Neuroradiology and Ultrasound

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David G. Hughes

With a contribution on Ultrasound by

Roger Chisholm

Summary

Neuroradiology utilises a wide range of imaging modalities in the diagnosis and treatment of CNS pathologies. MRI is the investigation of choice for most neuro-radiological imaging. CT remains the foremost modality in the emergency situation, and is superior to MRI in the visualisation of calcification, bone detail and acute hemorrhage. Angiography should be considered for all patients without a clear cause of hemorrhage and who are surgical candidates. Digital subtraction angiography is currently the gold standard in the investigation of subarachnoid hemorrhage, but in the future MRA and CTA will replace it. Technological advances are moving towards less invasive imaging modalities, supported by functional and physiological data. Ultrasound is the primary investigation in a neonate with an enlarging head and will reliably diagnose ventriculomegaly. It is accurate in the assessment of internal carotid artery stenosis for potential carotid endarterectomy patients.

Introduction

Neuroradiology has evolved as a subspecialty of radiology by the application of different radiological techniques to the investigation of clinical problems related to the central nervous system (CNS) and spine. Initially limited to radiographs, a number of techniques became available that required skill in performance and interpretation, demanding the establishment of "neuroradiology". We now have a core of imaging modalities that allow ever more accurate diagnosis, and increasingly treatment, of CNS pathologies. These modalities include radiographs, computed tomography (CT), magnetic resonance imaging (MRI), angiography, ultrasound, nuclear medicine, myelography and interventional neuro-radiology. These present a complex permutation of possible investigation of given clinical conditions that may be further influenced by local availability and expertise.

This chapter will review these imaging modalities and discuss the basic principles, indications, weaknesses and complications illustrated by clinical examples. A comprehensive imaging review of neurological disease is not possible in the length of this chapter and the reader is referred to recent neuroradiological textbooks for further reading [1, 2].

Radiographs

Radiographs, once the only investigation available, are nearly redundant in modern neuroradiology. The use of skull radiographs has been greatly reduced even in trauma, and are now used in the UK as part of a triage exercise in minor head injury cases to decide on the safe discharge of a patient.

A person who has sustained a mild head injury, has no skull fracture, is Glasgow Coma Scale 15 and has adequate support at home can be discharged with a head injury advice chart. Even in this situation there is a case for CT scanning, the limiting factors being radiation dosage (ten times that of skull radiographs) and extensive workload to the CT scanner. There may be a role for skull radiographs in mild trauma to exclude a depressed skull fracture that is suspected from the mechanism of injury. The skull radiograph is still requested in myeloma and renal bone disease "screens".

Radiographs of the spine can be more helpful. They still form the basis of trauma cervical spine imaging "clearing the spine", although there are advocates of CT in this role if the patient is already undergoing CT of another part of the body.

A vast number of radiographs are still used in the assessment of neck and back pain. The yield of significant abnormalities is generally very low; in low back pain it is more productive if the use of radiographs is limited to the young patient (under 20 years) for the detection of spondylolisthesis (Fig. 2.1) and to older patients (over 55 years) where metastasis is more likely. Degenerative disease seen on a radiograph correlates poorly with clinical signs and symptoms. Where surgical management of degenerative disease is considered, then there is a case for MRI only [3].

Computed Tomography

The first patient to be scanned using CT was at Atkinson Morley's Hospital in London in 1972. The technology invented by Sir Godfrey Hounsfield [4] (an engineer at the Central Research Laboratories, EMI, England) was the single most important development in neuro-radiology.

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