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William G. Obana, Lawrence H. Pitts and Merry C. Nishimura

✓ The authors examined the effect of the opiate antagonists naloxone and thyrotropin-releasing hormone (TRH) on neurological outcome and the size of areas of cerebral infarction in a rat model of focal cerebral ischemia. The middle cerebral artery (MCA) was permanently occluded in 66 adult Sprague-Dawley rats. The rats were randomly divided into three groups. In 20 Group I rats, TRH in normal saline was administered initially as a 2-mg/kg bolus followed by continuous infusion of 2 mg/kg/hr for 4 hours. In 20 Group II rats, naloxone in normal saline was administered initially as a 2-mg/kg bolus followed by continuous infusion of 2 mg/kg/hr for 4 hours. In 26 Group III rats, physiological saline was administered as an initial 0.5-cc bolus followed by continuous infusion of 0.5 cc/hr for 4 hours. All solutions were given in volumes of 0.5 cc for the bolus and 0.5 cc/hr for continuous infusion, and all infusions were begun within 10 minutes of MCA occlusion. Twenty-four hours after treatment, the rats underwent a careful neurological examination and were then sacrificed immediately. The size of areas of cerebral infarction was evaluated using 2,3,5-triphenyltetrazolium chloride staining techniques.

The neurological grade of the rats correlated with the size of infarcted areas among all grades, irrespective of treatment (p < 0.01). Neither naloxone nor TRH improved neurological function or reduced the size of infarction compared to saline-treated control rats. Treatment with TRH caused a significant increase in mean arterial blood pressure during infusion, but naloxone had no effect. These results suggest that neither TRH nor naloxone are effective in the treatment of acute focal cerebral ischemia.

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William Kelly, Michael Brant-Zawadzki and Lawrence H. Pitts

✓ The authors report on a series of 60 patients who underwent arterial injection-digital subtraction angiography (AI-DSA) for evaluation of suspected cerebrospinal disease. High-quality images were consistently obtained, facilitating accurate diagnosis of a wide variety of traumatic, inflammatory, and neoplastic conditions. As experience has accumulated, the AI-DSA technique has all but supplanted conventional film-screen serialography at this institution. Important advantages of AI-DSA include reduced procedural time and decreased contrast agent burden, which mean increased patient safety. Film costs can also be markedly reduced. Moreover, image quality (information content) is not significantly affected. The technique is especially useful in emergency situations, in cases where multiple arterial injections and serialograms are required, and in cases in which transcatheter embolization is carried out. We feel these considerations will insure broadened application of this diagnostic modality as the AI-DSA equipment becomes more widely available.

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Brian T. Andrews, Arthur Lutz, Joshua B. Bederson and Lawrence H. Pitts

✓ A new microclip for use on blood vessels 300 µ to 1 mm in diameter is described. This clip is suitable for either temporary or permanent occlusion and has been used in experimental applications. Potential clinical applications are described.

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Lawrence H. Pitts, Charles B. Wilson, Herbert H. Dedo and Robert Weyand

✓ The authors describe a case of massive pneumocephalus following ventriculoperitoneal shunting for hydrocephalus. After multiple diagnostic and surgical procedures, congenital defects in the tegmen tympani of both temporal bones were identified as the sources for entry of air. A functioning shunt intermittently established negative intracranial pressure and allowed ingress of air through these abnormalities; when the shunt was occluded, air did not enter the skull, and there was no cerebrospinal fluid leakage. Repair of these middle ear defects prevented further recurrence of pneumocephalus.

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Isabelle M. Germano, Lawrence H. Pitts, Isabelle Berry and Michael Moseley

✓ Recent advances in magnetic resonance (MR) imaging and MR spectroscopy (MRS) allow the noninvasive in vivo study of a variety of anatomical, physiological, and biochemical alterations that may occur in different cerebral pathologies. The authors have investigated the use of MR imaging and MRS to monitor the evolution of experimental focal cerebral ischemia in rats. Permanent focal cerebral ischemia was induced in 36 rats, and 12 normal rats were used as a control group. Changes in high-energy phosphate metabolites were followed in vivo using MRS during the 1st hour and at 3 and 6 hours after ischemic insult. Changes in in vivo MR images were evaluated at 1, 3, 6, 12, and 24 hours after ischemic insult. Significant decreases (p < 0.05) in phosphocreatine/inorganic phosphate ratios and intracellular pH values occurred immediately after the induction of ischemia. The presence of an infarcted area seen on MR images was a constant finding at 3 hours after ischemic insult, and was well defined and localized at 12 and 24 hours. The location of areas of infarction seen on MR images correlated well with areas identified histopathologically. The T1 and T2 MR relaxation times were significantly increased 3 hours after ischemic insult and remained prolonged for at least 24 hours. The results show that MR imaging is a sensitive method to measure cerebral infarction, and that MRS is a sensitive measure of changes that occur in the early phases of ischemia, perhaps when cellular changes may still be reversible. At 3 and 6 hours after the ischemic insult, however, 31P-MRS spectra may appear to be “normal” despite the presence of well-documented areas of infarction.

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Matthew D. Smyth, Lawrence Pitts, Robert K. Jackler and Kenneth D. Aldape

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Shiro Kobayashi, Brian T. Andrews, Lawrence H. Pitts and Shozo Nakazawa

✓ A new dural elevator is described that simultaneously lifts and retracts the dura from the frontal and temporal surfaces of the sphenoid wing, allowing safe removal of this structure during pterional craniotomy.

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Richard M. Irving, Robert K. Jackler and Lawrence H. Pitts

Object. The goal of this retrospective study was to evaluate hearing preservation after surgery for vestibular schwannoma in which the middle fossa (MF) or retrosigmoid (RS) approaches were used. Hearing preservation in vestibular schwannoma surgery can be achieved by using either the MR or RS approach. Comparative outcome data between these approaches are lacking, and, as a result, selection has generally been determined by the surgeon's preference.

Methods. The authors have compared removal of small vestibular schwannomas via MF and RS approaches with regard to hearing preservation and facial nerve function. The study group was composed of consecutively treated patients with vestibular schwannoma, 48 of whom underwent operation via an MF approach and 50 of whom underwent the same number of RS operations. Tumors were divided into size-matched groups. Hearing results were recorded according to the American Academy of Otolaryngology—Head and Neck Surgery criteria, and facial nerve outcome was recorded as the House—Brackmann grade. Overall, 26 (52%) of the patients treated via the MF approach achieved a Class B or better hearing result compared with seven (14%) of the RS group. Some hearing was preserved in 32 (64%) of the patients in the MF group and in 17 (34%) of the RS group. The results obtained by using the MF approach were superior for intracanalicular tumors (p = 0.009, t-test), and for tumors with a cerebellopontine angle (CPA) component measuring 0.1 to 1 cm (p = 0.006, t-test). For tumors in the CPA that were 1.1 to 2 cm in size, our data were inconclusive because of the small sample size. Facial weakness was seen more frequently after MF surgery in the early postoperative period, but results were equal at 1 year.

Conclusions. The results of this study have demonstrated a more favorable hearing outcome for patients with intracanalicular tumors and tumors extending up to 1 cm into the CPA that were removed via the MF when compared with the RS approach.