List of Abbreviations
Flowchart 3. 2C: Step II Process of data gathering
3.4.5.3 Implement the questionnaire
< 36
(% within QUALITY)
16 (48.5%)
0 (0%)
16 (42.1%)
≥ 36
(% within QUALITY)
17 (51.5%)
5 (100.0%)
22 (57.9%)
Total Number 33 5 38
% within QUALITY 100.0% 100.0% 100.0%
P< 0.0267 (statistically significant)
TABLE 5: Other Findings (non contrast study)
Formatted: Normal
FINDINGS
Number
Percentage (%)
Tumour 11 44.0
Oedema 4 16.0
Calcifications 3 12.0
Infarction 2 8.0
Intracerebral haemorrhage 2 8.0
Bone cyst 1 4.0
Antral polyp 1 4.0
Aneurysmal clip 1 4.0
TOTAL 25 100
Figure 6: Axial source image before 3D reconstruction showing area of increased density in the left parasellar region suggestive of an aneurysm.
Figure 7: 3D MIP image showing fusiform aneurysmal dilatation of the left posterior communicating artery (arrow)
Figure 8: MIPVR image showing a normal carotid artery bifurcation and branches
Figure 9: Coronal MIP image showing a spinal AVM (arrow)
Figure 10: 3D MIP image showing encasement and compression of left carotid vessels (white arrows) due to a huge carotid body tumour.
Formatted: Line spacing: 1.5 lines
Figure 11a: Axial MIP image showing the venous phase of CTA and demonstrating the internal cerebral vein as draining vein (arrow) of a supratentorial
Arteriovenoussupratentorial Arteriovenous Malformation.
Figure 11b: Sagittal view of a Surface Shaded Display image of the same patient showing extent of the lesion and flow into the straight sinus through the great vein of Galen (arrow)
Figure 12: MIP image showing compression of right common carotid artery and jugular vein (arrow) by a thyroid mass
Figure 13: .MPVR image showing a saccular dilatation in the region of the anterior communicating artery suggestive of an aneurysm. Close examination of other views showed it to be a turn of the middle cerebral artery in profile.
Figure 14: Multi-planar volume reformatted (MPVR) image showing a right middle cerebral arteriovenous malformation
Figure 15: PA view of a 3D surface shaded display image showing tortuous network of intra-spinal vessels (arrow) in the neck of a patient with a Spinal Arteriovenous Malformation
Formatted: Line spacing: 1.5 lines
Figure 16: 3D MIP image showing an AVM (arrow) involving the posterior cerebral artery with calcifications within it.
I
P A
S
Formatted: Line spacing: 1.5 lines
Figure 17: MIP image shows saccular aneurysmal dilatation (arrow) in the region anterior communicating artery in a 56 year old woman with sudden severe headaches.
Formatted: Line spacing: 1.5 lines
Figure 18: SSD image of the same the patient patient as in (Fig. 17) with an anterior communicating
artery aneurysm.
Figure 19: Lateral view of a 3D surface shaded display image showing dilated tortuous occipital vessels in a patient with an extracranial Arteriovenous Malformation.
Formatted: Line spacing: 1.5 lines
A B
C D
Figure 20: Contrast Axial (A) and MIP images (B-D) showing an arteriovenous
malformation involving the right posterior cerebral artery. The lesion almost doubled in size following CTA study
TABLE 4: Correlation of Age with Image Quality
AGE (years)
QUALITY
Total Good Suboptimal
Formatted: Line spacing: 1.5 lines
Formatted: Tab stops: 1.04", Left
Formatted: Indent: First line: 0.5"
< 36
(% within QUALITY)
16 (48.5%)
0 (0%)
16 (42.1%)
≥ 36
(% within QUALITY)
17 (51.5%)
5 (100.0%)
22 (57.9%)
Total Number 33 5 38
% within QUALITY 100.0% 100.0% 100.0%
P< 0.0267 (statistically significant)
TABLE 5: Other Findings (non contrast study)
FINDINGS
Number
Percentage (%)
Tumour 11 44.0
Oedema 4 16.0
Calcifications 3 12.0
Infarction 2 8.0
Intracerebral haemorrhage 2 8.0
Bone cyst 1 4.0
Antral polyp 1 4.0
Aneurysmal clip 1 4.0
TOTAL 25 100
DISCUSSION
One of the most undeniable advantages of CT angiography is the ability to provide all of the information which previously required two or more radiological studies which may, in the case of conventional angiography, be much more expensive and hazardous than CT.
A fundamental concept of 3D imaging of any application is that the quality and accuracy of the resulting images is limited by the quality and resolution of the dataset. In view of this, care was taken to ensure that an appropriate protocol was used for each patient.
Formatted: Centered
Formatted: Centered, Indent: Left: 0", First line: 0"
Formatted: Centered
Formatted: Centered, Indent: Left: 0", First line: 0"
The 2 poor angiograms that necessitated a repeat in this study were due to motional distortion from patient’s’ movement in response to the heat felt during contrast injection and a too long pre-scan delay (20seconds) for a patient having a Circle of Willis Angiography.
These repeated cases were later assessed as good.
Usually, CT angiography is requested when a conventional regular CT scan raises a high suspicion of a vascular disease. However, occasionally a CT angiography is requested without a prior CT scan when the referring physician suspects a vascular anomaly.
A CT n angiographic scan can provide all the details of a post contrast axial scan. In addition, the vessels are demonstrated without having to expose the patient to a second dose of radiation.
The small size of the study population may be due to the prohibitive cost of the examination.
A CT angiographic study in Ibadan costs N60, 000.00 ($450.00) which is unaffordable for most patients in a country where 70.2% of the population live on less than $1.00 per day.587 It may also have been due to the level of awareness of the availability of this non-invasive vascular imaging modality, by surgeons and physicians both within and outside the hospital.
The slight female predominancepreponderance in this study is in contrast with the male predominancepreponderance reported by Adeloye et al. 13. Also, the ratio of arteriovenous malformation to aneurysm of 2 to 1 recorded here is in contrast with 1 to 3 of the study by Adeloye et al; 13 their study may be more representative due to the longer study period (15 years) and larger study population. This study however confirms the low incidence of intracranial vascular anomaly in Nigeria as the finding of 5 intracranial AVMs and 3 cerebral aneurysms agrees with their report of an incidence of 2-3 intracranial vascular anomalies per year in Ibadan.13
The symptomatology of ruptured intracranial aneurysm and bleeding AVM is often so serious that the patient seeks medical attentionadvice to relieve distressing headache, neck stiffness, alteration in consciousness or neurological deficit. Nevertheless, some patients never make it to the hospital. The cases reported here show that the clinical picture of intracranial vascular anomalies is no different from that of similar studies in our environment and in Caucasians.11-13, 21, 45, 48
CTA is a quick and relatively safe imaging modality compared with catheter angiography and is a reliable method of establishing or ruling out vascular anomalies in suspected patients.
The images obtained are assessed based on the opacification and definition of the vessels of interest. Thirty-three (86.8%) of the patients had good quality CT angiograms. This fairly impressive result may be attributed to the use of reference guidance of other workers38, 42,
44,45,47,54 whose studies using newer image acquisition and analysis protocols have yielded impressive results, signifying that protocol optimization can lead to progressively higher quality CTA.
For single detector helical studies, a section collimation of 1mm, and a 0.5mm reconstruction interval, a pitch of 1.5, mA of ≥280, a matrix size of ≥ 512 x 512 and a field of view just enough to include areas of interest (generally 18cm) has been suggested for cerebral angiography. Similar parameters were used in this study.
The results however indicate a statistically significant (P<0.0267) correlation of the patient’s age with the image quality.
In this study, patients above 36 years of age were more likely to have suboptimal images.
This is due to a possibly reduced cardiac output in older patients and the use of identical delay time for all patients.
Delay time is another vital protocol variable, it is the selected time for contrast injection before initiating helical scan. Previous investigators have used empirical fixed injection delays ranging between 15 and 45 seconds.43
Some workers have suggested that a timing run or automatic peak opacification – sensing software should always be used.41 This is to ensure dynamic scanning during peak intraluminal contrast attenuation, minimal radiation exposure, and minimal total contrast dose.
In this study the empirical delay time was based on the reference manual of GE Medical Systems. The delay time was usually increased by a couple of seconds (usually 2-3 seconds) for patients suspected to have a poor haemodynamic status. It has been reported that the empirical delay method may result in decreased sensitivity. 598
Furthermore, an injection rate of 3.5ml/second was used in all patients (except in the 9 year old patient, where 2.5ml/second was used) to achieve a reasonablye homogenous vascular opacification, with good results.
Some workers believe that an injection rate >3.5 ml/second is not necessary in terms of the resultant opacification. Claves et al, 6059 found in phantom studies that luminal attenuation of 150HU gives optimal results – this level of enhancement is easily achieved with injection rate of 3-4ml/sec.
The scan duration of 37 to 53 seconds recorded for cerebral CTA in this study compares well with 35 to 45 seconds reported by Alberico et al.45
In the cases of carotid arterial stenosis, the three types of reconstruction techniques were used (MIP, SSD and axial) to describe the area of stenosis. The reliability of carotid stenosis measurement depends on the scanning technique.
The protocol used in this study was very similar to that of previous studies51, 52, 54-56
that have recorded impressive results. Castillo who used a 5mm collimation, a small amount of contrast material (60ml) and 3mm increment had comparatively poorer results.33
In assessing stenosis, intramural calcification was not a limiting factor,factor; axial sections were helpful in delineating the vascular lumen.
In the cerebral aneurysms detected, aneurysm al location, shape and size were demonstrated but the neck was difficult to delineate, this may have been due to positioning and aneurysmal orientation.
Preliminary data suggest that 3D-CTA also plays a favourable role in the assessment of patients with intracranial AVMs by demonstrating arterial supply, venous drainage, configuration of the nidus and relationship to surrounding structures. 47
In the present studyIn this series, the AVMs demonstrated, showed satisfactory definition of the nidus in 4(57%) patients.
The feeding arteries were delineated in all 7 (100%) and the site and extent of the lesions were demonstrated. However, only in 2 (28.6%) cases, was a draining vein identified.
Two (28.6%) of the AVMs have been confirmed by surgery.
The neurosurgeons found the CTA images adequate for surgical planning and intervention.
In the patient with a spinal AVM, surgical excision following diagnosis by CTA enabled her to ambulate with minimal effort after six months of incomplete quadriplegia.
The angiographic findings in the 38 patients evaluated showed a positive statistically significant correlation with the referring physician’s clinical impression (p<0.001).
This indicates that there is likelihood for the referring physician to be correct when he makes an impression of a vascular abnormalitynomaly in the head and neck.
Although the clinical impression may be subjective, further studies with a larger patient population may confirm this to be a true association and not a confounding variable.
No case of contrast reaction was recorded. This may be due to the use of recommended low osmolar non-ionic contrast medium.
Hypertension and atherosclerosis haves been incriminated as important factors in the aetiology of intracranial aneurysms.18 In the presenthis serie study, hypertension was not present in most patients and correlation of hypertension with intracranial vascular anomaly was not statistically significant.
Sasiadek et al 21 reported their experience with CTA in 86 patients and diagnosed 44 cases of vascular malformations (38 aneurysms and 6 AVMs). T this was not unexpected, in view of the higher incidence of intracranial vascular malformation in their population. Their report also believed that CTA may replace conventional angiography in the future. The unavailability of conventional angiography in Ibadan has made neurosurgeons to rely on CTA in patient management with notable results thus far. This study is also in agreement with many other authors 26, 43-45 who have reported the clinical usefulness of CT angiography with MIP and three-dimensional SSD rendering techniques.
SUMMARY
Between December 2003 and July 2005, thirty-eight patients with clinically suspected cranio-cervical vascular abnormalitynomaly had CT angiography using a helical CT scanner at the University College Hospital Ibadan. 20 females and 18 males whose ages ranged from 9-76 years were examined. Severe headaches, tumours and seizures were the commonest presenting features. The average scan time was 45.5 seconds. Twenty-one vascular
Formatted: Line spacing: Double
aabnormalitiesnomalies were demonstrated including seven arteriovenous malformations, three cerebral aneurysms and five carotid artery stenoses.
CONCLUSION
Three-Dimensional Computed Tomographic Angiography is a welcomed development in CT imaging. It is not only non invasive but very precise in delineating the cranio-cervical vasculature, which otherwise would have been evaluated by catheter angiography.
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CTA is also valuable in the pre and post surgical evaluation of intracranial vascular abnormalitiesanomalies and can serve as an important adjunct in the diagnostic armamentarium of the radiologist studying the neurovascular tree.
Though its cost is prohibitive, there is a positive statistical correlation between its findings and the clinical working diagnosis.
It is therefore recommended for patients with suspected vascular abnormalitiesanomalies of the head and neck.
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