Shigeki Nakano

The effect of EC-IC bypass surgery on resting cerebral blood flow and cerebrovascular reserve capacity studied with stable Xe-CT and acetazolamide test

SummaryCerebral blood flow (CBF) and cerebrovascular reserve capacity (CRC) were measured by stable xenon computerized tomography (Xe-CT) and acetazolamide test in 15 patients with cerebrovascular disease before and after extracranial-intracranial (EC-IC) bypass surgery for minor stroke, reversible ischemic neurological deficit or transient ischemic attack. All had angiographically shown occlusive lesions of the major arterial trunk. In the present series, global analysis showed that the bypass did not increase the resting rCBF, but did increase the rCRC. We divided the patients into four groups according to the preoperative resting rCBF and rCRC. All 3 patients with normal resting rCBF and reduced rCRC showed postoperative improvement of rCRC. Of 6 patients with reduced CBF and reduced CRC, three had postoperative increase in resting CBF and four had increased CRC. One of two patients with reduced CBF and normal CRC showed only an increase in CRC. We propose that reduced CRC or reduced CBF with reduced CRC are criteria for selection of candidates for bypass surgery. We conclude that Xe-CT with the Diamox test is a useful and simple method for evaluating cerebral hemodynamics. Preoperative grouping with a combination of preoperative resting cCBF and preoperative rCRC is useful for predicting the effect of EC-IC bypass surgery.

Brain perfusion studies by xenon-enhanced CT using washin/washout study protocols.

Very short inhalation times and short total examination times are desirable in cerebral blood flow measurements by xenon enhanced CT to minimize the possibility of flow activation and--more importantly for practical purposes--the probability of patient motion due to the effects of xenon. We have investigated washin/washout procedures and have compared them with conventional washin scanning protocols by simulation and in clinical studies. Examination protocols with only 3 min of inhalation and up to eight scans, all taken at 1 min intervals, provide flow estimates with smaller SDs than would be obtained for washin studies taken with the same total radiation dose. Compared with a standard 8 min washin procedure, a 3 min washin/5 min washout study using the same dose yields an SD reduction by a factor of 1.3 for low flow areas and of 1.8 for high flow gray matter. A 3 min washin/3 min washout study, employing only 78% of the dose of an 8 min washin study, will still provide an SD reduction factor of 1.7 in gray matter. These results have been confirmed qualitatively by studies carried out both in volunteers and in patients.

Cerebrovascular reserve capacity in ischemia due to occlusion of a major arterial trunk: studies by Xe-CT and the acetazolamide test.

Classifications based on clinical and radiographic criteria have proved to be inadequate predictors of the course of cerebral ischemia or its response to therapy. In this study the cerebrovascular reserve capacity (CRC) of 46 patients with symptomatic cerebrovascular ischemia was studied by stable xenon-enhanced CT (Xe-CT) combined with the acetazolamide test. Fifteen patients had internal carotid artery (ICA) occlusion, 10 had ICA stenosis, 10 had middle cerebral artery (MCA) occlusion, and 11 had MCA stenosis. In the patients with chronic cerebral ischemia due to occlusive lesions of the ICA and MCA, the CRC was reduced most in those with MCA occlusion, followed, in descending order, by those with ICA stenosis, MCA stenosis, and ICA occlusion. Our results indicate that measurement of the CRC elucidates cerebral hemodynamic factors that cannot be detected by angiography in patients with chronic cerebral ischemia and that Xe-CT combined with the acetazolamide test is useful for this purpose.

The relationship of cloverleaf skull syndrome to hydrocephalus

In 1960, Holtermüller and Wiedemann described chondrodystrophic hydrocephalus as Kleeblattschädel syndrome. In the present paper, we review 23 cases of this syndrome associated with hydrocephalus, including 2 cases of our own. Of these 23 cases, 8 involved communicating hydrocephalus and 15 non-communicating hydrocephalus. It has been speculated that the associated hydrocephalus results from basilar impression, compression of infratentorial structures, aqueductal stenosis in non-communicating hydrocephalus, and impairment of venous drainage and cerebral spinal fluid flow at the level of the constrictive cranial ring in communicating hydrocephalus. Our present cases also showed this cranial ring, as demonstrated by skull X-rays and computed tomography scans. Since cloverleaf skull syndrome often has other general anomalies, we consider the hydrocephalus in this syndrome to have causes associated wtih the osteocartilaginous system.

Modulation of cerebral hemodynamics by surgical revascularization in patients with moyamoya disease

The purpose of this study was to evaluate hemodynamic compromise in the patients with moyamoya discase and surgical modulation of the hemodynamics using stable xenon enhanced computed tomographic CBF measurement with the acetazolamide challenge. The study group consisted of 15 preoperative cases and 17 postoperative cases. In the preoperative group, regional resting cerebral blood flow (rCBF) and regional cerebrovascular reserve capacity (rCRC) were reduced. The reduction was more prominent in the anterior circulation than in the posterior circulation. In the postoperative group, rCBF and rCRC were still low in the anterior circulation. Revascularization increased the resting CBF but did not change the CRC. Postoperative CBF did not increase in adults but increased in children. These findings suggest that the misery perfusion state may be present only in the childs brain. Measurement of CBF and CRC is useful to evaluate the hemodynamics of moyamoya disease.

Surgical modulation of the natural course of collateral circulation in chronic ischemic patients

The purpose of this study was to evaluate hemodynamic compromise in terms of baseline CBF and CRC in patients with chronic cerebral occlusive lesions and its modulation by a superficial temporal artery to middle cerebral artery (STA‐MCA) anastomosis. The study subjects were 10 healthy volunteers and 49 chronic ischemic patients with stenosis or occlusion of the internal carotid artery (ICA) or middle cerebral artery (MCA) The hemodynamics were measured using stable xenon enhanced computed tomographic CBF measurement with the acetazolamide challenge. The compromised hemodynamics in patients with chronic steno‐occlusive lesions did not improve during their natural course after two months. STAMCA bypass modulated hemodynamic compromise in the ischemic patients. We recommend STAMCA bypass for patients with reduced CRC, regardless of whether baseline CBF is reduced or normal. Hemodynamic classification using a combination of baseline CBF values and CRC values is useful for evaluating cerebral hemodynamics and for choosing the best treatment for cerebral ischemia with occlusive lesions.

Indication and Timing of Surgery for Cochleovestibular Neurovascular Compression Syndrome

Objective: Optimal surgical indications for cochleovestibular neurovascular compression syndrome (CNVC) remain controversial. We examined the surgical indications and timing of surgery for CNVC. Methods: The surgical outcomes of 30 patients (32 sides) with vertigo, tinnitus and hearing loss were evaluated. CNVC was diagnosed according to five items for clinical features with a scoring system of 1 or 0 based on the following features: a history, neurological and otological findings, an ABR evaluation, and vascular contact with the eighth cranial nerve on MR or air CT imaging. Patients with scores of 4-5 were diagnosed with CNVC. In addition, three modulation types of tinnitus using median nerve stimulation were evaluated in CNVC (28 sides) and other diseases (12 sides), and classified as suppression (S-type), no change (N-type), and excitation (E-type). Results: At early time, results of 16 sides evaluated using the modulation test before surgery for CNVC, the relationship between modulation of tinnitus and surgical results was evaluated. The ratio of the tinnitus intensity early after the surgery to that before the surgery was significantly lower for the S-type than for the other two types (P<0.01). At one year follow-up, the results of 32 sides were excellent in 8 sides, good in 19 sides, fair in 2 sides and poor in 3 sides. The duration of preoperative symptoms in the excellent group (1.9 ± 6.7 years) was shorter than that in the good group (5.8 ± 5.8 years). Results of CNVC with a chief complaint of vertigo and the duration of symptoms over 15 years and CNVC with a chief complaint of tinnitus and the duration of symptoms over 3 years was not always satisfactory. Conclusion: Indications for good outcomes are limited and need to consider not only the duration of symptoms, but also the modulation of tinnitus. Our findings suggest that the timing of surgery for CNVC with a complaint of vertigo should be within about 15 years, but that for CNVC with tinnitus should be within 3 years of onset of symptoms. Furthermore, some patients with S-type of less than 6 years are good candidates for surgery.

Cerebellopontine angle facial schwannoma relapsing towards middle cranial fossa

Facial nerve schwannomas involving posterior and middle fossas are quite rare. Here, we report an unusual case of cerebellopontine angle facial schwannoma that involved the middle cranial fossa, two years after the first operation. A 53-year-old woman presented with a 3-year history of a progressive left side hearing loss and 6-month history of a left facial spasm and palsy. Magnetic resonance imaging (MRI) revealed 4.5 cm diameter of left cerebellopontine angle and small middle fossa tumor. The tumor was subtotally removed via a suboccipital retrosigmoid approach. The tumor relapsed towards middle cranial fossa within a two-year period. By subtemporal approach with zygomatic arch osteotomy, the tumor was subtotally removed except that in the petrous bone involving the facial nerve. In both surgical procedures, intraoperative monitoring identified the facial nerve, resulting in preserved facial function. The tumor in the present case arose from broad segment of facial nerve encompassing cerebellopontine angle, meatus, geniculate/labyrinthine and possibly great petrosal nerve, in view of variable symptoms. Preservation of anatomic continuity of the facial nerve should be attempted, and the staged operation via retrosigmoid and middle fossa approaches using intraoperative facial monitoring, may result in preservation of the facial nerve.

Coronal flow mapping with Xe/Helical CT

Transverse section is utilized for ordinary flow mapping in Xe/CT. Transverse flow map is adequate to see horizontal flow distribution, but not so convenient to know vertical flow distribution. To know vertical flow distribution, the shuttle method with multiple transverse flow maps is used in general (1). But this method does not give us a direct visual image of vertical flow distribution. Then a new method of coronal flow mapping was developed with a helical CT scanner to visualize a direct image of vertical flow distribution. This method of coronal flow mapping needs a speedy CT scanner such as a helical CT scanner. This study is an examination of our method of coronal flow mapping on anatomical resolution, validity of flow values and flow distribution patterns in clinical cases.