Computerised axial tomography and magnetic resonance imaging bridging the gap - abstract

ABSTRACT

Since 1983, computerised axial tomography (CAT) has been the mainstay of neurological imaging in Trinidad and Tobago. In 1988, magnetic resonance imaging (MRI) became available in nearby South America. This study was done to examine the capabilities, limitations and pitfalls of CAT scanning and to provide guidelines for patients referral for MRI. The most recent 2,000 head and 68 body CAT scans performed from 1984 to 1988 were reviewed. Abnormalities were seen in 759 (38 percent) of head scans tumours 262 (34.5 percent), cerebral atrophy 128 (17 percent), ischaemic infarcts 121 (16 percent), intracranial haemorrhage 105 (14 percent), hydrocephalus 42 (5.5 percent), traumatic cerebral contusions 40 (5 percent), infection 36 (5 percent) and vascular malformations 14 (2 percent). Abnormalities were seen in 45 (66 percent) body scans spinal lesions 20 (44 percent), and lesions of the pancreas 8, liver 8, kidneys 4, adrenals 2, and 1 each in the lung, oesophagus and spleen. CAT scanning, however, was sometimes unable to resolve diagnostic dilemmas, and in 1988, 32 patients were referred for 22 head and 10 spine MRI studies. MRI head abnormalities were tumours 4, absceses 3 (1 in the brain stem), and 1 each of subdural haematoma, demyelinating disease and hydrocephalus. There were 12 normal head MRI studies. MRI spine abnormalities (7) were lumbar disc herination, cervical spondylosis 2, and syringomyelia 1, and 3 studies were normal. CAT scan limitations were most apparent with bone artefacts in the posterior and temporal fossae and the pituitary region, isodense subdural collections, differentiating enhancing infarcts from tumour and in demyelinating disease. MRI did not have these limitations and had the advantage of direct multiplanar (coronal and sagittal) imaging, superior tissue type differentiation, no ionizing radiation or allergenic contrast media. MRI is especially useful in imaging pituitary, parasellar and brain stem lesions, the spine and spinal cord, the heart, abdominal viscera, and joints. Its realtive disadvantages include slower scan times, danger to patients with indwelling ferromagnetic material, claustrophobia and higher equipment cost (AU)