Is stagnating flow in former feeding arteries an indication of cerebral hypoperfusion after resection of arteriovenous malformations?

Hemodynamic alterations following a cerebellar arteriovenous malformation resection: Case report and densitometric quantitative analysis from CT imaging

BACKGROUND

Cerebellar arteriovenous malformations (cAVMs) are rare and challenging lesions with an aggressive natural history. The mechanisms whereby a patient can worsen clinically after a supratentorial AVM resection include an acute alteration in cerebral hemodynamics, which is a known cause of postoperative hyperemia, edema and/or hemorrhage. These phenomena has not been described for cAVMS. Moreover, the underlying pathophysiology of edema and hemorrhage after AVM resection still remains controversial.

METHODS

We report a patient that presented an abrupt neurological deterioration after cAVM surgical resection. Emergent external ventricular drainage to treat incipient hydrocephalus only partially reverted the patient's deterioration. Consecutive post-surgery CT images revealed fourth ventricle compression secondary to cerebellar swelling that concurred with a new neurological deterioration. Densitometric analysis was performed in these CT images to reveal the nature of these changes as well as their evolution over time.

RESULTS

Importantly, we demonstrated a dynamic increase in the cerebellum mean density at the interval of Hounsfield values which correspond to hyperemia values. These changes were dynamic, and when hyperemia resolved and cerebellar density returned to basal levels, the fourth ventricle re-expanded and the patient neurologically recovered.

CONCLUSIONS

This study demonstrated the utility of quantitative CT image analysis in the context of hemodynamic alterations following cAVM resection. Densitometric CT analysis demonstrated that hyperemic changes, but not ischemic ones, were time-dependent and were responsible for swelling and hemorrhage that conditioned neurological status and patient's evolution.

Hemodynamic alterations following a cerebellar arteriovenous malformation resection: Case report and densitometric quantitative analysis from CT imaging

BACKGROUND

Cerebellar arteriovenous malformations (cAVMs) are rare and challenging lesions with an aggressive natural history. The mechanisms whereby a patient can worsen clinically after a supratentorial AVM resection include an acute alteration in cerebral hemodynamics, which is a known cause of postoperative hyperemia, edema and/or hemorrhage. These phenomena has not been described for cAVMS. Moreover, the underlying pathophysiology of edema and hemorrhage after AVM resection still remains controversial.

METHODS

We report a patient that presented an abrupt neurological deterioration after cAVM surgical resection. Emergent external ventricular drainage to treat incipient hydrocephalus only partially reverted the patient's deterioration. Consecutive post-surgery CT images revealed fourth ventricle compression secondary to cerebellar swelling that concurred with a new neurological deterioration. Densitometric analysis was performed in these CT images to reveal the nature of these changes as well as their evolution over time.

RESULTS

Importantly, we demonstrated a dynamic increase in the cerebellum mean density at the interval of Hounsfield values which correspond to hyperemia values. These changes were dynamic, and when hyperemia resolved and cerebellar density returned to basal levels, the fourth ventricle re-expanded and the patient neurologically recovered.

CONCLUSIONS

This study demonstrated the utility of quantitative CT image analysis in the context of hemodynamic alterations following cAVM resection. Densitometric CT analysis demonstrated that hyperemic changes, but not ischemic ones, were time-dependent and were responsible for swelling and hemorrhage that conditioned neurological status and patient's evolution.

Normal perfusion pressure breakthrough theory: a reappraisal after 35 years

The intrinsic ability of the brain to maintain constant cerebral blood flow (CBF) is known as cerebral pressure autoregulation. This ability protects the brain against cerebral ischemia and hyperemia within a certain range of blood pressures. The normal perfusion pressure breakthrough (NPPB) theory described by Spetzler in 1978 was adopted to explain the edema and hemorrhage that sometimes occur after resection of brain arteriovenous malformations (AVMs). The underlying pathophysiology of edema and hemorrhage after AVM resection still remains controversial. Over the last three decades, advances in neuroimaging, CBF, and cerebral perfusion pressure (CPP) measurement have both favored and contradicted the NBBP theory. At the same time, other theories have been proposed, including the occlusive hyperemia theory. We believe that both theories are related and complementary and that they both explain changes in hemodynamics after AVM resection. The purpose of this work is to review the current status of the NBBP theory 35 years after its original description.

Delayed ischemic stroke following spontaneous thrombosis of an arteriovenous malformation

Spontaneous obliteration of an arteriovenous malformation (SOAVM) is a rare event that is not completely understood. Less than 100 cases of SOAVMs have been reported in the literature. We present a unique case of a middle-aged patient with spontaneous obliteration of a cerebral arteriovenous malformation (AVM) who developed an ischemic stroke due to thrombosis of the stagnant proximal segment of the inferior branch of the middle cerebral artery feeder. Although the pathophysiology is not well understood, the arterial feeder hemodynamic changes post SOAVM may behave similarly to what occurs in rare cases after surgical resection of AVMs. Our case raises the hypothesis that stagnation of flow in spontaneous AVM obliteration may lead to delayed ischemic stroke in the territory of the feeding artery.

Delayed ischemic stroke following spontaneous thrombosis of an arteriovenous malformation

Spontaneous obliteration of an arteriovenous malformation (SOAVM) is a rare event that is not completely understood. Less than 100 cases of SOAVMs have been reported in the literature. We present a unique case of a middle-aged patient with spontaneous obliteration of a cerebral arteriovenous malformation (AVM) who developed an ischemic stroke due to thrombosis of the stagnant proximal segment of the inferior branch of the middle cerebral artery feeder. Although the pathophysiology is not well understood, the arterial feeder hemodynamic changes post SOAVM may behave similarly to what occurs in rare cases after surgical resection of AVMs. Our case raises the hypothesis that stagnation of flow in spontaneous AVM obliteration may lead to delayed ischemic stroke in the territory of the feeding artery.

Delayed Intracerebral Hemorrhage After Uneventful Embolization of Brain Arteriovenous Malformations Is Related to Volume of Embolic Agent Administered: Multivariate Analysis of 13 Predictive Factors

BACKGROUND:

The mechanisms and management of delayed intracerebral hemorrhage (dICH) after treatment of brain arteriovenous malformations (AVMs) are poorly understood and widely debated. Many clinical predictive factors have been theorized for dICH after an otherwise uneventful AVM embolization, but there is an absence of data to discern their significance.

OBJECTIVE:

To analyze 13 proposed predictive factors and to assess their potential in guiding prevention strategies.

METHODS:

One hundred sixty-eight embolization procedures were performed on 67 patients with brain AVMs by a single surgeon. Patients were divided into 2 groups: those with symptomatic dICH and control subjects. Thirteen factors were analyzed: age, sex, race, previous ICH, Spetzler-Martin grade, AVM size, eloquence, embolic volume, embolic agent, percent obliteration, and timing, number, and stage of embolizations. Univariate and multivariate analyses were performed on these factors to determine significance.

RESULTS:

Six procedures were complicated by dICH; 5 (83%) occurred after the final planned procedure. The volume of embolic agent was significantly higher in the dICH group (4.5 ± 1.0 mL) compared with control subjects (1.7 ± 0.2 mL) in both univariate and multivariate analyses (P < .01), even after controlling for AVM size. AVM size was significant in univariate analysis but not multivariate analysis. There were no statistically significant differences between the groups for any of the other possible predictive factors.

CONCLUSION:

High volume of embolic agent administered per procedure is an independent predictive factor for dICH. Limiting the injected volume for each procedure may reduce this poorly understood complication.

The regional oxygen saturation of pituitary adenomas is lower than that of the pituitary gland: microspectrophotometric study with potential clinical implications

OBJECTIVE

To study the regional oxygen saturation (rSO(2)) of pituitary adenomas, in comparison with that of the pituitary gland.

METHODS

Microspectrophotometric (MSP) measurements of rSO(2) in adenomas and pituitary tissue were performed for a series of patients undergoing first-time transsphenoidal pituitary adenoma surgery, in a standardized anesthesia setting. The areas of measured tissue were sampled for histopathological and immunohistochemical (CD34 and CD45) assessments. The results of MSP measurements were compared with the results of the histopathological and immunohistochemical assessments.

RESULTS

Thirty-six MSP measurements and tissue samples were obtained among 22 patients with pituitary macroadenomas, including 14 from adenoma tissue, 17 from the anterior pituitary lobe, and 5 from the posterior pituitary lobe. The rSO(2) of adenoma tissue (mean +/- standard deviation, 43.3 +/- 23.2%) was statistically significantly (P = 0.001) lower than the values for the anterior pituitary lobe (mean +/- standard deviation, 71.8 +/- 18.3%) and posterior pituitary lobe (mean +/- standard deviation, 74.9 +/- 4.8%). The difference between the rSO(2) values for the anterior pituitary lobe and posterior pituitary lobe was not significant. There were no statistically significant differences in microvessel density (as assessed with CD34 staining) or lymphocyte density (as assessed with CD45 staining) among the three tissue types.

CONCLUSION

As assessed with MSP measurements, the rSO(2) of adenoma tissue was significantly lower than that of the pituitary gland, indicating differences in their blood supply and/or metabolism in pituitary macroadenomas. Further studies are needed to determine whether MSP measurements can reliably facilitate intraoperative delineation of adenoma and pituitary tissue, in the effort to achieve complete tumor removal with minimal injury to pituitary tissue.

Intraoperative measurement of cortical oxygen saturation and blood volume adjacent to cerebral arteriovenous malformations using near-infrared spectroscopy

OBJECTIVE

Both cortical oxygen saturation (SaO(2)) and cortical blood volume (BV) are related to regional cerebral blood flow. Among a series of patients with cerebral arteriovenous malformations, we examined the problem of hyperemia after embolization/resection or resection with the intraoperative application of near-infrared spectroscopy.

METHODS

Cortical SaO(2) and BV (intracapillary total hemoglobin concentrations) were measured, with near-infrared spectroscopy, in areas adjacent to the arteriovenous malformation for 20 patients, before and after resection. The absolute values for both parameters and postexcision/preexcision ratios (P-P ratios) were determined. Data were correlated with multiple clinical and preoperative angiographic parameters.

RESULTS

Before resection, the mean SaO(2) was 49 +/- 16% and the mean BV was 12.65 +/- 7.41 mg/ml. After resection, SaO(2) increased for 17 of 20 patients and BV increased for 18 of 20 patients. The differences between pre- and postexcision values for both parameters were observed to be statistically significant (P < 0.01). The average P-P ratios were 1.5 +/- 0.4 for SaO(2) and 1.7 +/- 0.4 for BV. Correlation between the P-P ratios for the two parameters was good. The initial BV and the P-P ratios for both SaO(2) and BV were exclusively dependent on the extent of preoperative embolization. Postoperatively, two patients developed intracerebral hemorrhage or severe edema. Both demonstrated high P-P ratios for SaO(2) (2.3 and 2.1) and BV (1.6 and 2.1).

CONCLUSION

Intraoperative near-infrared spectroscopy is able to detect the hyperemic status of adjacent cortex after arteriovenous malformation resection. However, staged therapy with embolization and surgery results in less hyperemia after resection. While two patients with hyperemic complications exhibited very large increases in SaO(2) and BV, we cannot refute the normal-perfusion pressure breakthrough theory.

Vision of the future: initial experience with intraoperative real-time high-resolution dynamic infrared imaging. Technical note

High-resolution dynamic infrared (DIR) imaging provides intraoperative real-time physiological, anatomical, and pathological information; however, DIR imaging has rarely been used in neurosurgical patients. The authors report on their initial experience with intraoperative DIR imaging in 30 such patients. A novel, long-wave (8-10 microm), narrow-band, focal-plane-array infrared photodetector was incorporated into a camera system with a temperature resolution of 0.006 degrees C, providing 65,000 pixels/frame at a data acquisition rate of 200 frames/second. Intraoperative imaging of patients was performed before and after surgery. Infrared data were subsequently analyzed by examining absolute differences in cortical temperatures, changes in temperature over time, and infrared intensities at varying physiological frequencies. Dynamic infrared imaging was applied in a variety of neurosurgical cases. After resection of an arteriovenous malformation, there was postoperative hyperperfusion of the surrounding brain parenchyma, which was consistent with a loss of autoregulation. Bypass patency and increased perfusion of adjacent brain were documented during two of three extracranial-intracranial bypasses. In seven of nine patients with epilepsy the results of DIR imaging corresponded to seizure foci that had been electrocorticographically mapped preoperatively. Dynamic infrared imaging demonstrated the functional cortex in four of nine patients undergoing awake resection and cortical stimulation. Finally, DIR imaging exhibited the distinct thermal footprints of 14 of 16 brain tumors. Dynamic infrared imaging may prove to be a powerful adjunctive intraoperative diagnostic tool in the neurosurgical imaging armamentarium. Real-time assessment of cerebral vessel patency and cerebral perfusion are the most direct applications of this technology. Uses of this imaging modality in the localization of epileptic foci, identification of functional cortex during awake craniotomy, and determination of tumor border and intraoperative brain shift are avenues of inquiry that require further investigation.

Role of venous drainage in cerebral arteriovenous malformation surgery, as related to the development of postoperative hyperperfusion injury

OBJECTIVE

To elucidate the role of venous drainage in cerebral arteriovenous malformation (AVM) surgery, with respect to the development of postoperative hyperperfusion injury.

METHODS

For 52 patients with supratentorial AVMs, cortical capillary oxygenation (SaO(2)) was assessed intraoperatively, before and after resection, in the vicinity of the AVMs, by using a microspectrophotometric method. Assessed areas were defined as being related to feeding arteries or draining veins or as distant areas. Patients were divided into three groups on the basis of postoperative angiographic findings, as follows: Group 1, all former draining veins preserved (8 patients); Group 2, > or =1 former draining vein visible (12 patients); Group 3, no former draining veins visible (32 patients). Patients and SaO(2) values were pooled and compared by using paired and unpaired t tests (P < 0.05). Venous circulation times were calculated from digital subtraction angiography films.

RESULTS

The postresectional relative increases in SaO(2) values were highest in draining vein areas (+40.8%, compared with +25% in feeder areas and +25.5% in distant areas). Five postoperative hyperemic complications occurred (9.6%), none in Group 1 (with all draining veins preserved), two (16.7%) in Group 2, and three (9.4%) in Group 3 (with all draining veins occluded). The lowest preresectional SaO(2) values (31.7 +/- 6.2%) were measured in the drainer areas of the five patients who subsequently developed hyperperfusion injuries. Among those patients, postresectional increases in SaO(2) values were significantly greater in drainer areas (+167.8%) than in feeder areas (+28.3%) or distant areas (+25.8%). Postoperative venous circulation times in former draining veins in Group 2 were significantly greater than those in Group 1 (8.9 +/- 1.5 s versus 6.3 +/- 0.6 s). Circulation times in normal veins in the five patients with hyperperfusion injury increased from 5.6 +/- 1.0 seconds (preoperatively) to 8.4 +/- 1.9 seconds (postoperatively).

CONCLUSION

Postoperative hyperperfusion injury after resection of cerebral AVMs can be explained on the basis of unconstrained arterial inflow into cortical areas, which are rendered hypoxic/ischemic by longstanding preoperative venous hypertension. The risk for postoperative breakthrough complications seems higher in the presence of multiple draining veins, which also participate in the physiological venous drainage system of the ipsilateral hemisphere.