The Neuroradiology Journal

Whereas CT imaging techniques such as multiple detector spiral imaging with multi-planar reconstructions are desirable in the evaluation of congenital and developmental anomalies of the midface and skull base, there is an essential role for MRI whenever there are related intracranial anomalies. This presentation will focus on describing and classifying the known craniofacial anomalies that have common manifestations in the sinonasal regions, the orbits, and the skull base. Diagrams and clinical cases are utilized to demonstrate the key embryological events leading to the common dysplasias of the craniofacial and sinonasal regions.

Cardiac-gated Phase Contrast MR (PC MR) is used in the evaluation of the Chiari I malformation to assess the CSF flow though the foramen magnum. Images may show reduced CSF flow posterior to the spinal cord in patients with a Chiari I malformation. MR images however do not differentiate with sufficient accuracy between symptomatic and asymptomatic Chiari I malformations. In the presence of the Chiari I malformation, CSF velocities are elevated. Measuring the velocity of flow and determining the degree of inhomogeneity in CSF flow aid in the detection of clinically significant flow abnormalities.

Dementia is an increasingly frequent clinical syndrome that is characterised by deficits in multiple cognitive domains, changes in behaviour and functional deterioration. Alzheimer's disease, together with vascular dementia, account for 2/3 of all cases of dementia. Other less frequent causes of dementia include dementia with Lewy bodies and frontotemporal dementia. This paper reviews the clinical, pathophysiological and neuroimaging aspects of these four prevalent causes of dementia.

Dementia is an impairment of mental ability representing a decline from that level previously reached by the individual. It is usually of insidious onset, associated with neurologic changes, and results in the inability to appropriately interact with one's environment. Dementias may be static, progressive, or reversible, and have many etiologies. One percent of the population above age 40 suffers from dementia and this figure rises to 7% above age 80 and 50% above age 90. Forty-five percent of dementias are due to Alzheimer disease (AD) followed closely by vascular dementia. A stage along the way to dementia is mild cognitive impairment (MCI). There are various definitions but the simplest ones refer to a person who has some memory problems but can continue to live independently. A more specific description refers to deficits in two or more areas of cognition >1.5 SD below mean for the individuals age and education. Although previously considered a part of normal aging, a recent study has shown MCI to be a precursor of Alzheimer disease¹. In a cohort of nuns and priests studied annually until they developed MCI or dementia and died. 180 brains in this study have already been autopsied (37 MCI, 60 with no impairment, 53 with dementia). Pathologists measured theamount of AD pathology and cerebral infarcts. Of 37 with MCI, more than half had AD by pathology, 1/3 had infarcts (5 with both) and 14 did not have either pathology. One third of the 180 with average age of 85 had no cognitive decline! Since this study showed MCI patients to have Alzheimer disease pathology in their brains, recognition of MCI clinically is important for institution of therapy, although there has not yet been an effective therapy developed.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterised by the gradual onset of dementia. The pathological hallmarks of the disease are Aβ amyloid plaques, neurofibrillary tangles (NFT), synaptic loss and reactive gliosis. Current diagnosis of AD is made by clinical, neuropsychologic, and neuroimaging assessments. Routine structural neuroimaging evaluation with computed tomography (CT) and magnetic resonance imaging (MRI) is based on nonspecific features such as atrophy, a late feature in the progression of the disease, hence the crucial importance of developing new approaches for early and specific recognition at the prodromal stages of AD. Functional neuroimaging techniques such as functional magnetic resonance imaging (fMRI), magnetic resonance spectroscopy (MRS), positron emission tomography (PET) and single photon emission computed tomography (SPECT), possibly in conjuction with other related Aβ biomarkers in plasma and CSF, could prove to be valuable in the differential diagnosis of AD, as well as in assessing prognosis. With the advent of new therapeutic strategies aimed at reducing the Aβ amyloid burden in the brain, there is increasing interest in the development of MRI contrast agents and PET and SPECT radioligands that will permit the assessment of Aβ amyloid burden in vivo.

It is almost a century since Dandy made the first experimental studies on hydrocephalus, but its underlying mechanism has been unknown up to now. The conventional view is that cerebrospinal fluid (CSF) malabsorption due to hindrance of the CSF circulation causes either obstructive or communicating hydrocephalus. Analyses of the intracranial hydrodynamics related to the pulse pressure show that this is an over-simplification. The new hydrodynamic concept presented here divides hydrocephalus into two main groups, acute hydrocephalus and chronic hydrocephalus. It is still accepted that acute hydrocephalus is caused by an intraventricular CSF obstruction, in accordance with the conventional view. Chronic hydrocephalus consists of two subtypes, communicating hydrocephalus and chronic obstructive hydrocephalus. The associated malabsorption of CSF is not involved as a causative factor in chronic hydrocephalus. Instead, it is suggested that increased pulse pressure in the brain capillaries maintains the ventricular enlargement in chronic hydrocephalus. Chronic hydrocephalus is due to decreased intracranial compliance, causing restricted arterial pulsations and increased capillary pulsations. The terms “restricted arterial pulsation hydrocephalus” or “increased capillary pulsation hydrocephalus” can be used to stress the hydrodynamic origin of both types of chronic hydrocephalus. The new hydrodynamic theories explain why third ventriculostomy may cure patients with communicating hydrocephalus, a treatment incompatible with the conventional view.

MR and CT demonstrate morphological changes in intervertebral disks. However the images do not provide an effective means to document interval changes in the disk due to degeneration, aging or healing. Functional imaging that may assesses the biomechanical or the biochemical integrity of the disk, may provide a measure of changes in the disk over time. To study the biomechanical function of the disk, translation and rotation of spinal vertebrae can be measured with CT or MR as the spine is subjected to a specific load or torque. Biochemical integrity of the disk can be assessed by the estimation of the water content from a measurement of the T2 relaxation time of disk tissue.

Unruptured intracranial aneurysms (UIAs) are a major public health issue. These lesions have become increasingly recognized in recent years with the advent of advanced cerebral imaging techniques. Epidemiological evidence from multiple sources suggests that most intracranial aneurysms do not rupture. Therefore, it is desirable to identify which UIAs are at greatest risk of rupture when considering which to repair. It is important to compare size-, site-, and group-specific natural history rates with size-, site-, and age-specific morbidity and mortality associated with UIA repair because increased natural history risk often is associated with increased risk of aneurysm repair. Patient age is crucial in decision making because of its major effect on operative morbidity and mortality; however, it does not substantially affect natural history. The effect of age is most notable in patients about 50 years of age and older for open surgery and about 70 years of age and older for endovascular procedures. In general, rupture risk is lowest for patients in asymptomatic group 1 (no history of subarachnoid hemorrhage) with UIAs less than 7 mm in diameter in the anterior circulation. Surgical morbidity and mortality are most favorable for asymptomatic patients younger than 50 years who have UIAs less than 24 mm in diameter in the anterior circulation and no history of ischemic cerebrovascular disease. Endovascular morbidity and mortality may be less age dependent, and this could favor endovascular procedures, particularly in patients aged 50 to 70 years. An important issue is determining immediate vs long-term risk regarding treatment effectiveness and durability. This issue emphasizes the importance of long-term follow-up in patients after surgical and endovascular procedures.

The clinical presentation of central nervous system venous thrombosis (CNSVT) is variable and non specific. Advances in CT and MRI technology have redefined the role of these 2 modalities in assessing suspected CNSVT. T1, T2, FLAIR and DWI/ADC (diffusion weighted imaging/apparent diffusion coefficient) MRI (magnetic resonance imaging) sequences together with a gadolinium enhanced MRV (magnetic resonance venography) would the imaging of first choice in suspected venous thrombosis of the central nervous system. Where there are still problems with identifying the thrombus and this is crucial to the management, a CTV (computed tomographic venography) should be performed. Catheter angiography would be used as a last resort or associated with direct thrombolysis. There may be circumstances where CT may be used as the first choice. There may be contraindication to MRI such as pacemakers, aneurysms clips etc.

A retrospective study was conducted on 17 consecutive patients with DAVF admitted to Monash Medical Centre over 12 years. 15 patients, 82.4%, were treated by endovascular means with the intention to obliterate the fistula. Three of these patients also had surgery following embolisation. Angiographic cure was achieved when we have successfully embolised both the arterial and the venous side whether by penetration of liquid adhesive or packing with coils. Our cure rate of 60% (95% CI: 37–83%) compare favourably with published results of 50 to 70%. Our clinical complication rate is 1/15, 6%; and technical complication is1 from 32 embolisation sessions, 3.1%. Endovascular therapy is effective in achieving a durable angiographic and clinical cure in the treatment of intracranial DAVF. Both arterial and venous side need to be occluded.

We reviewed the follow-up findings of patients who received percutaneous vertebroplasty, in order to understand the effects of vertebroplasty on following issues: pain relief, height restoration, wedge deformity correction, kyphosis correction, and other radiological findings found in follow up studies, such as new fractures. Generally, the pain relieving effect after vertebroplasty is long lasting except when new fracture occurred, or presence of other problems that caused the back pain. Height restoration and wedge deformity correction last for more than one year. The effect of kyphosis angle correction may vanish one year after procedure due to occurrence of new fracture in adjacent vertebral bodies.