Gerrit J. Bouma

Orthogonal polarization spectral imaging: a new method for study of the microcirculation.

Different disease states, including diabetes, hypertension and coronary heart disease, produce distinctive microvascular pathologies. So far, imaging of the human microcirculation has been limited to vascular beds in which the vessels are visible and close to the surface (for example, nailfold, conjunctiva). We report here on orthogonal polarization spectral (OPS) imaging, a new method for imaging the microcirculation using reflected light that allows imaging of the microcirculation noninvasively through mucus membranes and on the surface of solid organs. In OPS imaging, the tissue is illuminated with linearly polarized light and imaged through a polarizer oriented orthogonal to the plane of the illuminating light. Only depolarized photons scattered in the tissue contribute to the image. The optical response of OPS imaging is linear and can be used for reflection spectrophotometry over the wide range of optical density typically achieved by transmission spectrophotometry. A comparison of fluorescence intravital microscopy with OPS imaging in the hamster demonstrated equivalence in measured physiological parameters under control conditions and after ischemic injury. OPS imaging produced high-contrast microvascular images in people from sublingual sites and the brain surface that appear as in transillumination. The technology can be implemented in a small optical probe, providing a convenient method for intravital microscopy on otherwise inaccessible sites and organs in the awake subject or during surgery for research and for clinical diagnostic applications. At present, the use of microvascular imaging in diagnosis and treatment of human disease is limited. Use has been made of nailfold capillaroscopy in the diagnosis and treatment of peripheral vascular diseases, diabetes and hematological disorders 1‐3 . Problems with movement have restricted the use of the bulbar conjunctiva for clinical applications in opthalmology 4‐6 . Other lo

Comparison of two Types of Surgery for Thoraco-Lumbar Burst Fractures: Combined Anterior and Posterior Stabilisation vs. Posterior Instrumentation Only

Summaryu2003This retrospective study compares clinical outcome following two different types of surgery for thoracolumbar burst fractures. Forty-six patients with thoracolumbar burst fractures causing encroachment of the spinal canal greater than 50% were operated on within 30 days performing either: combined anterior decompression and stabilisation and posterior stabilisation (Group 1) or posterior distraction and stabilisation using pedicle instrumentation (AO internal fixator) (Group 2). We evaluated: neurological status (Frankel Grade), spinal deformities, residual pain, and complications. The average follow-up was 6 years. There were no significant differences between the patients in both groups concerning age, sex, cause of injury and the presence of other severe injuries. Neurological dysfunction was present in 39% of all cases. Bony union occurred in all patients. Loss of reduction greater than 5 degrees and instrumentation failure occurred significantly more often in Group 2 compared to Group 1, but the kyphosis angle at late follow-up did not differ between groups, due to some degree of overcorrection initially after surgery in Group 2. The clinical outcome was similar in both groups, and all but one patient with neurological deficits improved by at least one Frankel grade.u2003Indirect decompression of the spinal canal by posterior distraction and short-segment stabilisation with AO internal fixator is considered appropriate treatment for the majority of unstable thoracolumbar burst fractures. This is a less extensive surgical procedure than a combined anterior and posterior approach.

Direct observation of the human cerebral microcirculation during aneurysm surgery reveals increased arteriolar contractility.

Background and Purpose— The effects of aneurysmal subarachnoid hemorrhage on morphology and function of the cerebral microcirculation are poorly defined, partly due to the lack of suitable techniques to visualize the microvessels in vivo. We used orthogonal polarization spectral (OPS) imaging on the brain cortex during aneurysm surgery to directly observe the small cortical blood vessels and quantify their responses to hypocapnia. Methods— In 16 patients undergoing aneurysm surgery, the diameter changes of small cortical vessels (15 to 180 μ m) were observed using OPS imaging. Ten patients were operated on early (within 48 hours after bleeding) and 6 underwent late surgery. Immediately after dura opening, the response to hyperventilation of arterioles and venules was observed with OPS imaging under sevoflurane anesthesia. Results— In patients operated on early, layers of subarachnoid blood were clearly visible. In this group, hyperventilation resulted in a 39±15% decrease in arteriolar diameter with a “bead-string” constriction pattern occurring in 60% of patients. In late surgery and in controls, no subarachnoid blood was seen. The arteriolar diameter decrease with hyperventilation was 17±20% in patients undergoing late surgery and 7±7% in controls. Venules were not affected by hyperventilation in any of the groups studied. Conclusions— OPS imaging allows direct in vivo observation of the cerebral microcirculation enabling us, for the first time, to visually observe and quantify microvascular reactivity in the human brain. The present study demonstrates increased contractile responses of the cerebral arterioles in the presence of subarachnoid blood, suggesting increased microvascular tonus with possibly greater susceptibility to ischemia.

Abnormal microcirculation in brain tumours during surgery

Orthogonal Polarisation Spectral imaging is a new clinical technique that uses polarised light to visualise the microcirculation of organ surfaces. We have used this technique to compare the functional microcirculatory properties of three types of brain tumour with those of the normal cortex. Meningiomas were characterised by chaotic and dilated vessels with almost no erythrocyte movement and a dark background, glioblastoma by few vessels with low flow and a background close to that of the healthy cortex, and metastases by a very dark background, almost no flow, and a chaotic vascular pattern. This technique could provide useful information about microcirculatory morphology and kinetics for diagnostic use during neurosurgery.

Evaluation of regional cerebral blood flow in acute head injury by stable xenon-enhanced computerized tomography.

Measurement of regional cerebral blood flow (rCBF) in head-injured patients is considered useful for understanding the cerebral hemodynamics of brain trauma and for determining the optimal therapy. Most data thus far obtained with 133Xe clearance techniques have made only relative contribution, due to limitations of the 133Xe method. More recently, is has become possible to measure rCBF by xenon-enhanced computerized tomography (Xe-CT), which obviates most problems inherent to the 133Xe method. On the other hand, computational errors and concerns regarding the safety of xenon inhalation have thwarted the clinical use of Xe-CT. Recent advances in CT technology, however, have largely eliminated these problems. Xe-CT CBF measurements in severe head injury demonstrate a good correlation between CBF values obtained with 133Xe and Xe-CT. By consistently applying these studies in conjunction with conventional CT, information on very early flow derangements (within 1 to 2 hours after injury) can be obtained, in relation to anatomical lesions. Preliminary data reveal higher incidences of global and focal ischaemia than found previously. Local ischaemia tends to evolve to hyperemia in the ensuing days.

Pathogenesis of Traumatic Brain Swelling: Role of Cerebral Blood Volume

The pathogenesis of traumatic brain swelling is unclear. Brain edema (increased water content) is considered an important cause of swelling, but there is also evidence that vasodilatation with increased cerebral blood volume (CBV) plays a role. We have evaluated early posttraumatic changes in CBV in 37 head-injured patients, using dynamic contrast-enhanced computerized tomography (CT) in combination with stable Xenon-enhanced CT for measurement of cerebral blood flow (CBF). This technique enables rapid determination of CBV without interfering with patient care. CBV values ranged from 2.0 to 10.1 ml/100 g. There was no relationship the time after injury at which the measurements were taken. CBV did not correlate with CBF in the early posttraumatic period. Patients with raised ICP (> 20 mm Hg) had significantly higher CBV that patients with normal ICP (5.4 +/- 2.1 vs 3.7 +/- 0.9 ml/100 g). Yet, the presence of signs of brain swelling on CT had no relation to the level of CBV. These data suggest that increased CBV may contribute to raised ICP, but that brain swelling is not caused by increased CBV alone, and is more likely accounted for by brain edema. We speculate that cerebral energy failure is the unifying cause of both intracellular edema and cerebral vasodilation leading to swelling of brain tissue.

Abnormal Responses of the Human Cerebral Microcirculation to Papaverin During Aneurysm Surgery

Background and Purpose— The role of the cerebral microcirculation in delayed ischemia after subarachnoid hemorrhage remains obscure. To test the hypothesis that cerebral arterioles have a reduced capacity to dilate after subarachnoid hemorrhage, we studied the microvascular responses to papaverine (PPV) in patients undergoing aneurysm surgery. Method— In 14 patients undergoing aneurysm surgery, the diameter changes of cortical microvessels after topical application of PPV were observed using orthogonal polarizing spectral imaging. Results— In control subjects, neither arterioles nor venules showed diameter changes in response to topical PPV. In patients operated <48 hours after subarachnoid hemorrhage, PPV resulted in vasodilatation of arterioles with 45±41% increase in arteriolar diameter (P=0.012). In 2 of these patients, arteriolar diameter returned below baseline value. In patients undergoing late aneurysm clipping, the diameter increase of the arterioles after PPV was 25±24% (not significant). In 2 patients of this group, no vasodilatation but focal arteriolar narrowing occurred. Conclusions— In patients with subarachnoid hemorrhage, unpredictable response patterns to PPV were observed with “rebound” vasoconstriction suggesting increased contractility of the microcirculation. Yet, diminished vasodilatory capacity of the cerebral microcirculation after subarachnoid hemorrhage was not confirmed by this study.

Intraoperative monitoring of brain tissue oxygen and carbon dioxide pressures reveals low oxygenation in peritumoral brain edema.

Brain edema and swelling often complicate surgery for brain tumors. Its pathophysiology is unclear, as is the relationship with brain tissue oxygenation. Our hypothesis was that brain edema around tumor is cytotoxic type caused by impaired local tissue oxygenation due to increased local tissue pressure. Therefore, we monitored brain tissue oxygen pressure (ptiO2) and carbon dioxide pressure (ptiCO2) in 19 patients undergoing craniotomy for removal of a brain tumor and specifically studied the effect of decompression by dura opening and by tumor removal with respect to the presence of brain swelling. Before craniotomy, multiparameter sensors were inserted into the peritumoral brain tissue guided by MRI-based stereotaxy. In eight patients who had severe brain swelling upon opening of the dura mater, ptiO2 immediately rose from 7 ± 8 mm Hg to 24 ± 15 mm Hg (P < 0.05), whereas in patients who did not have swelling, ptiO2 went from 16 ± 9 to 18 ± 10 mm Hg after opening of the dura. The mean ptiO2 of all patients at the start of resection of the tumor was 18 ± 11 mm Hg, and increased to 30 ± 15 mm Hg after resection was completed (P < 0.05). The effect on ptiO2 of raising the FiO2 to 1.0 was limited in this group of patients, as an increase greater than 50% was found in only six of twelve patients. Notably, in six patients, sensor malfunctions or associated hardware problems occurred, prohibiting useful data acquisition. We conclude that brain tissue oxygenation is reduced in the peritumoral area and improves after local tissue pressure relief, especially in patients with brain swelling. Thus, ischemic processes may contribute to brain edema around tumors. Intraoperative ptiO2 monitoring may enhance the safety of neuroanesthesia, but the high incidence of failures with this type of sensor remains a matter of concern.

Occurrence of discal and non-discal changes after sequestrectomy alone versus sequestrectomy and implantation of an anulus closure device

Sequestrectomy alone represents a procedure for the treatment of lumbar disc herniation. For selected cases, an anulus closure device (ACD) can be implanted which may result in lower reoperation rates. However, comparative magnetic resonance imaging (MRI) changes and their clinical relevance of both procedures are unclear and have not been reported so far. Clinical and MRI data of patients after limited discectomy with ACD implantation (group ACD; N=45) and patients after sequestrectomy alone (group S; N=40) with primary lumbar disc herniation were compared retrospectively. Pain intensity on the visual analogue pain scale (VAS), oswestry disability index (ODI) or the patient satisfaction index (PSI) were collected. Disc signal intensity, Modic type changes, endplate reactions, anular tears and reherniations were investigated using MRI before and <18months postoperative. Morphologic changes were correlated with clinical outcome. There was no difference in VAS back, VAS leg or ODI/PSI after the operation although group S showed significantly more reherniations in MRI. The overall rate of repeated surgery at the same level was similar with a trend in favour of the ACD group (P=0.729). Significantly more patients of the ACD group experienced endplate erosions after surgery (P<0.001). Both groups experienced progression of disc signal intensity, Modic type changes, and anular tears with most MRI signs being without clinical relevance. ACD implantation is associated with a significantly lower reherniation rate in MRI but showed a significantly higher rate of endplate erosions. The structural changes do not appear to be clinically relevant.

Effect of anular closure on disk height maintenance and reoperated recurrent herniation following lumbar diskectomy: two-year data.

OBJECTIVEnTo assess the potential benefits of disk reherniation reduction and disk height maintenance in limited diskectomy combined with the implantation of the anular closure device.nnnSUMMARY AND BACKGROUND DATAnPostoperative disk height loss is apparent in most patients undergoing lumbar diskectomy for herniated nucleus pulposus. Less favorable patient outcomes are associated with significant loss in disk height that can occur after aggressive disk tissue removal. More conservative disk removals, however, are often burdened by the increased risk of recurrent disk herniation.nnnMETHODSnTwo prospective single-arm studies on patients treated with limited diskectomy and an anular closure device were conducted. Outcome measures included disk height maintenance relative to preoperative values, Oswestry Disability Index, back pain, leg pain, and complications such as reherniations. Patients were evaluated preoperatively and postoperatively at 6 weeks and at 3-, 6-, 12-, and 24-month time points.nnnRESULTSnA total of 75 patients were included in this cohort consisting of 40 men and 35 women with an average age of 40 years. Disk height maintenance within the group overall was 90% at 24 months. Overall, 97% of the treated disks demonstrated disk height maintenance of at least 75% of preoperative levels at 12 months and 92% at 24 months. Disk height maintenance was correlated with less nucleus removal. Patient disability, back pain, and leg pain were significantly improved from preoperative levels at 6 weeks and maintained over the course of study. There was a single symptomatic reherniation requiring surgical intervention within this series.nnnCONCLUSIONSnLimited lumbar diskectomy combined with the use of an anular closure device provided very low rates of disk reherniation and exhibited excellent disk height maintenance and sustained disability, leg pain, and back pain improvement within a 24-month postoperative study period. As with prior diskectomy studies, disk height maintenance was correlated with lower nucleus removal, although recurrence was less than in prior reports of limited diskectomy. Anular closure may allow for achievement of both objectives.