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C S Ng

Publications and source records attributed to C S Ng.

At least 19 recordsLinked to original sources
PubMed2006

Minimal preparation CT for the diagnosis of suspected colorectal cancer in the frail and elderly patient.

Colorectal cancer is a common malignancy with an increased incidence in the elderly population. Traditional methods of evaluating this disease have included double contrast barium enema and colonoscopy. Unfortunately, in the frail and elderly patient, these investigations can be difficult to perform and are often not tolerated. Minimal preparation computed tomography (MPCT) of the colon has been suggested as an alternative in this patient population. In this technique, no bowel preparation is used apart from the administration of oral contrast medium. The patient is imaged only in the supine position, without per rectal insufflation of gas or barium. This article reviews the experience to date of MPCT in detecting colonic tumours, and compares its efficacy to the traditional methods. A meta-analysis of the studies allowed estimation of the pooled sensitivity of MPCT to be 83% (95% confidence interval: 76-89%), and pooled specificity to be 90% (95% CI: 85-94%). An added advantage of MPCT is the ability to identify extra-colonic pathology, and this aspect is also reviewed. In addition, the common radiological features and pitfalls in identifying colonic tumours by MPCT are discussed.

Aged↗
PubMed2006

Towards comprehensive population-based screening for diabetic retinopathy: operation of the North Wales diabetic retinopathy screening programme using a central patient register and various screening methods.

OBJECTIVES: To examine whether population-based retinopathy screening using a central diabetes register and employing various screening methods can achieve a high degree of population coverage to meet National Screening Committee (NSC) targets. To identify the main barriers to achieving comprehensive population coverage. To analyse referrals to ophthalmology and their outcome as a measure of previously unmet need. To assess the influence of modality of screening. SETTING: Three local health board areas in North Wales. METHODS: Establishment of a district diabetes register to hold records of all patients and subserve call-recall of general practitioner (GP) sole-care patients for screening by optometrists or digital photography. Hospital attenders were screened in diabetic clinic by direct ophthalmoscopy. Data were collected for years 1 and 2 of operation of the scheme. RESULTS: The system held a screening record for 86% of diabetic patients after year 1 and 93% after year 2. Failure to attend was the major barrier to comprehensive population screening, but this improved in year 2 (P<0.001). Both optometrists and photography identified substantial unmet need: 1% of all GP sole-care patients required immediate laser treatment. Photography was more sensitive than optometrist screening, but the additional retinopathy identified was mostly minor not requiring treatment. CONCLUSIONS: Lack of screening is much more important than modality of screening as a cause of missed sight-threatening retinopathy. A central, district-based patient register system identifies those patients not screened for further follow-up and can produce a high level of population coverage, close to NSC targets. Such schemes are needed, particularly to support primary care diabetes management.

Diabetic Retinopathy↗
PubMed2005

Bernstein-Greene-Kruskal modes in a three-dimensional plasma.

Bernstein-Greene-Kruskal modes in a three-dimensional (3D) unmagnetized plasma are constructed. It is shown that 3D solutions that depend only on energy do not exist. However, 3D solutions that depend on energy and additional constants of motion (such as angular momentum) do exist. Exact analytical as well as numerical solutions are constructed assuming spherical symmetry, and their properties are contrasted with those of 1D solutions. Possible extensions to solutions with cylindrical symmetry with or without a finite magnetic guide field are discussed.

Journal Article↗
PubMed2005

Instability of clonality in gastric lymphoid infiltrates: a study with emphasis on serial biopsies.

The evolution of low-grade B-cell mucosa-associated lymphoid-tissue (MALT) lymphoma of the stomach is a multistage process, reflected in the histologic continuum from Helicobacter pylori-chronic gastritis, to low-grade and high-grade lymphoma. Interestingly, in daily gastric biopsy sign-out, the authors observed that some biopsies showed monoclonality on polymerase chain reaction (PCR) even though there were no definite histologic features of malignancy and vice versa. To address the question, the authors studied the endoscopic gastric biopsies at first presentation of 46 patients to examine any clonality differences among various histologic patterns within the spectrum of MALT lymphoma evolution. The gastric biopsies were reviewed histologically and graded according to the Wotherspoon-Isaacson histologic scoring system from grade 0 (normal) to grade 5 (MALT lymphoma). The clonality of cases in each grade was determined by performing nested PCR for immunoglobulin heavy chain (IgH) gene rearrangement using FR2/JH and FR3/JH primer sets. The monoclonality rates among different grades were as follows: grade 2, 6.3% (1 of 16); grade 3, 27.3% (3 of 11); grade 4, 83.3% (5 of 6); grade 5, 69.2% (9 of 13). Statistically significant difference of monoclonality rate is demonstrated in histologic grade 4 versus grades 2 and 3, and grade 5 versus grade 2 (P < 0.05, Fisher exact test). The authors went on to examine the progress of disease by following up the clinical status, histologic changes, and clonality fluctuation of these cases. Four of the 8 patients with monoclonality on PCR, but no definite lymphoma at first presentation later progressed to frank MALT lymphoma. Our study shows that, during the progression to MALT lymphoma, there is an instability of clonality. Clonality can fluctuate between polyclonality, oligoclonality, and monoclonality, none of which defines an irreversible stage for progression to MALT lymphoma. Monoclonality is a risk factor for development of MALT lymphoma. Those cases with dense gastric mucosal lymphoid infiltrate (without definite MALT lymphoma) and monoclonality on PCR need to be closely monitored and Helicobacter infection promptly treated if present. In combination with clinicohistologic examination, PCR can serve as a complementary tool in arriving at a definite diagnosis of MALT lymphoma in cases with borderline histologic features.

Adult↗
PubMed2004

Complete spectrum of kinetic eigenmodes for plasma oscillations in a weakly collisional plasma.

Kinetic eigenmodes of plasma oscillations in a weakly collisional plasma, described by a collision operator of the Fokker-Planck type, are obtained in closed form for initial-value as well as for boundary-value problems. These eigenmodes, which are smooth and compose a complete discrete spectrum, play the same role for weakly collisional plasmas as the Case-Van Kampen modes do for collisionless plasmas.

Journal Article↗
PubMed2004

Extracolonic findings in patients undergoing abdomino-pelvic CT for suspected colorectal carcinoma in the frail and disabled patient.

AIM: The aims of this study were to evaluate the extracolonic findings identified in patients undergoing minimal preparation abdomino-pelvic CT in place of barium enema or colonoscopy for the detection of possible colorectal carcinoma. MATERIALS AND METHODS: The CT technique involved helical acquisition (10 mm collimation, 1.5 pitch) following 2 days of preparation with oral contrast medium only. Extracolonic findings were evaluated in the light of subsequent follow-up and accuracy. The evaluation included assessment of the potential contribution of the extracolonic finding(s) to staging the cancer in the subset of patients who had colorectal carcinoma, and to account for the patients' presenting symptoms and signs in the remaining patients. RESULTS: A total of 344 extracolonic findings were detected in 261 CT examinations, from amongst a total of 1077 cases (24%). Extracolonic findings were potentially important in staging in 32 of the 98 (33%) cases subsequently found to have colorectal cancer. There were 284 extracolonic findings amongst the 221 cases who proved not have colorectal cancer. One hundred and twenty-four (44%) of these 284 findings were actively followed up by clinicians, and 33 (12%) ultimately had a surgical intervention. Fifty-six percent (160/284) of the findings were determined to be correct (by further investigation, autopsy, and/or clinical follow-up); the remainder were incorrect or indeterminate (n = 56) or had no follow-up (n = 68). The commonest extracolonic findings were focal liver lesions (found in 42/1077, 4%) and abdominal aortic aneurysms (31/1077, 3%). Twenty-four (24/1077, 2%) previously unknown extracolonic malignancies were detected. Ten percent (106/1077) of the patients had extracolonic findings that could potentially have accounted for their presenting symptoms. CONCLUSIONS: CT has the added benefit, compared with colonoscopy and barium enema, of not just evaluating the colon but also of detecting extracolonic abnormalities. Such findings may be useful in staging the cancer, may explain the patient's presenting symptoms, and may detect other potentially serious disorders.

Aged↗
PubMed2003

Unusual causes of colonic wall thickening on computed tomography.

Computed tomography (CT) appearances in "colitis" are often non-specific, and include mural thickening and mesenteric fat stranding. In the western world, the majority of cases will have, or be subsequently diagnosed with, inflammatory bowel disease, pseudomembranous colitis or ischaemic colitis. However, other rare conditions may also produce these rather non-specific signs. We present a number of cases demonstrating colonic wall thickening on CT due to rarer diagnoses, which are correlated with the histopathological features. Some of these CT appearances have not been described previously in the literature.

Adult↗
PubMed2003

Ringworm causing childhood preseptal cellulitis.

A 4-year-old girl had redness and swelling of the left upper eyelid of 1 week's duration. She had been treated with topical fusidic add and oral flucloxacillin without resolution. Ophthalmic examination showed a diffuse, erythematous, tender lesion affecting the entire upper eyelid. There was a central area of skin ulceration with marked bleeding and discharge. Also found were small vesicles under the left eyebrow. The child's mother had noticed a scaly rash on her own forearm. Examination under anesthesia was carried out to assess the globe and to obtain samples for microbiology investigation. Microbiology scrapings showed fungal hyphae of the Dermatophyte group. Treatment with Griseofulvin was commenced, and complete resolution of the lesion occurred. To our knowledge there is only one similar case reported in the literature describing ring-worm as a cause of preseptal cellulitis. This case highlights the importance of considering alternative diagnoses when standard antibiotic treatment has failed.

Antifungal Agents↗
PubMed2002

The impact of helical computed tomography on the diagnosis of unsuspected inflammatory bowel disease in the large bowel.

Inflammatory bowel diseases (IBD) are diagnoses that can be easily overlooked clinically. The aim of this study was to investigate if CT is able to make a contribution to the identification of previously unsuspected cases of IBD. We retrospectively identified cases in which the possibility of an IBD was raised in CT reports (over a 4-year period), by utilising a keyword search of the radiology database. Cases with a previously known or suspected IBD were rigorously excluded by review of case notes, and endoscopic, radiological, histological and microbiological findings. The CT images of the identified cases were reviewed by a blinded observer to document the extent of bowel wall thickening, the location of lesion(s), and presence of peri-colic fat abnormality, ascites and/or collections. The observer also attempted to corroborate the presence, and to identify the type, of IBD based on the CT appearances alone. Thirty-five cases (out of approximately 19,000 body CTs performed) of clinically unsuspected IBD were identified, of which 27 underwent further investigation. An IBD was confirmed in 48% (13 of 27): Crohn's disease (n=6), ulcerative colitis (n=2), pseudomembranous colitis (n=3) and other (n=2), of which 70% (9 of 13) were correctly typed by the reviewer. Inflammatory bowel disease was not substantiated in the remainder (14 of 27), although 7 of these had other bowel pathologies: diverticular disease (n=4); and carcinoma (n=3). Prospectively determining the presence, and furthermore type, of IBD on CT is challenging largely because of the considerable overlap in the appearances of the individual IBDs and indeed of normality. Nevertheless, CT is able to identify clinically unsuspected cases and radiologists should be alert to this treatable and not infrequently elusive diagnosis.

Adult↗
PubMed2002

Evaluation of CT in identifying colorectal carcinoma in the frail and disabled patient.

Frail and physically or mentally disabled patients frequently have difficulty in tolerating formal colonic investigations. The aims of this study were to evaluate the accuracy of minimal-preparation CT in identifying colorectal carcinoma in this population and to determine the clinical indications and radiological signs with the highest yield for tumour. The CT technique involved helical acquisition (10-mm collimation, 1.5 pitch) following 2 days of preparation with oral contrast medium only. The outcome of 4 years of experience was retrospectively reviewed. The gold standards were pathological and cancer registration records, together with colonoscopy and barium enema when undertaken, with a minimum of 15 months follow-up. One thousand seventy-seven CT studies in 1031 patients (median age 80 years) were evaluated. CT correctly identified 83 of the 98 colorectal carcinomas in this group but missed 15 cases; sensitivity and specificity (with 95% confidence interval) 85% (78-92%) and 91% (90-93%), respectively. Multivariate analysis identified: (a) a palpable abdominal mass and anaemia to be the strongest clinical indications, particularly in combination (p<0.0025); and (b) lesion width and blurring of the serosal margin of lesions to be associated with tumours (p<0.0001). Computed tomography has a valuable role in the investigation of frail and otherwise disabled patients with symptoms suspicious for a colonic neoplasm. Although interpretation can be difficult, the technique is able to exclude malignancy with good accuracy.

Aged↗
PubMed2002

Caecal carcinomas in the elderly: useful signs in minimal preparation CT.

OBJECTIVE: Frail, elderly and immobile patients frequently have difficulty in tolerating formal colonic investigations. Caecal tumours may account for up to 35% of colonic tumours. Barium enema and colonoscopy have limitations in assessing this region. The aims of this study were to evaluate the accuracy of a minimal preparation CT technique (merely with prolonged oral contrast medium) in identifying caecal carcinomas and to determine helpful radiological signs. MATERIALS AND METHODS: The CT technique involved helical acquisition following 2 days of preparation with oral contrast medium. The outcome of 4 years' experience (1995-1998) was reviewed. The gold-standards were pathological and cancer registration records, together with colonoscopy and barium enema where available, with a minimum of 15 months' follow-up. RESULTS: CT correctly identified 27 of 30 caecal carcinomas, and missed three, in a total of 1077 CT studies in 1031 patients (median age 80 years). There were also 21 false-positive cases in which CT incorrectly raised the possibility of a caecal tumour. The sensitivity, specificity, negative predictive value (NPV) and positive predictive value (PPV) were 90%, 98%, 99% and 56%, respectively. Serosal margin blurring, tumour length, presence of abnormal peri-colic fat and terminal ileal wall thickening were identified as useful radiological signs. CONCLUSIONS: Minimal preparation CT is able to identify caecal carcinomas with fair accuracy. Such evaluation may become important given the increasing population age and evidence of a 'proximal shift' in the site of colonic tumours in the elderly.

Aged↗
PubMed2002

Histopathological correlates of abnormal pericolic fat on CT in the assessment of colorectal carcinoma.

The aim of this study was to assess the pathological significance of abnormal pericolic fat shown by CT in the context of colorectal carcinoma. CT and histopathological findings of 63 resected colorectal carcinomas were retrospectively reviewed. CT examinations were assessed by two observers for the presence or absence of abnormal pericolic fat (typically linear or nodular opacities) at tumour sites. Specimens were reviewed histopathologically for depth of tumour invasion, extramuscular tissue reaction, and number and largest size of tumour-involved and tumour-free lymph nodes. The sensitivity, specificity, positive predictive value and negative predictive value of pericolic fat in identifying extension of tumour infiltration beyond the muscle coat were 79% (42/53), 33% (2/6), 91% (42/46) and 15% (2/13), respectively. Despite these indicators of efficacy, the association between the presence of pericolic fat abnormality on CT and extramuscular extension of tumour (infiltration and/or nodal disease) or tissue reaction alone or in combination did not reach statistical significance (p>0.3 in all cases). Abnormal ("misty" or "mucky") pericolic fat in the assessment of colorectal cancer on CT is not a precise indicator of extramuscular extension of tumour, as it cannot clearly distinguish between tumour infiltration and tissue reaction beyond the muscle coat, or pericolic nodal involvement. However, it is a very helpful CT sign that may draw attention to the presence and site of a potential colonic abnormality.

Adipose Tissue↗
PubMed2002

Appendicitis: spectrum of appearances on helical CT.

Acute appendicitis has extremely varied clinical presentations. A delayed or missed diagnosis may result in severe adverse consequences. Helical CT is evolving as an important diagnostic aid, but the CT signs can be varied and can easily be overlooked by the unwary. This pictorial review illustrates the spectrum of radiological signs and appearances of appendicitis on helical CT.

Acute Disease↗
PubMed2001

Unusual 1/r-dependent radiation intensity in any biaxial crystal.

Lighthill's prediction of an unusual 1/r-dependent radiation intensity from a small monochromatic source is found to exist in any homogeneous and lossless biaxial crystal along the two optical ray axes, where r is the radial distance from the source. This is a consequence of the special shape of the wave-vector surface on which there is, around each singular point of self-intersection (or "dimple"), a circular locus of points all having the same surface normal direction and thus sharing a common tangent plane. A heuristic derivation of the result is given and a simple optical experiment is proposed to detect such an unusual distance dependence.

Journal Article↗