In this study we compared the position of the electronically active contact of the thalamic (Vim) deep brain stimulation (DBS) electrode to the stereotactic location of its tip. Fifteen patients with either Parkinson’s disease (PD) or essential tremor (ET) underwent stereotactic, MRI-based placement of the Medtronic quadripolar DBS electrode. An overall improvement of 69% was achieved in the tremor scores during a period of 1–13 months after implantation of the DBS electrode. Eleven patients with ET showed 70% clinical improvement of tremor, compared to a 58% response observed in the 4 patients with PD. The electrode tip center was 11.2 ± 1.54 mm lateral to the third ventricular wall, 5.38 ± 1.02 mm anterior to the posterior commissure and 2.9 ± 3.57 mm inferior to the level of AC–PC line. The most significant deviation from the planned stereotactic target was observed in the Z-coordinate. In our group of patients, stimulation settings favored the contacts closer to the AC–PC line, correcting the electrode tip position to 0.80 ± 2.84 mm (p < 0.001) inferior to the level of the AC–PC line. In our experience, thalamic DBS offers a reversible and adjustable ‘lesion’ to compensate for the anatomic variabilities encountered in the positioning of the DBS electrode tip.

The purpose of this study was to analyze the significance of perinidal T₂ hyperintensity appearance after radiosurgery of arteriovenous malformations (AVMs), as a predictor of treatment response. Our initial experience with linear accelerator (LINAC) radiosurgery at University of California, Los Angeles, between 1990 and 1997 involved treatment of 129 patients affected by cerebral AVMs. Based upon availability of neuroimaging follow-up, 48 patients with 50 AVMs were selected for review. Forty (80%) of the AVMs underwent complete obliteration or significant reduction on follow-up MRI, on average 20 months after radiosurgery. Thirteen (72%) of 18 obliterated AVMs were associated with perinidal T₂ hyperintensity signal, on average 18 months (6–49) after radiosurgery. Ten (20%) of 50 AVMs (average volume 23.1 cm³, ranging 7.5–46.5) were unchanged. Furthermore, only 3 AVMs in this group showed reversible T₂ signal changes. In patients with complete nidal obliteration, appearance of T₂ hyperintensity signal achieves 72% sensitivity in predicting successful treatment response.

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