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Biomedical subjects

S T Simpson

Publications and source records attributed to S T Simpson.

26 records · Page 2Linked to original sources
PubMedDate not supplied

Ventral surgical approach to the caudal brain stem in dogs.

OBJECTIVE: To develop a safe neurosurgical procedure that accessed the ventral pons and medulla of the dog primarily for the removal of brain stem neoplasms. STUDY DESIGN: In vivo study. METHODS: A cadaver study was performed on mesocephalic dog heads to develop a neurosurgical approach to the ventral brain stem. Based on this study, an approach to the ventral brain stem was developed by basioccipital craniectomy. This procedure was performed on 4 young neurologically normal Beagle dogs to assess morbidity and mortality associated with the procedure. Morbidity was evaluated by subjective criteria, daily complete neurologic examinations, comparison of preoperative and postoperative brain stem auditory evoked response (BAER) tests, and postmortem examinations. RESULTS: Three dogs developed a transient cough but were neurologically normal after surgery. One dog was euthanatized within 12 hours of surgery because of severe postoperative morbidity associated with basilar artery disruption due to improper development of the craniectomy. Prolongations of postoperative BAER latencies were observed in 2 dogs but did not appear to be associated with clinical deficits or histopathologic changes in the brain stem. Minimal histopathologic changes were observed except in the dog with basilar artery disruption. Results of this study indicate that, although technically challenging, this procedure can be performed with minimal morbidity. CLINICAL IMPLICATIONS: The main indication for this procedure is surgical reduction or biopsy of ventrally located brain stem neoplasms in dogs. The major disadvantage is anatomic restrictions that prevent access to laterally oriented ventral brain stem masses.

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PubMedDate not supplied

Surgical management of atlantoaxial subluxation in 23 dogs.

Twenty-eight surgical procedures were performed in 23 dogs with atlantoaxial subluxation. Dorsal stabilization in seven dogs resulted in two recoveries and five failures of fixation. Ventral decompression and stabilization in 18 dogs resulted in eight recoveries and four failures of fixation. Six dogs died or were euthanatized within 7 days of ventral stabilization. Using either technique, four of seven nonambulatory dogs recovered.

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PubMedDate not supplied

Clinicopathologic effects of a 21-aminosteroid compound (U74389G) and high-dose methylprednisolone on spinal cord function after simulated spinal cord trauma.

A model simulating acute-compressive spinal cord trauma at the second lumbar spinal cord segment (100 g, 300 seconds) was used to evaluate the efficacy of a vehicle control, methylprednisolone sodium succinate (MPSS), and a 21-aminosteroid compound (U74389G). Dogs were allocated into one of five treatment groups (A to E) using ultrasonographic determination of spinal cord diameters to ensure even distribution of spinal cord diameters among the treatment groups. Initial dosages of the vehicle control (A), methylprednisolone (30 mg/kg of body weight) (B), or U74389G (30 mg/kg, 3 mg/kg, or 10 mg/kg of body weight) (C, D, or E, respectively) were administered intravenously 30 minutes after trauma. Dosages were reduced by one-half for 2 and 6 hour treatments. Then every 4 hours for 42 hours, dosages were reduced one-third and one-sixth from the original dose of methylprednisolone and U74389G, respectively. Neurological examinations were performed daily for 21 days. Histopathological examination of the traumatized spinal cord showed malacic and degenerative lesions. Although significant differences in some portions of the neurological and histopathologic examinations were observed, clinical efficacy for MPSS and U74389G could not be established in this model.

Acute Disease↗
PubMedDate not supplied

Color flow Doppler imaging and Doppler spectral analysis of the brain of neonatal dogs.

Doppler ultrasonography was performed on the cerebral arteries of 19 neonatal dogs. Vascular structures were identified using anatomic preparations of brains pre-injected with a radiopaque silicone rubber product and cleared using a modified tissue clearing technique. Brain sections were subsequently radiographed or examined under a stereomicroscope. Color flow Doppler imaging was used to facilitate positioning of the Doppler calipers for measurement of peak systolic velocity, minimum diastolic velocity, and resistance index. Blood flow velocities in the internal carotid and middle cerebral arteries were lower when measured in transverse images than in sagittal images. The rostral cerebral arteries could be measured using either plane but values obtained from different locations or using different methods of measurement were statistically different. Blood flow velocities generally increased during the first month after birth. Arterial signals were diphasic with flow throughout diastole. Resistance indices most often were between 0.6 and 0.7 and did not exceed 0.86.

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