Effects of nitric oxide modulation on tumour blood flow and microvascular permeability in C6 glioma

C6 glioma strongly express nitric oxide synthase. Rats bearing C6 tumours were pre-treated with i.v. Ng-nitro-L-arginine methyl ester (L-NAME), 3-morpholinosydnonimine (SIN-1) or saline before local cerebral blood flow (LCBF) or tumour capillary permeability (TCP) was measured by the [14C]iodoantipyrine autoradiographic or [14C]alpha-amino-isobutyric acid techniques. L-NAME and SIN-1 caused significant TBF alterations (-44% and +136%, respectively) with less marked (-15% and +33%) alterations in normal brain. Calculated cerebrovascular resistance changes within tumour were indeed selective. Baseline TCP was increased compared with normal brain (20-fold). L-NAME and SIN-1 administration did not alter TCP. These effects have significant implications for human malignant glioma management. Selective i.v. manipulation of LCBF, without significant changes in TCP, could increase the efficacy of chemotherapy, radiotherapy or provide better peritumoural oedema control.

Can experimental models of rodent implantation glioma be improved? A study of pure and mixed glioma cell line tumours

To evaluate the hypothesis that co-implantation of different rodent glioma cell lines might result in experimental brain tumours that more closely resemble human gliomas the neuropathology and immunocytochemical features of implantation gliomas derived from single cell lines (C6, A15A5, F98), two cell lines admixed 50:50 prior to implantation (C6 + F98 and C6 + A15A5) and three cell lines equally admixed (C6 + A15A5 + F98) was studied in the adult Wistar rat. Tumours grew consistently following implantation of the single and the two admixed cell lines, however tumour growth following triple mix implantation was considerably and consistently impaired. The tumours derived from admixed cell lines showed regional heterogeneity with areas characteristic of both the primary cell lines. Foci of lymphocytic infiltrates, tumoural necrosis, often with pseudopallisading, and peritumoural edema were consistent features of all tumours. Limited parenchymal and more extensive perivascular tumoural invasion was seen predominantly in tumours containing the C6 cell line. There were no significant differences in GFAP, vimentin and HSP70 staining between the mixed tumours, although the pure F98 and A15A5 tumours were, unlike the pure C6 gliomas, S-100 negative. Using PCNA expression as a measure of the tumour proliferation all except the tumours derived from the three cell lines mix, which had a staining index of 7-10%, had focal staining indices in viable tumour of between 40-80%. There was focal positive staining in both perilesional brain and in regions of all tumours for the macrophage markers ED-1 and ED-2. None of the three cell lines stained in vitro for either ED1 and ED2 but all were constitutively positive in vitro for OX-6, a proposed marker for antigen presenting cells. The macrophage and lymphocytic response suggest a vigorous but largely ineffective immunological response had been mounted against all tumours. The consistent failure of the triple mix tumours to grow is unexplained. This work has shown the feasibility of producing 'mixed' cell line experimental gliomas by combining two cell lines at the time of innoculation. However, the relative failure to produce (i) mixed tumours that have properties not inherent to either parent cell line and (ii) implantation glioma with three cell lines suggest there are limits to this approach. Admixture of cell lines at the time of implantation therefore does not make experimental glioma models that more closely resemble natural gliomas, and also has some particular disadvantages. This experimental approach is therefore not recommended for use in the study of tumour biology and in evaluating the effectiveness of novel therapies.

Effects of nitric oxide manipulation on the disposition of platinum in an experimental glioma model

Rodents with striatal C6 glioma were given carboplatin (65 mg kg(-1) in a 10 mg ml(-1) solution, i.v.) after pretreatment with the NO modulating agents 3-morpholinosydnonimine (SIN-1), NG-nitro-L-arginine methyl ester (L-NAME), bradykinin or dexamethasone, to determine whether platinum disposition in the glioma and normal brain was altered. There was no significant change in mean glioma platinum disposition after 3 days of dexamethasone (32+/-9.7 microg/g). Treatment with SIN-1 (45.1+/-14.2 microg/g), L-NAME (42.9+/-4.9 microg/g) and bradykinin (45.7+/-11.3 microg/g) all resulted in increased tumour platinum concentration compared with controls (29+/-5.5 microg/g) but these results were not statistically significant. Dexamethasone significantly (p < 0.05) reduced the platinum concentration in normal brain but the other agents had no effect. Although glioma platinum concentration could be increased by some agents that alter tissue NO levels, the patterns of response were unpredictable and the magnitude (approximately 50%) of the increased platinum disposition is unlikely to be biologically significant.

Microsurgical excision of a pontomedullary epidermoid cyst with prepontine extension: case report

We report the case of a patient with a pontomedullary epidermoid cyst extending into the prepontine cistern. The patient presented with a progressive VIth nerve palsy, ataxia, and headache. Magnetic resonance imaging demonstrated a well-defined pontomedullary tumor with a high fat content. We excised the lesion using a microsurgical approach through the floor of the fourth ventricle. Postoperative magnetic resonance imaging confirmed the removal of both intra- and extra-axial components. We discuss the anatomic configuration, radiological appearances, and management of this unusual pathological finding.

Intracranial pressure in single-suture craniosynostosis

The indications for surgical correction of craniosynostosis in which there is involvement of only one of the cranial vault sutures have traditionally been based upon the cosmetic merits of the deformity alone. Whilst it is now appreciated that intracranial hypertension is commonly associated with the more complex forms of craniosynostosis, this aspect has not previously been addressed in detail among cases of single-suture craniosynostosis. This retrospective study reports our experience of overnight subdural intracranial pressure monitoring in 74 children with premature closure of a single cranial suture. A single coronal suture was involved in 37 patients, the sagittal suture in 25 and the metopic suture in 12. Intracranial pressure was raised in 13 (17%), borderline in 28 (38%) and normal in 33 (45%). Elevated intracranial pressure was seen more commonly where a midline suture was involved (sagittal or metopic) than when a single coronal suture was fused. We conclude that intracranial hypertension occurs in a significant proportion of children with single-suture craniosynostosis and suggest that this factor should be borne in mind during the initial assessment of these children so as to enable timely intervention where required and appropriate counselling of parents.

Treatment of non-rheumatoid occipitocervical instability. Internal fixation with the Hartshill-Ransford loop

We performed posterior fixation with a Hartshill-Ransford contoured loop in 43 patients with instability at the craniocervical junction. No external bracing was used. Fifteen patients had congenital malformations, ten had tumours, seven had 'bone-softening' conditions (such as osteogenesis imperfecta), five had suffered complicated fractures, three had occipito-C1-C2 hypermobility due to lax ligaments and three had severe degenerative spondylosis with pseudotumours of the transverse ligament. Twenty-nine patients had transoral decompression of the cord before fixation. In most cases, cancellous bone grafts taken from the iliac crest were used to induce fusion; in nine very ill patients, no bone graft was used. In the whole series there was no instance of construct failure, broken wire or laminar fracture. The best results were achieved in patients with tumours or bone-softening conditions. No patient with normal neurology deteriorated after surgery but seven had worse neurological deficits after operation than before. Neck stiffness caused half the patients to change their lifestyle.

Treatment of non-rheumatoid occipitocervical instability. Internal fixation with the Hartshill-Ransford loop

We performed posterior fixation with a Hartshill-Ransford contoured loop in 43 patients with instability at the craniocervical junction. No external bracing was used. Fifteen patients had congenital malformations, ten had tumours, seven had 'bone-softening' conditions (such as osteogenesis imperfecta), five had suffered complicated fractures, three had occipito-C1-C2 hypermobility due to lax ligaments and three had severe degenerative spondylosis with pseudotumours of the transverse ligament. Twenty-nine patients had transoral decompression of the cord before fixation. In most cases, cancellous bone grafts taken from the iliac crest were used to induce fusion; in nine very ill patients, no bone graft was used. In the whole series there was no instance of construct failure, broken wire or laminar fracture. The best results were achieved in patients with tumours or bone-softening conditions. No patient with normal neurology deteriorated after surgery but seven had worse neurological deficits after operation than before. Neck stiffness caused half the patients to change their lifestyle.

Single-frequency diode-pumped Nd:YAG ring laser with no intracavity elements

We report on a technique for unidirectional operation of a ring laser with no intracavity elements other than the gain material. The Faraday effect in the gain medium combined with an out-of-plane Brewster-angled rod design produces an optical diode. Fabrication of the gain material as a prism permits a simple two-mirror ring-cavity arrangement. Single-frequency operation of a diode-pumped Nd:YAG laser based on this design is demonstrated. Using a 1-W diode pump, we achieved a single-frequency output of 190 mW at 1.064 microm.

Self-mode locking of a diode-pumped Nd:YLF laser

We report on the self-mode locking of a diode-laser-pumped Nd:YLF laser. Pulses of 6-ps duration have been obtained by using only a glass rod placed at an intracavity focus and an aperturing slit near the output coupler to achieve pulse shaping. The mode-locking mechanism is believed to be that of self-focusing (Kerr lens mode locking) owing to the optical Kerr effect in the glass rod. The pulses are approximately bandwidth limited, and the process can be self-started by a mechanical perturbation to the system.

1-GHz repetition-rate frequency-modulation mode-locked neodymium lasers at 1.3 microm

We report on high-repetition-rate frequency-modulation mode locking of all-solid-state neodymium lasers operating at a 1.3-microm wavelength. At a repetition rate of 1 GHz, pulses of 12- and 8-ps durations with average powers of 162 and 240 mW have been obtained for 3-W diode-laser-pumped Nd:YAG and Nd:YLF lasers, respectively. Driven relaxation oscillations of a frequency-modulation mode-locked cw laser are also described.

Surgical anatomy of donor extended right trisegmentectomy before orthotopic liver transplantation in children

Liver transplantation is now accepted as the treatment of choice for children with end stage liver disease. A major constraint has been the shortage of donor organs of appropriate size. The use of reduced size adult organs has partially alleviated this problem but the previous technique employed was limited to a donor:recipient body-weight disparity of not greater than 3:1. Recently a new technique has been described that allows safe transplantation with a donor:recipient weight ratio of greater than 10:1. This should greatly increase the paediatric donor pool. Anatomical landmarks and techniques necessary for donor reduction hepatectomy are described from the dissection of 50 adult cadaveric livers. Variations in all important biliary and vascular structures necessitated adjustments in operative technique.

Intracranial neurenteric cysts. Report of two cases

Two cases of intracranial neurenteric cysts are reported and the literature is reviewed. Neurenteric cysts are rare congenital lesions that tend to occur in the spinal intradural space. An intracranial location is exceptional.

Astrocytoma and associated arteriovenous malformation

A case is reported of a cerebral arteriovenous malformation occurring in continuity with an astrocytoma. Possible etiologies of this unusual association are discussed.

Resonant frequency quadrupling of a mode-locked diode-pumped Nd:YLF laser

We report on a novel method of efficient frequency quadrupling of a mode-locked diode-pumped Nd:YLF laser to 262 nm in the ultraviolet region of the spectrum using two external ring enhancement cavities in series. With 6 W of pump power the mode-locked Nd:YLF laser produced 1 W of power incident into the first enhancement cavity. The fundamental has been resonantly frequency doubled using a crystal of lithium triborate with a conversion efficiency of 60% to produce 600 mW of usable mode-locked output at 523.5 nm. Fourth-harmonic radiation was generated by frequency doubling this green output in a second ring enhancement cavity using a crystal of beta-barium borate. Conversion efficiencies from green to ultraviolet of 11% have been achieved, producing a maximum usable average power at 262 nm of 42 mW in picosecond pulses.

Synchronously pumped continuous-wave dye laser pumped by a mode-locked frequency-doubled diode-pumped Nd:YLF laser

We report an efficient technique of resonant frequency doubling of a mode-locked diode-pumped Nd:YLF laser for producing 250 mW of continuous-wave mode-locked output in the green region of the spectrum. The Nd:YLF laser, which was pumped by a 3-W laser-diode array, was mode locked by using frequency-modulation mode locking to produce 650-mW output in pulses of 12-ps duration at a repetition rate of 225 MHz. This output was resonantly doubled by using MgO:LiNbO(3) in an external ring enhancement cavity. Doubling efficiencies of as much as 56% were achieved to produce usable mode-locked output of 250 mW at 523.5 nm. The frequency-doubled output was used to pump synchronously a continuous-wave mode-locked Rhodamine R6G dye laser. The dye laser produced pulses of approximately 1-ps duration and an output power of 40 mW.

Fatigue and melatonin in Parkinson's disease

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Additive-pulse mode locking of a diode-pumped Nd:YLF laser

We investigate the passive self-starting technique of additive-pulse mode locking of a diode-laser-pumped Nd:YLF laser. Pulses of 1.5-psec duration at a repetition rate of 123 MHz have been obtained, using only a single-mode optical fiber in an external feedback cavity to achieve pulse formation. The sech(2) pulses are approximately transform limited and to our knowledge the shortest that have been produced by a Nd:YLF laser. The laser was pumped by two 1-W laser-diode arrays and had usable output power of 20 mW, corresponding to a peak power of 108 W.