Imaging

Structural

Patients with obsessive-compulsive disorder and anxiety disorders who had a stereotactic gamma anterior capsulotomy were assessed by magnetic resonance imaging.(33) Patients in whom the left-sided lesion was absent or minimal did not experience a good clinical outcome. In addition, a strong correlation was found between the adequacy of the lesion and the postoperative level of social functioning.

In stereotactic subcaudate tractotomy (with an yttrium-rod insertion) prominent oedema, which caused a change in signal of between 23 and 48 per cent of the total brain volume, was observed 2 weeks postoperatively using magnetic resonance imaging.(34) However, the oedema does subside, and by 1 year only the lesion is visible with an estimated volume of between 200 and 1300 mm3. Loss of tissue and gliosis were reflected in significant ventricular enlargement, which had been measurable 3 months after surgery and had not progressed further at 6 months or 1 year.

Structural magnetic resonance imaging is likely to remain a useful tool in verifying the extent and position of lesions.

Functional

The effects of stereotactic anterior capsulotomy have been examined using the 133Xe inhalation technique(35) and [11C]glucose positron emission tomography,(36> which have demonstrated medial frontal, orbitofrontal, and caudate nuclei decreases in brain metabolism postoperatively. These brain areas have all been demonstrated to have abnormal metabolism in obsessive-compulsive disorder, thus indicating that the capsulotomy affects relevant anatomical targets.

Hexamethylpropylene amine oxide (HMPAO) single-photon emission tomography has been used to examine cerebral blood flow changes following stereotactic subcaudate tractotomy^,37) in patients with treatment-resistant affective disorders. Large decreases were observed in the orbitofrontal, frontal, anterior cingulate, and ventral striatal HMPAO signal 2 weeks after surgery. However, none of these were predictive of outcome. At 6 months there were significant decreases in HMPAO activity in low frontal (orbitofrontal) and low anterior cingulate cortex, while there were significant increases in the parietal lobe. These changes were mostly accounted for by outcome, whereby ventral anterior cingulate and frontal decreases were associated with a good outcome and parietal increases with a poor outcome. These findings are congruent with the notion that stereotactic subcaudate tractotomy affects brain anatomical circuits of human mood.

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