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Indications for contrast medium enhancement in computed tomography of the brain
Clin. Radiol. (1977) 28, 535-537 INDICATIONS FOR CONTRAST MEDIUM ENHANCEMENT IN COMPUTED TOMOGRAPHY OF THE B R A I N N. ANN BARRINGTON and NORMAN A. LEWTAS
From the,Department o f Radiology, SheffieM Royal Infirmary The use of contrast medium enhancement in computed tomography almost doubles the duration of each examination. As the clinical demand is far greater than the Scanningtime available, it is desirable to use contrast medium with discrimination. ~' " The following indications are suggested for extended examinations with contrast: -,
(
.
1. 2. 3. 4.
?
Lesions shown by alternative neuroradiological investigations. Local abnormality shown on plain scan. Suspected posterior fossa lesions. Suspected supraseltar lesions.
In a retrospective review of 3000 patient examinations, 430 patients falling outside the above criteria had been given contrast medium. In only one patient in this latter group was an abnormality shown after contrast enhancement. In the other 429 patients, no additional information was obtained. These figures support the indications suggested for the use of contrast enhancement. The value of contrast medium enhancement in computed tomography of the brain is unquestioned. It not only renders many lesions more clearly apparent, but when taken in conjunction w i t h t h e patient's history, it frequently indicates the type of lesion present (Ambrose, 1973;Paxton and Ambrose, 1974; Ambrose et al., 1975a; Kramer et al., 1975). Its use, however, almost doubles the time needed for each patient examination, as well as adding a small, but definite, risk to the patient. At the present time, the clinical need for examination of the brain by computed tomography is infinitely greater than the scanning time available. For economic reasons, this situation is unlikely to change in the near future. It is, therefore, necessary for contrast enhancement to be used with discrimination. In an attempt to define some general principles for its employment, we reviewed its overall contribution to diagnosis in 3000 consecutive patient examinations, after excluding those patients whose scans were not of diagnostic quality.
METHOD OF REVIEW Virtually all our patients had been referred through the neurological or neurosurgical units and had, therefore, received a detailed and specialised neurological assessment. For each patient, three cuts were routinely taken, at 3, 5.5 and 8 cm above the orbito-meatal line, giving six slices. Additional views were taken for suspected posterior fossa and suprasellar lesions. Plain scans were shown to an experienced radiologist who, with knowledge of the clinical history and signs, assessed the need for
contrast medium enhancement. 40 ml of sodium iothalamate containing 420 mg of iodine per ml was the average dose used in the series. We examined the scans of the patients retrospectively, with knowledge of the clinical presentation, but not of the original report. The plain scans were carefully studied with special attention to whether any lesion was shown before contrast enhancement, either by a local abnormality, or indirectly by ventricular displacement, distortion or dilatation. Our group of patients with scans classed as 'normal' included patients with atrophy but no significant local lesion. Patients with suspected posterior fossa or suprasellar lesions were routinely examined before and after contrast medium. We accept the need for this in investigating these technically difficult areas (Huckman, 1975; Kramer et al., 1975). In these regions it is recognised that the plain scans may be normal, despite the presence of lesions.
RESULTS Three thousand patients were studied and in 1357 the scan had been repeated after injection of contrast medium. Of these 1357, in 795 patients the plain scan was abnormal. This is an accepted indication for the use of contrast medium and in many cases the contrast enhancement gave additional diagnostic information. Supraseller or posterior fossa lesions were suspected clinically in a further 132 patients receiving contrast medium. We have disregarded these for the purpose of this trial as the need for supplementary scans after contrast medium is accepted in these groups. Of the 430 patients remaining with normal
536
CLINICAL
Fig. 1 - 42 year old female with recurrent embolisation from heart valve replacement. CT scans seven days after an acute left hemiplegia showed a right hemisphere lesion only after contrast enhancement, due to the luxury perfusion syndrome. (The low density area in the left hemisphere was thought to be due to an additional asymptomatic infarct.) A repeat CT scan 10 months later showed generalised atrophy with a low density scar without contrast uptake on the right. (a) Plain scan; (b) after contrast. plain scans, only one showed an abnormality after injecting the contrast medium (Fig. 1). In one other case, it is arguable whether the lesion would have been recognised on the plain scan, although it becomes obvious after the contrast (Fig. 2). In this patient, the diagnosis had been established by previous angiography.
DISCUSSION We have been concerned by the amount of scanning time which has been taken up by examinations extended by giving contrast medium when the latter has provided no useful or additional diagnostic information. In our series of 3000 examinations this amounted to 429 patients in whom both plain and contrast scans were normal. We feel that this is largely because objective guide lines for supplementary examination with contrast medium have not been established.
RADIOLOGY
On the basis o f this review, we suggest the following indications for contrast enhancement in primary diagnosis: 1. Patients in whom an abnormality has been shown by other investigations - isotope study, angiography or encephalography/ventriculography, in whom further information is desirable. 2. In most, but not necessarily all, patients showing a local abnormality on plain scan. This is, to a certain extent, dependent on the history and clinical diagnosis. 3. Suspected posterior fossa lesions. 4. Suspected suprasellar lesions. It has been suggested that contrast medium should be given in all cases with focal symptoms and signs. This was, in fact, our policy for the period under review. The results of the survey, however, have not confirmed the need for this practice. In making these proposals, it is axiomatic that the plain scan should be monitored by an experienced observer with full access to the history and clinical findings. With regard to 3 and 4, we have already accepted the need for contrast scans in these areas. These proposals should be given a flexible interpretation. If, on subsequent clinical review, there is a discrepancy between a normal scan and the patient's history and signs, or if there is any change or
C O N T R A S T MEDIUM E N H A N C E M E N T
537
Fig. 2 - 31 year old female with a right sided arteriovenous malformation shown angiographically 10 years previously. (a) Plain scan; (b) after contrast. progression o f s y m p t o m s , t h e n the n e e d for a further e x a m i n a t i o n - b o t h with and w i t h o u t contrast m e d i u m - is accepted. CONCLUSION It is c o n c l u d e d that, if the suggested proposals are adopted for restricting the use o f contrast enh a n c e m e n t , additional scanning time w o u l d be available. In this review, one, or at the m o s t two diagnoses would have been missed (Figs. 1, 2). However, it w o u l d have been possible to scan an additional 430 patients and we believe that this w o u l d have produced a higher diagnostic yield. Acknowledgement. - We wish to thank Mr. D. M. C. Forster for his advice and for providing the stimulus for this survey.
REFERENCES Ambrose, J. (1973). Computerised transverse axial scanning (tomography): Part II. Clinical Application. British Journal of Radiology, 46, 1023-1047. Ambrose, J., Gooding, M. R. & Richardson, A. E. (1975a). Sodium iothalamate as an aid to diagnosis of intracranial lesions by computerised transverse axial scanning. Lancet, 11 October, 669-674. Huckman, M. S. (1975). Clinical experience with the intravenous infusion of iodonated contrast material as an adjunct to computed tomography. Surgical Neurology, 4, 297-318. Kramer, R. A., Janetos, G. P, & Perlstein, G. (1975). An approach to contrast enhancement in computed tomography of the brain. Radiology, 116, 641-647. Paxton, R. & Ambrose, J. (1974). The EMI Scanner. A brief review of the first 650 patients. British Journal of Radiology, 47, 530-565.
From the,Department o f Radiology, SheffieM Royal Infirmary The use of contrast medium enhancement in computed tomography almost doubles the duration of each examination. As the clinical demand is far greater than the Scanningtime available, it is desirable to use contrast medium with discrimination. ~' " The following indications are suggested for extended examinations with contrast: -,
(
.
1. 2. 3. 4.
?
Lesions shown by alternative neuroradiological investigations. Local abnormality shown on plain scan. Suspected posterior fossa lesions. Suspected supraseltar lesions.
In a retrospective review of 3000 patient examinations, 430 patients falling outside the above criteria had been given contrast medium. In only one patient in this latter group was an abnormality shown after contrast enhancement. In the other 429 patients, no additional information was obtained. These figures support the indications suggested for the use of contrast enhancement. The value of contrast medium enhancement in computed tomography of the brain is unquestioned. It not only renders many lesions more clearly apparent, but when taken in conjunction w i t h t h e patient's history, it frequently indicates the type of lesion present (Ambrose, 1973;Paxton and Ambrose, 1974; Ambrose et al., 1975a; Kramer et al., 1975). Its use, however, almost doubles the time needed for each patient examination, as well as adding a small, but definite, risk to the patient. At the present time, the clinical need for examination of the brain by computed tomography is infinitely greater than the scanning time available. For economic reasons, this situation is unlikely to change in the near future. It is, therefore, necessary for contrast enhancement to be used with discrimination. In an attempt to define some general principles for its employment, we reviewed its overall contribution to diagnosis in 3000 consecutive patient examinations, after excluding those patients whose scans were not of diagnostic quality.
METHOD OF REVIEW Virtually all our patients had been referred through the neurological or neurosurgical units and had, therefore, received a detailed and specialised neurological assessment. For each patient, three cuts were routinely taken, at 3, 5.5 and 8 cm above the orbito-meatal line, giving six slices. Additional views were taken for suspected posterior fossa and suprasellar lesions. Plain scans were shown to an experienced radiologist who, with knowledge of the clinical history and signs, assessed the need for
contrast medium enhancement. 40 ml of sodium iothalamate containing 420 mg of iodine per ml was the average dose used in the series. We examined the scans of the patients retrospectively, with knowledge of the clinical presentation, but not of the original report. The plain scans were carefully studied with special attention to whether any lesion was shown before contrast enhancement, either by a local abnormality, or indirectly by ventricular displacement, distortion or dilatation. Our group of patients with scans classed as 'normal' included patients with atrophy but no significant local lesion. Patients with suspected posterior fossa or suprasellar lesions were routinely examined before and after contrast medium. We accept the need for this in investigating these technically difficult areas (Huckman, 1975; Kramer et al., 1975). In these regions it is recognised that the plain scans may be normal, despite the presence of lesions.
RESULTS Three thousand patients were studied and in 1357 the scan had been repeated after injection of contrast medium. Of these 1357, in 795 patients the plain scan was abnormal. This is an accepted indication for the use of contrast medium and in many cases the contrast enhancement gave additional diagnostic information. Supraseller or posterior fossa lesions were suspected clinically in a further 132 patients receiving contrast medium. We have disregarded these for the purpose of this trial as the need for supplementary scans after contrast medium is accepted in these groups. Of the 430 patients remaining with normal
536
CLINICAL
Fig. 1 - 42 year old female with recurrent embolisation from heart valve replacement. CT scans seven days after an acute left hemiplegia showed a right hemisphere lesion only after contrast enhancement, due to the luxury perfusion syndrome. (The low density area in the left hemisphere was thought to be due to an additional asymptomatic infarct.) A repeat CT scan 10 months later showed generalised atrophy with a low density scar without contrast uptake on the right. (a) Plain scan; (b) after contrast. plain scans, only one showed an abnormality after injecting the contrast medium (Fig. 1). In one other case, it is arguable whether the lesion would have been recognised on the plain scan, although it becomes obvious after the contrast (Fig. 2). In this patient, the diagnosis had been established by previous angiography.
DISCUSSION We have been concerned by the amount of scanning time which has been taken up by examinations extended by giving contrast medium when the latter has provided no useful or additional diagnostic information. In our series of 3000 examinations this amounted to 429 patients in whom both plain and contrast scans were normal. We feel that this is largely because objective guide lines for supplementary examination with contrast medium have not been established.
RADIOLOGY
On the basis o f this review, we suggest the following indications for contrast enhancement in primary diagnosis: 1. Patients in whom an abnormality has been shown by other investigations - isotope study, angiography or encephalography/ventriculography, in whom further information is desirable. 2. In most, but not necessarily all, patients showing a local abnormality on plain scan. This is, to a certain extent, dependent on the history and clinical diagnosis. 3. Suspected posterior fossa lesions. 4. Suspected suprasellar lesions. It has been suggested that contrast medium should be given in all cases with focal symptoms and signs. This was, in fact, our policy for the period under review. The results of the survey, however, have not confirmed the need for this practice. In making these proposals, it is axiomatic that the plain scan should be monitored by an experienced observer with full access to the history and clinical findings. With regard to 3 and 4, we have already accepted the need for contrast scans in these areas. These proposals should be given a flexible interpretation. If, on subsequent clinical review, there is a discrepancy between a normal scan and the patient's history and signs, or if there is any change or
C O N T R A S T MEDIUM E N H A N C E M E N T
537
Fig. 2 - 31 year old female with a right sided arteriovenous malformation shown angiographically 10 years previously. (a) Plain scan; (b) after contrast. progression o f s y m p t o m s , t h e n the n e e d for a further e x a m i n a t i o n - b o t h with and w i t h o u t contrast m e d i u m - is accepted. CONCLUSION It is c o n c l u d e d that, if the suggested proposals are adopted for restricting the use o f contrast enh a n c e m e n t , additional scanning time w o u l d be available. In this review, one, or at the m o s t two diagnoses would have been missed (Figs. 1, 2). However, it w o u l d have been possible to scan an additional 430 patients and we believe that this w o u l d have produced a higher diagnostic yield. Acknowledgement. - We wish to thank Mr. D. M. C. Forster for his advice and for providing the stimulus for this survey.
REFERENCES Ambrose, J. (1973). Computerised transverse axial scanning (tomography): Part II. Clinical Application. British Journal of Radiology, 46, 1023-1047. Ambrose, J., Gooding, M. R. & Richardson, A. E. (1975a). Sodium iothalamate as an aid to diagnosis of intracranial lesions by computerised transverse axial scanning. Lancet, 11 October, 669-674. Huckman, M. S. (1975). Clinical experience with the intravenous infusion of iodonated contrast material as an adjunct to computed tomography. Surgical Neurology, 4, 297-318. Kramer, R. A., Janetos, G. P, & Perlstein, G. (1975). An approach to contrast enhancement in computed tomography of the brain. Radiology, 116, 641-647. Paxton, R. & Ambrose, J. (1974). The EMI Scanner. A brief review of the first 650 patients. British Journal of Radiology, 47, 530-565.