Biomedical subjects

Alexander H Hoon

Publications and source records attributed to Alexander H Hoon.

6 recordsLinked to original sources

PubMed2006

Cerebral palsy.

Cerebral palsy (CP) is a group of disorders of movement and posture resulting from nonprogressive disturbances of the fetal or neonatal brain. More than 80% of cases of CP in term infants originate in the prenatal period; in premature infants, both prenatal or postnatal causes contribute. The most prevalent pathological lesion seen in CP is periventricular white matter injury (PWMI) resulting from vulnerability of the immature oligodendrocytes (pre-OLs) before 32 wk of gestation. PWMI is responsible for the spastic diplegia form of CP and a spectrum of cognitive and behavioral disorders. Oxidative stress and excitotoxicity resulting from excessive stimulation of ionotropic glutamate receptors on preOLs are the most prominent molecular mechanisms for PWMI. Asphyxia around the time of birth in term infants accounts for less than 15% of CP in developed countries but the incidence is higher in underdeveloped areas. Asphyxia causes a different pattern of brain injury and CP than is seen after preterm injuries. This type of CP is associated with the clinical syndrome of hypoxic-ischemic encephalopathy shortly after the insult, and the cortex, basal ganglia, and brainstem are selectively vulnerable to injury. Experimental models indicate that neurons in the neonatal brain are more likely to die by delayed apoptosis extending over days to weeks than those in the adult brain. Neurons die by glutamate-mediated excitotoxicity involving downstream caspase-dependent and caspase-independent cell death pathways. Recent reports indicate that males and females preferentially utilize different pathways. Clinical trials indicate that mild hypothermia reduces death or disability in term infants following asphyxia and basic research suggests that this approach might be combined with pharmacological strategies in the future.

Asphyxia Neonatorum↗

PubMed2005

Neuroimaging in cerebral palsy: Patterns of brain dysgenesis and injury.

Despite advances in obstetric and neonatal care, the overall prevalence of cerebral palsy has remained stable, supporting the belief that pathogenesis is primarily due to prenatal brain dysgenesis and injury. Neuroimaging studies have consistently shown abnormalities in 70% to 90% of affected children, facilitating clinical classification into groups with early brain malformations, white-matter injury, neonatal encephalopathies, and a heterogeneous group of postnatally acquired disorders. White-matter injury, well seen on conventional magnetic resonance imaging (MRI), is the leading cause of cerebral palsy in children born preterm. As many as 20% of very low birthweight infants have cystic and/or diffuse white-matter injury, termed periventricular leukomalacia, with evidence of associated pathology in other cortical and subcortical structures. In the group with acute, term perinatal pathology, a variety of imaging modalities, in addition to MRI, have diagnostic utility. In general, when added to conventional MRI, advanced techniques, such as diffusion tensor imaging, diffusion-weighted imaging, and magnetic resonance spectroscopy, provide a more complete picture of structural and functional brain abnormalities. The results have led to improved understanding of pathogenesis, especially in regard to periventricular leukomalacia and hypoxic-ischemic encephalopathy. This information might lead to interventions preventing brain injury in preterm infants and asphyxiated term newborns.

Brain↗

PubMed2004

Neuroimaging in cerebral palsy.

Parents and clinicians concerned about high-risk infants and children with motor delay or cerebral palsy seek information on cause, treatment, prognosis, and recurrence risk. Used in combination with history and examination, neuroimaging studies can improve diagnosis and management. In premature infants, cranial ultrasound is a reliable, noninvasive diagnostic modality. Nuclear magnetic resonance techniques including magnetic resonance imaging and diffusion weighted imaging can be used effectively in neonatal encephalopathies. In children with motor delay and cerebral palsy syndromes including spastic diplegia, quadriplegia, hemiplegia, and extrapyramidal movement disorders, conventional magnetic resonance imaging has become an important determinant of diagnosis and management. The aim of this article is to help clinicians select and interpret imaging studies of benefit in clinical care.

Age Factors↗

PubMed2003

Oral baclofen in cerebral palsy: possible seizure potentiation?

Baclofen, a gamma-aminobutyric acid agonist, is widely used to treat spasticity of cerebral and spinal origin. Patients with both acute baclofen overdose and withdrawal have developed seizures. After several reports of new-onset seizures in children treated with oral baclofen at our institution, we reviewed our experience regarding possible effects of baclofen on seizure induction in a childhood movement disorders program over a 2-year period. Of 54 children (ages 1-10) treated with oral baclofen, 19 (35%) had a prior history of seizures. Five children (14%) developed new-onset seizures after starting baclofen. Although epilepsy is very common in children with cerebral palsy, these findings raise the possibility that baclofen may potentiate seizures in certain young children with cerebral palsy. Further study of the effects of baclofen on seizures is warranted.

Administration, Oral↗

PubMed2003

Neuroimaging in spasticity and movement disorders.

Advances in neuroimaging provide unique opportunities to evaluate brain structure, biochemistry, and function. Although a number of imaging techniques have been used in newborns, cranial ultrasonography in premature infants and nuclear magnetic resonance modalities, including magnetic resonance imaging and diffusion-weighted imaging, in high-risk term infants are of foremost benefit. Interpretation is based on knowledge of characteristic imaging findings in specific childhood neurologic disorders and an understanding of differential diagnosis in cerebral palsy syndromes, such as spastic diplegia and various subtypes of extrapyramidal cerebral palsy. This review focuses on imaging studies that can be effectively used in at-risk infants and in children with spasticity and movement disorders to refine diagnosis and guide therapeutic interventions.

Brain↗

PubMed2002

Unusual migration of the distal catheter of a ventriculoperitoneal shunt into the heart: case report.

OBJECTIVE AND IMPORTANCE: Placement of a ventriculoperitoneal (VP) shunt is the most common form of treatment for hydrocephalus. Thoracic complications with VP shunts are rare, but we present the second documented case of the distal migration of the distal catheter of a VP shunt into the heart. CLINICAL PRESENTATION: A 14-year-old boy, who underwent placement of a right occipital VP shunt at another institution after closed-head injury, presented with hypertension. Plain chest x-rays and computed tomography revealed the distal catheter to be in the right ventricle of the heart. INTERVENTION: A joint surgical procedure was performed with the cardiac surgery team. The cardiac surgeons created a pericardial window through a subxyphoid incision. Simultaneously, a right occipital incision was made to access the distal catheter, which was then slowly pulled out with the pericardium under direct visualization. No hemorrhage or change in the pericardium was observed, and, therefore, the need for a thoracotomy was eliminated. A new distal catheter was placed into the peritoneal cavity. CONCLUSION: The migration of the distal catheter probably occurred during the initial VP shunt placement. The internal jugular vein probably was perforated by the tunneler during the creation of the distal catheter tract. Slow venous flow and negative inspiratory pressure may have gradually pulled the catheter up into the right atria and ventricle. As demonstrated by our case report, the catheter can be extracted safely in a joint procedure with cardiac surgeons, and a thoracotomy is not always necessary. The patient did not experience postoperative complications, and his hypertension was alleviated.

Adolescent↗