Dynamics of Trion formation in InxGa1-xAs quantum wells

We show a double path mechanism for the formation of charged excitons (trions); they are formed through bi- and trimolecular processes. This directly implies that both negatively and positively charged excitons coexist in a quantum well, even in the absence of excess carriers. The model is substantiated by time-resolved photoluminescence experiments performed on a very high quality InxGa1-xAs quantum well sample, in which the photoluminescence contributions at the energy of the trion and exciton and at the band edge can be clearly separated and traced over a broad range of times and densities. The unresolved discrepancy between the theoretical and experimental radiative decay time of the exciton in a doped semiconductor quantum well is explained by the same model.

Determination of the exciton formation in quantum wells from time-resolved interband luminescence

We present the results of a detailed time-resolved luminescence study carried out on a very high quality InGaAs quantum well sample where the contributions at the energy of the exciton and at the band edge can be clearly separated. We perform this experiment with a spectral resolution and a sensitivity of the setup, allowing us to keep the observation of these two separate contributions over a broad range of times and densities. This allows us to directly evidence the exciton formation time, which depends on the density as expected from theory. We also denote the dominant contribution of excitons to the luminescence signal, and the lack of thermodynamical equilibrium at low densities.

Appropriateness of indications for surgery of lumbar disc hernia and spinal stenosis

STUDY DESIGN

This prospective study examines the appropriateness of indications for surgery of herniated intervertebral disc and spinal stenosis in patients undergoing surgery in a university hospital setting.

OBJECTIVE

To evaluate the appropriateness of surgery using explicit criteria developed by an expert panel in the United States.

SUMMARY OF BACKGROUND DATA

The use of surgery for herniated intervertebral disc and spinal stenosis varies widely within and among countries. It has been postulated that the main reason for treatment failure is poor selection of candidates for the procedure.

METHODS

The authors prospectively evaluated appropriateness of surgical indications for herniated lumbar intervertebral disc or spinal stenosis in 328 consecutive patients undergoing the operation in two university neurosurgery departments. Outcome was measured 1 year after surgery by a standardized interview.

RESULTS

Indications for surgery were considered to be appropriate or equivocal in 202 (62%) patients and inappropriate in 126 (38%). Among the 126 inappropriate procedures, 66 were so rated because of insufficient activity restriction before the procedure. One year after surgery, 74% of the patients perceived the results of the operation as good or very good.

CONCLUSIONS

Appropriateness as measured by the criteria established by the American panel identified a large percentage of day-to-day practice in the two surgical units as inappropriate. However, use of criteria that include new findings about lack of efficacy of bed rest probably would lower this percentage. Criteria of appropriateness of medical and surgical procedures, developed through the panel process, need to be updated regularly.

Head injuries in children: a chronicle of a quarter of a century

Children aged 0-15 years hospitalized in Geneva for head trauma during the last quarter of a century are reviewed. More than half of the severely injured children were not from Geneva area. New methods of management have been introduced progressively. The cases are divided in four successive time periods and classified according to their pathology. A continuous improvement in mortality is obvious, decreasing from 29.4% to 2.2%, but climbing again to 15.2% in the last period, probably due to more severe pathologies. For the Geneva area the mortality decreased progressively from 10.4/100,000 to 3.5/100,000 annually, due to better organization and management, but also to a drop in the incidence of severe cases from 35.5-13.5/100,000 per year. A decrease in the number of traffic accidents is responsible for this. However, the number of handicapped children has not changed.

Paediatric head trauma: influence of age and sex. II. Biomechanical and anatomo-clinical correlations

A consecutive, unselected series of 1812 cases of head trauma in children less than 15 years of age and admitted hospital over a period of 8.5 years was studied. Data concerning the grade of energy involved, the ages of the victims, the types of pathologies caused and the clinical features noted were collected and statistically analysed. Babies and toddlers (0-3 years) were shown to sustain rather low-energy trauma and suffer more skull fractures, more subdural haematomas and more benign injuries. They lost consciousness less frequently and were less frequently in coma than the other children. By contrast, they had more frequent signs of lateralization, and early seizures were much more frequent in babies than in other children. Young children (3-9 years) had rather higher-energy accidents, frequently lost consciousness, were more frequently in coma and have more frequently had a free interval associated with the development of brain swelling. They did not suffer subdural effusion or contrecoup lesions. Schoolchildren (9-15 years) were statistically more or less like young adults: the clinical sequences of trauma were more severe than in the other children, mortality was a little bit higher, the risk of extradural haematoma was higher, and they rarely suffered subdural haematomas or contrecoup lesions. Traffic accidents, with higher energy involved, were more severe.

Paediatric head trauma: influence of age and sex. I. Epidemiology

A consecutive unselected series of 1812 children (up to 15 years old) admitted for head injuries over a period of 8.5 years was studied. The cases were divided up according to five categories of pathology: benign injury, extradural haematoma, subdural haematoma, open brain laceration and brain contusion in a broad sense. All cases of benign injury were from the Geneva area (57000 children) and 52% of the cases of severe injury were referred from other places. To these 1812 cases were added those of 23 children who died before admission recorded by the police. In the Geneva area the mortality was 6.8/100,000 per year. Patients were divided into three age groups: I (0-3 years), II (3-9 years), and III (9-15 years); group I was further subdivided into subgroups I a (0-1 year) and I b (1-3 years). The incidence of each type of accident was calculated for each age group, separately for girls and boys. Each type of pathology was correlated, sex by sex and for different ages, with the type of accident. Overall, two boys were injured for each girl. Road accidents were responsible for 15% of head injuries in group I girls, 17% in group I boys, 43% in group II girls, 45% in group II boys, 50% in group III boys and 61% in group III girls. They were responsible for 94% of all deaths and 85% of deaths of hospitalized patients. Falling was the most frequent cause of injury. Benign injuries were more frequent in group I. Only 1 of 25 patients with extradural haematomas died, and there were only 8 patients with subdural haematomas, 4 in subgroup I a (babies aged less than 1 year).

Chronic subdural haematomas. Results of a closed drainage method in adults

This paper concerns 106 consecutive subdural haematomas in adults, 94 of whom were chronic and 12 subacute. Among these, 78 subdural haematomas were operated upon according to a new protocol--two burr holes, irrigation and closed drainage of the haematoma for 48 hours in the supine position. The others were treated by decompressive craniectomy according to the clinical judgement of the surgeon. The results are presented.

Pathogenesis of diastematomyelia: can a surgical model in the chick embryo give some clues about the human malformation?

To reproduce diastematomyelia, a sagittal incision was carried out at the level of the rhomboidal sinus of 36- to 40-h-old chick embryos. A small piece of membrane shell, a small agar screen, or a piece of quail isochronous isotopic notochord was inserted into the gap. The embryos were killed and fixed after 9 days' incubation. Diastematomyelia was obtained in several embryos treated with interposition of a membrane screen or a piece of quail notochord. Microscopic examination revealed two hemicords, each containing its own central canal; in some cases one of the cords showed hydromyelia. Absence of the rump was seen in association with experimental diastematomyelia. The interposition of a resorbable agar screen did not succeed in reproducing diastematomyelia. The results of these surgical manipulations suggest that diastematomyelia cannot be explained by a primary disorder of neurulation. It supports the theory of noninvolution of a firm midline structure (probably the neurenteric canal, rapidly surrounded by mesodermal cells originating from the notochord), which prevents the fusion of the separated parts.

The future of neurosurgery

Many factors influence the future of neurosurgery, among them the general growth of the world population with an increasing number of older persons and the political-economical development which differs markedly from region to region. Another important factor will be the biological and molecular revolution which has just begun and makes it likely, that some of the pathologies, which needed neurosurgical management, become accessible to conservative treatment in the future. Finally the neurosurgical sphere of activity is endangered by take-over tendencies of neighbouring medical specialties. Those of us who are in charge of neurosurgical organization and planning should take these and additional factors into consideration early enough, in order to give neurosurgery and neurosurgeons a chance to adapt to the future.

Diagnosis of cerebellopontine angle tumors

Between 1980 and 1990, 9,176 patients suffering from otoneurological disorders were investigated in our clinic. Sixty-six (0.72%) internal auditory canal or other cerebellopontine angle tumors (CPAT) were diagnosed. Brainstem auditory evoked potentials (BAEP), interaural time discrimination, and magnetic resonance imaging (MRI) revealed to be the most sensitive and efficient tests for the detection of CPAT. However, the investigation of otoneurological symptoms cannot be limited to BAEP and MRI on the a priori of a hypothetical CPAT. Electrophysiologic tests such as impedancemetry, and electronystagmographic testing are also needed to elucidate the many causes of otoneurological symptoms.

Anterior-sacral meningocele; value of magnetic resonance imaging and abdominal sonography. A case report

With the presentation of a case of giant anterior sacral meningocele, the evident superiority of magnetic resonance imaging over any other methods for the diagnosis of this rare condition is demonstrated. Ultrasound as a screening tool is often the first to reveal the presence of the intrabdominal cystic abnormality and furthermore is an excellent means for checking the post-operative course. In addition this particular case is interesting because the dural stalk linking the meningocele to the dural abdominal sac was not entirely free from nervous structures inspite of macroscopic appearances to the contrary.

Radicular compression due to lumbar intraspinal gas pseudocyst: case report

A case of sciatic pain syndrome is reported. Computed tomography showed evidence of gas in the spinal canal, and at operation a gas-filled pseudocyst was found in the spinal canal, without herniated disc. The cause of this unique case is discussed in relation to the spinal vacuum phenomenon.

Surgical treatment of congenital fronto-orbitomalar asymmetries

Congenital fronto-orbital asymmetries can be of various origin. Correction of these malformations, whether due to maldevelopment of the foetus or to a congenital tumour, generally require a combined intracranial and extracranial approach. In recent years, a working group of plastic surgeons and neurosurgeons in the French-speaking part of Switzerland have been particularly interested in these problems. Some of their results are presented here.

Oligodendroglial tumors in childhood

A series of 20 hemispheric tumors in children less than 16 years of age, over a period of 20 years, is presented. Among them, 8 were oligodendroglial tumors, a proportion well above the level reported in the literature. The World Health Organization (WHO) classification, which includes mixed oligoastrocytomas, in the oligodendrogliomas was used. This addition does not explain this unusually high proportion. Selection of cases and the correct histological diagnosis are probably important.

Lagophthalmos in acquired oculomotor synkinesis

Two consecutive patients who exhibited classic signs of unilateral acquired oculomotor synkinesis demonstrated an inability to appose eyelid margins on the affected side, when attempting gentle closure of the eyes. In one patient, this occurred in conjunction with a unilateral upper eyelid crease on the affected side, and in the other patient it was associated with accentuation of the crease in comparison with that of the opposite side. Bilateral eyelid closure normally induces a contraction of the superior recti muscles. The lagophthalmos and accentuated upper eyelid crease observed in our patients when they attempted gentle eyelid closure presumably resulted from inappropriate coactivation of the levator palpebrae superioris muscle by impulses destined for the superior rectus muscle.

Macular reflexes in optic atrophy

We investigated the annular reflex of the macula and the foveal reflex in 14 eyes with various degrees of optic atrophy by means of red-free fundus photographs. The patients ranged in age from 13 to 34 years (mean age, 25.9 years). We compared our observations with data obtained from 51 age-matched normal eyes. Optic atrophy was found to be associated with changes in the reflexes of the macular area. Alterations occurred in all eight eyes that had visual acuities of 20/50 or worse. Changes in the annular reflex of the macula were more significant in younger patients (less than or equal to 25 years of age) than in older patients. In the younger group, the annular reflex was blunt, distorted, and fragmented, and showed an irregular extension toward the foveal area, whereas in the old group it showed less specific attenuation. Fading of the foveal reflex was observed in both groups. Changes in the retinal reflexes of these patients result from alterations in the ganglion cell and nerve fiber layer and should be included among the signs of optic atrophy. They can help determine the extent of optic atrophy and can be useful clinical clues in children whose optic disks are difficult to examine. They should not be mistaken for signs of associated primary retinal disorders.

Spinal subarachnoid hematoma of spontaneous origin and complicating anticoagulation. Report of four cases and review of the literature

Four cases of spinal subarachnoid hematoma are reported and three cases from the literature reviewed. Clinical presentation is characterized by a combination of back pain and meningismus and progressive compression of the spinal cord. Pathogenesis, diagnosis, and differential diagnosis are discussed. Information obtained from myelography was limited, and two patients underwent operation without it. Prognosis for functional recovery is poor unless decompression is performed at an early stage.

[The Glasgow coma scale]

The value of the Glasgow coma scale is definite and widely accepted. It is a help in teaching a difficult subject, in mutual understanding in a few words, and in comparison of cases. It uses accurate and practical observations. It is the best method of measuring the state of consciousness, provided observation of the diameter and light reaction of the pupils is added It avoids what Jamieson and Yelland feared in 1968. "It is tragic if the wardmaid assesses deterioration by recognizing that a patient is not as bright now as earlier while trained staff await the development of the next stage in their preconceived, rigid scale of deterioration."

Convergence-evoked eyelid nystagmus

We studied two patients with eyelid nystagmus induced by ocular convergence. The first patient, a 29-year-old man, had the signs of a cerebellar syndrome after sustaining severe craniocerebral injuries. The second patient, a 12-year-old girl, had a tumor of the anterior vermis cerebelli. After treatment with corticosteroids (Patient 1) and surgery (Patient 2), the eyelid nystagmus gradually disappeared. An alteration in the cerebellar system is the most likely cause of convergence-evoked nystagmus.

Benign ependymal cyst of the pons

Clinical presentation, radiological aspects, surgical treatment and histology of a case of an ependyma-lined cyst of the pons are depicted. Slight psychomotor retardation and long-standing neurological signs associated with a marked dolichocephalic skull and right aortic arch suggest a congenital anomaly. Differential diagnosis of cystic lesions in the posterior fossa is discussed.

Monocytes in inflammatory bowel disease: absolute monocyte counts

Using a cytochemical staining technique, peripheral blood monocytes have been precisely identified and enumerated in patients with inflammatory bowel disease and compared with healthy and disease control subjects. For ulcerative colitis there was a significant monocytosis, which was closely correlated with the total white cell count and with the activity of the disease. For patients with Crohn's disease, the peripheral blood monocyte count was also raised compared with that of the control groups, but the difference did not reach statistical significance. There was no correlation between the monocyte count in patients with Crohn's disease and the total white cell count or the disease activity. Some of the mechanisms that may influence the production and distribution of peripheral blood monocytes are discussed.

[The computerized tomography in findings posttraumatic hematoma (author's transl)]

The authors report two cases of posttraumatic hematoma in the orbit. The first patient presents an unilateral amaurosis through indirect trauma of the optic nerve. The computerized tomography reveals a hematoma of the optic nerve sheath, confirmed by surgery. The second patient presents a posttraumatic limitation of the ocular motility and the computerized tomography reveals a hematoma of two extraocular muscles.

[Computerized tomography in finding tumours in the orbit and in the base of the skull (author's transl)]

Two cases of tumours - a pleomorphic poorly differentiated malignant neoplasm and a juvenile angiofibroma - involving the orbit and extending to the base of the skull are reported. In both cases computerized tomography showed with great precision the localization and the extension of the tumours.

[Preventive antibiotic therapy in neurosurgery]

The swiss neurosurgeons were asked to give their own politics on prophylactic antibiotics. The results of this enquiry are given. Post-operative infections in the Neurosurgical Clinic of Geneva in a four-year period were at a satisfactorily low rate and demonstrated the importance of many factors of risk. Guide lines for a reasonable prophylaxis in three groups of operations are given, with a precise schedule for each group. It is suggested that ones own surgical technique be severely criticized before considering prophylactic antibiotics.

[Neurosurgery of chiasma syndromes (author's transl)]

The conditions for the success of surgical interventions within the chiasmal region are careful preparation of the patient, ideal general anesthesia, precise surgical technique especially improved by the use of the microscope and bipolar coagulation. The surgical results also depend on the age of the patient, on his general condition, on the volume of the tumoral lesion and on the extent and kind of implication of the vascular and nervous structures of this region. The lesions are classified into extraparenchymatous lesions, intraparenchymatous lesions, giant aneurysms and inflammatory lesions. The extensive extraparenchymatous lesions represent the most important group: they comprise the pituitary adenomas, the cranio-pharyngiomas, the meningiomas and finally rarer tumors like the chordomas, or other tumors of the sphenoid. In these regions the choice of access is extremely important: transphenoidal, subfrontal intracranial or mixed. Among the intraparenchymatous lesions one has to mention first of all the gliomas of the chiasm and then the ectopic pinealomas. The giant aneurysm in older persons is improved the symptomatology by ligation of the internal carotid. The inflammatory arachnoidal lesions of the chiasm (specific or nonspecific) generally profit from an intervention aiming to disconnect the adhesions. X-ray therapy represents very often an indispensable component of the surgical treatment of the tumoral lesions. Apart from death the complications are postoperative infection, aggravation of the neuro-ophthalmological symptoms, the neuro-psychological consequences and the endocrinological and hypothalamic complications. Early diagnosis represents the best means to diminish the importance of the complications. An alternative complication is the tumor recurrence.

Electro-clinical follow-up of shunted hydrocephalic children

In a survey of 29 hydrocephalic children treated by ventriculoatrial shunt (Holter valve) with a follow-up of 4 years, EEG records before the operation and at least once a year thereafter, the authors can support the view that an epileptogenic focus has developed around the place of insertion of the ventricular catheter in 19 cases, leading to epileptic seizures in 17 up to now. Thus the incidence of convulsions in this particular group of patients is 0.59 (17/29), the limits of confidence 95% being 0.39-0.76. The irritative abnormalities occur usually during the second year after the operation and the delay for the onset of clinical seizures is variable. The age at operation seems to influence the occurrence of the epileptogenic scar. The type of hydrocephalus and especially the presence of an associated cerebral focal lesion can be of importance in the development of clinical seizures.

Value of gas myelography in early management of acute cervical spinal cord injuries

Gas myelography was carried out in 22 patients with acute cervical spinal cord injuries in whom oily contrast media seemed contraindicated. The authors believe this technique makes a valuable contribution to the basic decision regarding the surgical versus medical treatment of a specific patient with a cervical cord injury. They emphasize the importance of visualizing cord compression due to disc herniation in these cases and conclude that gases are the optimal contrast agents for visualization of the entire circumference of the spinal cord.