No abstract

The authors report the results of a long-term follow-up study of the effects of the physiologically defined selective VIM (nucleus ventralis intermedius)-thalamotomy on tremor of Parkinson's disease in 27 patients and essential tremor in 16 patients. The follow-up period ranged from 3.25 to 10 years (mean 6.58 years). In 43 patients a total of 50 operations (including four bilateral operations and three reoperations) were carried out. The early (2 to 4 weeks after surgery) and late effects on the tremors were determined clinically and electromyographically. Fourteen parkinsonian cases were treated with minimal lesions (about 40 cu mm). Their late results were very similar to the early results: in 10, the tremors were completely abolished, three had a slight residual tremor, and one underwent reoperation 3 months after the first surgery. Eleven essential tremor cases were treated with minimal lesions. Six of these tremors were completely abolished, four patients had slight residual tremors, and one patient with a recurrence underwent reoperation 2 years after the initial surgery. In these 23 successful operations with minimal lesions (excluding two cases with reoperation), the tremor was abolished without discernible long-lasting side effects. The other 23 operations on 16 patients with Parkinson's disease (including one reoperation) and on seven with essential tremor (one of whom also had a minimal lesion on the other side) involved relatively large lesions. In this group, the surgery was successful in almost every case. It was concluded that radiographically and physiologically monitored selective VIM-thalamotomy for parkinsonian and essential tremor is effective even when lesioning is minimal. Moreover, the beneficial effect is maintained over a long period of time.

GK thalamotomy is an alternative treatment for intractable tremors of PD as well as for ET. Less invasive intervention may be beneficial to patients.

After stereotactic radiosurgery (SRS) for brain metastases, delayed radiation effects with mass effect may occur from several months to years later, when tumors may also recur. Aggressive salvage treatment would be beneficial for patients with recurrence, but may be contraindicated for those with dominant radiation effect. Conventional magnetic resonance (MR) imaging does not provide sufficient information to differentiate delayed radiation effects from tumor recurrence. Positron emission tomography, MR spectroscopy, and other modalities sometimes may lead to false findings of tumor recurrence. We prospectively applied perfusion MR imaging for the management strategy after SRS because it gives microvascular information about the lesions. Twenty-eight lesions were enlarged on serial MR images in 27 patients 2-35 months (median: 11.8 months) after SRS for metastatic brain tumors. Each patient underwent MR perfusion imaging within a month after appearance of the growing enhanced lesion. To calculate the relative cerebral blood volume ratio (rCBV ratio), the regions of interest were located in the enhanced areas on the contrast-enhanced T1-weighted images and compared with the corresponding contralateral normal brain tissue. They were then followed-up with scheduled MR images with gadolinium enhancement at 1 to 2-month intervals afterward. Lesions which progressively increased in size on MR images were diagnosed as recurrences; lesions which disappeared or decreased in size were diagnosed as radiation necrosis. In addition, two lesions surgically removed were diagnosed by pathological examination. Follow-up MR images revealed that 21 of 28 lesions were radiation necrosis. Five lesions were diagnosed as recurrence on MR images, and the other two lesions were revealed as recurrence by pathological examination. An rCBV ratio of greater than 2.1 provided the best sensitivity and specificity for identifying recurrent metastatic tumors, at 100 and 95.2%, respectively. Perfusion MR imaging provides useful, less invasive and in-vivo information for management of growing lesions after SRS, and rCBV may be a valuable index for this diagnostic purpose.

In 51 cases (6 cases with bilateral operations) with various kinds of tremor, stereotaxic ventralis intermedius (Vim) thalamotomies were performed using Leksell's apparatus and the results of operation evaluated. Several characteristics of the tremor, including clinical features and EMG, were correlated with the assumed location and volume of the coagulative lesion. In 54 of the 57 operations, the thalamic Vim nucleus was identified physiologically and a therapeutic lesion placed at a site that included the Vim neurons. In all these cases, except one in which the lesion was estimated to be too small, tremor was immediately abolished by a relatively small lesion. The estimated volume of the lesion was about 40 to 200 mm3 and the effect persisted over a long follow-up period (maximum ten years). The size of the lesion that was necessary apparently depended on several features of the tremor. A larger lesion was required in cases of movement type tremor, tremor with a low rate (less than 4 Hz), tremor of high amplitude (more than 600 microV), and tremor involving proximal muscles or with a wide distribution. Tremor following a cerebrovascular lesion and post-traumatic tremor were characterized by coarse oscillation (high amplitude and low frequency) involving proximal muscles. A relatively larger coagulative lesion was therefore necessary to relieve this type of tremor. In contrast, parkinsonian and essential tremor were usually of low amplitude and distal in distribution. For the relief of such tremor, the lesion could be very small: if aided by electrophysiological methods to identify Vim neurons, the minimal effective volume of the lesion was estimated as about 40 mm3 and restricted to the Vim nucleus. Based on these results, the importance of the Vim nucleus in tremor mechanisms is discussed.