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Biomedical subjects

K R Davis

Publications and source records attributed to K R Davis.

At least 19 recordsLinked to original sources
PubMed1992

Skull base dumbbell tumor: surgical experience with two adolescents.

Pediatric skull base tumors are rare and until recently were considered unresectable. We present two patients with tumors of similar anatomic position with an extracranial component in the infratemporal fossa and parapharyngeal space, an isthmus at the foramen ovale, and a superior component in the middle cranial fossa in the region of the cavernous sinus. A 15-year-old girl experienced contiguous spread of a spindle cell sarcoma; an 18-year-old boy developed a chondrosarcoma. A middle fossa approach provided the advantage of surgical avoidance of structures such as the middle ear and mastoid, facial nerve, and mandible. Postoperative recovery was rapid. Our impression is that preoperative carotid artery occlusion and a middle fossa approach for tumor resection can be performed in a young patient with acceptable morbidity and at least short-term benefit. Surgery can, therefore, provide an additional therapeutic approach to complement irradiation and chemotherapy.

Adolescent↗
PubMed1992

Efficacy of gadoteridol for magnetic resonance imaging of the brain and spine.

RATIONALE AND OBJECTIVES: The efficacy of gadoteridol for contrast enhancement of central nervous system pathology was assessed in a multicenter clinical trial involving 411 patients suspected of having intracranial or spinal pathology. METHODS: Magnetic resonance imaging was performed before and after intravenous administration of 0.10 mmol/kg gadoteridol. Two groups of images were interpreted by one of two neuroradiologists blinded to patient history. The results were analyzed separately. RESULTS: Patients with radiologic evidence of disease demonstrated enhancement of intracranial pathologic lesions in 44 of 63 (70%) and in 91 of 111 (82%) cases, respectively, whereas enhancement of spinal lesions was observed in 36 of 58 (62%) and in 65 of 78 (83%) cases, respectively. Subjectively, postcontrast scans provided more information than precontrast images in 37 of 63 (59%) and 84 of 111 (76%) intracranial cases, respectively, and in 25 of 58 (43%) and 55 of 78 (71%) spinal cases, respectively. Additional information included the subjective sense that there was improved visualization of pathology and definition of lesion borders. CONCLUSIONS: Subjective assessment of magnetic resonance scans suggest gadoteridol is an effective intravenous contrast agent for magnetic resonance imaging.

Adolescent↗
PubMed1991

Induction of Arabidopsis defense genes by virulent and avirulent Pseudomonas syringae strains and by a cloned avirulence gene.

We developed a model system to study the signal transduction pathways leading to the activation of Arabidopsis thaliana genes involved in the defense against pathogen attack. Here we describe the identification and characterization of virulent and avirulent Pseudomonas syringae strains that elicit disease or resistance symptoms when infiltrated into Arabidopsis leaves. The virulent and avirulent strains were characterized by determining growth of the pathogen in Arabidopsis leaves and by measuring accumulation of mRNA corresponding to Arabidopsis phenylalanine ammonia-lyase (PAL), beta-1,3-glucanase (BG), and chalcone synthase (CHS) genes in infected leaves. The virulent strain, P. syringae pv maculicola ES4326, multiplied 10(5)-fold in Arabidopsis leaves and strongly elicited BG1, BG2, and BG3 mRNA accumulation but had only a modest effect on PAL mRNA accumulation. In contrast, the avirulent strain, P. syringae pv tomato MM1065, multiplied less than 10-fold in leaves and had only a minimal effect on BG1, BG2, and BG3 mRNA accumulation, but it induced PAL mRNA accumulation. No accumulation of CHS mRNA was found with either ES4326 or MM1065. We also describe the cloning of a putative avirulence (avr) gene from the avirulent strain MM1065 that caused the virulent strain ES4326 to grow less well in leaves and to strongly elicit PAL but not BG1 and BG3 mRNA accumulation. These results suggest that the Arabidopsis PAL and BG genes may be activated by distinct signal transduction pathways and show that differences in plant gene induction by virulent and avirulent strains can be attributed to a cloned presumptive avr gene.

Cloning, Molecular↗
PubMed1991

Abnormal corpus callosum: a sensitive and specific indicator of multiple sclerosis.

The authors investigated whether identification of corpus callosal (CC) involvement might increase the specificity of magnetic resonance (MR) imaging in differentiating multiple sclerosis (MS) from other periventricular white matter diseases (PWDs). They prospectively evaluated 42 patients with MS and 127 control patients with other PWDs. Ninety-three percent of the MS patients demonstrated confluent and/or focal lesions involving the callosal-septal interface (CSI). These lesions characteristically involved the inferior aspect of the callosum and radiated from the ventricular surface into the overlying callosum. CSI lesions were optimally demonstrated on sagittal long repetition time (TR)/short echo time (TE) images and frequently (45% of cases) went undetected on axial images. Only 2.4% of the control patients had lesions of the CC. The authors conclude that midsagittal long TR/short TE images are highly sensitive and specific for MS and that callosal involvement in MS is more common than previously reported.

Adult↗
PubMed1990

Phenylketonuria: MR imaging of the brain with clinical correlation.

Fifteen patients with biochemically documented phenylketonuria (PKU) were studied with use of magnetic resonance (MR) imaging with spin-echo T2-weighted pulse sequences. The resulting images demonstrated varying degrees of symmetric high signal intensity of the white matter within the posterior cerebral hemispheres. Involvement of the anterior hemispheres was seen only in cases with severe signal intensity changes. There was no involvement of the cerebral cortex, brain stem, or cerebellum. Moreover, no anatomic structural abnormalities were observed. Mild cortical atrophy was observed in eight of the 15 patients. There was no significant correlation between the patients' IQ scores and the level of MR signal intensity changes. Although MR imaging routinely shows relatively distinct abnormalities in patients with PKU, the clinical severity of the disease does not parallel its imaging severity.

Adolescent↗
PubMed1989

Wallerian degeneration after cerebral infarction: evaluation with sequential MR imaging.

The dynamic signal intensity changes at magnetic resonance (MR) imaging in active and chronic wallerian degeneration in the corticospinal tract were evaluated. Forty-three patients with wallerian degeneration seen on MR images after cerebral infarction were studied. When possible, patients with acute stroke were examined with MR imaging prospectively at the onset of symptoms and then at weekly intervals for several months. Focal infarction without distal axonal degeneration is demonstrated for the 1st month following onset of clinical symptoms. At 4 weeks, a well-defined band of hypointense signal appears on T2-weighted images in the topographic distribution of the corticospinal tract. After 10-14 weeks, the signal becomes permanently hyperintense. Over several years, accompanying ipsilateral brain stem shrinkage occurs. The dark signal intensity observed on T2-weighted images between 4 and 14 weeks is believed to result primarily from transitory increased lipid-protein ratio.

Adult↗
PubMed1989

Intracerebral arteriovenous malformations: evaluation with selective MR angiography and venography.

Magnetic resonance (MR) angiography and spin-echo methods were used to evaluate intracerebral arteriovenous malformations (AVMs) in 10 patients. Spin-echo images obtained with flow presaturation demonstrated the nidus of the AVM in all cases, but it was difficult to determine feeding vessels. These vessels were directly visualized with three-dimensional MR angiography; their presence could be indirectly determined by means of selective presaturation of individual vessels, which resulted in a marked decrease in signal within the portion of the AVM supplied by that vessel. Vascular supplies from the internal carotid artery and anterior, middle, or posterior cerebral arteries were detected in all cases, but in three large malformations it was not possible to demonstrate small feeding vessels. MR angiograms were also helpful for further defining the nidus. The combination of MR angiographic and spin-echo methods provides information useful for therapeutic planning not provided by either technique alone.

Adult↗
PubMed1988

Wallerian degeneration: evaluation with MR imaging.

Twenty-three patients who underwent routine magnetic resonance (MR) imaging of the brain were found to have signal or structural abnormalities corresponding to white matter tracts. Images were evaluated for anatomic and MR signal characteristics of the involved tract, associated primary lesions, and, when possible, changes in MR signal and anatomic structures with time. Images from 20 patients demonstrated a thin band of abnormal signal contiguous with the primary lesion and conforming to the known anatomic pathway of a white matter tract. Cerebral infarction was the most common associated primary disorder (n = 17). Neoplasms (n = 2), demyelinating (n = 1) and posthemorrhagic (n = 2) conditions, and an idiopathic movement disorder (n = 1) were associated with white matter tract signal abnormalities that were indistinguishable from those seen with infarction. Signal abnormality corresponding to the corticospinal tract was the type most commonly seen. No change in signal characteristics was seen with time (six cases) or following contrast material administration (two cases). The authors conclude that MR imaging provides a sensitive method of evaluating wallerian degeneration in the living human brain.

Adult↗
PubMed1988

Correlation of continuous-wave Doppler spectral flow analysis with gross pathology in carotid stenosis.

Preoperative continuous-wave Doppler spectral analysis was used to generate two parameters, peak frequency in the internal carotid artery (fmax) and the ratio of peak frequencies in the internal and common carotid arteries (carotid index). These were compared with direct measurement of residual lumen diameter in pathologic specimens obtained from carotid endarterectomy in 37 patients. Doppler shift frequency parameters were well correlated with residual lumen diameter when the latter was at least 1 mm. Residual lumens of less than or equal to 2 mm were found to have an fmax of greater than 7.5 kHz and a carotid index of greater than 3.8. If fmax was greater than 14 kHz or the carotid index was greater than 7, the residual lumen diameter was nearly always less than or equal to 1 mm. Thus, the severity of the stenosis correlated directly with Doppler shift frequencies. The length of stenoses did not affect the correlations.

Arteriosclerosis↗
PubMed1988

Indications for treatment and classification of 132 carotid-cavernous fistulas.

Classification of carotid-cavernous fistulas (CCFs) into the four types described by Barrow allows the surgeon to choose the optimal therapy for each patient. Type A patients have fast flow fistulas that are manifest by a direct connection between the internal carotid arterial siphon and the cavernous sinus through a single tear in the arterial wall. The best therapy is obliteration of the connection by a detachable balloon. Ninety-two of 95 traumatic CCFs were treated in this fashion. Direct surgical exposure of the cervical or cavernous internal carotid artery (ICA) was necessary in the remaining 3 patients, who had undergone unsuccessful surgical trapping. Three ruptured cavernous aneurysms and 2 spontaneous CCFs also had Type A connections. Other carotid-cavernous fistulas are slow flow, spontaneous dural arteriovenous malformations (AVMs) that have been classified into B, C, and D types on the basis of arterial supply. Occlusion of the ICA is not a logical choice in the treatment of dural AVMs that occur in the elderly, are relatively benign, and are often bilateral. Type B are rare and are fed by meningeal branches of the ICA only. We have not seen this type of dural fistula in our series. Type C are supplied by feeders from the external carotid only and can almost always be obliterated successfully by embolizing the external carotid artery (ECA) branches. There are 4 Type C cases in this series of 37 spontaneous CCFs. All occurred in patients less than 30 years of age and were shunts between the middle meningeal artery and the cavernous sinus.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1987

Comparison of magnetic resonance and roentgen ray computed tomography in dementia.

To compare the merits of magnetic resonance imaging (MRI) and roentgen ray computed tomography (CT) in assessing patients with dementia, we examined pairs of MR and CT brain images obtained from 26 patients with Alzheimer's disease (AD), eight patients with vascular or mixed dementia, and two patients with Parkinson's disease plus dementia. Magnetic resonance and CT images were independently rated on a qualitative scale of 0 (normal) to 3 (severely abnormal) in 39 separate brain regions. Ratios of anterolateral and third ventricular linear spans to linear skull spans were measured. Abnormalities in subcortical white matter and in hippocampus, enlargement of basal and sylvian cisterns, and ventriculomegaly were more evident on MR than CT scans, but qualitative ratings in all other brain regions were similar. Linear ventricular span ratios based on MR images did not differ significantly from those measured on CT. White matter abnormalities on MR were high signal foci on T2-weighted images whose pathologic substrate was uncertain; in a single case studied pathologically, no abnormalities were detected in brain regions that contained high signal foci. Dementia severity correlated with periventricular white matter abnormalities on both MR and CT images.

Aged↗
PubMed1987

Embolization of epistaxis and juvenile nasopharyngeal angiofibromas.

This article reviews arterial embolization of epistaxis and juvenile nasopharyngeal angiofibromas. A protocol for the complete and rapid exploration of epistaxis is suggested that is based upon which arteries providing blood to the nasal fossa may be responsible for the bleeding and the most optimal way for their demonstration and evaluation. The relevant anatomy of the major arteries, their branches, and important anastomoses are described. The goals of embolization are to control severe or recurrent epistaxis, prevent recurrence if possible, and avoid occlusion of any vessels not responsible for the hemorrhage. The most appropriate embolic material is chosen, realizing that recurrence can be caused by the use of resorbable embolic material or by a very proximal or too complete embolization. Embolization may be used for specific causes of epistaxis including idiopathic, hereditary hemorraghic telangiectasia, hemorrhagic tumors, vascular malformations, trauma, disorders of hemostasis, and postsurgical problems. Juvenile nasopharyngeal angiofibromas are discussed with respect to their clinical presentation, classification, computed tomographic, MR imaging, and angiographic evaluation, treatment, future trends in treatment, and precautions and complications.

Adolescent↗
PubMed1986

Threatened carotid artery rupture: a complication of radical neck surgery.

Carotid artery rupture is an infrequent but highly dangerous postoperative complication of radical head and neck surgery. The principal predisposing factors are radiation therapy, infection, tissue necrosis, vessel exposure, and pharyngeal fistula formation. Actual or threatened carotid artery rupture has been most commonly managed by ligation of the involved vessel. We present a patient who showed signs of impending carotid artery rupture after both irradiation and radical neck surgery. Balloon embolization was employed in preference to traditional carotid artery ligation. The patient's risk factors for carotid artery rupture are analyzed and the application of balloon embolization is discussed.

Carotid Arteries↗
PubMed1986

Multiphasic MR imaging: a new method for direct imaging of pulsatile CSF flow.

A new technique is described that allows for the creation of pure pulsatile flow magnetic resonance (MR) images in a single acquisition. Five to 16 electrocardiographically gated images spanning the entire cardiac cycle are obtained with use of a gradient-echo pulse sequence. The section can be varied from 4 mm thick to full thickness projection. Taken singly, each image provides direct assessment of flow direction and velocity. Subtraction of image pairs eliminates signal detected from stationary protons, producing images of pulsatile flow. In this study the technique was used to image the flow of cerebrospinal fluid (CSF) in healthy subjects and in one patient with syringohydromyelia. The data suggest that multiphasic MR imaging provides a powerful means for the noninvasive assessment of CSF pulsatile flow dynamics and may have potential clinical application for the investigation of a variety of abnormalities such as normal pressure hydrocephalus, syrinx, and spinal block.

Cerebrospinal Fluid↗
PubMed1986

Assessment of ventricular shunt patency by sonography: a new noninvasive test.

This report describes a new test of patency of the ventricular component of a ventriculoperitoneal shunt that precludes injection into the shunt reservoir. Preliminary clinical experience confirms that digital compression of the ventricular shunt reservoir (Cordis standard and pediatric reservoir), while occluding the shunt distal to the reservoir, generates microbubbles that increase the echogenicity of the catheter, demonstrating shunt patency. In vitro, the extrusion of microbubbles from catheter side holes can be imaged during digital compression of the reservoir, but so far this has not been imaged in patients as a direct sign of shunt patency. A sonographic means of assessing shunt function offers the advantage of simultaneously imaging the ventricular catheter, determining its location, and assessing the etiology of shunt failure. Its usefulness is limited to pediatric cases in which an adequate transfontanelle cranial sonographic study can be obtained and to individuals with large craniotomy defects.

Adolescent↗
PubMed1986

MR and CT of occult vascular malformations of the brain.

The need for improved specificity in the diagnosis of "occult" vascular malformations led to the use of MR in suspected cases in order to determine MR's potential for improved diagnostic accuracy. Six patients with six lesions histologically diagnosed as vascular malformation after partial (1) or complete (5) microsurgical excision were studied by CT, MR, and selective magnification subtraction angiography. In all cases, the cerebral lesions were apparently solitary and were visible as focal lesions on both CT and MR. Since angiography failed to reveal the pathologic blood vessels of the lesions, and no arteriovenous shunting was evident, these lesions were termed vascular malformations occult to angiography (VMOTA). Angiography revealed a mass effect in only two cases. MR did not reveal additional vascular malformations missed by CT. In each case, MR, which was performed in an attempt to support the diagnosis suggested by CT, did in fact do so by revealing signal abnormalities indicative of nonacute hemorrhage within the lesion on T1- and T2-weighted pulse sequences. Although, as on CT, MR features of these lesions were found to be nonspecific, the MR criteria reinforced the probable diagnosis of VMOTA in an additional 30 cases that had shown similar nonspecific CT features. In this second group, excluded from this study, in which histologic verification was not obtained because of perceived hazards of surgery, the increased assurance regarding the diagnosis led to proton-beam therapy without histologic verification in 18 cases. It is concluded that MR can provide significant improvement in the accuracy of diagnosing VMOTA beyond that obtainable just by plain and contrast-enhanced CT.

Adult↗
PubMed1985

High-resolution surface-coil imaging of lumbar disk disease.

Seventeen patients with lumbar disk disease were studied using a prototype magnetic resonance (MR) surface coil. The high signal-to-noise ratio achieved with the surface coil permitted increases in spatial resolution to 0.9 X 0.9 mm in-plane resolution with 5 mm slice thickness. The surface coil was also compatible with multiplanar, multiecho imaging techniques. The spatial resolution achieved in this study was nearly equivalent to that achieved by state-of-the-art computed tomographic (CT) scanners, and MR showed a superior range of soft-tissue contrast. One significant limitation of MR was its inability to demonstrate small calcifications. Nevertheless, MR imaging provided diagnostic information comparable to CT or myelography in a completely noninvasive manner. With further technical advances, MR is likely to become the initial procedure of choice for evaluating patients with suspected lumbar disk disease.

Humans↗