Eric C. Peterson

Regulation of Cerebral Blood Flow

The control of cerebral blood flow is complex, and only beginning to be elucidated. Studies have identified three key regulatory paradigms. The first is cerebral pressure autoregulation, which maintains a constant flow in the face of changing cerebral perfusion pressure. Flow-metabolism coupling refers to the brains ability to vary blood flow to match metabolic activity. An extensive arborization of perivascular nerves also serves to modulate cerebral blood flow, so-called neurogenic regulation. Central to these three paradigms are two cell types: endothelium and astrocytes. The endothelium produces several vasoactive factors that are germane to the regulation of cerebral blood flow: nitric oxide, endothelium-dependent hyperpolarization factor, the eicosanoids, and the endothelins. Astrocytic foot processes directly abut the blood vessels, and play a key role in regulation of cerebral blood flow. Lastly, new research has been investigating cell-cell communication at the microvascular level. Several lines of evidence point to the ability of the larger proximal vessels to coordinate vasomotor responses downstream.

Impacts of frequent, acute pulses of corticosterone on condition and behavior of Gambel's white-crowned sparrow (Zonotrichia leucophrys gambelii)

Little is known about how frequent, acute stressors affect wild animals. We present two experiments conducted on captive, Gambels white-crowned sparrow (Zonotrichia leucophrys gambelii) that explore how frequent, acute doses of corticosterone (CORT) affect condition and behavior. CORT was administered either once or three times a day to birds in pre-breeding, early-breeding, or late-breeding life-history stages. Two additional groups were included to control for the CORT delivery vehicle, DMSO, and the treatment process. Our results indicate that CORT treatment decreases condition, but that its effects are dependent on frequency and life stage. Specifically, CORT-treated birds delayed the onset of molt and had reduced body mass, flight muscle, and food consumption. CORT treatment did not affect fat stores, bile retention in the gallbladder, or the expression of migratory restlessness behavior. These results increase our understanding of the effects of frequent, acute stressors and the development of chronic stress states.

Talk and Die Revisited: Bifrontal Contusions and Late Deterioration

BACKGROUNDnSevere bifrontal contusions in an awake traumatic brain injury (TBI) patient is a challenging clinical picture, as they are prone to late deterioration. We evaluated our series of patients with severe bifrontal contusions, characterizing their clinical course and suggestions for management.nnnMETHODSnWe examined a prospectively collected database of TBIs for patients with severe bifrontal contusions, defined as >30 cm. Only patients with Glasgow Coma Scale score of 10 or greater were included. Patients were divided into two groups: deterioration and nondeterioration. Clinical variables were compared between the two groups.nnnRESULTSnThirteen patients met the above criteria. The mean Glasgow Coma Scale score was 13, and all were low mechanism injuries. All patients were managed with intensive care unit observation and hyperosmolar therapy to maintain serum osmolarity >300. Overall, 7 of 13 (54%) suffered an acute clinical deterioration a mean of 4.5 days postinjury. Of those managed with immediate surgical decompression, all had good outcomes and returned to work. There was no difference in contusion or edema volumes between the two groups.nnnCONCLUSIONSnAwake patients with bifrontal contusions represent a unique cohort of TBI patients who are prone to rapid deterioration late in their clinical course. They have extensive frontal edema and mass effect, yet we were unable to find a correlation between edema volumes and incidence of deterioration. Based on this series and our experience in other TBI patients, we no longer utilize prophylactic infusions of hypertonic saline in the setting of TBI. We recommend managing these patients with intensive care unit admission and early intracranial pressure monitoring. If they do deteriorate despite these measures, rapid bifrontal decompression can lead to good functional outcomes.

Radiation-induced complications in endovascular neurosurgery: Incidence of skin effects and the feasibility of estimating risk of future tumor formation

BACKGROUNDnThe incidence of radiation-induced complications is increasingly part of the informed consent process for patients undergoing neuroendovascular procedures. Data guiding these discussions in the era of modern radiation-minimizing equipment is lacking.nnnOBJECTIVEnTo quantify the rates of skin and hair effects at a modern high-volume neurovascular center, and to assess the feasibility of accurately quantifying the risk of future central nervous system (CNS) tumor formation.nnnMETHODSnWe reviewed a prospectively collected database of endovascular procedures performed at our institution in 2008. The entrance skin dose and brain dose were calculated. Patients receiving skin doses >2 Gy were contacted to inquire about skin and hair changes. We reviewed several recent publications from leading radiation physics bodies to evaluate the feasibility of accurately predicting future cancer risk from neurointerventional procedures.nnnRESULTSnSeven hundred two procedures were included in the study. Of the patients receiving >2 Gy, 39.6% reported subacute skin or hair changes following their procedure, of which 30% were permanent. Increasing skin dose was significantly associated with permanent hair loss. We found substantial methodological difficulties in attempting to model the risk of future CNS tumor formation given the gaps in our current understanding of the brains susceptibility to low-dose ionizing radiation.nnnCONCLUSIONnRadiation exposures exceeding 2 Gy are common in interventional neuroradiology despite modern radiation-minimizing technology. The incidence of side effects approaches 40%, although the majority is self-limiting. Gaps in current models of brain tumor formation after exposure to radiation preclude accurately quantifying the risk of future CNS tumor formation.

Static autoregulation is intact in majority of patients with severe traumatic brain injury.

BACKGROUNDnThe management of severe traumatic brain injury (sTBI) patients with and without intact cerebral pressure autoregulation (CPA) varies markedly. Recent studies, analyzing beat-to-beat interactions between intracranial pressure (ICP) and systolic blood pressure, or transcranial Doppler velocity changes during a rapid drop in cerebral perfusion pressure (CPP), suggest that CPA is disrupted after sTBI. We use computed tomography perfusion (CTP) to guide blood pressure manipulation in sTBI and have found CPA results that differ with this literature. We present these results here and suggest modifying our basic concepts of CPA disruption.nnnMETHODSnWe tested CPA in 24 consecutive sTBI patients using CTP. ICP was monitored intraparenchymally and blood pressure with an arterial line. After a CTP study at baseline, a phenylephrine infusion was used to raise the CPP by 20 mm Hg, and a second CTP was performed immediately thereafter. Quantitative analysis of cerebral blood flow (CBF) was done offline. CPA was considered intact if CBF was unchanged despite the increase in CPP and disrupted if CBF rose after CPP manipulation.nnnRESULTSnCPA was intact in 25 of 33 patients (75.7%) and disrupted in 8 of 33 patients (24.3%). The mean age was significantly different for the 2 groups; 52 years for the disrupted group, 29 years for the intact group (p < 0.0003). The mean ICP change was also statistically different; 3.8 for the disrupted group and 1.5 for the intact group (p < 0.006). Injury Severity Score (ISS), Glasgow Coma Scale, and CPP were not statistically different between the two groups.nnnCONCLUSIONnBy using direct measurement of CBF in response to a CPP challenge, we found CPA disruption to be much less common than reported in similar groups of sTBI patients. This difference reflects potentially important separate aspects of CPA. We suggest that CPA measurement using beat-to-beat interactions and transcranial Doppler measurements reflect dynamic CPA processes (dynamic autoregulation), whereas our method reflects steady-state conditions (static autoregulation). If the major disruption of CPA after sTBI involves dynamic vascular responsiveness, perhaps we need more focus on this aspect and less on static-CPP manipulation in terms of pathophysiology and treatment.

Superior semicircular canal dehiscence syndrome: Successful treatment with repair of the middle fossa floor: Technical case report

OBJECTIVE Superior semicircular canal dehiscence syndrome has recently been reported as a cause of pressure- or sound-induced oscillopsia (Tullio phenomenon). We report the presentation and successful treatment of 3 patients with superior semicircular dehiscence syndrome by a joint neurosurgical/neuro-otology team. CLINICAL PRESENTATION Patient 1 is a 37-year-old man who presented with complaints of disequilibrium, fullness in the left ear, hearing loss, and oscillopsia when pressure was applied to the left external auditory canal. Patient 2 is a 46-year-old man who presented with complaints of disequilibrium, fullness in the left ear, and blurred vision associated with heavy lifting or straining. On examination, pneumatic otoscopy produced a sense of motion. Patient 3 is a 29-year-old woman who presented with chronic disequilibrium that resulted in frequent falls. She had a positive fistula test on the left, and vertical nystagmus was elicited when pressure was applied to the left ear. In each patient, high-resolution computed tomographic scanning through the temporal bone revealed dehiscence of the superior semicircular canal on the symptomatic side. INTERVENTION In all 3 cases, a subtemporal, extradural approach was performed with repair of the middle fossa floor using calcium phosphate BoneSource (Howmedica Leibinger, Inc., Dallas, TX). All patients recovered well, with resolution of their symptoms. CONCLUSION Superior semicircular canal dehiscence syndrome is a cause of disequilibrium associated with sound or pressure stimuli. The workup includes a detailed history, electronystagmography including Valsalva maneuvers, and a high-resolution computed tomographic scan though the temporal bone. An extradural repair of the middle fossa floor with BoneSource can successfully treat this condition.

Atlantal fracture with transverse ligament disruption in a child: Case report

Even though fractures in children with immature spines occur predominantly in the upper cervical spine, isolated C-1 fractures are relatively rare. The fractures in almost all cases reported to date were considered stable due to the presence of the intact transverse ligament. The authors report the case of a young child who sustained a Jefferson fracture and in whom MR imaging revealed disruption of the transverse ligament. Although surgical treatment has been suggested as the treatment of choice for children with unstable atlantoaxial injuries, external immobilization alone allowed a full recovery in the patient with no evidence of instability at follow-up.

Epidural metastases from endodermal sinus tumor arising from benign sacral teratoma: Case report and review of the literature

The recurrence of benign sacral teratomas is a small but significant possibility. Recurrence as an endodermal sinus tumor (EST) with epidural metastases, however, has not been previously reported. The authors describe a case of a mature sacrococcygeal teratoma in a 4-day-old female patient that recurred after 22 months as an EST with epidural metastases. The child presented with abdominal pain, urinary retention, and difficulty walking. On imaging, a large pelvic mass and an epidural spinal mass were revealed. The patients alpha-fetal protein (AFP) level was 68,000 ng/ml. Her neurological examination was significant for 3/5 plantar and dorsiflexion strength bilaterally. The patient underwent L-3, L-4, and L-5 bilateral laminectomies followed by subtotal resection of the recurrent pelvic tumor. Pathological testing of samples of both the recurrent pelvic and the extradural spinal tumors led to a diagnosis of EST. The patient underwent four cycles of chemotherapy with normalization of her AFP level to 13 ng/ml. In the weeks that followed, her AFP level steadily rose again to 167 ng/ml. Follow-up imaging revealed no tumor recurrence. The patient underwent a second course of chemotherapy followed by two tandem courses of high-dose chemotherapy with autologous stem-cell rescue. Since completing this therapy the patient has been clinically stable with an AFP level of 1.3 ng/ml for 14 months. At the 1-year follow-up examination, her plantar and dorsiflexion strength had markedly improved to 4+/5 bilaterally. To the authors knowledge, this is the first case of a mature sacrococcygeal tumor that recurred as an EST and caused spinal canal compromise.