Biomedical subjects
J M Findlay
Publications and source records attributed to J M Findlay.
Craniocervical fusion with contoured Luque rod and autogeneic bone graft.
OBJECTIVE: To examine the efficacy of internal craniocervical fixation with a Luque rod and autogeneic bone graft for craniocervical instability. DESIGN: A case series. SETTING: A university-affiliated hospital. PATIENTS: Six patients with craniocervical instability from diverse causes. INTERVENTIONS: Craniocervical fusion with a custom-formed Luque rod wired to the occiput and a variable number of vertebrae overlaid with autogeneic bone graft, followed by bracing with either a halo vest or a removable, stiff, plastic cervical orthosis. MAIN OUTCOME MEASURES: Craniocervical fusion and neurologic stability. RESULTS: All patients maintained good craniocervical alignment. Radiologic bony fusion was achieved in five patients. Three patients remained neurologically stable and three had improved neurologic status. CONCLUSION: Craniocervical fusion with the contoured Luque rod and autogeneic bone grafting, usually in combination with a temporary plastic cervical orthosis, is of value in managing craniocervical instability.
Horizontal saccades to dichoptically presented targets of differing disparities.
Horizontal saccades were elicited to targets of various disparities displayed dichoptically. When the left eye and right eye targets were in the same hemifield, the resulting saccade demonstrated spatial averaging (42%, where 50% represents perfect averaging) between the left and right eye target positions. When the left eye and right eye targets were in opposite hemifields, the saccade was directed to one of the stimuli and was only minimally influenced by the presence of the other. This pattern is similar to that obtained when saccades are made to double targets, both of which are visible to both eyes. These data are discussed in terms of an ecological role for the global effect.
William John Horsey, M.D., F.R.C.S.C. Neurosurgeon to St. Michael's Hospital, Toronto.
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William M. Lougheed and the development of vascular neurosurgery at the Toronto General Hospital.
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Aneurysmal cyst, bone type, primary in an artery.
An aneurysmal bone cyst-like reaction involving the left common carotid artery bifurcation in an otherwise healthy 7-year-old boy is described. The patient presented with a 6-week history of an enlarging pulsatile neck mass. The mass was excised with connection of arteries on either side with a saphenous vein graft. There were no associated intracranial arterial aneurysms or associated skeletal lesions. A history of trauma could not be elicited. To the best of our knowledge this is the first report of an aneurysmal cyst, bone type, involving a large blood vessel.
Carotid microendarterectomy.
The illumination and magnification provided by the operating microscope allow for the accurate and complete removal of atherosclerotic plaque from the carotid arterial wall, for precise arterial repair at the distal end of the internal carotid endarterectomy, and for a fine, nonstenosing arteriotomy closure. A high dissection of the internal carotid artery, allowing arterial exposure above the plaque, is particularly helpful in the performance of carotid microendarterectomy. The technique of carotid microendarterectomy has been used in a consecutive series of 60 patients with symptomatic carotid stenosis, all but 5 of whom had carotid stenoses of 70% or more. In this series, there were no deaths and only one postoperative stroke, due to occlusion at the operative site. Emergency thrombectomy and angioplasty restored blood flow, and the patient recovered. In this and all other patients, carotid patency after surgery has been confirmed (angiography in 6 and Doppler examination in 54). Although postoperative stroke risk is dependent upon many factors, we feel that the refinements afforded by the operating microscope help reduce the risks associated with surgical technique to a minimum.
Treatment of intraventricular hemorrhage with tissue plasminogen activator.
The patients with intraventricular hemorrhage (IVH) were treated with recombinant tissue plasminogen activator (rt-PA) injected directly into the lateral ventricles, followed by ventricular drainage. All had a decreased level of consciousness before treatment (Glasgow Coma Scale score 10 +/- 3.4). A total dose between 2 and 12 mg of rt-PA (6.4 +/- 3.3) was administered. For eight patients with aneurysmal IVH, treatment with rt-PA began with two patients the same day as the aneurysm clipping, and the day after with six patients. For a patient with an excision of a ruptured arteriovenous malformation and a patient with IVH resulting from a lateral ventricular catheterization during posterior fossa tumor surgery, treatment with rt-PA started 24 hours after surgery. After an injection of rt-PA, the ventricular drain was closed for 1 hour, followed by alternate-hourly drainage and intracranial pressure (ICP) monitoring. Five patients received a second injection of rt-PA on the second postoperative day, and one patient received a third dose on the third day. Among the eight patients given rt-PA the day after surgery, the volume of external cerebrospinal fluid (CSF) drainage for 24 +/- 8 hours before treatment was 61 +/- 57 ml, and the mean ICP was 22 +/- 5 mm Hg during this same time. Younger age and poorer neurological condition correlated with higher ICP before treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
Comparison of intrathecal administration of urokinase and tissue plasminogen activator on subarachnoid clot and chronic vasospasm in a primate model.
Safety and efficacy of the thrombolytic agent urokinase (URO) in the elimination of subarachnoid clot and prevention of chronic vasospasm was compared with tissue-type plasminogen activator (rt-PA) in a blind, randomized placebo-controlled trial. Twenty monkeys were randomly assigned to one of five groups of four. Each group underwent baseline cerebral angiography followed by bilateral craniectomy and experimental subarachnoid hemorrhage. An Ommaya reservoir was inserted on the right side with its catheter placed into the ipsilateral subarachnoid space. Twenty-four hours later, depending upon group assignment, the animals received 100,000 IU URO, 200,000 IU URO, 1 mg rt-PA, 2 mg rt-PA, or the equivalent volume of normal saline (control group). On Day 7, angiography was repeated and the animals were killed. One animal died as a result of complications during the baseline angiography, presumably due to blood loss and prolonged anesthesia, and a replacement animal was obtained. No animals demonstrated any delayed neurological deficits. The study demonstrated that a single intracisternal bolus injection of rt-PA, 2.0 mg in 2 ml sterile water, or URO, 200,000 IU in 2 ml sterile water, 24 hours after induction of experimental subarachnoid hemorrhage in primates, was equally effective in thrombolysing ipsilateral clot, but neither dosage prevented angiographic vasospasm. Vasospasm occurred bilaterally in all groups. Whereas gross subarachnoid clot was found bilaterally in all animals in the placebo group and both smaller-dose URO and rt-PA groups, right-sided subarachnoid clot was virtually absent and left-sided clot reduced in both higher-dose URO and rt-PA groups.(ABSTRACT TRUNCATED AT 250 WORDS)
The spatial signal for saccadic eye movements emphasizes visual boundaries.
By investigating the visual processing involved when saccades are made to newly appearing targets, we show that this processing is significantly nonlinear and that texture boundary information predominates. We used the global, or center-of-gravity, effect whereby a saccadic eye movement directed to a target consisting of a pair of elements has an amplitude intermediate between that of saccades directed to the individual elements. We measured the effect using target elements with different visual characteristics, including phase-reversal checkerboard targets that had the same space-average luminance as the background. The contribution to the center-of-gravity calculation was used to measure relative salience. We found that positive and negative contrast elements contribute almost equal weightings. Thus, salience, assessed in this way, is a highly nonlinear function of luminance. The salience of checkerboard targets was found to decrease as check size was decreased and increase as the overall size of the target was increased. Checkerboards with an empty center were as effective as were full checkerboards, showing the importance of boundaries in the salience signal.
Scrutinization, spatial attention, and the spatial programming of saccadic eye movements.
Results are presented from an experiment in which subjects' eye movements were recorded while they carried out two visual tasks with similar material. One task was chosen to require close visual scrutiny; the second was less visually demanding. The oculomotor behaviour in the two tasks differed in three ways. (1) When scrutinizing, there was a reduction in the area of visual space over which stimulation influences saccadic eye movements. (2) When moving their eyes to targets requiring scrutiny, subjects were more likely to make a corrective saccade. (3) The duration of fixations on targets requiring scrutiny was increased. The results are discussed in relation to current theories of visual attention and the control of saccadic eye movements.
Saccades to targets in three-dimensional space: dependence of saccadic latency on target location.
The latency of saccadic movements to targets appearing at various positions in three-dimensional visual space was measured in four experiments. The first experiment confirmed that latencies of saccades to visual targets are greater in the lower visual field and showed that the increase is not influenced by the vertical starting position of the eye in the orbit, nor by a time gap between the fixation offset and the target onset. A hypothesis that this visual field difference was caused by a link between downward saccades and convergence movements was tested by recording saccade latencies when the targets were in a different depth plane from that of the original fixation. We did not find any direct support for the vergence involvement hypothesis, although the lower/upper visual field effect was shown to decrease consistently in monocular viewing. It was also shown that saccades to targets positioned in a different depth plane have longer latencies. In a final experiment, the visual field effect was shown to depend on the egocentric rather than the gravitational vertical.
A survey of vertebral burst-fracture management in Canada.
In the management of burst fractures, the role of direct surgical removal of retropulsed bony fragments encroaching upon the spinal canal (direct decompression) is controversial. A questionnaire was mailed to 65 neurosurgeons and 36 orthopedic surgeons across Canada to determine the current management of vertebral burst fractures and the willingness of these surgeons to participate in a longitudinal study of the effects of direct surgical decompression in the management of burst fractures. Sixty-nine (44 neurologic and 25 orthopedic) surgeons responded to the questionnaire. Of those who responded, 97% of the neurologic surgeons and 95% of the orthopedic surgeons stated that they used plain radiography and computed tomography in their pretreatment investigations, and at least 50% in each specialty repeated these investigations at follow-up examinations. Standard tomography, magnetic resonance imaging and myelography were used less frequently both before and after surgery. There were no significant differences between specialties in the use of tests. Neurologic status and the treating surgeon's specialty were found to significantly influence management of burst fractures. According to 56% of neurologic surgeons and 81% of orthopedic surgeons, neurologically intact patients were usually treated with stabilization only (p less than 0.05). The greater number of neurosurgeons who used direct decompression was balanced by the number of orthopedic surgeons who used indirect decompression. Patients with partial, stable neurologic injuries were usually managed by direct decompression and stabilization according to 84% of the responding neurologic surgeons and 77% of the responding orthopedic surgeons.(ABSTRACT TRUNCATED AT 250 WORDS)
Express saccades: is there a separate population in humans?
It is well known that the latencies of target elicited saccades are significantly reduced when the target onset is preceded shortly by the offset of a fixation point (Saslow 1967). Fischer and Boch (1983) reported the discovery that, with monkeys as subjects, in addition to the general reduction in saccade latencies previously reported, there occurred a separate population of saccades with extremely short reaction times. They termed this population "express saccades", and more recently reported the discovery of an equivalent population of express saccades for humans (Fischer and Ramsperger 1984; Fischer 1987). In this paper, work is reported which confirms the existence of short latency visually guided saccades in humans but questions whether these form a separate population of "express saccades". The conditions used were very similar to those used by Fischer and Bocn.
Disentangling neglect and hemianopia.
In this paper we report findings which question the diagnosis of a hemianopia in B.Q., a 66-year-old lady who shows unilateral spatial neglect following a lesion to the right parietal lobe. The presence of a hemianopia has been indicated following two independent assessments of B.Q.'s visual fields. We examined B.Q.'s performance on a visuo-spatial task in which single or double stimuli were displayed left and right of a central fixation point. B.Q. failed to report left stimuli when the fixation point was continuously displayed (OVERLAP CONDITION). This performance is consistent with the suggestion of a left hemianopia as indicated by perimetric field testing. In a further condition the fixation point was extinguished prior to stimuli onset (GAP CONDITION). B.Q. consistently responded to left stimuli in the gap condition and also showed improved performance to right stimuli. Eye movements were recorded on a separate testing session, in which B.Q. showed a normal saccadic response to left targets in the gap condition, but not during the overlap condition. These results suggest that B.Q.'s failure to report left stimuli during field plotting is due to her neglecting left stimuli and not because she has a visual field defect. By using a testing procedure which reduces the severity of neglect B.Q. is able to respond to left stimuli. Reducing the severity of B.Q.'s neglect also abolishes the apparent hemianopia. Standard field plotting techniques which use a consistently displayed fixation point may not be appropriate for the testing of neglect patients' visual fields.
Subarachnoid fibrinolytic treatment for the prevention of cerebral vasospasm.
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Lysis of intraventricular hematoma with tissue plasminogen activator. Case report.
A 42-year-old woman suffered a severe intracerebral and intraventricular hemorrhage from a ruptured anterior cerebral artery aneurysm. Evacuation of the frontal hematoma and clipping of the aneurysm was performed but the intraventricular blood clot persisted, causing ventricular dilatation and high intracranial pressure (ICP) 24 hours after surgery despite external ventricular drainage. Over this period of time the patient's clinical condition improved from Grade V to Grade IVb (World Federation of Neurological Surgeons classification). The intraventricular hematoma was lysed with a total of 8 mg recombinant tissue plasminogen activator injected directly into the ventricles on the 1st and 2nd postoperative days, resulting in rapid normalization of ventricular size and ICP. The patient has since made a substantial recovery and has been able to return home.
Intracisternal recombinant tissue plasminogen activator after aneurysmal subarachnoid hemorrhage.
Fifteen patients undergoing surgery within 48 hours of aneurysm rupture were administered recombinant tissue plasminogen activator (rt-PA) directly into the basal subarachnoid cisterns after minimal surgical clot removal and aneurysm clipping. Preoperatively, 13 patients had diffuse or localized thick subarachnoid blood clots on computerized tomography (CT), and two had diffuse thin clots. The rt-PA was given as a single intraoperative injection of 7.5 mg (one patient), 10 mg (nine patients), or 15 mg (five patients). Postoperative cisternal drainage was employed in three patients. All patients except one demonstrated partial to complete cisternal clot clearance on CT scans within 24 hours after surgery. The patient who showed no clot reduction was the only patient in this series to develop symptomatic vasospasm and was the only fatality, dying 8 days after rupture. No vasospasm was seen on follow-up cerebral angiography in six of the 14 responding patients, and mild-to-moderate arterial narrowing was seen in at least one major cerebral artery in the remaining eight patients. Severe angiographic vasospasm was not seen, although the patient who died did not undergo repeat angiography. There was one major complication early in the series which seemed clearly related to treatment, and that was a large extradural hematoma occurring within several hours of craniotomy. Intrathecal fibrinolytic treatment appears effective in clearing subarachnoid clot and reducing vasospasm, and may be associated with acceptable risks if given to patients with large-volume subarachnoid hemorrhages at high risk for severe vasospasm.