The myodural bridge of the American alligator (Alligator mississippiensis) alters CSF flow.

Disorders of the volume, pressure or circulation of the cerebrospinal fluid (CSF) lead to disease states in both newborns and adults; despite this significance, there is uncertainty regarding the basic mechanics of the CSF. The suboccipital muscles connect to the dura surrounding the spinal cord, forming a complex termed the 'myodural bridge'. This study tests the hypothesis that the myodural bridge functions to alter the CSF circulation. The suboccipital muscles of American alligators were surgically exposed and electrically stimulated simultaneously with direct recordings of CSF pressure and flow. Contraction of the suboccipital muscles significantly changed both CSF flow and pressure. By demonstrating another influence on CSF circulation and pulsatility, the present study increases our understanding of the mechanics underlying the movement of the CSF.

Early detection of brainstem herniation using electroencephalography monitoring - case report.

BACKGROUND: Continuous electroencephalography (cEEG) is an important neuromonitoring tool in brain injured patients. It is commonly used for detection of seizure but can also be used to monitor changes in cerebral blood flow. One such event that can cause a change in cerebral blood flow is imminent, cerebral herniation. cEEG monitoring and quantitative electroencephalography (QEEG) can be used as neurotelemetry to detect cerebral herniation prior to onset of clinical signs. CASE PRESENTATION: We discuss two cases highlighting the use of cEEG in cerebral herniation accompanied by clinical examination changes. The first case is a patient with multiorgan failure and intracerebral hemorrhage (ICH). Given his coagulopathy status, his ICH expanded. The second case is a patient with intraventricular hemorrhage and worsening obstructive hydrocephalus. In both cases, the cEEG showed increasing regional/lateralized slowing. The Quantitative electroencephalography (QEEG) showed a decrease in frequencies, worsening asymmetry, decreasing amplitude and increasing burst suppression ratio corresponding with the ongoing herniation. Clinically, these changes on cEEG preceded the bedside neurological changes by up to 1 h. CONCLUSIONS: The use of cEEG to monitor patients at high risk for herniation syndromes may identify changes earlier than bedside clinical exam. This earlier identification may allow for an earlier opportunity to intervene.

Lighting Strikes Twice: Recurrent Guillain-Barré Syndrome (GBS) after Influenza Vaccination.

Guillain-Barré syndrome (GBS) is a rare acute demyelinating syndrome of the peripheral nervous system that is commonly preceded by infection. Vaccinations have also been associated with an increased incidence of GBS, though the risk is low. Caution with revaccination is recommended in patients with a history of GBS. Risks of revaccination compared with the risks of influenza complications should be considered. Patients who experience GBS after vaccination have not been shown to have an increased incidence of recurrent GBS after the influenza vaccine, though evidence is limited. We report a case of recurrent GBS in a patient following the influenza vaccine.

Variations in the cerebrospinal fluid dynamics of the American alligator (Alligator mississippiensis).

BACKGROUND: Studies of mammalian CSF dynamics have been focused on three things: paravascular flow, pressure and pulsatility, and "bulk" flow; and three (respective) potential motive forces have been identified: vasomotor, cardiac, and ventilatory. There are unresolved questions in each area, and few links between the different areas. The American alligator (Alligator mississippiensis) has pronounced plasticity in its ventilatory and cardiovascular systems. This study was designed to test the hypothesis that the greater cardiovascular and ventilatory plasticity of A. mississippiensis would result in more variation within the CSF dynamics of this species. METHODS: Pressure transducers were surgically implanted into the cranial subarachnoid space of 12 sub-adult alligators; CSF pressure and pulsatility were monitored along with EKG and the exhalatory gases. In four of the alligators a second pressure transducer was implanted into the spinal subarachnoid space. In five of the alligators the CSF was labeled with artificial microspheres and Doppler ultrasonography used to quantify aspects of the spinal CSF flow. RESULTS: Both temporal and frequency analyses of the CSF pulsations showed highly variable contributions of both the cardiac and ventilatory cycles. Unlike the mammalian condition, the CSF pressure pulsations in the alligator are often of long (~ 3 s) duration, and similar duration CSF unidirectional flow pulses were recorded along the spinal cord. Reduction of the duration of the CSF pulsations, as during tachycardia, can lead to a "summation" of the pulsations. There appears to be a minimum duration (~ 1 s) of isolated CSF pulsations. Simultaneous recordings of cranial and spinal CSF pressures reveal a 200 ms delay in the propagation of the pressure pulse from the cranium to the vertebral canal. CONCLUSIONS: Most of the CSF flow dynamics recorded from the alligators, are similar to what has been reported from studies of the human CSF. It is hypothesized that the link between ventilatory mechanics and CSF pulsations in the alligator is mediated by displacement of the spinal dura. The results of the study suggest that understanding the CSF dynamics of Alligator may provide unique insights into the evolutionary origins and functional regulation of the human CSF dynamics.

Fulminant Herpes Simplex Virus Type I Encephalitis Despite Maximal Medical Therapy.

Herpes simplex-1 virus encephalitis (HSE) is the most commonly recognized cause of sporadic encephalitis in the United States. Historically HSE has been considered extremely detrimental given the associated relentless neurological deterioration secondary to cerebral edema and status epilepticus. With recent advances in antiviral therapeutics in past decades, the majority of complications can be managed effectively although the associated morbidity and mortality still remains high. The key modifiable factor determining recovery is the rapid initiation of antiviral therapy. We discuss the case of a 19-year-old female with HSE who received standard acyclovir therapy. Despite using recommended dosage and duration of acyclovir, her clinical condition worsened significantly and subsequently required multiple antiviral therapeutics and steroid therapy.

Improvement in Sonographic Vasospasm Following Intravenous Milrinone in a Subarachnoid Hemorrhage Patient with Normal Cardiac Function.

Cerebral vasospasm and delayed cerebral ischemia are well-known complications of an aneurysmal subarachnoid hemorrhage (aSAH), generally occurring days to weeks after hemorrhagic ictus. Management strategies for these complications are controversial and vary in efficacy. There is a growing interest in supporting the use of intravenous (IV) milrinone to manage vasospasm. A 31-year-old male presented to the hospital after being found down outside his home. Computed tomography (CT) of the head and subsequent CT angiogram revealed a Fisher Grade 4 aneurysmal subarachnoid hemorrhage (aSAH). Six hours after admission, he became hypotensive and his neurological examination declined. A repeat CT head showed a new, left frontoparietal intracerebral hemorrhage (ICH) along with increasing SAH. He was stabilized with vasopressors and underwent emergent decompressive hemicraniectomy with subsequent clipping of the aneurysm. Approximately one week later, transcranial Doppler (TCD) showed increasing mean flow velocities in the bilateral anterior and middle cerebral arteries consistent with cerebral vasospasm. He was treated with intravenous milrinone. Repeat TCD 6.5 hours after the initial TCD showed improved mean flow velocities. His cardiac function by echocardiogram assessment was normal. The decrease in TCD velocity following treatment with milrinone indicates an improvement in the cerebral vasospasm regardless of cardiac output in a patient with subarachnoid hemorrhage. This case suggests that augmenting cardiac output may not be the only mechanism for the therapeutic benefit of milrinone.

Somatosensory Evoked Potentials as a Tool to Evaluate Brainstem Herniation in the Neuroscience Intensive Care Unit.

Somatosensory evoked potentials (SSEPs) are a sensitive, minimally invasive technique used to localize dysfunction of myelinated peripheral and central axons in the nervous system. The utility of SSEPs in acutely assessing central nervous system function in brainstem herniation in the neuroscience intensive care unit (NICU) has not been well established. We discuss a case of an 18-year-old, postpartum female who presented with intermittent headache, diplopia, nausea/vomiting and cachexia following delivery two months prior. Shortly after arrival to the emergency department, she developed flaccid quadriparesis and complete ophthalmoplegia. Computed tomography (CT) of the head showed effacement of the basal cisterns along with 2 cm cerebellar tonsillar herniation into the foramen magnum concerning for intracranial hypotension. Raising the head of bed caused hemodynamic instability necessitating prolonged Trendelenburg positioning. The patient was evaluated with serial SSEPs which initially showed a bilateral low amplitude N20 response and normal N13 response. Subsequent SSEP testing showed increased N20 amplitude which correlated with clinical improvement in the patient. SSEP is a minimally invasive and sensitive method used to assess the integrity of the somatosensory nervous system pathway; SSEPs may be a useful monitoring adjunct to assess the evolution of posterior fossa lesions leading to brainstem compression.

Delayed Post-hypoxic Leukoencephalopathy: A Case Series and Review of the Literature.

Delayed post-hypoxic leukoencephalopathy (DPHL) is a unique clinical entity that presents with cognitive impairment days to weeks after an episode of acute hypoxic brain injury. Frequently hypoxia is unrecognized as a mechanism for clinical decline and extensive workup ensues. We present two cases of DPHL highlighting the neuroimaging findings. In both patients, a cerebral hypoxic event was followed by a recovery phase with subsequent delayed clinical decline. Patient 1 suffered hypoxia from drug-induced respiratory depression and lack of post-operative positive airway pressure (PAP) support. Her neurological exam on follow-up revealed progressive cognitive decline. Magnetic resonance imaging (MRI) brain showed bilateral white matter changes involving the centrum semiovale. Patient 2 developed a generalized tonic-clonic seizure during an endobronchial biopsy procedure and was found to have multiple air emboli on computed tomography (CT) head scan. She was initially in a drug-induced coma for her seizures. Electroencephalography (EEG) on day 14 of admission showed changes consistent with diffuse encephalopathy. MRI brain showed bilateral white matter changes particularly at the watershed zones and in the centrum semiovale. DPHL is a rare and under-recognized clinical entity that requires clinical suspicion and detailed evaluation for diagnosis. Neuroimaging studies can provide prognostic information regarding the extent of neurological injury.

Pitfall in Pupillometry: Exaggerated Ciliospinal Reflex in a Patient in Barbiturate Coma Mimicking a Nonreactive Pupil.

Although a neurological examination is fundamental to the evaluation of comatose patients, it is less reliable in a medically induced coma. A commonly misinterpreted finding in patients in a pentobarbital coma is altered pupillary reactivity secondary to an exaggerated ciliospinal reflex. Recognizing an exaggerated ciliospinal reflex in patients in a pentobarbital coma is important and may prevent unnecessary intervention. We present a patient induced in a pentobarbital coma for the treatment of status epilepticus who exhibited a nonreactive pupil secondary to an exaggerated ciliospinal reflex confirmed by pupillometry. We also discuss the anatomy of the ciliospinal reflex and literature regarding its clinical relevance.