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Biomedical subjects

W K Chong

Publications and source records attributed to W K Chong.

At least 73 records · Page 4Linked to original sources
PubMed1994

A new appraisal of abnormalities of the odontoid process associated with atlanto-axial subluxation and neurological disability.

It is well known that abnormalities of the odontoid process may be associated with subluxation and neuraxial compression. Modern computerized imaging is demonstrating that existing classifications are in need of revision since they no longer reflect current views on development, nor do they adequately explain the patterns of abnormality commonly encountered in clinical practice. This study is a description of 62 varied clinical cases examined by high definition computerized myelography or MRI in flexion and extension, some before and after stabilization procedures. From these descriptions, and a review of the old and more recent literature concerning phylogenesis and ontogenesis of the odontoid, the following conclusions were drawn. The dens within the atlas ring is not morphologically a centrum of the first cervical vertebra, but a projection arising from it. In os odontoideum the dens forms normally, but ossifies abnormally because of abnormal motion; it is a result rather than the cause of instability. Hypoplasia of the dens is usually incorrectly diagnosed. When present it is associated with atlanto-occipital assimilation, fusion of the second and third, or more, cervical vertebrae, loss or reduction in axial rotation of the head, basilar invagination and hindbrain deformity of Chiari type. Therefore it is part of a regional anomaly involving hypoplasia of the derivatives of the occipital and upper cervical somites. Recognition of these aspects simplifies both diagnosis and the formulation of therapeutic strategies for different types of clinical presentation.

Adolescent↗
PubMed1994

Cerebrospinal fluid-intracranial volume ratio measurements in patients with HIV infection: CLASS image analysis technique.

PURPOSE: To prospectively study the cerebrospinal fluid volume-total intracranial volume ratio (CSF/ICV) in human immunodeficiency virus (HIV)-infected patients at various stages of disease. MATERIALS AND METHODS: A total of 258 volume measurements were obtained with use of a 1.5-T magnetic resonance (MR) imager and the cluster localized automated spherical segmentation technique (which reduces two-dimensional pixel data from dual spin-echo MR images to a one-dimensional histogram) in 69 control subjects and 189 HIV-infected patients. RESULTS: The CSF/ICV was statistically significantly increased in patients with late-stage (Centers for Disease Control and Prevention group IV) acquired immunodeficiency syndrome (AIDS) (0.16 +/- 0.05 [standard deviation]) compared with seronegative control subjects (0.12 +/- 0.03) and patients without symptoms (0.13 +/- 0.03). CONCLUSION: No substantial change in CSF/ICV occurs until development of late-stage AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1994

Localized cerebral proton MR spectroscopy in HIV infection and AIDS.

PURPOSE: To document differences in the cerebral proton MR spectra of patients with early and late stages of human immunodeficiency virus (HIV) infection. METHOD: We studied the relative N-acetyl-aspartate (NAA) levels by localized proton spectroscopy of the parietooccipital region of the brain in 43 HIV-seropositive patients, including 26 with an acquired immunodeficiency syndrome (AIDS)-defining diagnosis, and in eight control subjects. RESULTS: Reduced relative NAA levels were shown in those HIV-1-seropositive patients: 1) with AIDS against HIV-1-seropositive patients without AIDS (P < .04); 2) with HIV-1-associated cognitive/motor complex against neurologically healthy patients (P < .007); 3) with encephalopathic changes on MR against those with normal imaging (P < .001); and 4) on follow-up against their results on initial study (P < .03). CONCLUSIONS: By clinical (Centers for Disease Control classification) and radiologic (MR evidence of white-matter disease) criteria indicating late-stage HIV infection, reduced relative levels of NAA have been demonstrated. Spectroscopic abnormalities can be quantitatively tracked with time. This paper demonstrates the clinical use of detecting NAA as a putative in vivo measure of the neuronal loss that has been demonstrated in postmortem studies of patients with AIDS. This neuronal loss, which is believed to underlie the HIV-1-associated cognitive/motor complex, is thought to be attributable directly or indirectly to the presence of HIV in the brain. Proton spectroscopy may serve as a quantitative noninvasive indicator of this aspect of cerebral involvement in HIV disease.

AIDS Dementia Complex↗
PubMed1993

Structure-activity relationships of the antimalarial agent artemisinin. 1. Synthesis and comparative molecular field analysis of C-9 analogs of artemisinin and 10-deoxoartemisinin.

A series of C-9 beta-substituted artemisinin analogs (2-21) were synthesized via dianion alkylation of the total synthetic intermediate 57 followed by subsequent ozonolysis/acidification, or by alkylation of the enolate derived from (+)-9-desmethylartemisinin, 2. Inactive acyclic analogs 22 and 23 were synthesized by nucleophilic epoxide opening and the ring contracted analog 24 was prepared by an alternate route. 10-Deoxo-9-alkyl derivatives 68 and 70 were synthesized convergently from intermediates in the preparation of 9-alkyl derivatives. In vitro bioassay was conducted in W-2 and D-6 clones of drug resistant Plasmodium falciparum. Comparative molecular field analysis (CoMFA) of the 9-alkyl lactone derivatives provided a model with a cross-validated r2 = 0.793. Inclusion of inactive 1-deoxyartemisinin analogs 26-42 provided a model with a value of 0.857. The activities of a number of other analogs of divergent structure (43-56) were predicted with good accuracy using the CoMFA model.

Animals↗
PubMed1993

The prevalence of paranasal sinus disease in HIV infection and AIDS on cranial MR imaging.

Sinusitis poses a difficult clinical challenge in the management of patients with AIDS because of high rates of relapse and the association with unusual pathogens. To determine the prevalence and severity of sinus disease in this group we prospectively analysed the condition of the paranasal sinuses shown on cranial MR scans of 156 patients referred for the investigation of suspected intracranial pathologies. These included 104 HIV seropositive patients, including 93 with an AIDS-defining diagnosis (CDC IV). Forty-two scans were performed on age-matched controls. The scans were timed to control for seasonal variations in sinus disease and were interpreted by two radiologists who were blinded to the clinical and serological status of the patients. Severe mucosal disease (more than one sinus showing > 75% obliteration) or moderate mucosal disease (only one sinus showing > 75% obliteration) was seen in 15.1% (14/93) patients with AIDS and none of the 42 controls (chi 2 = 6.73, P < 0.01). The mean maximum mucosal thickness in patients with AIDS was significantly greater than the control group (P < 0.001) and also significantly greater than in seropositive patients who had not had an AIDS-defining diagnosis (CDC II/III) (P = 0.006). Paranasal sinus mucosal abnormalities seen on MRI are greater in prevalence and severity in patients with AIDS and about one in seven would be expected to have at least one sinus largely obliterated.

Acquired Immunodeficiency Syndrome↗
PubMed1993

The appearance of normal and abnormal arterial morphology on intravascular ultrasound.

The ultrasonic appearance of in vitro normal and atherosclerotic arterial wall was investigated with an intravascular ultrasound (IVUS) probe. Fresh cadaver specimens were used: two carotid, two aorta, four iliac and eight superficial femoral arteries. The wall of muscular arteries has a three-layered sonographic appearance. The central hypoechoic layer corresponds to the media, which is primarily composed of smooth muscle. Elastic arteries whose media have a high elastin content appear uniformly echogenic. Calcified plaque is strongly echogenic with acoustic shadowing, fibrous plaque is moderately echogenic, and where there is no cellular matrix the plaque is poorly echogenic. IVUS can provide information about internal plaque architecture. Three-dimensional reconstructions can be generated using a transputer-based workstation coupled to the transducer, providing detailed views of surface contour.

Angioplasty, Balloon↗
PubMed1993

Proton spectroscopy of the brain in HIV infection: correlation with clinical, immunologic, and MR imaging findings.

Abnormalities at cerebral proton spectroscopy occur in patients with the acquired immunodeficiency syndrome (AIDS). N-acetyl aspartate (NAA) is believed to be a neuronal marker, and neuronal loss is thought to underlie the human immunodeficiency virus (HIV)-associated cognitive/motor complex. The proton spectra in 103 HIV-seropositive patients and 23 control subjects were compared and correlated with clinical, immunologic, and radiologic measures of HIV infection. Significant (P < .05) reductions in the mean NAA/choline (Cho) and NAA/creatine (Cr) ratios were seen in patients with immune suppression and neurologic signs. Significant increases in the Cho/Cr ratios were seen in patients with low CD4 lymphocyte counts and abnormal magnetic resonance (MR) images. Reduced NAA ratios correlated with diffuse but not focal MR imaging abnormalities. Combined MR imaging and spectroscopy provides closer relationships to clinical and immunologic measures of disease than either modality alone. Spectroscopy is an adjunct to MR imaging and augments the value of an MR imaging study.

Adult↗
PubMed1993

MR cholangiography: clinical evaluation in 40 cases.

PURPOSE: To determine the reliability and efficacy of magnetic resonance (MR) cholangiography in demonstrating the site and extent of stricture. MATERIALS AND METHODS: In 40 patients with obstructive jaundice, three-dimensional MR cholangiography was performed with a sequence of mirrored fast imaging with steady-state precession and was compared with conventional cholangiography in 39 cases. The level of obstruction was determined by examining all imaging data available. RESULTS: Diagnostic MR cholangiograms were acquired in 39 patients; absence of obstruction was confirmed in three, and obstruction was seen in 36. The level of obstruction or absence of obstruction was accurately shown in 36 of 40 patients with MR cholangiography and in 37 of 39 patients with conventional cholangiography. The peripheral biliary tree was shown more completely with MR cholangiography than with endoscopic retrograde cholangiography in all 32 patients undergoing diagnostic studies with both modalities. CONCLUSION: Three-dimensional MR cholangiography shows particular promise for the assessment of complex strictures, in which conventional cholangiography carries a higher risk of sepsis, for planning optimal drainage before intervention.

Adult↗
PubMed1993

Transjugular intrahepatic portosystemic shunt: US assessment with maximum flow velocity.

PURPOSE: To evaluate the ability of Doppler ultrasonography (US) to depict the patency of a transjugular intrahepatic portosystemic shunt (TIPS). MATERIALS AND METHODS: Twenty-eight patients were followed up after creation of TIPS with US, angiography, and endoscopy performed at regular intervals. Magnetic resonance (MR) angiography was performed in four patients. US was performed first, and the results were correlated with those at angiography. Measurements of maximum flow velocity (Vmax) were taken from the proximal part of the shunt. RESULTS: In normal shunts, mean Vmax was 95 cm/sec. Shunt obstruction was seen in 12 cases: occlusion in four and stenosis in eight. All cases of occlusion were detected with US and appeared as absent flow within the shunt. There was one false-positive diagnosis of occlusion. All cases of stenosis resulted in reduced Vmax (mean, 32 cm/sec; P < .001). After successful revision in seven patients, Vmax rose to a mean of 122 cm/sec. Artifact from the metal stent prevented flow assessment with MR imaging. CONCLUSION: US can be performed to evaluate shunt status, and Vmax is an accurate noninvasive parameter for assessing shunt patency.

Blood Flow Velocity↗
PubMed1992

The technique of laparoscopic cholecystectomy in children.

Twelve children underwent elective laparoscopic cholecystectomy for symptomatic cholelithiasis during a 10-month period in one institution. The operative technique that has been described for adults was modified because of the smaller dimensions of pediatric patients. These modifications are discussed in this report, as are new alternatives for evaluating the common duct. No operative complications or conversions to open cholecystectomy occurred, and no complications after surgery were seen during an average follow-up period of 4.5 months. The benefits of laparoscopic cholecystectomy include decreased pain and ileus after surgery, shortened hospitalization, and improved cosmesis. Laparoscopic cholecystectomy is safe and efficacious in children, and it compares favorably with traditional cholecystectomy in the pediatric age group.

Adolescent↗
PubMed1992

US-guided percutaneous pancreatography: an essential tool for imaging pancreatitis.

The pancreatic duct can be opacified when contrast material is injected through a fine needle percutaneously placed under ultrasound (US) guidance. Percutaneous pancreatography was performed in 63 patients with chronic pancreatitis diagnosed at US or computed tomography (CT). In 52 of these patients, endoscopic retrograde pancreatography (ERP) was unsuccessful or did not enable complete visualization of the duct. The percutaneous pancreatograms and other relevant images of these patients were retrospectively reviewed. Percutaneous pancreatography was successful in 54 patients (86%), in whom it clearly mapped the full ductal anatomy, depicted the relationship between cavities seen at US or CT and the duct, and allowed assessment of duct drainage after antegrade injection of contrast material. This information was not provided by other modalities. Percutaneous pancreatography is a valuable complement to CT, US, and ERP for imaging chronic pancreatitis.

Cholangiopancreatography, Endoscopic Retrograde↗
PubMed1991

Retroperitoneal fibrosis in Marfan's syndrome.

To our knowledge, an association between Marfan's syndrome and retroperitoneal fibrosis (RPF) has never been described. We describe two cases who presented acutely with aortic disease and were later found to have changes of undiagnosed retroperitoneal fibrosis causing hydronephrosis on computed tomography (CT). An association is readily understandable based on the current hypotheses for the aortic disease in Marfan's syndrome and the etiology of RPF. We suggest why this has not been noted previously. CT has an established role in the diagnosis and follow up of RPF as well as in the assessment of the aortic complications of Marfan's syndrome. Awareness of the possibility of RPF and it's demonstration on CT may allow early diagnosis and help prevent significant renal impairment.

Acute Disease↗
PubMed1990

Gastrobronchial fistula.

Gastrobronchial fistula is an extremely rare condition. Trauma, subphrenic abscess and gastro-oesophageal surgery are the most commonly reported causes. We describe a case of gastrobronchial fistula occurring due to a peptic ulcer within a hiatus hernia six years following fundoplication.

Bronchial Fistula↗
PubMed1990

Iliac artery rupture during percutaneous angioplasty.

Percutaneous transluminal angioplasty of the iliac vessels is a generally safe procedure with good results. A rare but potentially fatal complication is iliac artery rupture; we present such a case with its management and review the literature.

Aged↗
PubMed1990

Synthesis and antiinflammatory activity of novel 12 beta-substituted analogues of betamethasone.

A series of 9 alpha-halo-12 beta-hydroxy and 12 beta-acyloxy analogues of betamethasone 17,21-dipropionate were synthesized and tested for topical antiinflammatory potency in the croton oil ear assay. The compounds were assayed for systemic absorption in the contralateral ear assay, in which it was found that 12 beta-hydroxy analogues 9, 13, and 15 were all absorbed but the corresponding 12 beta-esters 11a-e, 14, and 16 were not. On repeated high-dose applications to the mouse ear, there was no evidence of systemic absorption of any 12 beta-propionate ester as gauged by thymus weights (thymic involution) and plasma cortisol levels (adrenal suppression). Results of limited SAR studies showed that topical antiinflammatory activity and systemic absorption were not greatly influenced by the 9 alpha-halogen but were largely dependent on the polarity and size of the 12 substituent. While the optimal compounds 14 and 16 were less topically active than the controls beta- and beclomethasone dipropionate, unlike the controls, they displayed no systemic effects, even after repeated high-dose applications. Surprisingly, propionate 14 was devoid of atrophogenic activity.

Animals↗