Computed tomography in the investigation of dementia

Modern Diagnostic Imaging Technique Applications and Risk Factors in the Medical Field: A Review

Medical imaging is the process of visual representation of different tissues and organs of the human body to monitor the normal and abnormal anatomy and physiology of the body. There are many medical imaging techniques used for this purpose such as X-ray, computed tomography (CT), positron emission tomography (PET), magnetic resonance imaging (MRI), single-photon emission computed tomography (SPECT), digital mammography, and diagnostic sonography. These advanced medical imaging techniques have many applications in the diagnosis of myocardial diseases, cancer of different tissues, neurological disorders, congenital heart disease, abdominal illnesses, complex bone fractures, and other serious medical conditions. There are benefits as well as some risks to every imaging technique. There are some steps for minimizing the radiation exposure risks from imaging techniques. Advance medical imaging modalities such as PET/CT hybrid, three-dimensional ultrasound computed tomography (3D USCT), and simultaneous PET/MRI give high resolution, better reliability, and safety to diagnose, treat, and manage complex patient abnormalities. These techniques ensure the production of new accurate imaging tools with improving resolution, sensitivity, and specificity. In the future, with mounting innovations and advancements in technology systems, the medical diagnostic field will become a field of regular measurement of various complex diseases and will provide healthcare solutions.

The quality of computerised tomography use in two psychogeriatric services

The aim of medical audit is to improve the quality of medical care (Department of Health, 1989). There was concern that patients referred to a psychogeriatric service (Service X) did not have adequate access to computerised tomography. The nearest computerised tomography scanner was located in a neighbouring district and direct referrals were not accepted. Computerised tomography scans could be obtained indirectly by referral to neurosurgeons. Because of these difficulties “potentially treatable structural lesions” (such as cerebral tumours and subdural haematomas) may have been missed. We decided to compare the use of computerised tomography scans with a nearby service (Service Y) which had a computerised tomography scanner on site. Service X had a catchment population of 33,000 aged over 65 and Service Y a catchment population of 23,420 aged over 65.

Computed Tomography in Patients with Dementia Probably Due to Toxic Encephalopathy

Computed tomography (CT) was performed in 181 patients with dementia probably caused by organic solvents. No treatable causes of dementia were revealed. All but one of the patients had dementia symptoms for more than one year. Only three patients had focal neurologic signs. No indication for cranial CT was found in this group of patients, owing to the fact that no treatable causes of dementia were revealed.

The appropriate use of neuroimaging in the diagnostic work-up of dementia: an economic literature review and cost-effectiveness analysis

BACKGROUND

Structural brain imaging is often performed to establish the underlying causes of dementia. However, recommendations differ as to who should receive neuroimaging and whether computed tomography (CT) or magnetic resonance imaging (MRI) should be used.

OBJECTIVES

This study aimed to determine the cost-effectiveness in Ontario of offering structural imaging to all patients with mild to moderate dementia compared with offering it selectively according to guidelines from the Canadian Consensus Conference on the Diagnosis and Treatment of Dementia (CCC). We compared the cost-effectiveness of CT and MRI as first-line strategies.

METHODS

We performed a systematic literature search (2000 to 2013) to identify cost-effectiveness studies of clinical prediction rules and structural imaging modalities. Studies were assessed for quality and applicability to Ontario. We also developed a model to evaluate the cost-effectiveness of clinical guidelines (image all versus according to CCC) and modalities (CT versus MRI). Transition probabilities, utilities, and costs were obtained from published literature or expert opinion. Results were expressed in terms of costs and quality adjusted life years (QALYs).

RESULTS

No relevant cost-effectiveness analyses were identified in the published literature. According to the base-case results of our model, the most effective and cost-effective strategy is to image patients who meet CCC criteria with CT and to follow-up with MRI for suspected cases of space-occupying lesions (SOL). However, the results were sensitive to the specificity of MRI for detecting vascular causes of dementia. At a specificity of 64%, the most cost-effective strategy is CCC followed by MRI.

LIMITATIONS

Studies used to estimate diagnostic accuracy were limited by a lack of a gold standard test for establishing the cause of dementia. The model does not include costs to patients and their families, nor does it account for patient preferences about diagnostic information.

CONCLUSIONS

Given the relative prevalence of vascular dementia and SOLs, and the improvement in QALYs associated with treatment, the strategy with the greatest combined sensitivity (CCC with CT followed by MRI for patients with SOLs) results in the greatest number of QALYs and is the least costly. Due to limitations in the clinical data and challenges in the interpretation of this evidence, the model should be considered a framework for assessing uncertainty in the evidence base rather than providing definitive answers to the research questions.

The appropriate use of neuroimaging in the diagnostic work-up of dementia: an evidence-based analysis

BACKGROUND

Diagnosis of dementia is challenging and requires both ruling out potentially treatable underlying causes and ruling in a diagnosis of dementia subtype to manage patients and suitably plan for the future.

OBJECTIVES

This analysis sought to determine the appropriate use of neuroimaging during the diagnostic work-up of dementia, including indications for neuroimaging and comparative accuracy of alternative technologies.

DATA SOURCES

A literature search was performed using Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid Embase, the Wiley Cochrane Library, and the Centre for Reviews and Dissemination database, for studies published between 2000 and 2013.

REVIEW METHODS

Data on diagnostic accuracy and impact on clinical decision making were abstracted from included studies. Quality of evidence was assessed using GRADE.

RESULTS

The search yielded 5,374 citations and 15 studies were included. Approximately 10% of dementia cases are potentially treatable, though less than 1% reverse partially or fully. Neither prediction rules nor clinical indications reliably select the subset of patients who will likely benefit from neuroimaging. Clinical utility is highest in ambiguous cases or where dementia may be mixed, and lowest for clinically diagnosed Alzheimer disease or clinically excluded vascular dementia. There is a lack of evidence that MRI is superior to CT in detecting a vascular component to dementia. Accuracy of structural imaging is moderate to high for discriminating different types of dementia.

LIMITATIONS

There was significant heterogeneity in estimates of diagnostic accuracy, which often prohibited a statistical summary of findings. The quality of data reported by studies prohibited calculation of likelihood ratios in the present analysis. No studies from primary care were found; thus, generalizability beyond tertiary care settings may be limited.

CONCLUSIONS

A diagnosis of reversible dementia is rare. Imaging has the most clinical utility in cases where there is potentially mixed dementia or ambiguity as to the type of dementia despite prolonged follow-up (e.g., 2 years or more). Both CT and MRI are useful for detecting a vascular component of dementia.

Evaluation of Dementia: The Case for Neuroimaging All Mild to Moderate Cases

Introduction: The aim of this study was to assess the usefulness of 4 clinical prediction rules, the neuroimaging guidelines from the Canadian Consensus Conference on Dementia (CCCAD) and the modified Hachinski’s Ischaemic Score (HIS) in identifying patients with suspected dementia who will benefit from neuroimaging. Materials and Methods: Two hundred and ten consecutive patients were referred to the memory clinic in a geriatric unit for the evaluation of possible dementia. Sensitivity, specificity and likelihood ratios (LR) were calculated for each of the prediction rules and the CCCAD guidelines, in terms of their ability to identify patients with significant lesions [defined firstly as space-occupying lesions (SOL) alone and secondly as SOL or strokes] on neuroimaging. Similar analyses were applied for the HIS in the detection of strokes. Results: When considering SOL alone, sensitivities ranged from 28.6% to 100% and specificities ranged from 21.7% to 88.4%. However, when strokes were included in the definition of significant lesions, sensitivities ranged from 16.2% to 79.0% and specificities ranged from 20.9% to 92.4%. The modified HIS had a similarly poor sensitivity and specificity (43.3% and 78.9% respectively). The LR for the clinical decision tools did not support the use of any particular instrument. Conclusions: Clinical decision tools do not give satisfactory guidance for determining the need for neuroimaging patients with suspected dementia, when the detection of strokes, in addition to SOL, is regarded as important. We recommend therefore that neuroimaging be considered for all patients with suspected mild or moderate dementia in whom the potential benefits of any treatment outweigh the potential risks. Key words: Diagnostic medical imaging, Practice guidelines, Sensitivity and specificity

Prediction rules for computed tomography in the dementia assessment: do they predict clinical utility of CT?

Neuroimaging is widely employed in the dementia assessment in refining clinical decision-making. However, with rising interest in cost-effective medical practice, efforts have been made in the literature to define clinical prediction rules that select for a subgroup of patients who would most likely benefit from neuroimaging. This short study examined the ability of a group of published clinical predictors to identify patients whose diagnoses or management would be influenced by CT scan results. The study finds that none of the published predictors bears a significant relationship to actual influence of CT scans in a group of memory clinic patients, highlighting the need for the development of clinical predictors for neuroimaging that will impact patient care.

Use of computerized tomography by old age psychiatrists: an examination of criteria for investigation of cognitive impairment

OBJECTIVES

To determine the prevalence of the Royal College of Psychiatrists' consensus criteria for the detection of potentially reversible intracranial pathology in a group of patients over 65 years old referred for computerized tomography (CT) head scanning from a specialist old age psychiatry service, to test the association of Royal College audit criteria with the presence of potentially reversible intracranial pathology.

METHODS

A retrospective case-note survey of all patients referred from Psychiatric Services for the Elderly at High Royds Hospital to the Neuro-imaging Suite at Leeds General Infirmary in the period April 1994-March 1996.

RESULTS

The records of 143 patients were examined. One or more guideline items were present in the notes in 97 (67.8%) subjects. Ten cases of potentially reversible intracranial pathology were detected and all were correctly predicted by the Royal College guidelines. All were in patients of 71 years of age or older. The false positive rate for the guidelines was 89%. History duration of less than 1 year was the only guideline found to be associated with the detection of potentially reversible intracranial pathology.

CONCLUSIONS

The Royal College of Psychiatrists' consensus criteria can correctly classify patients with potentially reversible intracranial pathology but lack the specificity to usefully reduce unnecessary CT referral or act as valid audit criteria.

Diagnostic testing and dementia

The prevalence of dementia is expected to increase markedly as our population ages. Although only a minority of cases currently are found to have treatable causes, the personal and financial costs of misdiagnosis are great. Furthermore, progress in developing effective therapy hinges on accurate diagnosis. This article reviews the current state of diagnostic testing in the diagnosis of dementia.

The incidence of primary central nervous system neoplasms before and after computerized tomography availability

The observed incidence of primary intracranial neoplasms has increased dramatically among the elderly over the past several years. It is unclear to what extent this increase can be attributed to improved detection by new imaging technology and what portion might represent a true increase in incidence. The first computerized tomography (CT) scanner was operative in Norway in 1975 and became available in all geographical regions within 4 years. The author analyzed incidence data from the population-based Cancer Registry of Norway, placing particular emphasis on the basis for diagnosis (histological, imaging, or clinical findings) for the registrations. In the decade from 1983 to 1992, when the use of CT was widespread, incidence rates of primary intracranial neoplasms for individuals aged 55 to 74 and above 74 years were, respectively, 1.76 (95% confidence interval (CI), 1.63-1.90) and 3.35 (95% CI, 2.70-4.15) times the rates in 1963 to 1972 before CT was available. For persons older than 74 years, the relative incidence increase was 1.98-fold (95% CI, 1.53-2.56) for histologically verified tumors; 15.20 (95% CI, 7.80-29.61) when based on imaging (without histological evidence); and 3.33 (95% CI, 1.93-5.76) when based on clinical diagnosis (without imaging or histological evidence). In this age group, the increase for gliomas was 1.77 (95% CI, 1.18-2.65) and 2.28 (95% CI, 1.53-3.39) for meningioma patients. The present study demonstrates that new imaging technology has improved the diagnostic yield of primary intracranial neoplasms. For those older than 74 years, a large part of the three-fold incidence increase from the pre-CT decade 1963 to 1972 to the post-CT decade 1983 to 1992 can be attributed to improved tumor detection.

Do surgical brain lesions present as isolated dementia? A population-based study

OBJECTIVE

To determine the incidence of clinically important subdural hematoma (SDH), hydrocephalus not associated with a recent intracranial bleed, and intracranial tumor that is not obviously metastatic, and to test the sensitivity of a promising decision rule for computerized tomography (CT) in dementia.

DESIGN

Population-based, retrospective, sequential case series.

SETTING

Staff model health maintenance organization (HMO).

PATIENTS

Patients aged 65 years and older with one of the three lesions, diagnosed over a 4.5-year period, identified mainly through computerized databases of hospital discharge diagnoses and a registry of malignant tumors.

MEASUREMENTS

Clinical data were based on chart review. The decision rule, based on one that had been previously proposed and tested, stated that CT would be required if any one of 11 clinical criteria were met by a patient with cognitive impairment. Rule sensitivity was evaluated using clinical information recorded before CT.

MAIN RESULTS

One hundred forty-five clinically important lesions were identified among 137,100 person-years at risk. Average annual incidence per 100,000 was 46.7 (95% CI 36.0, 59.6) for SDH, 5.8 (95% CI 2.5, 11.5) for hydrocephalus not associated with a recent intracranial bleed, and 53.2 (95% CI 41.7, 66.9) for intracranial tumors that were not obviously metastatic. Using the 65 to 74- year age strata as a reference, the relative risk for SDH was 4.8 (95% CI 2.7, 8.5) in 75 to 84-year-olds and 13.1 (95% CI 7.7, 22.5) in the 85 and older strata. Among 59 patients who presented with cognitive impairment, without altered sensorium or physical evidence of trauma, decision rule sensitivity was 93.2% (95% CI 83.5%, 98.1%). Sensitivity was 90.7% (95% CI 77.9%, 97.4%) in the subgroup that presented to an ambulatory care clinic rather than to an emergency department.

CONCLUSIONS

These three lesions, which are the most common surgical lesions that may present as dementia, are rare. Most cases have presentations that easily distinguish them from typical Alzheimer's disease. This case series indicates that it may be feasible to develop a decision rule for the selective use of CT in dementia. Disease spectrum will influence measures of decision rule performance such as sensitivity and specificity.

Probabilistic diagnosis of normal pressure hydrocephalus and other treatable cerebral lesions in dementia

Clinical profiles of dementia patients, differing with respect to age, presence of gait abnormalities and urinary incontinence are discussed. Epidemiological data, subjective probabilities and clinical reasoning are used to predict a treatable cerebral lesion, i.e., an intracranial space occupying lesion or normal pressure hydrocephalus (NPH). Our calculations help in distinguishing clinically between demented patients who are, and who are not likely to benefit from computed tomography (CT) investigation for treatable lesions and, eventually, from cerebrospinal fluid shunting for NPH. Utility calculations show that shunting can be recommended only for a patient with the full triad of symptoms of NPH, and CT evidence of NPH, when no other prognostic information is available. Future clinical research should address the long-term prognosis of (treated) NPH patients, and the mortality of shunting, because these two factors are critical to the shunting decision.

The usefulness of CT scanning in diagnosing dementia of the Alzheimer type

In order to determine the usefulness of Computerized Tomography (CT) scanning in making a diagnosis of dementia of the Alzheimer type, a group of patients diagnosed by NINCDS-ADRDA criteria (n = 22) were compared to a group of normal subjects (n = 49) using certain defined linear CT scan measurements. These measurements included specific measurements of the temporal lobes (temporal horns). Subjects were classified correctly 91.5% of the time with a high degree of probability. A diagnostic equation is presented which will allow testing of these methods in a prospective fashion.

Evaluation of 110 consecutive patients with dementias: a prospective study

We prospectively investigated 131 consecutive cases (both in- and outpatients) of suspected dementia to evaluate the relative frequency of different types of dementia in Chinese patients. Dementia was confirmed in 110 cases (84.0%). In contrast to the Western series, vascular dementia (39.1%) was slightly more frequent than the Alzheimer's disease (36.4%). Twelve cases (10.9%) of potentially treatable dementia were found. Careful clinical observation was the most useful part of the evaluation. CT scan of brain was the most useful laboratory test.

Multi-infarct dementia: a computed tomographic study

CT Scan of 30 patients with multi-infarct dementia (MID) were compared with age- and sex-matched controls. Infarcts were seen in 93% of MID cases and 10% of controls. A marked difference in the occurrence of white matter low attenuation was seen between the groups. All the parameters of cerebral atrophy studied showed a statistically significant correlation with the presence of dementia.

Neoplasms of the central nervous system in Norway. II. Descriptive epidemiology of intracranial neoplasms 1955-1984

A population-based study of 8480 patients - 4508 (53%) males and 3972 females - with primary intracranial neoplasms reported to the Norwegian Cancer Registry during the period 1955-84, is presented. 81% of the cases were histologically verified. The peak age-specific incidence rate in the total series occurred in the age-group 55-64 years. Gliomas constituted the largest histological group with an age-adjusted incidence rate of 5.0 cases per 100,000 population per year for males and 3.5 for females. Case ascertainment of primary intracranial neoplasms is reduced above the age of 60 in Norway, mostly due to a a low autopsy rate. The major impact of the introduction of computer tomography (CT) in the case ascertainment of intracranial neoplasms has been a raised incidence, in patients over the age of 60, of neoplasms which are not histologically verified.

Assessing dementia. Part I: Difficulties, definitions and differential diagnosis

Despite the pressures of an increasingly ageing population and an ever increasing scientific knowledge, the clinical characteristics of dementia remain poorly defined. This relative lack of clarity in clinical understanding has led to diverse diagnostic problems, including those of mistaken diagnosis as well as over- and under-diagnosis in different settings. This paper focuses on the syndromal and aetiological diagnosis of dementia by outlining current clinical definitions, considering differential diagnosis in detail and reviewing characteristics of common dementing disorders. The past emphasis on a search for treatable causes, the reliance on laboratory investigations and the concept of subcortical dementia are all questioned. Aspects of evaluation that are stressed include the value of brief objective cognitive testing, a knowledge of normal age-related cognitive changes, flexible criteria for Alzheimer's disease and a comprehensive individualised evaluation of the person. Broader assessment issues will be dealt with in a second paper.

CT in the differential diagnosis between Alzheimer's disease and vascular dementia

A prospective series of consecutively admitted patients with Alzheimer's disease (AD) (n = 68), multi-infarct dementia (MID) (n = 79) and probable vascular dementia (PVD) (n = 46) were studied by CT of the head. In MID 88.6% and in PVD 41.3% of the patients had at least one brain infarct on CT, but only one patient (1.5%) with AD. White matter low attenuation (WMLA) also differentiated MID and PVD from AD, especially among patients aged 75 years or less, and with mild or moderate dementia. In all types, brain atrophy on CT had a positive correlation with the degree of dementia. Infarcts and WMLA on CT, but not brain atrophy seem to be of differential diagnostic value between vascular and degenerative dementia.

Moyamoya disease: an unusual cause of cerebral infarction

A South African Bantu patient presenting with recurrent strokes and a change in personality was found to have cerebral infarction due to moyamoya disease. The disease has a characteristic radiological pattern of narrowing or occlusion of the distal internal carotid arteries associated with a profuse vascular network at the base of the brain and in the basal ganglia: the moyamoya vessels. The clinical features and the collateral vascular pathways that may develop after cerebral vascular occlusion are discussed and the surgical options for increasing cerebral blood flow described. In this patient a development of the technique in which the superficial temporal artery is laid onto the brain without interruption of the donor vessel was used, with improvement in the clinical picture.

Antemortem laboratory diagnosis of Alzheimer's disease

The accuracy of diagnosis for AD by conventional clinical and laboratory means is in the order of 80%. Neurophysiological techniques (EEG, evoked potentials) show abnormalities in AD that could prove to be useful for diagnosis after pharmacological challenges. CSF analysis show a reduction of the concentration of various neuropeptides, reduction shared by other types of dementias. Among the existing imaging techniques PET using 18F-fluorodeoxyglucose is the most diagnostic in AD because of the early and often asymmetrical decrease in parietotemporal metabolic activity. Cortical biopsy with histological and biochemical analysis can provide an accurate in vivo diagnosis of AD.

Value of CT scanning in outpatients: preliminary report on a controlled study

A series of 100 consecutive new outpatients attending the neuroradiology service for a cranial CT scan between 1 October and 24 December 1984 were analyzed. On the day of the investigation each patient was examined by a neurologist, who gave his opinion on the value of a CT scan. The neurologist's ratings were then compared with the CT reports. More than 2/3 of the requests for CT were useless and could have been avoided by thorough clinical evaluation of the patients and full awareness of what CT scanning can contribute to diagnosis and treatment.

Sudden deaths in the mentally handicapped

Trends in the incidence and causes of sudden deaths in a hospital group for the mentally handicapped were identified during a 50-year period, and the two halves of the period were compared. There were significantly more deaths in the second 25-year period than in the first. Longevity was greater during the second period, and a decrease in deaths due to status epilepticus was outweighed by an increase in deaths from arterial degenerative disease in the larger number of older patients. In the second period there was also a significant rise in sudden deaths due to asphyxia, probably attributable to modern medication with side-effects giving rise to feeding difficulties.

Risks of intracranial haematoma in head injured adults

A study was conducted to estimate the risk that an adult (age 15 or over) will develop a surgically significant intracranial haematoma after a head injury. Two simple features were used that can be recognised by clinicians with minimal training: a skull fracture and the conscious level. The risks were calculated from samples of 545 patients with haematomas, 2773 head injured patients in accident and emergency departments, and 2783 head injured patients in primary surgical wards. With radiological evidence of skull fracture and any impairment of consciousness (including disorientation) one patient in four in an accident and emergency department or primary surgical ward will develop a haematoma. With no skull fracture and preserved orientation the risk to a patient in an accident and emergency department is one in 6000. The use of risk levels as a basis for decision making about head injured patients may result in fewer haematomas being detected too late and savings of resources by reducing the admission and investigation of low risk categories of patients.