Visually evoked changes of blood flow velocity and pulsatility index in the posterior cerebral arteries: a transcranial Doppler study

OBJECTIVE

Transcranial Doppler sonography (TCD) can detect visual evoked blood flow responses non-invasively and continuously with high temporal resolution. While the mean flow velocity response to visual stimuli is well documented, the response of the pulsatile characteristics of the waveform is less well known.

METHOD

We examined the changes of blood flow velocity and pulsatility index (PI) in the posterior cerebral artery (PCA) in 50 healthy volunteers. TCD responses were measured in response to metabolic activation of the visual cortex by visual stimulation.

RESULTS

A specific, stimulus-related increase of the mean flow velocity (MFV) in the PCA was found. The intensity of the blood flow response was significantly influenced by the complexity of the stimulus. During complex visual stimulation we found a mean flow velocity (MFV) increase of 29.4 % from the baseline in the subjects. However, a stimulus-related decrease was observed in the pulsatility index (PI); although the mean PI with closed eyes during baseline measurement was 1.18 (SD 0.27), on average, it fell significantly to 0.95 (SD 0.23) with the alternating chessboard and 0.82 (SD 0.22) during the complex stimulus condition. The relative decrement of the pulsatility index with increasing complexity of the visual stimulus is highly significant, with values of -19.5 % and -30.5 % compared to the baseline.

CONCLUSION

These findings demonstrate the inverse correlation between MFV response and pulsatility index in the PCA. We assume that this decrease of the PI in the PCA may reflect the reduced regional vascular resistance in the visual cortex during visual stimulation.

Intracerebral Abscess after Abutment Change of a Bone Anchored Hearing Aid (BAHA)

OBJECTIVE

Brain abscesses are life-threatening and sometimes difficult to detect. A brain abscess after placement, manipulation of a bone anchored hearing aid, or a periauricular implant for fixation of an ear prosthesis has never been reported in the literature.

PATIENT

A 42-year-old man suffered from a right-sided temporodorsal brain abscess after change of a bone anchored hearing aid abutment. The fixture itself had been inserted 8 years before without any complications in the peri- or postoperative period. A CT-guided puncture of the abscess could be performed via the screw-hole in the temporal bone after removal of the fixture, and the patient was treated with antibiotics.

RESULTS

The outcome of the procedure was good without neurologic deficits for the patient.

CONCLUSION

The insertion of periauricular screw implants bears the risk of meningeal lesions as well as a small risk of purulent intracranial and intracerebral complications perioperatively or in the context of later manipulations. Minimally invasive therapy of such brain abscesses can be performed by removal of the foreign body, CT-guided puncture, and antibiotic medication.

Cerebral vascular reactivity response to anaesthetic induction with propofol in patients with intracranial space-occupying lesions and vascular malformations

BACKGROUND AND OBJECTIVE

In clinical trials, autoregulation and carbon dioxide reactivity are preserved during propofol anaesthesia. Paradoxical increases of blood flow velocity during induction of anaesthesia could be demonstrated in patients with brain tumours. This study evaluates the effects of propofol on cerebral blood flow velocity in patients undergoing surgery for brain tumours and vascular malformations.

METHODS

Changes in cerebral blood flow velocity after the administration of propofol were assessed using bilateral 2 MHz transcranial Doppler probes in 47 patients undergoing surgery for brain tumours and in 22 patients undergoing surgery for aneurysms and angiomas.

RESULTS

Flow reduction after propofol was slightly less pronounced on the side of the tumour; in patients with cerebrovascular lesions, no difference between the two sides was detectable. After the administration of propofol a flow increase was present on the side of the tumour in 2 patients. In 3 patients with angiomas, the flow decrease after the administration of propofol was less pronounced on the side of the angioma. Neither observation gave statistical proof of abnormality.

CONCLUSIONS

The flow changes after propofol may give a hint of cerebrovascular reactivity. Further investigations should focus on combined measurements of cerebral autoregulation and carbon dioxide reactivity and should focus on patients with impaired consciousness to test for reliability.

Dynamic cerebral autoregulation in patients undergoing surgery for intracranial tumors

OBJECTIVE

Alterations of cerebral perfusion in brain parenchyma adjacent to tumors have been reported in the literature. The aim of this study was to test cerebral autoregulation in patients scheduled for tumor resection.

METHODS

Dynamic cerebral autoregulation was evaluated perioperatively using bilateral transcranial Doppler sonography and the thigh cuff method to alter arterial blood pressure in 50 patients (26 females and 24 males) with a mean age of 49.8 years (range 15-73 years). The alterations of cerebral autoregulation were correlated to size, location and histology of the tumor and the presence of accompanying diseases.

RESULTS

Mean cerebral autoregulation was normal before the induction of anesthesia, after intubation under normoventilation, after intubation under hyperventilation and after surgery on intensive care unit. Location, size or histological classification of the lesion was without influence on autoregulation. The patients with accompanying diseases, such as diabetes mellitus and/or hypertension had significantly lower autoregulation values prior to surgery and a significantly lower increase after hyperventilation.

CONCLUSION

Cerebral autoregulation is preserved in patients with intracranial tumors regardless of tumor size, if the patient's clinical status prior to surgery is good. The influence of accompanying diseases was demonstrable and should be considered in the perioperative patients management.

Virtual image navigation: a new method to control intraoperative bleeding in neuroendoscopic surgery. Technical note

In this neuroendoscopic study the authors tested the newly developed "red-out module" of their visual navigation system that enables the neurosurgeon to achieve hemostasis if total visualization is lost due to hemorrhage ("red out") within the visual field. An optical position measurement system connected to the endoscope guarantees that digitized endoscopic images are coupled with the accurate endoscopic position. Computerized images are simultaneously stored with their respective position data, and this creates a virtual anatomical landscape. The system was tested in in vivo bleeding conditions in a rat model. Artificial endoscopic cavities were created in the inguinal, pelvic, and jugular regions in rats to imitate the conditions of the human ventricular system. Two experimental settings were tested: Technique I, in which a computer landmark has been previously determined at the point where the vessel will be lesioned; and Technique II, in which a landmark has been previously set in the surrounding area of the vessel. Immediately after hemorrhage obscures the visual field (red out), the computer automatically displays the virtual images on a separate monitor. The previously set landmarks and the graphic overlay of the coagulation fiber enable the surgeon to navigate within the operative field based on the virtual images and to perform coagulation at the site of the lesion. A total of 175 vessels were coagulated: 43 arteries and 132 veins. In using Technique I, 130 (90.9%) of 143 vessels and in using Technique II, 26 (81.2%) of 32 arteries were successfully coagulated. The authors' data revealed that virtual image guidance has the potential to be a helpful tool in neuroendoscopy.

Preoperative planning and intraoperative navigation: status quo and perspectives

An essential step in modern microneurosurgery involves preoperative planning of procedures. For difficult lesions neuronavigation is being used in conjunction with complex and detailed radiological investigations. This article shows how these examinations are used for computerized planning of surgical steps. Although planning and navigation are still two separate entities, the combination of the two may help in neurosurgery.

Operative approach due to results of functional magnetic resonance imaging in central brain tumors

Since 1995 we have been investigating the localization of the cortical motor strip by functional magnetic resonance imaging (fMRI) in central brain tumor cases. Forty patients have been operated on using these data for preoperative planning. Intraoperative sensory evoked potentials (SEP) and cortical motor evoked potential (performed in 18 patients) showed a good correlation with fMRI data with the exception of two cases. Only 12.5% of cases were permanently worsened as a result of increasing postoperative pareses.

Extraspinal dural arteriovenous fistula in a patient with lipomyelodysplasia: value of MRI and MRA

Spinal dural arteriovenous fistulae are extremely rare in spinal dysraphism. A fistulous malformation within a lipomyelomeningocele has not been reported previously. A 50-year-old man presented with progressive paraparesis and bladder dysfunction. MRI revealed a large lumbar lipomyelomeningocele. A vascular malformation was indicated by abnormal signal in the thoracolumbar spinal cord and dilated perimedullary veins. Phase-contrast MRA demonstrated only the slow-flow veins of the fistula and an intradural ascending vein. Contrast-enhanced ultra-fast MRA gave excellent delineation of all parts of the fistula within the dysraphic lesion.

Clinical utility of magnetic resonance angiography in the evaluation of aneurysms from a neurosurgical point of view

The possibilities and limitations of MRA in the evaluation of intracranial aneurysms were investigated in this study. 54 patients, 30 with acute SAH were diagnosed using the three dimensional time-of-flight MRA in comparison with a conventional four vessel digital subtraction angiography prior to surgery. Furthermore, postoperative MRA was performed to assess clip placement and vessel patency and to search for innocent additional aneurysms in patients with emergency surgery due to intracerebral hemorrhage causing mass effect in whom preoperatively only the side of the lesion was investigated in DSA. 64 aneurysms in all vessel territories were detected. Three aneurysms were missed in MRA and there were three false positive results. Four baby-aneurysms were missed by both imaging modalities and were found during surgery. In all patients with CT scans suspicious of aneurysms MRA was able to detect or rule out the aneurysm. Postoperative MRA to demonstrate clip placement and vessel patency was not possible due to susceptibility artefacts. MRA should be the diagnostic procedure of first choice in CT findings suspicious of aneurysms. The follow-up of confirmed aneurysms is safely possible. MRA is very well applicable in the acute setting after SAH. The axial acquisition films and the rotatable maximum intensity projection reconstructions provide useful insights into the location of the aneurysm and its neighboring structures thus influencing the preoperative planning of surgical strategies. Keeping the limitations in mind it is a safe tool in the evaluation of aneurysms, especially with the rapidly improving postoprocessing possibilities.

Reconstruction of an extreme frontal and frontobasal defect by microvascular tissue transfer and a prefabricated titanium implant

A 30-year-old man was referred to us with an extreme frontal and frontobasal defect from a motorbike accident 12 years before. Multiple attempts at frontal and frontobasal revision and reconstruction had been performed over the years, with several episodes of meningitis. Reconstruction was planned in two steps. First, a revision of the anterior skull base with mobilization of meningeal adhesions and duraplasty, removal of infected masses of polymethylmethacrylate out of the upper ethmoid sinuses, and coverage with a deepithelialized latissimus dorsi free flap were performed. In the second step 3 months later, aesthetic forehead reconstruction was achieved with a pre-fabricated individual titanium implant. The predictable result of this two-step reconstruction was very pleasing. Safe separation of the cranial cavity from the upper airways was essential, requiring free tissue transfer in this case, and is a prerequisite for any alloplastic forehead reconstruction. Timing of the two-step procedure, including the CT data acquisition; handling of soft tissues, bone, and foreign material; and construction details of the implant demonstrate the necessary complex management of this, the most difficult case of the 88 applications of the new computer aided design and manufacturing technique thus far. Even the most elaborate computer aided preparation cannot be successful without consideration of established surgical principles.

Surgical treatment of recurrent trigeminal neuralgia

In this retrospective investigation 7 patients operated on for recurrent trigeminal neuralgia via a suboccipital enlarged burr hole trepanation were evaluated. The intraoperative findings indicate that neo-compressive effects due to foreign material used during prior surgery are more important than adhesions around the nerve. Furthermore, the results of recurrent operations are encouraging as 6 of the 7 patients were painfree without additional neurological deficits.

Factors influencing shunt dependency after aneurysmal subarachnoid haemorrhage

In this retrospective analysis of 138 patients treated for ruptured aneurysms the development of shunt dependent hydrocephalus was evaluated regarding possible predictive factors. In 15 patients (11%) ventriculo-atrial shunt was implanted due to hydrocephalus. One predictive factor was the localisation of aneurysms as patients with hydrocephalus had PcoA aneurysms in 40% compared to 20% in the group of patients without hydrocephalus and only 7% compared to 28% MCA aneurysms. An other predictive factor was the severity of the subarachnoid haemorrhage (SAH) as 7 patients out of the 15 were graded Fisher IV on admission. Furthermore, an important predictive factor was the presence of acute hydrocephalus as 13 out of the 15 patients (87%) with shunt dependent hydrocephalus had acute hydrocephalus requiring external ventricular drainage. An other possible factor was the intraoperative opening of the lamina terminalis as in 73% of the patients with shunt dependent hydrocephalus compared to 82% in the group of patients without hydrocephalus this procedure was performed during surgery. The results suggest that shunt dependency is more likely after severe SAH especially in the presence of an acute hydrocephalus and in patients with aneurysms located in the basal cisterns. Therefore treatment of the acute hydrocephalus and possible the opening of the lamina terminalis could have a positive effect on the development of shunt dependent hydrocephalus after SAH.

[Delayed lumbar epidural hematoma. Discussion of the risk factors: hypertension, anticoagulation and spinal anesthesia]

This case report deals with the very rare complication of an intraspinal haematoma: a 70 year old male underwent anticoagulation because of supraventricular dysrhythmias followed by two transient ischaemic attacks. He accidentally received an intramuscular injection for tetanus prophylaxis and developed a deep intramuscular haematoma, which was operated upon, after normalisation of coagulation parameters, under spinal anaesthesia. No primary complication was noted. Heparin therapy was started perioperatively, on the day of the operation. Sixteen days postoperatively, the patient resumed oral anticoagulation; 3 months later he developed a progressive cauda-equina-syndrome due to an epidural haematoma at the level of L2 to L4. This could be diagnosed by magnetic resonance imaging, but not by computed tomography. Acute surgical decompression was performed. The haematoma showed various ages as suspected by the intraoperative morphology and proven by histological examination. The neurological findings improved, and 6 months after rehabilitation only slight neurological deficits remained. Hypertension, anticoagulants, and spinal anaesthesia are discussed as risk factors for this complication.

[CAD/CAM (computer-aided design/computer-aided manufacturing) titanium implants for cranial and craniofacial defect reconstruction]

The reconstruction of craniofacial bone defects with intraoperatively modeled prosthesis restricts the choice of material and its biocompatibility and the prediction of the esthetic result. A prolonged duration of the surgical procedure and an increased stress on the patient are consequences. In contrast, modern industrial CAD/CAM-systems allow the prefabrication of titanium prosthesis: An individual computer-based 3D model of the bony defect is generated after acquisition, transfer and evaluation of helical CT data. Basing on these data the individual prosthesis-shape is designed using freeform surfaces geometries and fabricated by a numerically controlled milling machine. The conical margins of this prosthesis-geometry are generated by the borders of the defect with a minimal gap of 0.25 mm, and the surface contours by considering the non-affected neighbouring contours with a constant thickness of 1.5 mm. Individual osteosynthesis-microplates for fixation are integrated in design and manufacturing if screw-holes cannot be integrated in the thin margins of the implants. The radiological and clinical results of 17 patients after reconstruction of craniofacial bone defects with CAD/CAM titanium implants were good. Complications were not observed.

CO2 reactivity in patients after subarachnoid haemorrhage

CO2 reactivity was tested in patients with transcranial Doppler sonography (TCD) and endtidal CO2 measurements after an average time interval of ten months after subarachnoid haemorrhage (SAH). After deliberately changing breathing there was a significant change in endtidal CO2 and in flow velocities in all three examination groups. Comparing 27 patients with SAH and 5 patients treated for incidental aneurysms and 20 patients without cerebrovascular disease there were no significant differences in CO2 reactivity. Furthermore, there were no right to left differences. In 12 patients with vasospasm, two of them treated by percutaneous transluminal angioplasty for delayed ischaemic deficits, CO2 reactivity was normal at the time of investigation. Furthermore, normal CO2 reactivity was found in patients after SAH and surgery for ruptured aneurysms regardless of the severity of the SAH.