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Tetsuya Takahata, Yoichi Katayama, Takashi Tsubokawa, Hideki Oshima and Atsuo Yoshino

✓ Intracranial ectopic pituitary adenoma occurs most frequently in the suprasellar cistern, usually in continuity with the pituitary stalk. Such tumors probably originate from cells of the pars tuberalis located above the diaphragma sellae or from aberrant anterior pituitary cells of the pituitary stalk. The authors report the case of a 37-year-old woman with Cushing's syndrome caused by an ectopic pituitary adenoma of unique location: the tumor was separate from the pituitary stalk and confined within the interpeduncular cistern. After surgical removal of the tumor, continued improvement in the patient's laboratory results and disappearance of her endocrine symptoms strongly indicated the absence of adenoma cells in the pituitary gland or stalk. The tumor in the present case appears to have arisen from aberrant pituitary cells that were present in the leptomeninges of the basal surface of the hypothalamus.

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Takao Watanabe, Yasuhide Makiyama, Hiroshi Nishimoto, Masatomo Matsumoto, Akira Kikuchi and Takashi Tsubokawa

✓ A case of suprasellar germ-cell tumor in a 9-year-old girl who later developed ovarian dysgerminoma is reported. The clinical course of the case is described and a double-primary tumor, rather than metastasis from either tumor to the other, is suggested by the authors to explain the oncogenesis in this patient.

The authors strongly encourage that patients with intracranial germinoma be examined for associated extraneural lesions before, as well as after, the completion of the initial therapy.

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Takashi Tsubokawa, Yoichi Katayama and Takamitsu Yamamoto

✓ Persistent hemiballismus after stroke is often difficult to treat. The ballistic movement is sometimes so violent that progressive exhaustion results. The authors report two such cases, which were successfully treated by chronic thalamic stimulation. The lesions responsible for the ballistic movement in these patients were located near the subthalamic nucleus and in the putamen, respectively. The thalamic nucleus ventrolateralis and nucleus ventralis intermedius were stimulated with 0.2 to 0.3 msec pulses at 50 to 150 Hz and 4 to 7 V continuously during the day. Several weeks later, complete control of the hemiballismus was achieved during stimulation. The improvement was clearly not attributable to spontaneous recovery, because ballistic movement reappeared after termination of the stimulation. The stimulation has remained effective for more than 16 months in both cases without any serious complications. Chronic thalamic stimulation appears to be useful for controlling persistent hemiballismus, as it is for other involuntary movement disorders.

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Yoichi Katayama, Takashi Tsubokawa, Teruyasu Hirayama and Kazuhisa Himi

✓ Jugular bulb oxygen saturation (SjO2) was monitored during preoperative embolization procedures in a consecutive series of 15 patients with large supratentorial arteriovenous malformations (AVM's) in order to test the hypothesis that changes in the shunt flow ratio can be continuously evaluated from the SjO2. A fiberoptic catheter was placed at the dominant jugular bulb. The SjO2 measured using jugular blood withdrawn before embolization was significantly higher than the SjO2 measured at the end of the final embolization procedure (mean ± standard deviation 84.1% ± 12.7% vs. 74.2% ± 10.9%, p < 0.0001), showing a positive correlation with the AVM volume (r = 0.66, p < 0.001). Continuous monitoring of SjO2 via the fiberoptic catheter revealed a progressive decrease in association with the embolization procedures. Microsurgical resection of the AVM was performed at 1 to 2 weeks after the final embolization. Cases in which postoperative hemispheric deformation was revealed on computerized tomography demonstrated a higher SjO2 at the end of embolization compared to that in the remaining cases (81.6% ± 8.6% vs. 67.8% ± 8.4%, p < 0.008). Hemispheric deformation was observed in all cases in which the SjO2 did not decline to a level below 90% following embolization. The risk of severe hyperemic complications appeared to be greatly diminished when the SjO2 fell to below 80%. Assuming that the oxygen saturation of the perfusion flow (SjpO2) ranges from 50% to 75%, the ratio of the shunt flow to total flow at an SjO2 of 90% was estimated to be 0.6 to 0.8 based on the following equation: shunt flow/(perfusion flow + shunt flow) = (SjO2 − SjpO2)/(arterial oxygen saturation − SjpO2). These results suggest that monitoring the SjO2 provides real-time information concerning the progress of embolization and helps to determine whether the embolization has progressed sufficiently to avoid postoperative hyperemic complications.

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Yoichi Katayama, Takashi Tsubokawa, Tsuyoshi Maeda and Takamitsu Yamamoto

✓ In order to determine adequate therapeutic approaches for cavernous malformations of the third ventricle, the authors reviewed a series of five such malformations managed at their institution and nine others reported in the literature. Four subgroups were identified in terms of the site of origin and could be characterized by different clinical manifestations: visual field defects and endocrine function deficits in patients with malformations in the suprachiasmatic region (six cases); symptoms caused by hydrocephalus in those with malformations in the foramen of Monro region (five cases); and deficits of short-term memory in those with malformations in the lateral wall (two cases) or of the floor of the third ventricle (one case). Unlike cavernous malformations at other locations, malformations of the third ventricle frequently demonstrated rapid growth (43%) and mass effects (71%). The surgical or autopsy findings suggested that the growth was attributable to repeated intralesional hemorrhages. Extralesional hemorrhage was also not uncommon, occurring in 29% of patients. Such tendencies require the adoption of a more aggressive approach to this particular group of cavernous malformations as compared to those in other locations. The risks of regrowth and extralesional hemorrhage appear to be reduced only by complete excision. The surgical approaches adopted should be aimed at providing the best access to the site where the malformation has arisen. The translamina terminalis approach for cavernous malformations in the suprachiasmatic region, the transventricular or transcallosal interfornicial approaches for those in the foramen of Monro region and the transvelum interpositum approach for those in the lateral wall or the floor of the third ventricle appear to be appropriate. In order to select the adequate surgical approach, precise diagnosis of the site of origin is crucial. In addition to neuroimaging techniques, the patient's initial symptoms provide valuable information.

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Takashi Tsubokawa, Yoichi Katayama, Takamitsu Yamamoto, Teruyasu Hirayama and Seigou Koyama

✓ Analysis of the authors' experience over the last 10 years has indicated that excellent pain control has rarely been obtained by thalamic relay nucleus stimulation in patients with thalamic pain. In the present study, 11 patients with thalamic pain were treated by chronic stimulation of the precentral gyrus. In eight patients (73%), the stimulation system was internalized since excellent pain control was achieved during a 1-week test period of precentral gyrus stimulation. In contrast, no clear effect was noted or the original pain was even exacerbated by postcentral gyrus stimulation. The effect of precentral stimulation was unchanged in five patients (45%) for follow-up periods of more than 2 years. In the remaining three patients, the effect decreased gradually over several months. This outcome was significantly better than that obtained in an earlier series tested by the authors with thalamic relay nucleus stimulation (p < 0.05). The pain inhibition usually occurred at intensities below the threshold for production of muscle contraction (pulse duration 0.1 to 0.5 msec, intensity 3 to 8 V). When good pain inhibition was achieved, the patients reported a slight tingling or mild vibration sensation during stimulation projected in the same area of distribution as their pain.

The authors discuss the possibility that, in deafferentation pain, sensory neurons below the level of deafferentation cannot exert their normal inhibitory influences toward deafferented nociceptive neurons because of the development of aberrant connections. Thus, while stimulation of the first- to third-order sensory neurons at the level of the thalamic relay nucleus or below cannot bring about good pain inhibition in patients with thalamic pain, activation of hypothetical fourth-order sensory neurons through precentral stimulation may be able to inhibit deafferented nociceptive neurons within the cortex. None of the patients developed either observable or electroencephalographic seizure activity.

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Yoichi Katayama, Takashi Tsubokawa, Takehiko Hirasawa, Tetsuya Takahata and Norimichi Nemoto

✓ Chordomas that are entirely extraosseous and intradural are extremely rare. The tumors described in the literature were observed mostly in the prepontine region. This is the first case reported of an intradural extraosseous chordoma occurring in the foramen magnum region. The tumor was totally excised. The distinction between an intradural extraosseous chordoma and a classic chordoma is important from a clinical viewpoint because of the potential for complete surgical excision and a more benign growth pattern.

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Kenshi Yoshida, Saburo Nakamura, Takashi Tsubokawa, Jun Sasaki and Tadashi Shibuya

✓ A case of epithelial cyst in the fourth ventricle of a 4-year-old child is described. A single epithelial layer with a clear basement membrane lining the cyst wall was observed. There were no prominent histological findings to suggest a pathogenesis for this cyst based on immunohistochemical or ultrastructural studies; however, the cyst fluid contained significant amounts of carcinoembryonic antigen. It is considered that the epithelial layer lining the cyst wall was possibly of endodermal origin.