Lesson of the week: Playing the odds in clinical decision making: lessons from berry aneurysms undetected by magnetic resonance angiography

Pharmacogenetics in clinical practice: considerations for testing

Pharmacogenetics is a rapidly evolving field that will undoubtedly lead to the development of pharmacogenetic tests. Such tests will need to be assimilated into healthcare systems, but represent a further call on scarce healthcare resources. Therefore, in order for a pharmacogenetic test to fulfill its potential beyond the laboratory and into the clinical environment, it must prove itself on a wide range of multifaceted criteria. The test must have proven and reproducible analytical and clinical validity, and stand up to critical appraisal of clinical utility and cost-effectiveness. Pharmacogenetic testing can be considered to be a form of screening, and the experience that has been gained to date in evaluating other forms of screening tests may prove beneficial in evaluating pharmacogenetic technology. It is essential that the goals of pharmacogenetic testing are defined as early as possible to ensure that appropriate studies can be designed to provide the evidence base, and thereby enable appropriate evaluation of the technology by clinicians and healthcare administrators for incorporation into clinical practice. This review focuses on issues that will need to be considered in the scientific assessment of pharmacogenetic testing.

Pitfalls in the management of headache in the emergency department

Headache is the fifth most common primary complaint of patients presenting to an emergency department (ED) in the United States. The emergency physician (EP) plays a unique role in the management of these patients, one that differs from that of the primary care physician, the neurologist, and other specialists. Diagnostic nomenclature used in the ED is necessarily less specific, as care is more appropriately focused on the relief of symptoms and the identification of life-threatening causes. By seeking a limited number of specific critical features on history and physical examination, the EP can minimize the risk of overlooking one of these dangerous causes of headache. When certain features are present, empirical therapies and diagnostic testing should be initiated in the ED. The most frequently encountered pitfalls in the management of patients with headache in emergency medicine practice, and those with the greatest likelihood to adversely affect patient outcomes, are discussed.

Imaging of intracranial aneurysms causing isolated third cranial nerve palsy

Isolated third cranial nerve palsies may be caused by compressive intracranial aneurysms located at the junction of the internal carotid and posterior communicating arteries or, less commonly, at the apex of the basilar artery or its junction with the superior cerebellar or posterior cerebral arteries. Such aneurysms typically measure at least 4 mm in diameter. Technical improvements in noninvasive techniques, including CT and MRA, have yielded a detection rate of such aneurysms that approaches that of catheter cerebral angiography (CCA), which itself carries a small but serious risk. Multidetector technology, which allows a rapid scan time, has promoted CT to the first choice for investigating aneurysms in this setting except when dye or radiation exposure is unacceptable, as with pregnant women, children, and those with renal or severe cardiac disease. Major impediments to accurate detection are a lack of availability of trained technicians, who must perform manipulation of the raw imaging data ("post-processing"), and a paucity of certified neuroradiologists with the time, skill, and experience to devote to interpreting difficult cases. To avoid diagnostic mishaps, noninvasive studies should be reviewed by at least one neuroradiologist before aneurysm is rejected as the cause or before the patient undergoes CCA.

Computed tomography angiography for the detection and characterization of intra-cranial aneurysms: Current status

Multidetector computed tomography angiography (MD-CTA) of the intra-cranial vessels is now a routine examination, and is becoming fully integrated into the imaging and treatment algorithm of patients presenting with acute subarachnoid haemorrhage in many centres in the UK and Europe. The development and current status of CTA for cerebral aneurysms, and the strengths and limitations of this technique are herein reviewed.

Clinical experience did not reduce the variance in physicians' estimates of pretest probability in a cross-sectional survey

BACKGROUND AND OBJECTIVES

In light of the increasing popularity of the threshold approach in clinical decision-making, this study assesses the role of expertise in physicians' agreement in estimating the probability of disease in patients.

METHODS

A cross-sectional survey of physicians of different specialties, attending weekly staff meetings in four teaching hospitals in Jerusalem, Israel. An anonymous questionnaire describing three case scenarios of patients with chest pain was administered and participants were asked to estimate pretest probabilities of disease.

RESULTS

Eighty-six physicians (practicing cardiology, internal medicine, and family medicine, as well as general practitioners and internists) out of 125 approached (response rate 69%). The mean estimated probabilities were very similar for residents and specialists; however, the standard deviation was higher for specialists in all three cases: 20.7, 21.0, and 19.1 among specialists and 16.4, 20.5, and 14.9 among residents, respectively.

CONCLUSION

This study, based on case scenarios, did not find that medical expertise improved agreement among doctors when estimating the probability of disease in patients-despite the common belief that senior physicians should have smaller interobserver differences in probability estimates. The wide variation observed calls into question the applicability of the threshold approach.

Radiological error: analysis, standard setting, targeted instruction and teamworking

Diagnostic radiology does not have objective benchmarks for acceptable levels of missed diagnoses. Until now, data collection of radiological discrepancies has been very time consuming. The culture within the specialty did not encourage it. However, public concern about patient safety is increasing. There have been recent innovations in compiling radiological interpretive discrepancy rates which may facilitate radiological standard setting. However standard setting alone will not optimise radiologists' performance or patient safety. We must use these new techniques in radiological discrepancy detection to stimulate greater knowledge sharing, targeted instruction and teamworking among radiologists. Not all radiological discrepancies are errors. Radiological discrepancy programmes must not be abused as an instrument for discrediting individual radiologists. Discrepancy rates must not be distorted as a weapon in turf battles. Radiological errors may be due to many causes and are often multifactorial. A systems approach to radiological error is required. Meaningful analysis of radiological discrepancies and errors is challenging. Valid standard setting will take time. Meanwhile, we need to develop top-up training, mentoring and rehabilitation programmes.

Radiological error: analysis, standard setting, targeted instruction and teamworking

Diagnostic radiology does not have objective benchmarks for acceptable levels of missed diagnoses. Until now, data collection of radiological discrepancies has been very time consuming. The culture within the specialty did not encourage it. However, public concern about patient safety is increasing. There have been recent innovations in compiling radiological interpretive discrepancy rates which may facilitate radiological standard setting. However standard setting alone will not optimise radiologists' performance or patient safety. We must use these new techniques in radiological discrepancy detection to stimulate greater knowledge sharing, targeted instruction and teamworking among radiologists. Not all radiological discrepancies are errors. Radiological discrepancy programmes must not be abused as an instrument for discrediting individual radiologists. Discrepancy rates must not be distorted as a weapon in turf battles. Radiological errors may be due to many causes and are often multifactorial. A systems approach to radiological error is required. Meaningful analysis of radiological discrepancies and errors is challenging. Valid standard setting will take time. Meanwhile, we need to develop top-up training, mentoring and rehabilitation programmes.

Distal anterior inferior cerebellar artery aneurysm occult on magnetic resonance angiography one month prior to rupture--case report

A 77-year-old man suffered subarachnoid hemorrhage due to a ruptured aneurysm of the distal anterior inferior cerebellar artery (AICA). He had a history of hearing disturbance in the left ear for more than 3 years. Computed tomography on three separate occasions had found no abnormalities. One month before the hemorrhage, he came to our outpatient service complaining of vertigo. Magnetic resonance (MR) imaging and MR angiography detected no abnormality. Conventional angiography demonstrated an aneurysm of 8 mm diameter in the distal AICA region after the hemorrhage. Filling and wash out of the aneurysm sac by contrast medium was markedly delayed, which suggested that MR imaging had failed to detect the flow void because of the slow blood flow in the dome. The aneurysm was clipped successfully. He was discharged with mild dysarthria on the 33rd postoperative day. MR angiography has limitations in detecting unruptured aneurysms and there is certainly a high risk group of false negatives, including aneurysms located in the distal region of the main trunk.

About time: diagnostic guidelines that help clinicians

Clinical guidelines often make recommendations on the use of diagnostic tests. Compared with sensitivity and specificity, the use of pre- and post-test probabilities allows a more explicit and rational selection and interpretation of diagnostic tests. Ideally, clinical guidelines relating to diagnosis should routinely incorporate this information to enhance individualised decision making. We report our experience of incorporating pre- and post-test probabilities into a guideline on the investigation of women with postmenopausal bleeding developed by the Scottish Intercollegiate Guidelines Network. Issues relating to their application are highlighted, including the limitations of available evidence on diagnostic tests and prevalence of disease, acceptability to guideline users, and the uncertain impact on actual clinical decision making. Despite these potential difficulties, the incorporation of data on pre- and post-test probabilities into the development and presentation of guideline recommendations may offer an important opportunity to make clinical decision making more transparent for both clinicians and patients.

Comparison of MR angiography and conventional angiography in the investigation of intracranial arteriovenous malformations and aneurysms in children

BACKGROUND

Magnetic resonance angiography (MRA) is an attractive alternative to conventional catheter angiography (CCA) in children, especially for the detection of intracranial arteriovenous malformations (AVMs) or aneurysms in the out-of-hours setting, because it has fewer risks and complications. OBJECTIVE. To compare MRA with CCA for the detection of intracranial AVMs, aneurysms and arterial anatomy in children.

MATERIALS AND METHODS

Retrospective blinded review of MRAs and CCAs by two independent paediatric radiologists, in a group of 19 children already diagnosed with AVMs, aneurysms and subarachnoid haemorrhage (SAH) and who had undergone both imaging techniques.

RESULTS

Abnormalities were identified on MRA in 15 of 19 patients and by CCA in 11 of 19 patients. MRA showed one aneurysm, nine AVMs, three haemorrhages and two indeterminate lesions. CCA showed nine AVMs and two indeterminate lesions. The two modalities showed excellent correlation in the detection of AVMs in nine patients. Vascular supply to the AVMs correlated well in four cases. There was complete disagreement in the determination of vessel supply in one case, and in two cases CCA showed additional vessel supply compared to MRA, while in two further cases MRA showed an additional vessel supply compared to CCA. CCA was superior to MRA in demonstrating arterial anatomy, except with regard to the anterior and posterior communicating arteries where MRA was superior.

CONCLUSIONS

The high sensitivity of MRA in the detection of AVMs when compared to CCA and the low incidence of aneurysms support the use of MRA as the initial imaging modality when intracranial haemorrhage is diagnosed on CT, especially in the out-of-hours setting.

Diagnosis of subarachnoid hemorrhage in the emergency department

To decide which patients with headache ought to be evaluated for SAH, physicians should focus on specific elements of the patient history, such as onset, severity, and quality of the headache and associated symptoms. These questions should be asked and the responses documented for every patient with a headache. The physical examination should be compulsive with regard to vital signs, HEENT. and neurologic signs. Then, the physician should form an explicit differential diagnosis and have reasons for diagnosing migraine, tension, or sinus headache and other benign causes. If there is no clear-cut alternative hypothesis, the patient should be evaluated by CT and LP (if the CT is negative, equivocal, or technically inadequate). Physicians should understand the limitations of this diagnostic algorithm. In addition, the CSF should be carefully analyzed, including measuring the opening pressure. In patients whose CT scans and CSF analyses are normal, further testing is rarely indicated.