CT angiography and its role in the investigation of intracranial haemorrhage RD Magazine, 39, 458, 29-30 Dr M Igra Radiology SPR Leeds General Infirmary Dr I Djoukhadar Research fellow Wolfson Molecular Imaging Centre University of Manchester Dr T Goddard Consultant neuroradiologist Leeds General Infirmary Introduction Spontaneous intracranial haemorrhage constitutes only 15% 1 of acute stroke but remains the most devastating form, with a death and severe disability rate of more than 75%. 2,3 Prompt identification of a structural vascular abnormality, or lack of it, is a major factor in improving the clinical management of these patients and ultimately their outcomes. Digital subtraction angiography (DS) has been the gold standard imaging technique allowing for a detailed assessment of the circle of Willis. However, it is an invasive examination carrying significant risks (1% stroke rate) to the patient, 4 is time consuming and requires a certain level of experience limiting its availability. The wide availability of CT angiography, on the other hand, coupled with the introduction of multi-detector row CT angiography (MDCT) and the improved post processing techniques, has resulted in an increased use of CT as an imaging tool for the assessment of the intracranial vascular structure. CT angiography techniques and role CT angiography is proving to be a suitable alternative method of assessing the cerebral vessels. This is due to its non-invasive nature, lower radiation dose, 5 wide availability and the ability to perform the examination in conjunction with non-contrast CT. The introduction of multi-detector row CT angiography has revolutionised the CT technique with its quicker acquisition times and improved post-processing image quality. Following image acquisition, the volumetric data is transferred to a working station for further processing. In our institution this includes multi-planar reformation (MPR) with 1mm thickness in multiple planes, thin slab maximum intensity projections (MIP) and volume rendered technique (VRT) algorithm. systematic and thorough approach is adopted in reviewing all the images. The main role of CT is to identify the culprit vascular lesion and assess treatment options. With respect to aneurysms, this is achieved by examining the following features: size, shape, location in relation to the haemorrhage, calcification, number of vessels involved and the presence of any other lesions or anatomical variants. Subarachnoid haemorrhage In our institution, once an unenhanced CT has demonstrated subarachnoid haemorrhage (SH), a CT is usually acquired in the same setting, saving the patient and the medical team an extra visit to the radiology department. Intracranial aneurysms are responsible for most cases of SH, approaching 90%. 6 In addition to identifying the aneurysm, the radiologist should look for certain features including location of the aneurysm in relation to the blood (figure 1), neck size, number of vessels incorporated within the aneurysm and the presence of vasospasm. Occasionally, in the presence of multiple aneurysms, it might not be possible to identify the culprit lesion and the neuro-interventionist will need to treat more than one lesion (figure 2). Many authors have published data indicating the high sensitivity and specificity of CT in detecting acutely ruptured intracranial aneurysms. Using MDCT, gid et al 7 quote a 98% sensitivity and 100% specificity for the detection of aneurysm. Similar results are also published by Sideman, Lourenco and yyny. 8-10 meta-analysis by Westerlaan et al 11 showed a specificity of 99% for ruptured aneurysms and a sensitivity of 92%. Despite these impressive rates, CT lags slightly behind conventional DS and can occasionally yield false negatives, especially in cases of tiny aneurysms measuring less than 2mm 12 and ones that are close to bony structures. 13 In late SH presentation, the accuracy of unenhanced CT and lumbar puncture sensitivity and accuracy drop significantly. CT is a very powerful tool in assessment of this subgroup of patients. negative unenhanced CT and CT can exclude aneurysmal SH with a post-test probability of 99%. 14 s interpretation is user dependent, technological advances coupled with increased familiarity with the investigation should yield greater detection rates. systematic approach to assessing the arterial tree, its branches and Table 1 CT angiography to aneurysm therapy chart.
MIPs in three orthogonal planes with different postprocessing techniques should be implemented to ensure aneurysm detection. rteriovenous vascular malformation VM are another well-recognised cause of SH and intracerebral haemorrhage. The main modality for imaging these abnormalities is DS as it allows for dynamic assessment. However, when an VM is encountered on CT, certain radiological features should be actively assessed to try and stratify the risk of recurrent haemorrhage. Venous pouches or intra-nidal aneurysms (figure 3) confer a higher risk for VM rupture and can cause a diagnostic dilemma due to their wide range and locations; hence identification of these lesions is essential. Sanelli et al 12,15 demonstrated that, while DS remains the gold standard, CT has an important role to play in the initial diagnostic vascular assessment. CT can assess both arterial supply of the nidus as well as its venous drainage, and is also useful in stereotactic localisation. recent study showed that CT was more sensitive (87%) than MRI and MR (83% and 87% respectively) at identifying ruptured VMs, and that sensitivity was 100% for VMs larger than 3cm. 16 They also showed that associated aneurysms were best detected with CT, compared to these other imaging modalities. lthough conventional cerebral angiography remains the modality of choice for the diagnosis of dural arteriovenous fistula, CT can be useful with certain imaging features suggestive of the diagnosis. For example, tortuous feeding arteries with dilated cortical draining veins and dilated external carotid artery branches are recognised imaging features (figure 4). Lobar haemorrhage Multiple structural abnormalities can cause isolated intracerebral lobar haemorrhage. These include aneurysms, VM as well as dural fistulae. The decision to investigate patients with an intracerebral haematoma using CT varies widely from one institution to another. In our unit, a multidisciplinary approach is followed, with each case assessed on an individual basis. Factors affecting the decision to investigate further include: patient age, haemorrhage location and the presence of risk factors such as hypertension. 17,2 For example, in an over 60-year-old hypertensive patient with a basal ganglionic haemorrhage, the yield of further CT will be limited. In 2009, Yoon et al 18 compared the accuracy of MDCT against conventional DS in 78 patients. CT successfully detected the underlying vascular abnormalities in all but one patient (a 4mm VM) with no false positive cases. The authors concluded that MDCT is a promising investigation in the assessment of lobar ICH but does not replace DS in all patients. Primary intracranial haemorrhage refers to a spontaneous haemorrhage where an underlying structural abnormality is not identified. In addition to the obvious exclusion value of CT, there is a potentially important prognostic value too. Over the last two decades there have been an increasing number of publications relating to the spot sign in CT. The concept has evolved but most authors refer to the spot sign as tiny areas of enhancement in the haematoma on CT source data. 19 lmandoz et al 20 proposed a scoring system reflecting certain imaging parameters including the number, maximum axial dimension and Hounsfield unit attenuation values of the spot sign. It is important to remember that the spot sign is mainly used in primary intracranial haemorrhage cases and its application in secondary haemorrhage is less clear. Recently, rouwers et al reviewed the available literature highlighting the consistent ability of the spot sign in predicting haematoma expansion, functional outcome and mortality. 21 Conclusion The increasing use of CT can be attributed to its noninvasive nature, wide availability and lower dose when compared with DS. In addition, when reviewed by an experienced operator (figure 5), CT is a highly sensitive and specific investigation and should be use as a gatekeeper limiting the need for DS. References 1. Qureshi I et al. Spontaneous intracerebral hemorrhage. N Engl J Med 2001;344(19):1450-60. 2. Zhu X L, Chan M S, Poon W S. Spontaneous intracranial hemorrhage: Which patients need diagnostic cerebral angiography? prospective study of 206 cases and review of the literature. Stroke 1997;28(7):1406-9. 3. Willinsky R et al. Neurologic complications of cerebral angiography: Prospective analysis of 2,899 procedures and review of the literature. Radiology 2003;227(2):522-8. 4. Hankey G J, Warlow C P, Molyneux J. Complications of cerebral angiography for patients with mild carotid territory ischaemia being considered for carotid endarterectomy. J Neurol Neurosurg Psychiatry 1990;(7)53: 542-8. 5. Manninen L et al. comparison of radiation exposure between diagnostic CT and DS examinations of cerebral and cervicocerebral vessels. m J Neuroradiol 2012;33(11):2038-42. 6. Kirkpatrick P J. Subarachnoid haemorrhage and intracranial aneurysms: what neurologists need to know. J Neurol Neurosurg Psychiatry 2002; 73(Suppl1):i28-33. 7. gid R et al. cute subarachnoid hemorrhage: Using 64-slice multidetector CT angiography to triage patients treatment. Neuroradiology 2006; 48(11):787-94. 8. Sidman R, Connolly E, Lemke T. Subarachnoid hemorrhage diagnosis: Lumbar puncture is still needed when the computed tomography scan is normal. cad Emerg Med 1996;3(9):827-31. 9. Lourenco P et al. Does 16-detector computed tomography improve detection of non-traumatic subarachnoid hemorrhage in the emergency department? J Emerg Med 2009;36(2):171-5. 10. yyny R L et al. Sensitivity of noncontrast cranial computed tomography for the emergency department diagnosis of subarachnoid hemorrhage. nn Emerg Med 2008;51(6):697-703. 11. Westerlaan H E et al. Intracranial aneurysms in patients with subarachnoid hemorrhage: CT angiography as a primary examination tool for diagnosis systematic review and meta-analysis. Radiology 2011;258(1):134-45. 12. Sanelli P C et al. CT angiography in the evaluation of cerebrovascular diseases. m J Roentgenol 2005;184(1):305-12. 13. Seruga T, unc G, Klein G E. Helical high-resolution volume-rendered 3- dimensional computer tomography angiography in the detection of intracranial aneurysms. J Neuroimaging 2001;11(3):280-6. 14. McCormack R F, Hutson. Can computed tomography angiography of the brain replace lumbar puncture in the evaluation of acute-onset headache after a negative noncontrast cranial computed tomography scan? cad Emerg Med 2010;17(4):444-51. 15. Sanelli P C, Mifsud M J, Stieg P E. Role of CT angiography in guiding management decisions of newly diagnosed and residual arteriovenous malformations. m J Roentgenol 2004;183(4):1123-6. 16. Gross, Frerichs K U, Du R. Sensitivity of CT angiography, T2- weighted MRI, and magnetic resonance angiography in detecting cerebral arteriovenous malformations and associated aneurysms. J Clin Neurosci 2012; 19(8):1093-5. 17. Halpin S F et al. Prospective evaluation of cerebral angiography and computed tomography in cerebral haematoma. J Neurol Neurosurg Psychiatry 1994;57(10):1180-6. 18. Yoon D Y et al. Multidetector row CT angiography in spontaneous lobar intracerebral hemorrhage; a prospective comparison with conventional angiography. m J Neuroradiol 2009;30(5):962-7. 19. Tanaka H et al. Initial experience with helical CT and 3D reconstruction in therapeutic planning of cerebral VMs; comparison with 3D time-offlight MR and digital subtraction angiography. J Comput ssist Tomogr 1997;21(5):811-7. 20. Romero J M et al. ccuracy of CT angiography for the diagnosis of vascular abnormalities causing intraparenchymal hemorrhage in young patients. Emerg Radiol 2009;16(3):195-201. 21. rouwers H et al. Clinical applications of the computed tomography angiography spot sign in acute intracerebral hemorrhage: review. Stroke 2012;43(12):3427-32.
Figures 1 and 1 () Unenhanced CT brain showing predominantly posterior fossa haemorrhage suggesting a posterior circulation aneurysm. () CT confirms a tiny left posterior inferior cerebellar artery aneurysm (2mm). Haematoma Haematoma Figures 2 and 2 xial () and coronal () CT angiography images demonstrating multiple vascular abnormalities. 1. VM in the left temporal region. 2. Left middle cerebral artery aneurysm, this is the culprit abnormality given the surrounding hematoma (red arrow). 3. Small and incidental right middle cerebral artery aneurysm.
C D Figures 3, 3, 3C and 3D () Unenhanced CT brain demonstrating large intraventricular haemorrhage and a small adjacent left corona radiata haemorrhage. () CT reveals a large left frontal VM. (C) CT also show a tiny aneurysm intimately related to the parenchymal haemorrhage. (D) 3D reconstructed images of a conventional angiogram showing the aneurysmal lesion within the VM. Figures 4 and 4 () CT showing a right cerebellar tortuous vessels and, interestingly, the right temporal artery is enlarged raising concerns for a dural fistula. () Conventional cerebral angiogram confirming a dural arteriovenous fistula.
C D Figures 5-D CT and initially CT was interpreted as negative. Figure 5E Conventional cerebral angiogram showing aneurysm in the right distal internal carotid artery. Figure 5F On retrospective review of CT, the lesion was present but difficult to see. E F