Biomedical subjects

Y L Chan

Publications and source records attributed to Y L Chan.

At least 55 records · Page 3Linked to original sources

PubMed2001

Deferoxamine-induced dysplasia of the knee: sonographic features and diagnostic performance compared with magnetic resonance imaging.

OBJECTIVE: To evaluate the features and diagnostic performance of sonography in the assessment of deferoxamine-induced dysplasia of the knee. METHODS: The left knees of 32 patients with thalassemia who were receiving regular blood transfusions and chelation therapy were studied with sonography for signs of deferoxamine-induced bone dysplasia. Abnormal physeal and metaphyseal changes detected on sonography included notching at the metaphyseal corner, a blurred or irregular peripheral juxtaphyseal metaphyseal contour, and widening of the peripheral juxtaphyseal metaphyseal echogenic interface. The accuracy of sonography in diagnosing dysplasia was evaluated by using magnetic resonance imaging as the standard of reference. RESULTS: There were 14 true-positive findings, 10 true-negative findings, 7 false-negative findings, and 1 false-positive sonographic diagnosis of dysplasia, giving 67% sensitivity, 91% specificity, a 93% positive predictive value, and a 59% negative predictive value. CONCLUSION: Sonography was specific but only moderately sensitive in the diagnosis of deferoxamine-induced dysplasia at the knee when compared with magnetic resonance imaging.

Adolescent↗

PubMed2001

Cerebrovascular disease among Chinese populations--recent epidemiological and neuroimaging studies.

Stroke mortality in individuals of Chinese descent has declined during the past decades, although the absolute number of patients with first-ever stroke is escalating. This review summarises recent epidemiological and imaging studies conducted among Chinese populations. Data indicating differences between Chinese and Caucasian ethnic groups in the pathophysiological mechanisms of stroke are highlighted, and the potential implications of these findings for prevention and management of stroke are discussed.

Cerebral Hemorrhage↗

PubMed2001

Variant Creutzfeldt-Jakob disease in Hong Kong.

A 34-year-old Chinese woman who had lived in the United Kingdom in the 1980s was admitted to hospital in Hong Kong because of a 7-month history of progressive neurological deterioration. Initially, she complained of heartburn and paraesthesia of the hands and feet. She then developed slowness of speech and gait, and was noted to be forgetful and irritable. In January 2001, she was brought back to Hong Kong for treatment. On admission in May she was dysarthric, ataxic, and dystonic. Magnetic resonance imaging showed high signals in both thalami suggestive of variant Creutzfeldt-Jakob disease. Other investigations, including electroencephalogram and lumbar puncture, were unremarkable. A tonsil biopsy showed the presence of prions. This patient's presentation is typical of the variant Creutzfeldt-Jakob disease cases that have been reported since 1996. Because of her residential history, we conclude that this is an imported case from the United Kingdom.

Adult↗

PubMed2000

TE-AFLP: combining rapidity and robustness in DNA fingerprinting.

A new type of fingerprinting technique is presented, based on amplified fragment length polymorphism (AFLP). Rather than two endonucleases as in AFLP, we propose the use of three enzymes, hence the method is called three endonuclease (TE)-AFLP. Genomic DNA is digested and two sets of adapters are selectively ligated onto the restriction fragments in a single reaction volume. No adapters complementary to the ends generated by a frequent cutter are added. Due to the addition of a third endonuclease, the TE-AFLP method provides a high discriminatory power and a reduction in the number of bands. The latter makes it especially suitable for the analysis of complex genomes. TE-AFLP fingerprints are suitable for detection by automatic fluorescent sequencers and are obtained in less than half the time and at reduced costs compared to a typical AFLP. The reliability of this method was investigated by determining the influence of varying digestion, ligation and PCR components on the fingerprint. Moreover, cross-experiments to study inheritance of loci were performed with a primitive insect and with tomato strains. The features of TE-AFLP are discussed in comparison with conventional AFLP.

Animals↗

PubMed2000

Aspirin-associated intracerebral hemorrhage: clinical and radiologic features.

OBJECTIVE: To identify the clinical and radiologic features of intracerebral hemorrhage (ICH) in aspirin users. BACKGROUND: Although the benefits of aspirin outweigh its hemorrhagic risks for patients at high risk of vascular diseases, prolonged use of aspirin is associated with an increased risk of ICH. METHODS: The authors enrolled consecutive patients with acute stroke who were admitted to a regional hospital from 1993 to 1998 into a stroke registry. From this registry, they identified all stroke patients who had ICH confirmed by CT scan and then selected those taking regular aspirin before ICH as the study group. For each study patient, they selected the immediate next two patients with ICH but not taking aspirin as controls. RESULTS: The authors identified 58 aspirin users and 1193 nonusers among all patients hospitalized for ICH. From the group of nonusers, they selected 116 patients as controls. The locations of the hematoma were different (p = 0.002), with more lobar hematoma in the aspirin group (32.8%) than in the control group (10.3%). Prior cerebrovascular disease was the reason for taking aspirin in 37 (64%) patients but five patients had prior ICH. CONCLUSIONS: The propensity for lobar hematoma in aspirin-associated ICH suggests its pathology may be somewhat different from spontaneous ICH among nonaspirin users. Further research to examine the risks and benefits of aspirin use in certain subgroups at risk of both thrombotic and hemorrhagic events is needed.

Adult↗

PubMed2000

The phenotype of mutations of the base-pair C2658.G2663 that closes the tetraloop in the sarcin/ricin domain of Escherichia coli 23 S ribosomal RNA.

The sarcin/ricin domain (SRD) in Escherichia coli 23 S rRNA is a part of the site for the association of elongation factors with ribosomes and for that reason is critical for the binding of aminoacyl-tRNA and for translocation during the reiterative elongation reactions of protein synthesis. The SRD has a GAGA tetraloop that is shut off by a Watson-Crick C2658 x G2663 pair. The contribution of this pair to the function of the ribosome has been evaluated by constructing mutations in the nucleotides and determining their phenotype. Constitutive expression of a plasmid-encoded rrnB operon with a G2663C transversion mutation that disrupts the Watson-Crick pair was lethal. Double transversion mutations, C2658G x G2663C and C2658A x G2663U, that reverse the polarity of the pyrimidine and the purine but restore the potential to form a canonical pair, were also lethal. Induction of transcription of 23 S rRNA with the same mutations, but encoded in a plasmid with a lambdaP(L) promoter and expressed at a lower level, retarded growth. The sedimentation profiles of ribosomes with transversion mutations in C2658 and/or G2663 are altered; the ratio of 50 S subunits to 30 S particles is changed and polysomes are reduced. Ribosomes with a G2663C, a C2658G x G2663C, or a C2658A x G2663U mutation in 23 S rRNA were not active in protein synthesis, indeed, they appeared to inhibit the activity of ribosomes with wild-type 23 S rRNA. Transversion mutations in the analogs of C2658 and G2663 decreased binding of EF-G to SRD oligoribonucleotides; the same mutations in 23 S rRNA decreased binding of the factor to intact ribosomes. The most severe phenotype, in growth, in protein synthesis, and in the binding of EF-G, was associated with a C2658G x G2663C mutation; it is surprising that this was more severe than an analogous C2658A x G2663U mutation. A double transition mutation, C2658U x G2663A, which is not known to have occurred in nature, had no effect on the growth of cells or on the function of ribosomes. The lethal phenotype of transversion mutations in C2658 and G2663 appears to derive from a loss of the capacity of ribosomes to bind EF-G and by indirection the EF-Tu ternary complex.

Bacterial Proteins↗

PubMed2000

Neck node metastases from nasopharyngeal carcinoma: MR imaging of patterns of disease.

BACKGROUND: The purpose was to use MR imaging to document the patterns of nodal involvement in the upper neck in nasopharyngeal carcinoma (NPC). METHODS: The MR images of 150 patients with newly diagnosed NPC were reviewed retrospectively. Nodes were considered abnormal on MR criteria of size, necrosis, and extracapsular spread. RESULTS: Retropharyngeal nodes (RN) were more frequently involved than nonretropharyngeal nodes (NRNs) (94% vs 76% in 115 patients with nodal metastases). NRN involvement without RN was seen in only 7 of 115 patients (6%). Involvement of RN at the level of the oropharynx (82%) was as common as at the nasopharynx (83%) level. Internal jugular nodes were the most frequently involved NRN nodes (72%). Spinal accessory nodal involvement was also common (57%) but seldom in isolation (8%). Submandibular (3%) and parotid (2%) nodal metastases were uncommon and were always associated with advanced nodal metastases in the ipsilateral RN, internal jugular, and spinal accessory regions. CONCLUSION: Retropharyngeal nodes are the first echelons of nodal metastases. Direct lymphatic spread to the neck without involvement of the RN nodes is uncommon. RN metastases at the level of the oropharynx are more common than previously suspected, and this should influence radiotherapy planning. NRN outside the internal jugular and spinal accessory chains are rare and only occur when the usual routes of lymphatic spread have already been blocked by tumor.

Adult↗

PubMed2000

Angiomatosis of the hand demonstrated by contrast-enhanced magnetic resonance angiogram.

Contrast-enhanced digital subtraction dynamic MR angiography has been applied to lower limb arteries, with accuracy comparable to that of conventional angiography. Application of this technique to hands has not been reported. A 2-year-old girl with a diffuse haemangioma of the right hand elegantly demonstrated by MR angiogram is presented. The feeding vessel and the relationship with surrounding palmar blood vessels were clearly identified. This provided essential preoperative information facilitating surgical resection, yet without the technical difficulties and morbidity associated with conventional angiography.

Angiomatosis↗

PubMed2000

Desferrioxamine-induced long bone changes in thalassaemic patients - radiographic features, prevalence and relations with growth.

AIM: To study the radiographic findings of desferrioxamine-induced bone dysplasia, its prevalence and relation to growth in thalassaemic patients. MATERIALS AND METHODS: A cross-sectional study was performed in 35 thalassaemic patients on a hypertransfusion scheme and chelation therapy at a dose not exceeding 50 mg/kg/day. Radiographs of the left hand taken for bone age assessment in consecutive patients over the past 12 months were evaluated for signs of desferrioxamine-induced bone dysplasia. The findings were correlated with data on growth, chelation and body iron content. RESULTS: Twelve of 35 patients had evidence of desferrioxamine-induced long bone dysplasia. There was no significant difference in the groups with and without radiographic evidence of bone dysplasia with respect to the height percentile at time of initiation of therapy, height percentile at time of radiography, skeletal age delay, age at starting chelation, chelation dose and duration, units of blood transfused, average chelation dose, and serum ferritin levels at time of radiography. Both groups showed a reduced percentile growth with a significantly greater reduction (P = 0.03) in the patients with dysplastic change. CONCLUSION: Desferrioxamine-induced bone dysplasia is associated with height reduction and can be seen in patients receiving desferrioxamine chelation therapy at doses of less than 50 mg/kg/day. Awareness of the diagnosis is of importance as reduction of the desferrioxamine dose may improve bone growth.

Adolescent↗

PubMed2000

A variant of an accessory common bile duct.

While variations of the common bile duct are relatively common, true duplication of the common bile duct is very rare. Such deviation from normal anatomy, if unrecognized, may cause problems during surgical intervention. Here we present a case of a unique variant of an accessory bile duct which arises from the confluence of the right and left hepatic ducts and runs down to join the pancreatic duct to form a long, common channel before opening into the papilla with the main duct.

Adult↗

PubMed2000

Use of transcranial Doppler ultrasound to predict outcome in patients with intracranial large-artery occlusive disease.

BACKGROUND AND PURPOSE: Intracranial large-artery occlusive disease is the predominant vascular lesion found in stroke patients of Asian, African, and Hispanic ancestry, making it numerically perhaps the most common vascular cause of stroke in the world. Relatively little is known about the clinical significance of finding such lesions. We investigate whether the presence and the extent of these vascular lesions help predict outcome after stroke. METHODS: On the basis of transcranial Doppler of the intracranial arteries with supplementary duplex ultrasound of the carotid arteries, we determined the number of occlusive arteries in the craniocervical circulation of consecutive patients who were hospitalized for acute cerebral ischemia. Patients were followed for 6 months for further vascular events (including transient ischemic attack, stroke, and acute coronary syndrome) or death. RESULTS: Among 705 consecutive Chinese patients studied, occlusive arteries were found in 345 patients (49%): 258 patients (37%) had intracranial lesions only, 71 (10%) had both extracranial and intracranial lesions, and 16 (2.3%) had extracranial lesions only. Sixty-three (18%) of the 345 patients with occlusive arteries and 35 (9.7%) of the 360 patients without occlusive arteries had further vascular event or death within 6 months. The risk of vascular events or death increased rapidly with rising numbers of occlusive arteries, after adjustment for vascular risk factors and stroke severity (adjusted odds ratio [OR] 1.25 per occlusive artery, 95% CI 1.12 to 1.39). Other independent risk factors included age (OR 1.03 per year of age, 95% CI 1.01 to 1.05) and atrial fibrillation (OR 3.00, 95% CI 1.40 to 6.69). CONCLUSIONS: In patients with predominantly intracranial large-artery occlusive disease, the presence and the total number of occlusive arteries in the craniocervical circulation predict further vascular events or death within 6 months after stroke. Transcranial Doppler ultrasound is an important investigation for the evaluation of patients with stroke in populations at risk of intracranial atherosclerotic disease.

Arterial Occlusive Diseases↗

PubMed2000

CT and DSA appearances of a ruptured congenital arteriovenous malformation of the posterior mediastinal aorta.

A case of symptomatic congenital arteriovenous malformation detected in an adult patient is presented. The diagnosis was not suspected clinically but was demonstrated by CT and digital subtraction angiography. Although very rare, a congenital arteriovenous malformation of the posterior mediastinal aorta could present as a catastrophic event if it ruptures. Serpiginous vascular channels in the retro-oesophageal posterior mediastinum on CT and angiography should raise the possibility of an arteriovenous malformation.

Angiography, Digital Subtraction↗

PubMed2000

Alveolar hypoventilation syndrome in brainstem glioma with improvement after surgical resection.

A 3-year-old boy presented with brainstem astrocytoma and central alveolar hypoventilation syndrome. Contrast MRI of the brain showed that the tumor involved the cerebellum, with compression of brainstem, and resolved after surgical resection. Polysomnography performed before and after total tumor resection showed significant improvement in nocturnal respiratory rate, respiratory disturbance index, and oxygen desaturation. It is apparent that central alveolar hypoventilation syndrome secondary to brainstem tumor may improve after surgical resection for those with favorable anatomic location and histology. Serial polysomnography and MRI scans are useful for diagnosis and in the management plan, and to monitor progress.

Astrocytoma↗

PubMed2000

Diagnostic accuracy of abdominal ultrasonography compared to magnetic resonance imaging in siderosis of the spleen.

A prospective study to compare the diagnostic performance of ultrasonography with magnetic resonance imaging using gradient-recalled echo technique in cases of siderosis of spleen was conducted in 53 cirrhotic patients with endoscopic proof of gastroesophageal varices. Of the 34 patients with splenic siderosis on MR imaging, punctate hyperechoic foci were detected in the spleen on ultrasonography in 24 patients. Using MR imaging as the reference standard for the diagnosis of splenic siderosis, the sensitivity of ultrasonography is 70.6%; specificity is 78.9%; positive predictive value is 85.7%; and negative predictive value is 40%. We conclude that ultrasonography is a fairly accurate technique in the diagnosis of splenic siderosis.

Adult↗

PubMed1999

The contribution of a zinc finger motif to the function of yeast ribosomal protein YL37a.

Eukaryotic ribosomes have a large number of proteins but the exact nature of their contribution to the structure and to the function of the particle is not known. Of the 78 proteins in yeast ribosomes, six have zinc finger motifs of the C2-C2 variety. Both genes encoding the essential yeast ribosomal protein YL37a, which has such a zinc finger motif, were disrupteXXPd. The double deletion, which is lethal, can be rescued with a plasmid-encoded copy of a YL37a gene. Mutations were constructed in a plasmid-encoded copy of YL37a; the mutations caused the cysteine residues in the motif (at positions 39, 42, 57 and 60) to be replaced, one at a time, with serine. The cysteine residue at position 39, the first of the four in the motif, is essential for the function of YL37a, since a C39S mutation did not complement the null phenotype. However, plasmids encoding variants with C42S, C57S, or C60S mutations in the zinc finger motif were able to rescue the null mutant. YL37a binds zinc, but none of the mutant proteins, C39S, C42S, C57S, or C60S, was able to bind the metal. Thus, all four cysteine residues are essential for the binding of zinc; only one, C39, is essential for the function of the ribosomal protein.

Amino Acid Sequence↗

PubMed1999

Correlation between curve severity, somatosensory evoked potentials, and magnetic resonance imaging in adolescent idiopathic scoliosis.

STUDY DESIGN: A prospective study in patients with adolescent idiopathic scoliosis of different clinical severity using whole-spine magnetic resonance imaging and somatosensory evoked potentials. OBJECTIVES: To correlate the presence of magnetic resonance imaging structural abnormalities with somatosensory evoked potential-detected functional disorders in the hind brain and spinal cord and the Cobb's angle in patients with adolescent idiopathic scoliosis and to compare the result with those in healthy matched control subjects. SUMMARY OF BACKGROUND DATA: Many different types of neurologic dysfunction have been reported in scoliosis. With the advent of magnetic resonance imaging, there are increased reports on the association of idiopathic scoliosis and syringomyelia, Chiari I malformation, or tonsillar ectopia. The actual link between structural and functional disorder in idiopathic scoliosis is, however, unclear. METHODS: Posterior tibial nerve evoked potentials and whole-spine magnetic resonance imaging were performed in 36 healthy control subjects, 135 patients with adolescent idiopathic scoliosis with Cobb's angle less than 45 degrees, and 29 patients with Cobb's angle more than 45 degrees. RESULTS: Tonsillar ectopia or syringomyelia, detected by magnetic resonance imaging, or functional disturbance in the somatosensory pathway, detected by somatosensory evoked potentials, was found to be significantly more frequent in the group of patients with severe scoliosis curvature, with an incidence of 31% and 27.6%, respectively. Incidence of tonsillar ectopia was 33.3% in patients with abnormal somatosensory evoked potentials in contrast to the much lower incidence of 2.9% in patients with normal somatosensory evoked potentials. There was a significant structural and functional link. The incidence of syringomyelia in patients with and without tonsillar ectopia was 33.3% and 0.7%, respectively. CONCLUSIONS: In patients with adolescent idiopathic scoliosis with severe curve, the significant association with tonsillar ectopia and abnormal somatosensory function points to a neural origin. Disorders in the somatosensory function may be one of the mechanisms linking tonsillar ectopia to scoliosis. Somatosensory evoked potentials and magnetic resonance imaging may have important diagnostic and predictive value and may help in the management of adolescent idiopathic scoliosis.

Adolescent↗

PubMed1999

Hypoglossal nerve palsy in nasopharyngeal carcinoma.

BACKGROUND: The aim of the study was to use magnetic resonance (MR) imaging to determine the cause of hypoglossal nerve palsy and the sites of injury in patients with nasopharyngeal carcinoma before radiation therapy and during postradiation therapy follow-up. METHODS: The clinical records and MR studies of 21 patients with hypoglossal nerve palsy were retrospectively studied. These 21 patients belonged to a cohort of 387 patients with nasopharyngeal carcinoma (153 with newly diagnosed disease and 234 on postradiation follow-up) who underwent MR imaging in a 2.5-year period. RESULTS: Four patients had hypoglossal nerve palsy at initial diagnosis and all of them had extensive skull base invasion from tumor extending postero-inferiorly to the level of the foramen magnum. The nerve was invaded in the carotid sheath (3), hypoglossal nerve canal (3), and premedullary cistern (1). In 17 patients developing hypoglossal nerve palsy after radiotherapy, only two (12%) had evidence of tumor recurrence. Radiation-induced neuropathy was the probable cause in 14 patients and 1 case was judged indeterminate. MR evidence of fibrosis was demonstrable along the course the nerve in four patients (29%), involving the carotid sheath (4), hypoglossal nerve canal (2), and premedullary cistern (1). No patient had MR evidence of radiation change in the brain stem. Seven patients had a history of a boost dose of radiation to the parapharyngeal region on one or both sides, and nerve palsy occurred on the boosted side in six of them. CONCLUSION: Hypoglossal nerve palsy on presentation was caused by locally advanced nasopharyngeal tumor whereas a palsy arising after radiation therapy was more frequently caused by postradiation damage rather than cancer.

Adenocarcinoma↗

PubMed1999

Proton magnetic resonance spectroscopy of late delayed radiation-induced injury of the brain.

We prospectively evaluated metabolite changes in late delayed radiation-induced injury to the temporal lobes on proton ((1)H) magnetic resonance spectroscopy (MRS) in 34 patients. Morphologically more severe injury on imaging tended to have lower N-acetyl aspartate (NAA)/creatine (Cr) and NAA/choline (Cho) ratios. A significantly higher Cho/Cr ratio was found in the most severe grade of cerebral necrosis, in which lactate might be present. The progressive decrease in NAA with increasing severity reflected neuronal loss at different stages of late delayed radiation-induced brain injury. The absence of Cho elevation in mild and moderate lesions did not suggest demyelination or glial hyperplasia as an etiologic mechanism of late delayed radiation-induced brain injury. The association of severe morphologic lesions with elevated lactate suggests ischemia as the underlying mechanism for severe lesions. (1)H MRS may provide metabolite information conducive to the understanding of the pathophysiology of late radiation-induced brain injury. J. Magn. Reson. Imaging 1999;10:130-137.

Adult↗