's second operation (A). This operation resulted in a decompression of these structures (B). Note that the images are oriented in “radiological” convention with the left side indicating right and the right side indicating left. RH = right hemisphere.

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    Retinotopic results. The retinotopic activation is superimposed on a reconstructed cortical surface viewed from the back for the left V1 representing the right visual field before surgery (A), the right V1 representing the left visual field before surgery (B), the left V1 representing the right visual field after surgery (C), and the right V1 representing the left visual field after surgery (D). Also displayed for illustrative purposes are the results from the Humphrey automated perimetry (in dB) after a cubic spline was used for data interpolation. The activation is color coded such that cool colors represent the lower visual field (dark blue to light blue: the vertical meridian to the horizontal meridian) and warm colors represent the upper visual field (red to yellow: the vertical meridian to the horizontal meridian).

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    Bar graphs showing the changes in fMRI retinotopy and changes in the Humphrey automated perimetry. The graphs demonstrate the amount of gray matter activation in V1 representation for different visual fields (VFs) (A), the intensity of light detected during the Humphrey automated perimetry in different visual fields (B), the correlation between the intensity of light during the Humphrey automated perimetry and the amount of activated gray matter V1 across different visual fields before and after the operation (C), and the correlation between differences (Diffs) in the Humphrey automated perimetry and the amount of V1 recruitment (D). Each circle represents a different visual field quadrant.

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