The role of atomic ensembles in the reactivity of bimetallic electrocatalysts.

Bimetallic electrodes are used in a number of electrochemical processes, but the role of particular arrangements of surface metal atoms (ensembles) has not been studied directly. We have evaluated the electrochemical/catalytic properties of defined atomic ensembles in atomically flat PdAu(111) electrodes with variable surface stoichiometry that were prepared by controlled electrodeposition on Au(111). These properties are derived from infrared spectroscopic and voltammetric data obtained for electrode surfaces for which the concentration and distribution of the respective metal atoms are determined in situ by atomic resolution scanning tunneling microscopy with chemical contrast. Palladium monomers are identified as the smallest ensemble ("critical ensemble") for carbon monoxide adsorption and oxidation, whereas hydrogen adsorption requires at least palladium dimers.

Electrochemical de-alloying in two dimensions: role of the local atomic environment.

We investigate by in situ scanning tunnelling microscopy (STM) the potential dependence of the electrochemical dealloying of NiPd monoatomic layers electrodeposited on Au(111). The dealloying process is achieved by Ni selective dissolution and was studied as a function of NiPd composition: for an alloy with a Ni content ≥70%, quasi-complete Ni dissolution is achieved at a potential of -0.9 VMSE whereas for a Ni content <70%, Ni dissolution at the same potential drastically slows down after the removal of small amounts of Ni. The alloy morphology at this "passivation state" is characterized by the presence of holes in the alloy monolayer with evidence for the Pd enrichment at the hole edges. These findings are confirmed by Monte Carlo simulations. Further Ni dissolution at passivation was achieved by applying more positive potentials which depend on the alloy composition. These results allowed us to determine the correlation between the Ni dissolution onset potential and the local Pd content.

Surgical pitfalls, their consequences, transient complications.

The methodology of this paper is based entirely on the experiential backgrounds of the authors. It outlines those factors which have become recognized as potentially important issues to patients who are considering recommendations of surgical treatment for their intractable epilepsy. Thus, on the one hand, it includes the important generic aspects of Informed Consent, while on the other hand there must be a very comprehensive and, when the operation is to be carried out under local anesthesia, a very detailed explanation of the preparation and the sequential steps in the surgical procedure. This should also entail a brief description of the roles of the various "team" members during the operative procedure. There are well-recognized complications associated with the various surgical procedures for the treatment of epilepsy. Further, there are predictable deficits following some of these procedures, some of which might be permanent and some of which may be transient. These pitfalls are briefly discussed.

Spinal subdural hematoma in association with anticoagulant therapy.

A case of spinal subdural hematoma occurring in association with anticoagulant therapy is reported. Seven similar cases from the literature are reviewed the emphasis on the clinical features, investigation, and the results of treatment. The prognosis for recovery is good, only if the condition is diagnosed and the clot evacuated before severe spinal cord compression and subsequent ischemic necrosis has occurred.

The Chiari malformation in adults.

The clinical features of the Chiari Malformation in seven adult patients are presented. It is suggested that the clinical syndromes associated with this malformation, in adults, can be classified as (a) compression of structures at the level of foramen magnum (with or without radiologically demonstrable associated bony anomaly at the cranio-vertebral junction (b) increased intracranial pressure or obstructive hydrocephalus and (c) intramedullary cervical cord syndrome. The usefulness of tomography, and demonstration of the vertebro-basilar circulation in the neuro-radiologic investigation of these patients is emphasized. The surgical procedures performed in the management of these patients are outlined.

Hemifacial spasm and craniovertebral anomaly.

Two patients with congenital anomaly of the craniovertebral junction causing disabling hemifacial spasm (HFS) are presented. In one patient, complete cessation of the HFS occurred for a period of two years following simple bony decompression of the craniovertebral junction raising unanswered questions as to the exact pathogenesis of HFS. Eventually both patients required microvascular decompression at the root entry zone of the facial nerve.

Historical vignette: cerebral cortical stimulation and surgery for epilepsy.

In 1909, in an isolated community hospital, on the northern tip of the Province of Newfoundland and Labrador, Canada, Dr. John Mason Little, Jr. performed electrical stimulation of the cerebral cortex, prior to cortical excision, as treatment of recurrent cerebral seizures in three patients. Extracts from Dr. Little's written records of the clinical features, the neurosurgical procedures and cerebral cortical stimulation are summarised. A brief review of the contemporaneous history of neurosurgical procedures for epilepsy provides a prospective of Dr. Little's remarkable surgical virtuosity.

Management of acute subdural hematomas from aneurysmal rupture.

Subdural hematomas (SDH) from ruptured aneurysm (RA) are much less common than intracerebral (ICH) hematomas or subarachnoid (SAH) or intraventricular hemorrhage (IVH). With computerized tomography, preoperative diagnosis is now made more often. The authors have collected 18 such cases from a review of 897 cases of RA admitted to eleven medical centers in 1980 and 1981. Nine (50%) of these patients died prior to discharge from hospital. Four (22%) had surgery and died postoperatively and 9 (50%) were operated upon and survived. Thirteen (72%) of the patients showed anisocoria, decreased consciousness and unilateral weakness prior to surgery. Eight (89%) of the fatalities had shown preoperative herniation as opposed to only 5 (56%) of the survivors. The overall incidence of delayed ischemia due to vasospasm was 11% (2 cases). Those who died had greater midline shift and larger SDH on the admission CT scan. Sixteen (89%) of these patients were female. Thirteen (72%) had ruptured aneurysms on the internal carotid artery. All of these hematomas were unilateral and uniformly hyperdense, and the convexity hematomas were crescentic in shape. Seventeen (94%) had evidence of blood in locations other than the subdural space. If the patient is potentially salvageable and has a midline shift, the SDH should probably be evacuated immediately and the aneurysm clipped at the same operation since the development of a tentorial herniation has such an adverse effect on outcome.

Primary malignant tumours of the trigeminal nerve.

We report a case of primary malignant schwannoma of the trigeminal nerve, and review the 5 previously reported cases. Clinical presentation, along with radiological and pathological features are discussed.

Sarcoidosis presenting as an intramedullary spinal cord lesion.

OBJECTIVES: Sarcoidosis affects the spinal cord in only 0.43% of patients with sarcoidosis. Usually there is systemic involvement prior to the development of cord lesions. We present a case of sarcoid isolated to the intramedullary spinal cord, which was a diagnostic and therapeutic challenge. We review the case and then present a review of the literature with an emphasis on presentation, diagnosis and treatment. METHODS: We have reviewed a patient who presented with an isolated sarcoid granuloma affecting the cervical spinal cord. All pertinent history and physical information was extracted from the patient's chart and through patient interview. Laboratory, radiographic and pathological investigations are presented. RESULTS AND CONCLUSIONS: Fourteen patients have been reported with isolated intramedullary spinal cord sarcoidosis. Current practice supports the role of surgery for biopsy; mainstay of treatment is corticosteroids.

Cervical myelopathy secondary to ossification of the posterior longitudinal ligament in a Caucasian patient.

Cervical myelopathy consequent on ossification of posterior longitudinal ligament (OPLL) is very rare in Caucasians. A 65-year-old Anglo-Saxon woman developed progressive gait disturbance, paresthesia in both legs and urinary urge incontinence. Radiological examination showed OPLL from fifth to seventh cervical vertebral level; the dense OPLL was graphically displayed by three-dimensional computerized tomography. Medial corpectomy, C5 to C7, and removal of OPLL, with subsequent fusion C4 to T1 using a free fibula graft resulted in clinical improvement. Three dimensional computerized tomographic imaging is a valuable diagnostic procedure in OPLL.

Adult diastematomyelia: a complex dysraphic state.

It is rare for patients with diastematomyelia to manifest initial symptoms in adult life. Clinical, radiological, and surgical features of a patient with symptomatic adult diastematomyelia are presented. Pathogenetic mechanisms are considered to include a variety of congenital spinal anomalies, distinct from the spur, as well as mechanical factors.

Familial intracranial aneurysms: report of three families.

The problem of intracranial aneurysm causing subarachnoid hemorrhage in several members of three different families is illustrated and discussed in this report.

Familial intracranial gliomas.

The pedigree of two interrelated families with 10 affected members suffering from malignant supratentorial gliomas is reported. In addition, three other unrelated families with two members each who were treated for different types of brain tumors are described. Genetic implications are discussed.

The impact of spina bifida on the medical services of Newfoundland and Labrador.

This institution receives all live spina bifida patients from Newfoundland and Labrador. The aim of this study is to determine the outcome of these patients and the impact on the medical system. On a retrospective chart review, 274 patients born between 1967 and 1990 were studied. An analysis of the statistical variables showed that the incidence per 1,000 live births has remained stationary in Newfoundland and Labrador; there is a slight female predominance; 64% were born to young mothers and the peak incidence occurred in March, April, and May. A total of 179 patients of 254 who underwent surgery were alive and underwent rehabilitation programmes. Only 35% are wheelchair bound; the rest are ambulatory. One hundred sixty-one are of school age or older, 78 are in regular high school (3 dropouts), 36 are in special education, 6 graduated from high school, 4 are in university, 15 had no neurological deficit, 7 were lost in follow-up, 5 died, 9 had gross mental retardation, and 1 is the mother of three normal children. To attain these results these patients had multiple admissions and surgical procedures and the patients are seen twice a year in a rehabilitation and multidisciplinary clinic. From this study, the utilization of the medical services and impact on the community is great. However, the majority of these patients appear to attain a surprisingly high quality of life.