Donald E. Richardson

Autopsy analysis of the safety, efficacy and cartography of electrical stimulation of the central gray in humans

Electrical brain stimulation is effective in controlling certain intractable chronic pain syndromes in humans, but the specific target site(s) for stimulation producing a maximal analgesic effect is (are) not well defined. This prospective study correlates the clinical results of chronic stimulation of the periaqueductal gray (PAG) and periventricular gray (PVG) matter in humans with the anatomic site of electrode placement as determined at autopsy, and documents the histologic reactions to electrode implantation and electrical stimulation of the area. Seven patients underwent electrode implantation to control their chronic pain; two had electrodes implanted bilaterally. All patients obtained complete analgesia with stimulation, although 3 subsequently found the stimulation to have diminished efficacy. The opiate antagonist naloxone reversed the analgesia in the 4 patients so tested. All 7 patients later died of causes unrelated to electrode implantation or stimulation. Postmortem analysis showed that, for 6 of the 9 electrodes implanted, the electrode tip was located in the ventrolateral PAG at the level of the posterior commissure; the other 3 electrodes were found in the white matter adjacent to the PAG. No evidence of gliosis or parenchymal reaction was observed along the tracts and tips of the electrodes. The results indicate that the ventrolateral PAG and PVG matter at the level of the posterior commissure is the optimal site for therapeutic electrical brain stimulation for opiate-responsive pain in humans.

Frontal sinus osteoma associated with cerebral abscess formation: a case report.

BACKGROUND Osteomas of the paranasal sinuses rarely lead to intracranial manifestations. We present an unusual case of a frontal sinus osteoma leading to intracerebral abscess formation. CASE DESCRIPTION A 51-year-old Hispanic man presented with increasing frontal headaches, new onset seizure, lethargy, global dysphasia, and unilateral hemiparesis. CSF studies demonstrated mild pleocytosis. Neuroradiological studies revealed an opacity filling the left frontal sinus, as well as a ring-enhancing mass with surrounding edema in the left frontal lobe. The patient was surgically treated with a left frontal osteoplastic craniotomy and removal of the abscess and bony mass. Intraoperative cultures were positive for Streptococcus pneumoniae. Pathology revealed bony tumor consistent with osteoma. The patients neurological status improved to baseline after surgery. CONCLUSION The frontal sinus osteoma was associated with rapid development of a frontal lobe abscess, requiring emergent surgical debridement. Although rare, intracerebral manifestations should be considered and expected as a cause of new neurological deficits in the presence of paranasal sinus osteoma.

Sacral fracture: case presentation and review

Sacral fractures are either transverse or longitudinal (vertical). Transverse fractures may be isolated and can be subdivided into two types. Upper transverse fractures occur in younger people and result from severe traumatic flexion of the upper body on the fixed pelvis. Lower transverse fractures result from a hard blow to the coccyx, as in a fall. Vertical fractures are essentially never isolated, always being associated with an anterior break in the pelvic ring. These result from extreme forces transmitted through the ilium. Any of these fractures can cause injury to neural elements, and surgical decompression may be indicated in certain of the transverse types.

Zenker diverticulum: a rare complication after anterior cervical fusion.

Esophageal injury is a rare but serious complication occurring after anterior cervical spine surgery. Pharyngoesophageal, or Zenker, diverticulum is an acquired outpouching of the pharyngeal musculature just proximal to a functional esophageal stricture, clinically manifesting as dysphagia, aspiration, and weight loss. We report a case in which a patient developed a pharyngoesophageal diverticulum, accompanied by retropharyngeal abscess, first identified 2 years after a 3-level anterior cervical fusion with allograft and anterior plating. The inferior portion of the cervical plate was dislodged anteriorly. In addition, the patient harbored pulmonary and mediastinal infection at the time of presentation. Despite incision and drainage of the abscess with repair of the diverticulum, the patient died in the early postoperative period. Prompt recognition and frequent follow-up, as well as patient education, may prevent this catastrophic complication.

Cranioplasty using gentamicin-loaded acrylic cement: A test of neurotoxicity

Cranioplasty represents a formidable challenge for neuro-surgeons, with a significant morbidity from both early and late wound infections. Polymethylmethacrylate (PMMA) is one of the most widely used materials in this setting. Despite the advantages of this material, such as ease of handling and inert biochemical properties, it is still a foreign body that is prone to infection. We present an animal model using a gentamicin-impregnated PMMA patch to assess the neurotoxicity as well as the efficacy of using this as an alternative material to lessen the infectious morbidity in this clinical setting. In part two of our experiment, we used a PMMA patch of similar weight and surface area in a physiological saline solution to determine the rate of gentamicin elution from the patch. The results obtained appear promising with no evidence of neurotoxicity and warrant further study to assess the clinical efficacy of PMMA in this setting.

A sympathoinhibitory area in cat rostral medulla: its role in cardiovascular tone regulation and baroreflex.

We have found a medullary vasodepressor area in cat centered 3 mm rostral to the obex and just lateral to the compact division of the ambiguus nucleus. The area is compact, extending at most 1 mm in any direction. Microinjection of L-glutamate into this rostral depressor area (RDA) elicited acute hypotension and bradycardia. These responses were not reduced by either peripheral atropine blockade or bilateral vagotomy, but they were nearly abolished by peripheral phentolamine/propranolol blockade or high cervical cord transection. Bilateral reversible blockade of the RDA by local microinjection of the neuronal hyperpolarizing agent muscimol yielded chronic hypertension and tachycardia. Sympathetically mediated baroreflex, observed as a bradycardic response to a peripherally administered phenylephrine bolus in atropinized animals, was partially (50%) abolished during this same blockade. We conclude that the RDA contains sympathoinhibitory cells which are involved in the regulation of cardiovascular tone and in the expression of the sympathetic component of baroreflex.

Sacral FractureCase Presentation and Review

Sacral fractures are either transverse or longitudinal (vertical). Transverse fractures may be isolated and can be subdivided into two types. Upper transverse fractures occur in younger people and result from severe traumatic flexion of the upper body on the fixed pelvis. Lower transverse fractures result from a hard blow to the coccyx, as in a fall. Vertical fractures are essentially never isolated, always being associated with an anterior break in the pelvic ring. These result from extreme forces transmitted through the ilium. Any of these fractures can cause injury to neural elements, and surgical decompression may be indicated in certain of the transverse types.

Cardiovascular sympathoinhibitory neurons form an extended longitudinal column in cat lateral medulla

A search for vasomotor depressor sites in the lateral medullary brainstem of anesthetized cat using microinjections of AMPA has delineated a longitudinal column of sympathoinhibitory neurons consisting of the rostral depressor area, the caudal ventrolateral medulla, and a new intermediate depressor area. Systematic blockade of these three subregions with bilateral microinjections of kynurenic acid indicates a uniform involvement of the entire column with sympathetic baroreflex, but a slightly greater involvement of the anterior portion, over the posterior, with regulation of cardiovascular tone.

Sympathetically-mediated cardiovascular responses induced by neurochemical microinjection in the brainstem lateral tegmental field of cat

This study examines sympathetically-mediated cardiovascular responses arising from microinjections of AMPA and kynurenic acid in the medullary lateral tegmental field (LTF). The resulting behavior, which is predominantly inhibitory, is nearly identical to that reported for the para-ambiguual area lying just lateral to the LTF, and suggests that the two regions may share other cardiovascular control functions.

Lateral tegmental field neurons with activity correlated to the 10-Hz rhythm in sympathetic nerve discharge.

Neurons in the lateral tegmental field (FTL) has been previously reported to have activity only minimally correlated (< 1% of neurons tested) with the 10-Hz rhythm of the slow wave of the sympathetic nerve discharge. We report here that 10% of the neurons recently tested in the FTL could be shown to correlate with the 10-Hz rhythm. The neuron-to-nerve coherence is weaker than in other medullary areas, but is nonetheless significant.