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Richard S. Polin, David L. Lilien, Jose Menendez and Anil Nanda

Any novel technological innovation is dependent more on the ingenuity of its users than its inherent properties and potential flaws. Positron emission tomography (PET) is unique in this regard because the limitations of this modality are defined by the ability of its users to identify tracers that will aid in the diagnosis of intracerebral processes. The limitations of PET scanning lay in the extent of tissue resolution and in the currently relatively small number centers equipped to perform PET scanning.

In this issue of Neurosurgical Focus, various applications of PET scanning are detailed. The traditional use of this technology in neurosurgery has been to determine the metabolic nature of cerebral neoplastic lesions so as to help differentiate neoplastic from benign or infectious processes. This determination, however, has not been foolproof, and the technique has been further refined to maximize diagnostic yield.

Nonetheless, the utility of PET scanning continues to grow. New applications have allowed for the precise measurements of cerebral blood flow, helping the neuroscientist understand the functional organization of cortex, the pathophysiology of normal-pressure hydrocephalus, and changes in cerebral blood flow following traumatic injury. Other radiotracers such as fluorodopa allow assessment of the metabolic state of cerebral tissue transplants in restorative neurosurgical procedures.

In this introduction, all of these issues will be considered, and a historical perspective and the potential future uses of this technology will be provided. Technology moves so quickly that new instruments are routinely introduced. The authors will try to assess what properties, in the 25-year history of PET scanning, will need to be improved to keep it as a cutting-edge technology and expand its clinical role.

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Richard S. Polin, Volker A. Coenen, Carolyn Apperson Hansen, Peter Shin, Mustafa K. Baskaya, Anil Nanda and Neal F. Kassell

Object. Transluminal angioplasty has become a widely used adjunct therapy to medical management of symptomatic cerebral vasospasm following subarachnoid hemorrhage (SAH). Despite anecdotal reports of universal, angiographically confirmed reversal of vasospasm and high rates of clinical improvement, no rigorous examination of the efficacy of this procedure has been conducted. In this study the authors assess the efficacy of the aforementioned procedure.

Methods. Thirty-eight patients enrolled as part of the North American trial of tirilazad in aneurysmal SAH underwent transluminal angioplasty for symptomatic cerebral vasospasm. Fifty-three percent of these patients showed good recovery or moderate disability based on their 3-month Glasgow Outcome Scale score.

Among the 38 patients who underwent angioplasty, the severity and type of vasospasm, use of papaverine in addition to balloon angioplasty, timing of treatment, and dose of study drug did not have an effect on the outcome. The results of their neurological examinations improved in only four of the 38 patients immediately after the procedure. A conditional logistic regression analysis was performed in which these patients were compared with individuals matched for age, sex, dose of study drug, admission neurological grade, and modified Glasgow Coma Scale score at the time of angioplasty. No effect on favorable outcomes was found for this procedure.

Conclusions. Transluminal cerebral angioplasty is very effective in reversing angiographically confirmed vasospasm, and anecdotal reports of its clinical utility are numerous. However, in this report the authors conclude that its superiority to medical management for symptomatic cerebral vasospasm is questionable.

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Jose A. Menendez, David L Lilien, Anil Nanda and Richard S. Polin

Intracranial mass lesions comprise approximately half of all acquired immune deficiency syndrome (AIDS)–related neurological complications. Although toxoplasmosis and lymphoma are the most common causes of these lesions, diagnosis and treatment can be delayed because computerized tomography and magnetic resonance imaging studies cannot accurately differentiate between them.

The authors retrospectively studied nine patients with AIDS in whom, after a 6-hour fast, [18F]-fluorodeoxyglucose (FDG)–positron emission tomography (PET) scanning demonstrated intracranial mass lesions. The FDG uptake within each lesion was classified as either increased or not increased. In six patients there was no increase in FDG uptake, which suggested a diagnosis of toxoplasmosis, and lymphoma was suggested in two patients in whom increased FDG uptake was demonstrated. In a patient with two lesions, one lesion was shown to have increased FDG uptake whereas the other was shown to have no increased FDG uptake. All patients in whom a diagnosis of toxoplasmosis was made were started on antimicrobial therapy. Two patients died of other AIDS-related complications before repeated neuroimaging could be performed to assess treatment response, one patient refused to undergo further treatment or follow up, and two patients responded well to treatment. One patient with toxoplasmosis did not respond to the drugs. Analysis of a biopsy sample of the lesion confirmed the diagnosis; however, the patient died shortly thereafter. The two patients with FDG-PET–diagnosed lymphoma began corticosteroid therapy and improved considerably. In the patient in whom PET demonstrated two different FDG uptakes, a biopsy sample was obtained that confirmed the diagnosis of lymphoma; this patient was started on corticosteroid therapy and improved. A safe and reliable diagnostic tool, FDG-PET scanning can be used to differentiate causes of human immunodeficiency virus-related intracranial mass lesions. When available, this diagnostic study should be conducted before initiating empirical treatment or obtaining a stereotactically guided brain biopsy sample.

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Prasad S. S. V. Vannemreddy, Marjorie Fowler, Richard S. Polin, John R. Todd and Anil Nanda

✓ Malignant glioma is the most common primary brain neoplasm, but generally it is not included in the differential diagnosis of enhancing lesions of the central nervous system (CNS) in patients suffering from acquired immunodeficiency syndrome. We report a case of glioblastoma multiforme (GBM) in a 29-year-old man with human immunodeficiency virus (HIV). Primary CNS lymphoma was suspected, making a definitive histological diagnosis crucial. An initial stereotactic biopsy sample was insufficient to establish a diagnosis and a second biopsy of the lesion was obtained. The histopathological investigation confirmed GBM and adjuvant external radiation treatment was given to the patient, who survived for 4 months after the initial biopsy. A decline in the rate of Toxoplasma infection and the changing diseases observed in HIV infection indicate the importance of obtaining a biopsy in cases of CNS mass lesions.