The limited role of cranial computerised tomography in the assessment of a medical patient

Introduction

Computerised tomography (CT) examinations are often used in the initial assessment of medical patients. Cranial CT scans are probably the most common CT examination performed in developed nations.¹ Although there are good indications for cranial CT in the context of trauma, the indications among non-trauma patients referred for medical assessment are not so clear.² In developed nations, many hospitals now have ready access to magnetic resonance scanners and magnetic resonance imaging (MRI) of the brain has a number of advantages over cranial CT in the assessment of medical patients.³ We recently audited the use of cranial CT in the assessment of patients referred to the medical assessment unit (MAU) in our hospital.

Methods

All patients referred to the MAU over a three-month period who underwent cranial CT scans were examined. Some of these patients also went on to have MRI of the brain. 192 patients were identified and the age ranged between 17 and 96 years old.

Results

The common indications for cranial CT were altered mental state (n = 52; 27%), headache (n = 36; 19%) and dizziness (n = 35; 18%). The key finding was that the cranial CT revealed an abnormality related to the patient's presenting symptoms in only 10 (5%) patients. Cerebral infarction was detected in 8 (4.2%) and a mass lesion in 2 (1%) patients. Other unrelated abnormalities detected were periventricular white matter changes (n = 42; 22%), cerebral atrophy (n = 26; 14%) and old cerebral infarction (n = 16; 7%). All patients who had an acute abnormality detected on the cranial CT had a focal neurological deficit on examination. Of the 192 patients, 52 patients also had a MRI study of the brain during their hospital stay. 12 of these patients had findings on MRI relevant to their presenting symptom that were not evident on the cranial CT (10 had features of cerebral ischaemia, 1 had leptomeningeal enhancement after contrast in keeping with carcinomatosis and 1 had facial nerve enhancement on MRI with clinical features of Bell's palsy).

Discussion

The poor yield of cranial CT in the evaluation of syncope, dizziness, confusion, delirium, headache and the older patient has been previously described.^4–8 These indications constitute a significant proportion of those referred for medical evaluation. Among the patients studied in this audit, altered mental state and focal neurological deficit on examination were good predictors for detecting an abnormality on cranial CT. If cranial CT was limited to those with focal neurological deficit and altered mental state, only 45 of the 192 patients would have needed a cranial CT and no clinically significant abnormality missed.

The substantial increase in the use of CT in recent years has resulted in increasing exposure to radiation and there is increasing recognition to minimize exposure.⁹ The relatively rapid access and lower cost have been important factors favouring CT use. It can be argued that the judicious use of cranial CT with better use of MRI may allow better use of resources and ultimately be cost effective. We don't feel that the liberal use of cranial CT is unique to our institution. Better awareness, adoption of clinical decision tools and the increasing availability of MRI in hospitals is likely to alter the way cranial CT is used in the future.