Delineation of unruptured cerebral computerized angiotomography

Transcription

1 J Neurosurg57: ,1982 Delineation of unruptured cerebral computerized angiotomography aneurysms by SYOJI ASARI, M.D., Tonu SATOH, M.D., MASARU SAKURAI, M.D., YuJI YAMAMOTO, M.D., AND KAZUHIKO SADAMOTO, M.D. Department of Neurological Surgery, Matsuyama Shimin Hospital and Sadamoto Hospital, Matsuyama, Ehime, Japan ~/ Unruptured aneurysms were diagnosed in 15 of 86 patients with cerebral aneurysms during 2 years beginning in April, One patient with severe head injury was excluded from the series. Fifteen aneurysms in the other 14 patients were first detected by computerized angiotomography. Six aneurysms were located in the middle cerebral artery, three in the upper half of the basilar artery, two in the anterior communicating artery, two in the posterior cerebral artery, and two at the internal carotid-posterior communicating artery junction (both in the same patient). Three were smaller than 5 mm, eight were between 6 and 10 mm, and four were larger than 10 mm. The noncontrast-enhanced computerized tomography (CT) findings associated with 15 aneurysms were as follows: five showed defects in the basal cistern or Sylvian fissure, four were calcified or high-density masses, and in six instances there was no evidence of an aneurysm. Unruptured aneurysms may be suggested by a well demarcated, round, isodense mass which forms a defect in the basal cistern or Sylvian fissure on a plain CT image, and are highly and homogeneously enhanced by computerized angiotomography. A carotid artery blood iodine level of 15 mg/ml is required to obtain clear images. The authors conclude that computerized angiotomography is useful in the delineation of unrnptured aneurysms. KF~Y WonDS 9 unruptured cerebral aneurysm 9 computerized angiotomography intravenous contrast injection 9 minimum-dose bolus injection method 9 multiplane scanning 9 blood iodine level C OMPUTERIZED tomography (CT) is a useful radiological diagnostic method for various kinds of intracranial diseases, especially ruptured intracranial aneurysms. With CT scanning, it is possible to define more easily and accurately the presence and extent of intracranial hemorrhage (subarachnoid, intraventricular, or intracerebral), infarction due to vasospasm, brain swelling, and ventricular dilatation secondary to aneurysm rupture. 3 On the other hand, CT has produced poor results in the direct detection of unruptured cerebral aneurysms, other than giant aneurysmsy Recently, we have used high-resolution CT, with a new technique, for the clear and accurate delineation of cerebral vessels. With this technique, we have been able to detect cerebral aneurysms (even unruptured ones previously difficult to delineate on the CT image) easily, noninvasively, and with a high success rate. To our knowledge, no reports of a large number of un- ruptured aneurysms diagnosed by CT have been published. We discuss the benefits of computerized angiotomography in the diagnosis of unruptured aneurysms in a series of patients. Clinical Material and Methods Eighty-six patients with cerebral aneurysms were admitted to our hospital during the 2 years beginning in April, In 15 of these patients, the aneurysms had been discovered incidentally. One of these 15 patients had severe head injury; the aneurysms in the remaining 14 patients were first detected in our outpatient clinic by computerized angiotomography and confirmed later by angiography. This study encompasses these 14 patients. A General Electric T8800 CT scanner with matrices was used in this series. The scanning time was 9.6 seconds, and the slice thickness was 10 J. Neurosurg. / Volume 57/October,

2 S. Asari, et al. FIG. 1. Case 9. Left: Computerized angiotomogram delineating a middle cerebral artery bifurcation aneurysm, which is shown as a well demarcated round high-density mass (arrow). The relationship of the aneurysm to its afferent and efferent arteries can be clearly seen. Right: Basalview carotid angiogram supports these findings. mm. Routine scanning was in the axial transverse plane, and a modified coronal plane scan was occasionally also done; in the former scanning, the gantry was parallel to the canthomeatal line (CML), and in the latter it was angled at approximately 60 ~ to the CML. s An intravenous minimum-dose bolus injection method, 1~ which had been especially devised for clear delineation of cerebral vessels on the CT image, was used in this series for contrast enhancement. By this method, 1 ml/kg of 60% meglumine iothalamate was injected into the antecubital vein through a No. 18 FIG. 2. Case 12. Left: Computerized angiotomographic image, modified coronal plane, of the middle cerebral artery (MCA) aneurysm. The horizontal portion of the MCA (large arrow) runs inferolaterally in the Sylvian fissure and then turns up and forms a localized complex. A well demarcated high-density mass (small arrow) is seen at the bifurcation of the MCA. Right: Carotid angiogram, anteropostenor view, showing an MCA bifurcation aneurysm and reflecting the findings of the computerized angiotomogram. 528 J. Neurosurg. / Volume 57/October, 1982

3 Computerized angiotomography in unruptured aneurysms FIG. 3. Case 10. Computerized angiotomogram (left) and brachial angiogram (right) of an upper basilar artery aneurysm. A round high-density mass (arrow) protrudes anteriorly from the top of the basilar artery. needle at a speed of 2 ml/sec. The scan was begun immediately after the contrast material had been administered. Usually, two or three serial tomograms at 5-mm intervals, centering on the basal cistern in the axial transverse scan and the anterior clinoid processes in the modified coronal plane, were sufficient for adequate CT delineation of the circle of Willis and other major cerebral arteries. Before each scan, contrast materials were added as in the first scan. Results The outcome in 14 patients whose unruptured aneurysms were first detected by computerized angiotomography are summarized in Table 1. The aneurysms were located as follows: six were in the middle cerebral artery (Figs. 1 and 2), three in the upper half of the basilar artery (Fig. 3), two in the anterior communicating artery (Fig. 4), two in the posterior cerebral artery, and two at the junction of the internal Fx6. 4. Case 5. Left: Computerized angiotomogram showing a homogeneously enhanced and sharply demarcated oval mass (large arrow) in the anterior portion of the suprasellar cistern. The right AI segment (arrowhead) is dominant, and two efferent arteries (small arrows) are delineated. Right: Right carotid angiography confirms the anterior communicating artery aneurysm. J. Neurosurg. / Volume 57/October,

4 none: unchanged none:unchanged O1 CO 0 TABLE 1 Summary of data in patients with unruptured aneurysm Case Age History & Neurological Original Aneurysm Aneurysm No. (yrs), Findings Disease Location Size (mm) Tomographic Findings Treatment & Result Sex 1 56, M weakness of rt upper limb rt MCA 12 x 13 x 12 plain CT: round defect of rt Sylvian fissure; CAT: homoge- neck clipping: good for 3 mos neous enhanced & well defined round mass at trifurcation of MCA in rt Sylvian fissure; mass was continuous witb M1 & M2 segment 2 43, M headache for 1 mo, no neu- upper 20x15 CAT: enhanced large round mass in basal cistern rological deficit basilar 3 41, F TIA (lt hemiparesis) 1 year moyamoya rt IC-PC plain CT: partially calcified round defects on both sides of earlier, progressive de- It IC-PC 6x7x6 pentagon; CAT: lesions enhanced markedly mentia, It hemiparesis 4 72, F sudden onset of unconsciousness, It hemiparesis, it hemisensory disturbance 5 74, M unconsciousness, seizure, no neurological deficit disease, cerebral infarction small pontine hemorrhage 6 52, M weakness of It lower limb cerebral rt PCA for 2 weeks infarction 7 62, F headache & dizziness, no rt MCA 7 x 7 8 neurological deficit aneurysm coating: good none: aneurysms disappeared 2 years later upper 5 x 4 x 4 plain CT: small oval isodense defect in prepontine cistern; none: unchanged basilar CAT: mass enhanced markedly & delineated sharply ACoA 8 x 8 7 CAT: homogeneously enhanced well defined oval mass in none: unchanged anterior part of suprasellar cistern, continuous with dominant right A1 segment; two efferent arteries (A2); aneu- rysm was buried in right rectus gyrus CAT: enhanced small oval mass continuous with it PCA in rt ambient cistern plain CT: oval isodense defect in rt Sylvian fissure; CAT: enhanced markedly; relation to afferent (M1) & efferent (M2) arteries was well shown none: unchanged neck clipping: acute heart failure 1 mo post-op; died 1 year later none: unchanged , F it hemiparesis for 2 weeks cerebral It MCA infarction 63, F It hemiparesis over previous cerebral rt MCA 5 mos infarction 69, M dysarthria, urinary inconti- cerebral upper nence for 5 mos infarction basilar 45, F transient It hemisensory It PCA disturbance 6x6 5x5x6 8x8x10 12 x CAT: round high-density mass continuous with MCA plain CT: small isodense defect in rt Sylvian fissure; CAT: round well defined high-density mass protruded anteriorly at bifurcation of MCA plain CT: round isodense defect in interpeduncular fossa; CAT: round high-density mass protruded anteriorly from top of basilar artery CAT: large round high-density mass was continuous with It PCA t~ -,q e~ e~ , F It putaminal hemorrhage It putaminal rt MCA 6 months earlier, rt hemi- hemorparesis rhage 64, F convulsion, no neurological epilepsy It MCA deficit 57, F patient presented in fear of ACoA cerebral disease because her husband had intracerebral hemorrhage x5x5 6 CAT: oval high-density mass protruded anteriorly at MCA bifurcation on axial plane; aneurysm shown more clearly on modified coronal plane CAT: round well defined high-density mass protruded laterally at end of left M1 segment; two efferent arteries well recognized CAT: round high-density mass in continuity with It A1 on axial plane; mass differentiated from basal bone structures on modified coronal plane none: died 5 mos after detection on rupture of aneurysm neck clipping: good neck clipping: good neck clipping: good > ga t~,~ * Abbreviations: MCA = middle cerebral artery; IC-PC = internal carotid-posterior communicating artery junction; CT = computerized tomography; CAT = computerized angiotomography; ACoA = anterior communicating artery; PCA = posterior cerebral artery; TIA = transient ischemic attack..'~

5 Computerized angiotomography in unruptured aneurysms TABLE 2 Plain CT findings in 15 unruptured aneurysms Aneurysm No Evi- Calcification Defect Location dence of or High- of Aneurysm density Mass Cistern anterior communicating artery middle cerebral artery IC-PC junction* posterior cerebral artery basilar artery (upper hall) total * IC-PC = internal carotid-posterior communicating artery. carotid and posterior communicating arteries (both in the same patient). The aneurysms varied in size: three were smaller than 5 mm, eight were between 6 and 10 mm, and four were larger than 10 mm. The smallest aneurysm detected by computerized angiotomography was found to be 5 x 4 4 mm in diameter on the angiogram. The aneurysm findings on conventional CT are shown in Table 2. In six cases CT showed no evidence of an aneurysm, and in four cases calcifications or high-density masses were visualized. Five aneurysms were delineated by well demarcated isodense defects of the basal cistern or Sylvian fissure; these defects were highly and homogeneously enhanced by computerized angiotomography (Fig. 5). In general, an aneurysm was demonstrated as a high-density, homogeneous round or oval mass, and it was often continuous with its arterial source of origin (Fig. 6). Discussion Hitherto, unruptured aneurysms have been recognized mainly in patients with severe neurological deficits (for example, patients with brain tumors, head injuries, or cerebral infarctions), 5 but most of the patients in our series had only mild symptoms that did not affect their daily lives (Table 1). Fourteen of the 15 cases of unruptured aneurysms, excluding the one associated with severe head injury, were initially diagnosed not by angiography, but by computerized angiotomography. It seems significant that aneurysms could be detected by this noninvasive diagnostic technique. In general, aneurysms are delineated by computerized angiotomography as small round or oval high-density masses that are continuous with the afferent and efferent arteries. We seldom miss the existence of giant or calcified aneurysms on a plain CT image, but it is extremely difficult to detect small aneurysms using that technique alone. Five aneurysms in our series were rec- FIG. 5. Case 7. Upper Left: Plain computerized tomography (CT) showing a well demarcated oval isodense defect (arrow) in the low-density area of the right Sylvian fissure. Upper Right: Contrast-enhanced CT scan showing the defect enhanced markedly and det-med sharply (arrow), strongly suggesting a middle cerebral artery (MCA) aneurysm. Lower: An MCA bifurcation aneurysm (arrow) was confirmed by computerized angiotomography using the multiple-overlapping method. ognized on plain CT scanning as being well demarcated round or oval isodense masses that formed defects of the basal cistern or Sylvian fissure. These isodense defects were then markedly enhanced and defined sharply by computerized angiotomography. Unruptured aneurysms may be suggested by these defects of the cistern on a plain CT image, but they are highly and homogeneously enhanced by computerized angiotomography. It is said that the limiting factors for the delineation of aneurysms are the size and location of the aneurysms, the anatomical variants of the circle of Willis (in which almost all aneurysms are present), the movement of the patient, and CT resolution. 6,7 The size of aneurysms is certainly a factor in diagnosis: small aneurysms at the base of the brain cannot be detected by CT. However, our experience shows that the detection of aneurysms larger than 5 mm in diameter may be possible by computerized angiotomography. Ghoshhajra, et al., 4 mentioned in their report on 59 cases of ruptured aneurysms that the location of aneu- J. Neurosurg. / Volume 57 / October,

6 S. Asari, et al. C a s e Computed Angiography Case Angiotomography Computed Angiography Angiotomography. BA o.,.ca 4 BA ~ 11 Lt.PCA Rt.MCA 6 Rt.PCA 13 Lt.MCA 7 F]~. 6. Tracings of computerized angiotomographic and angiographic findings of 15 unruptured aneurysms in 14 patients. In general, the aneurysm (arrows) is delineated as a round or oval, well demarcated, high-density homogeneous mass which is continuous with the afferent and efferent arteries. MCA = middle cerebral artery; BA = basilar artery; IC-PC = internal carotid-posterior communicating artery junction; AComA = anterior communicating artery; PCA = posterior cerebral artery. 532 J. Neurosurg. / Volume 57/October, 1982

7 Computerized angiotomography in unruptured aneurysms rysms made a difference in the detection rate. They reported a 76% detection rate for aneurysms in the middle cerebral artery, but only 36% for those in the internal carotid artery. They obtained a higher detection rate for aneurysms in the anterior half of the circle of Willis. However, in our study of the direct detection of ruptured aneurysms by computerized angiotomography, 1 we obtained a higher detection rate of aneurysms than is recorded in other previous reports. 4 We considered that there were two main factors necessary to clearly and accurately delineate the cerebral vessels and their lesions (such as aneurysms, moyamoya disease, or arteriovenous malformations) on a CT image: a detailed knowledge of the normal anatomy of the cerebrovascular structures and a suitable method of contrast enhancement. As has been pointed out, 6 the anatomical variants of the circle of Willis and the major cerebral arteries seen in association with many aneurysms lower the CT detection rate of aneurysms. Thus, it is important to know how to delineate clearly and accurately the major cerebral arteries, such as the circle of Willis, on a CT image. Recently, we carried out a fundamental postmortem study of the normal anatomy of the cerebrovascular structures on a multiplane (projection) CT image. 9 On the slice through the anterior clinoid processes in a modified coronal plane, which is angled approximately 60 ~ to the canthomeatal line, the supraclinoid internal carotid artery arises from the sphenoid bone just inside the anterior clinoid processes, and runs superolaterally. It then branches off the anterior and middle cerebral arteries and forms the so-called "carotid fork." Thus, the supraclinoid internal carotid artery and the carotid fork can be distinguished from the basal bone structures. Therefore, this plane is useful in the diagnosis of lesions of the supraclinoid internal carotid artery and the carotid fork (aneurysms, occlusions, and moyamoya disease), and of anterior communicating artery aneurysms, because it avoids artifacts of the basal bone densities. We now perform direct biplane or multiplane scanning 2 for accurate delineation of aneurysms when unruptured aneurysms are suspected in outpatients. A multiple overlapping section, centering on the basal cistern in the axial transverse or on the anterior clinoid processes in the modified coronal planes, delineates the circle of Willis and other major cerebral arteries with increased detail, and so prevents our making wrong diagnoses. It seems, then, that the degree of the delineation of the cerebral vessels on a CT image depends not on the extravasated contrast material in brain tumors or cerebral infarctions, but on the intravascular iodine concentration of the contrast material. In an earlier study 1~ we injected 60% meglumine iothalamate through the antecubital vein by various kinds of injection methods, then examined the blood iodine concentration of the carotid artery in 21 cases. A study of the relationship between the degree of the delineation of the cerebral vessels in the CT image and the iodine concentration of the contrast material in the carotid artery showed that an iodine level of more than 15 mg/ml was necessary to obtain a clear CT image of the cerebral vessels, especially in small vessels such as lenticulostriate arteries. The iodine level rose promptly, to over 15 mg/ml 20 seconds after injection, and was maintained higher than 15 mg/ ml for the next 20 seconds by the intravenous bolus injection of contrast material at a rate of 1 ml/kg at 2 ml/sec. We were able to obtain a clear image of the cerebral vessels if the scan was performed while a high carotid artery blood iodine level was maintained, when using a high-speed CT scanner. We obtained a clear and more accurate CT image of the cerebral vessels using this new method than with the conventional contrast enhancement CT method. We named this new contrast-enhancement method for the clear delineation of the cerebral vessels the "intravenous minimum-dose bolus injection method;" it is now used clinically as a screening system to detect cerebrovascular lesions, such as unruptured aneurysms. We expect a greater chance of discovering unruptured aneurysms by this method of noninvasive computerized angiotomography. As a result, the treatment of aneurysms that are discovered incidentally will surely become an important problem to be solved by neurosurgeons in the near future. In our series, six patients were operated on, five with good results; the other suffered acute heart failure 1 month after operation and died 1 year later. On the other hand, one of eight nonoperated patients died because of aneurysm rupture 5 months after its detection by computerized angiotomography. Acknowledgments We thank Mr. S. Kato and Mr. S. Ujike for their help in this work, and Miss K. Takasuka for her fine secretarial assistance. References 1. Asari S, Sakurai M, Yamamoto Y, et al: [Usefulness of computed cerebral angiotomography for direct detection of intracranial aneurysms.] Neuroi Med Chir 21: , 1981 (Jpn) 2. Asari S, Satoh T, Sakurai M, et al: [Demonstration of cerebral vessels by multiplane computed cerebral angiotomography.] Prog Comput Tomogr 3: , 1981 (Jpn) 3. Davis KR, New PFJ, Ojemann RG, et al: Computed tomographic evaluation of hemorrhage secondary to intracranial aneurysm. A JR 127: , Ghoshhajra K, Scotti L, Marasco J, et al: CT detection of intracranial aneurysms in subarachnoid hemorrhage. A JR 132: , Graf C J: Prognosis for patients with nonsurgicallytreated aneurysms. Analysis of the Cooperative Study J. 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8 S. Asari, et al. of Intracranial Aneurysms and Subarachnoid Hemorrhage. J Neurosurg 35: , Katada K, Kanno T, Sano H, et al: CT in evaluation of the circle of Willis. Neuroradiology 16: , Pressman BD, Gilbert GE, David DO: Computerized transverse tomography of vascular lesions of the brain. Part II: Aneurysms. A JR 124: , Sadamoto K: [Biplane CT. Theory and Practice.] Tokyo: Neuron, 1980, pp (Jpn) 9. Yamamoto Y, Satoh T, Asari S, et al: [Multiplane postaaortem cerebral computed angiotomography, Part II. Normal anatomy of cerebral vessels on the modified coronal, Towne and semisagittal planes.] No To Shinkei 34: , 1982 (Jpn) 10. Yamamoto Y, Satoh T, Sakurai M, et al: Minimum dose contrast bolus in computed angiotomography of the brain. J Comput Assist Tomogr 6: , 1982 Manuscript received October 22, Accepted in final form May 4, This work was presented at the 7th International Congress of Neurological Surgery, Miinchen, West Germany, July 12-18, Address for Dr. Sadamoto: Department of Neurological Surgery, Sadamoto Hospital, Matsuyama, Ehime, Japan. Address reprint requests to: Syoji Asari, M.D., Department of Neurological Surgery, Matsuyama Shimin Hospital, 2-6-5, Ohtemachi, Matsuyama, Ehime, 790, Japan. 534 J. Neurosurg. / Volume 57/October, 1982