Neuroradiology
The Base View in Vertebral Angiography An Aid in the Diagnosis of Extraaxial Cerebellopontine Angle Tumors 1 Richard S. Pinto, M.D., Ajax E. George, M.D., Irvin I. Kricheff, M.D., Thomas P. Naidich, M.D.,2 and Allan Fox, M.D.3 Though the advent of computed tomography has improved the detection of posterior fossa lesions, there are times when it can not be used to differentiate between an intra- and extraaxial lesion, particularly when the mass is anteriorly located. Base view angiography can be used to make this distinction, accurately localize the lesion, and demonstrate involvement or compression of vital adjoining structures. INDEX TERMS: Posterior fossa, angiography • Posterior fossa, neoplasms • (Vertebral, basilar artery, angiography, 1[75] .1243) • (Vertebral, basilar artery, special nonroutine projection,
1[75].125) Radiology 124: 157-164, July 1977
neurosurgeon in the preoperative assessment of the cerebellar vasculature, since accidental occlusion or laceration of vital arterial or venous structures may lead to irreparable neurological damage. In cerebellopontine angle surgery, the anterior inferior cerebellar artery (AICA) is the most important artery encountered by the surgeon. An acoustic neuroma with its origin at or adjacent to the
HOUGH THE ADVENT of computed tomography (CT) has aided in the detection of posterior fossa lesions, the CT scan will not always disclose whether a mass is intraor extraaxial. Angiography, though now less important in the detection of a mass, must take on a greater role in the precise localization of lesions, with definition of origin and demonstration of involvement or compression of adjacent vital structures. Angiography is also important to the
T
Fig. 1. A and B. Injected cerebellar specimen with corresponding radiograph. A normal PICA is demonstrated in the base view, with its anterior (AM), lateral (LM) and posterior medullary segments (PM) encircling the medulla oblongata. Foreshortening of the anterior and posterior medullary segments also occurs on the base view projection. The supratonsillar segment (ST) has a medial convexity on the base view as it courses over the cerebellar tonsil. The vermian branches (V) of the PICA are observed in paramedian locations, with hemispheric branches (H) noted to course laterally. A right common AICA-PICA trunk vessel is observed dividing in its cisternal portion into caudomedial (CM) and rostrolateral (RL) branches. Note the anterior convexity of the prepontine segment (PS) of the AICA on the base view, which changes to a posterior convexity in its cisternal segment, distal to the division of the AICA into RL and CM branches. There is an anterior convexity as the AICA reaches the floccular surface of the cerebellum (floccular segment = FS). 1 From the Department of Radiology, Section of Neuroradiology, New York University Medical Center, New York, N. Y. Presented at the Fourteenth Annual Meeting of the American Society of Neuroradiology, Atlanta, Geo., May 19, 1976. ss 2 Present address: Montefiore Hospital and Medical Center, Department of Radiology, New York, N. Y. 10467. 3 Present address: University Hospital, Department of Radiology, London 72, Ontario, Canada.
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porus acousticus will initially displace the AICA posteriorly. As the AICA may normally either pass superiorly or inferiorly to the seventh and eighth cranial nerves, it may be either elevated or depressed as seen on the straight anteroposterior projection, but it will always be displaced in an arcuate fashion posteriorly away from the petrous bone. This displacement, a key sign in differentiating between intra- and extraaxial lesions, is best evaluated by a base view angiogram (BVA). The frontal angiogram leaves much to be desired in determining brain stem compression by an extraaxial tumor, or extension of the tumor to the tentorial notch, information which, if known preoperatively, will frequently change the planned surgical approach from one of total excision of the tumor to that of a subtotal intracapsular removal. The BVA can provide this information; it will accurately demonstrate medial displacement of either the prepontine portion of the AICA or the circum-mesencephalic segment of the superior cerebellar artery (SCA). This is indicative of brain stem compression, with its im-
July 1977
plied adherence by tumor and extension to the tentorial notch. By determining the primary vascular displacement as seen on the BVA, differentiation between a low and high cerebellopontine angle mass may be made. BASE VIEW ANATOMY
Forty-six injected brain specimens and 18 normal vertebral base view angiograms were evaluated for the "typical" configuration of the posterior fossa vasculature. Our findings are summarized relative to the anatomic courses of the posterior inferior cerebellar artery (PICA), the anterior inferior cerebellar artery (AICA), and the superior cerebellar artery (SCA). The PICA supplies the inferior posterior quarter of the cerebellar hemisphere, including the cerebellar tonsil, the inferior portion of the vermis, and the choroid plexus of the fourth ventricle. One of its subdivisions is the anterior medullary segment, which is related to the medulla oblongata and courses inferoposteriorly to the medullary ridge
Fig. 2. Normal base view vertebral angiograms. A. Normal base view anatomy of the PICA and the SCA. Both PICAs are filled. The segments of the PICA are labelled (see legend to Figure 1).Note that the supratonsillar segments of both PICAs, which course superomedially over the cerebellar tonsils, come together in the midline (arrowheads). The normal course of the SCA is seen circling the mesencephalon. The crural (arrow), perimesencephalic (crossed arrow), and quadrigeminal segments of the SCA (double crossed arrow) are clearly observed outlining the normal midbrain. Note that the crural segment has an anterior convexity, the perimesencephalic segment has a lateral convexity, and the superior vermian branches of the SCA arise at the termination of the SCA at its quadrigeminal segment. These vermian arteries have a paramedian course. B. Normal base view anatomy of the AICA. Bilateral common AICA-PICA trunks are observed (arrows) with smaller accessory AICAs (arrowheads). The 3 segments of AICA are labelled (see legend to Figure 1). The normal sigmoid-shaped course of the AICA on the baseview angiogram is noted, and easily compared to the contralateral side.
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of the biventral lobule. This segment is foreshortened in the base projection, and is frequently projected as a loop; it occasionally may be absent (Figs. 1, A and S, and 2, A). The second segment of the PICA, the lateral medullary segment, is related to the IcHeral aspect of the medulla as the artery runs posteriorly in the, cerebellomedullary fissure. This segment is seen in its entirety on the base projection, having initially a stnooth curvature, laterally around the medulla, then returning to a paramedian position at the posterolateral aspect of the medulla. The vessel then abruptly turns superiorly adjacent to the medial aspect of the tonsil as the posterior medullary segment, which occasionally may be medial or lateral to the tonsil (7), and is closely related to the roof of the lower part of the fourth ventricle. This segment i~ foreshortened and is frequently observed as a sigmoid.:.shaped loop on the base view projection. The artery courses over the tonsil (supratonsillar segment) and reaches the posterior margin of the tonsil, runs downward in the retrotonsillar fissure (where it is the superior retrotonsillar segment) and finally terminates as the verrnlan branches (2, 5, 6). The normal AlGA may be divided into three segments: (a) the prepontine segment, related to the anterior margin of the pons; (b) the Cisternal segment, where the artery divides into rostrolateral and caudomedial branches; and (c) the floccular segment, which is related to the anterior surface of the cerebellum. In 30 % of the cases, accessory arteries may be present (9). The rostrolateral artery (RL) is larger than the caudomedial (GM) artery, except when the PICA is hypoplastic or absent. The entire course of the
AlGA and its major divisions is clearly observed on the base view (Figs. 1, A and B, and 2, B). The prepontine segment is anteriorly convex on a properly angled base projection. The cisternal portion of the AICA frequently demonstrates a slight posterior convexity immediately distal to its division into RL and CM branches. The RL reaches the seventh and eighth cranial nerves anterior to the flocculus; this portion is tethered and may not be displaced by extraaxial cerebellopontine angle masses. On the BV A, the RL is anteriorly convex distal to its origin within the cerebellopontine angle cistern, and describes a single or double arterial loop anterior to the flocculus. The RL then continues posterolaterally to enter the great horizontal fissure. The CM, in the base projection, has a slight posterior convexity in its cisternal portion distal to the sixth nerve. It continues anteriorly to lie beneath the flocculus and on the petrosal surface of the biventral lobule. The CM then turns posteromedially, coursing on the lateral aspect of the biventral lobule, and finally reaches the posteroinferior surface of the cerebellum (2, 3, 8, 10-13). The SCA originates from the basilar artery and passes anterior to the cerebral peduncles (crural segment), then courses laterally and posteriorly around the midbrain. This portion of the SCA has been termed the circum-mesencephalic segment. The marginal artery is a branch of this portion of the SCA; it supplies the anterior and superior surfaces of the cerebellum. The SCA approaches the midline posterior to the quadrigeminal plate (quadrigeminal segment), and terminates as the superior vermian
INPIUIlOA O ...ITOMEATAL LINE
A
Neuroradiology
B
ANTERIOR
PCA--m-n-"-"""""~""""
SCA'"--"JrN-~'--,~ '~I--~~:o....:------t-t\--AICA eup.rlor
poe'.rlor
POSTERIOR
Fig. 3. A. Schematic diagram demonstrating the 80-85° angulation of the central ray of the x-ray beam to the inferior orbitomeatalline to obtain a base view during vertebral angiography. This angulation was chosen to visualize the entire course of the AlGA without the superimposition of the crural segments of the SCA which occurs with greater angUlation,and to prevent flattening of the anterior convexity of the prepontine portion of the AlGA which is seen with a lesser degree of angulation. B. Schematic diagram of the base of skull with the "normal" vasculature superimposed. Note that the prepontine and cisternal segments of the AlGA are not obscured by overlying branches of the SCA and PCA, whereas the floccular segment is partially hidden. This is a frequent occurrence ih vertebral base view angiography, but does not hinder the angiographic interpretation of an extraaxial cerebellopontine mass, which depends primarily on the posteromedial displacement of the proximal segments of the AICA (PCA = posterior cerebral artery; SCA = superior anterior inferior cerebellar artery). cerebellar artery; AICA
=
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Table I:
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Diagnoses
Extraaxial Acoustic Neuromas Meningiomas Cholesteatoma 5th Nerve Neuromas* Craniopharyngioma Arachnoidal Cysts Subdural Hematoma Paraganglioma Intraaxial Brain Stem GI ioma/Metasteses** Cerebellar Hemispheric Metastases Medulloblastoma Hemangioblastoma Cerebellar Hemispheric Astrocytoma Diffuse Cerebellar Swelling*** Intraventricular (IV Ventricle) Cholesteatoma Glioma* Vascular AVM with Cerebellar Hematoma Aneurysms Supratentorial Thalamic Astrocytoma Falcine Meningioma Normal Total * 1 Case not pathologically proved. **4 Cases not pathologically proved. ***Not pathologically proved.
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branches (2, 4, 8, 9). The BVA delineates all 3 segments of the SeA in their entirety (Fig. 2, B). 6 5 1 3 2 2 1
1 5 2 3 2 1
1
1 4 1 1 18
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MATERIAL AND METHODS
The Schonander serial changer base was modified to permit a 25° angulation of the film plane. This complemented head extension so that the x-ray beam had an 80-85° angulation to the interior orbitomeatal line (Fig. 3, A). This degree of angulation is best for observing the entire course of the AlGA, particularly the prepontine segment, which would be hidden by superimposition of the crural portions of the SGA if a greater degree of angulation was used. With a lesser degree of angulation the prepontine segment of AlGA loses its typical anterior convexity, and the posterior convexity of the cisternal segment of the AlGA is accentuated (Fig. 3, B). RESULTS
In all cases, a routine 2X magnification lateral angiogram, half-axial frontal angiogram, and/or a straight anteroposterior frontal projection were obtained in addition to the base view angiogram. Sixty-two lesions were
Fig. 4. Base view angiogram and straight anteroposterior projections in a patient with a right acoustic neuroma. A. BVA: Two AICAs (main AICA, arrowheads; accessory AICA, crossed arrows) on the right are bowed posteriorly in arcuate fashion away from the petrous bone, a sign of the extraaxial origin of the tumor. The prepontine segment of the AICA is medially displaced, a sign of tumor impingement upon the lateral surface of the pons. The cisternal and floccular segments of the AICA (the lateral two arrowheads) indicate a tumor within the cerebellopontine angle cistern displacing the anterior surface of the cerebellum away from the petrous pyramid. Note the contralateral displacement of the ST segment of the PICA (arrows), indicative of an ipsilateral posterior fossa mass. B. Straight anteroposterior view demonstrates both main (arrowheads) and accessory AICAs (crossed arrows) displaced inferiorly. The crural segment of the SCA may be elevated. The ST segment of the PICA is obscured. When the AICA is depressed, one is unable to conclusively differentiate an intra- from an extraaxial mass.
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evaluated, including 14 intraaxial tumors, 21 extraaxial tumors (17 involving the cerebellopontine angle and/or cural cisterns), 2 intraventricular lesions, 5 vascular anomalies, and 2 supratentorial tumors; 18 normal studies were also evaluated (TABLE I). Of the extraaxial lesions that involved the cerebellopontine angle, there were 6 acoustic neuromas, 3 fifth nerve neuromas, 3 meningiomas, 1 primary cholesteatoma, 1 paraganglioma (from the jugular fossa involving the 9, 10 and 11th cranial nerves), 2 craniopharyngiomas (impinging upon the crural cistern), and a basilar artery aneurysm with a prepontine clot. The frontal angiograms revealed the AlGA to be elevated in 7 extraaxial cerebellopontine angle tumors, depressed in 5, and not displaced in 5 (TABLE II). In all 12 cases where the AlGA was displaced, the BVA demonstrated the AlGA to be stretched in an arcuate fashion away from the petrous bone, an infallible sign of the extraaxial origin of the lesion (Figs. 4, A and B; 5, A and B; 6, A and B). Of the 15 extraaxial tumors which involved the cerebellopontine angle, the cisternal portion of the AICA was displaced in 12, with the prepontine segment of the AlGA displaced medially in 11 (Figs. 4, A, 5, A, 6, A). At surgery, all 11 tumors were found to be adherent to the lateral or anterolateral aspect of the pons. Only the tumor that did not displace the prepontine segment, an acoustic neuroma measuring 2 X 2 X 3 em, was found at surgery to be separate from the lateral aspect of the pons.
Table II:
Neuroradiology
AICA Configuration on the Anteroposterior Projection Cases
Diagnoses
Elevated
7
Depressed
5
No Displacement
5
2 Acoustic Neuromas 2 CP Angle Meningiomas Paraganglioma Basilar Artery Aneurysm with Hematoma Clival Cholesteatoma 4 Acoustic Neuromas 1 CP Angle Meningioma 3 Fifth Nerve Neuromas 2 Craniopharyngiomas
--------
In our series of 6 acoustic neuromas, 4 demonstrated medial displacement of the circum-mesencephalic portion of the SGA; this finding correlated with the operative finding of extension of the tumor into the incisura. Two cerebellopontine angle meningiomas also produced similar SGA displacement (Fig. 6, A and B). All 6 cerebellopontine angle lesions with extension into the incisura were so diagnosed preoperatively on BV A. In only 2 of these cases was it possible to make this diagnosis from routine projections. Three fifth nerve neuromas were studied, 2 of which were histologically verified. The SeA was the primary vessel displaced by high cerebellopontine angle masses, with no displacement of the AlGA (Fig. 7, A and B). This
Fig. 5. Vascular acoustic neuroma, right cerebellopontine angle. A. BVA reveals the right AICA posteriorly displaced in arcuate fashion away from the petrous bone (arrowheads). An inferior accessory AICA is also arcuately displaced around the posterior margin of the tumor (arrows). The PICA is noted to be shifted posteriorly and across the midline (crossed arrows). The medial displacement of the prepontine segment of the AICA indicates brain stem impingement, with its implied adherence by tumor. The neovascularity of the tumor appears to originate from the inferior accessory AICA. B. Straight anteroposterior view demonstrates a confusing picture of the AICA because of the increased vascularity of the tumor. It is not clear on this view whether elevation or depression of AICA has occurred. A determination of the displacement of the PICA can not be determined on this view.
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pattern eliminates an acoustic neuroma from consideration. DISCUSSION
It is generally accepted that the half-axial or Towne projection is suboptimal for visualtzation of the total course of the AlGA, primarily because of superimposition of the prepontine and cisternal portions of the AICA by the posterior medullary segment and other branches of the PICA. Takahashi (12, 13) has recommended the routine use of the straight anteroposterior projection to best demonstrate the full course of the AICA. In a series of 14 cerebellopontine angle tumors he noted displacement of the AlGA in 9. Two lesions were intraaxial tumors with exophytic extension into the cerebellopontlne angle. Six lesions, all extraaxial in origin, displaced the AICA superiorly. Downward displacement was observed in 2: a meningioma and an astrocytoma with exophytic extension. By comparison, in a group of 24 intraaxial tumors cited by the same author (12), the AlGA was slightly depressed by 3 pontine tumors, a cerebellar hemisphere metastasis, and a cerebellar epidermoid tumor. Takahashi therefore concluded that elevation of the AlGA is strongly indicative of an expanding extraaxial lesion of the cerebellopontine
July 1977
angle, a finding which our results have fully corroberated. He further concluded that depression of the AlGA is unreliable in differentiating between an, intraaxial and an extraaxiallesion of the cerebellopontlne angle. From its origin, the AlGA passes anterior to the belly of the pons and dips slightly inferiorly while coursing laterally in the cerebellopontlne angle cistern anterior to the sixth cranial nerve. It then passes either superior or inferior to the seventh and eighth cranial nerves; this relationship determines whether an acoustic neuroma either elevates or depresses the cisternal portion of the AlGA (8). A certain number of extraaxial cerebellopontine angle tumors will therefore depress the AlGA on the frontal projection and difficulty may arise in differentiating an extraaxial lesion from an intraaxial mass. In our series of 12 extraaxial tumors of the cerebellopontine angle (exclusive of the 3 fifth nerve neuromas), the BV A demonstrated stretching of the AlGA in an arcuate fashion away from the petrous bone, a sign of the extraaxial origin of the lesion (Figs. 4, A; 5, A; 6, A). Thus in the 5 cases with depression of the AICA on the frontal projections, the BV A was more reliable than the anteroposterior projection in determining the origin of the mass (Figs. 4, A and B~ 5, A and B; 6, A and B). The radiological literature has not dealt with the medial
Fig. 6. Left acoustic neuroma with anterior incisural extension. A. The BVA demonstrates an extraaxial configuration of the AlGA, with medial displacement of the prepontine segment (arrow), indicative of brain stem involvement and its implied adherence by tumor. Medial displacement of a branch of the superior cerebellar artery (arrowhead) indicates extension of tumor to the incisura, with implied tumor adherence to the lateral aspect of the mesencephalon. Posterior displacement of the ipsilateral posterior medullary segment of PIGA is also noted (crossed arrow). B. Straight anteroposterior view reveals depression of the left AlGA. This projection is inconclusive regarding the occurrence of tumor extension into the tentorial notch and brain stem impingement.
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IN
VERTEBRAL
growth of extraaxial tumors to involve the brain stem, a phenomenon frequently associated with tumors greater than 2.5 cm in diameter. It is our feeling that neither the half-axial nor the anteroposterior projection gives any clear delineation of brain stem involvement. On the BVA, medial displacement of the prepontine segment of the AlGA indicates brain stem impingement and implies significant adherence by the tumor to the anterolateral aspect of the brain stem, which may render total excision impossible (Figs. 4, A and B; 5, A and B; 6, A and B). Growth of the tumor to and above the tentorial notch may preclude total removal of the tumor, or may require variations in the surgical approach. No angiographic signs of this extension, except in very massive lesions, are described in the radiographic literature. Keiffer (8) states the one may suspect extension of an extraaxial cerebellopontine angle mass which has grown upward anterior to the brain stem and through the tentorial notch on the basis of upward and posterior displacement of the proximal portions of the posterior cerebral and superior cerebellar arteries. He further suggests that these findings strongly favor a diagnosis of meningioma. We feel that these vascular displacements indicate only a very large lesion. Medial deviation of the circum-mesencephalic portion of the SGA, or posterior displacement of the crural segment of the SGA as demonstrated on the BVA, is a strong indication that the tumor has extended to the tentorial
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notch, and will be present with relatively small tumors in the area. Adherence of the tumor to the lateral aspect of the mesencephalon is frequent when these vascular displacements are present. The BVA may be used to differentiate between a low or high cerebellopontine angle mass. In cases of low cerebellopontine angle lesions with tentorial extension there is arcuate posterior displacement of the AlGA and medial displacement of the circum-mesencephalic segment of the SGA. This pattern is most frequently ~een with acoustic neuromas and low petrosal meningiomas. In high cerebellopontine angle lesions, marked medial displacement of the crural and circum-mesencephalic segments of the SGA is observed, with no displacement of the AlGA, which essentially eliminates an acoustic neuroma from the differential diagnosis (Fig. 7, A and B). We have observed this pattern in 3 cases of fifth nerve neuroma and also in a case of tentorial meningioma (14, 15). CONCLUSIONS
The BVA is helpful in differentiating intraaxial from extraaxial tumors, particularly when the frontal anteroposterior projection is inconclusive, by demonstrating posterior arcuate displacement of the AlGA. Medial displacement of either the prepontine segment of the AlGA or the circum-mesencephalic segment of the SGAindicates brain stem involvement, with its implied adherence by the
Fig. 7. Right fifth nerve neuroma with extension into the superior portion of the cerebellopontine angle cistern. A. BVA demonstrates marked medial displacement of the right superior cerebellar artery (arrow), indicative of "high" brain stem compression. The ipsilateral AICA is normal (arrowheads), which eliminates an acoustic neuroma from the differential diagnosis. This pattern of displacement of the superior cerebellar artery and a normal AICA is indicative of a high cerebellopontine angle, anterior incisural mass. B. Towne's projection, vertebral angiogram: medial displacement of the superior cerebellar artery is demonstrated. The course of the AICA, obscured by the PICA, cannot be evaluated.
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tumor. Medial displacement of the circum-mesencephalic segment of the SCA is highly suggestive of tumor extension into the incisura. Predominent displacement of the AICA with minimal displacement of the SCA indicates a low cerebellopontine angle lesion, which is most frequently an acoustic neuroma. Marked displacement of the SCA with little or no displacement of the AICA is seen with high cerebellopontine angle masses (at the anterior aspect of the incisura), and observed primarily with fifth nerve neuromas and petrosal and/or tentorial meningiomas. ACKNOWLEDGEMENTS: We sincerely wish to thank Ms LindaMichaels for her devotion to the preparation of this manscript, and Mr. George Ozaki and Brian Zietlow for their excellent photo-reproductions. Department of Radiology New York University Medical Center New York, N. Y. 10016
REFERENCES 1. Atkinson WJ: The anterior inferior cerebellar artery: its variations, pontine distribution, and significance in the surgery of cerebello-pontine angle tumors. J Neurol NeurosurgPsychiatr 12:137-151, May 1949 2. George AE: A systematic approach to the interpretation of posterior fossa angiography. Radiol Clin North Am 12:371-400, Aug 1974 3. Gerald B, Wolpert SM, Haimovici H: Angiographic anatomy of the anterior inferior cerebellar artery. Am J Roentgenol 118:617-621, Jul 1973 4. HoffmanHB, Margolis Mr, Newton TH: The superior cerebellar
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artery. Section 1. Normal gross and radiologicanatomy. [In]: Radiology of the Skull and Brain, ed by TH Newton and OGPotts. S1. Louis, Mosby, vol 2, book 2,1974, pp 1,809-1,830 5. Greitz T, Sjogren SE: The posterior inferior cerebellar artery. Acta Radiol (Diag) 1:284-297, 1963 6. HuangYP, Wolf BS: Angiographic features of fourth ventricle tumors with special reference to the posterior inferior cerebellar artery. Am J RoentgenoI107:543-564, Nov 1969 7. Huang,YP, Wolf BS: Differential diagnosis of fourth ventricle tumors. Neuroradiology 1:4-19, 1970 8. Kieffer SA, Binet EF, Gold LHA: Angiographic diagnosis of intra- and extraaxial tumors in the cerebellopontine angle. Am J RoentgenoI124:297-309, Jun 1975 9. Mani RL, Newton TH, Glickman MG: The superior cerebellar artery: an anatomic-roentgenographic correlation. Radiology 91: 1,102-1,108, Dec 1968 10. Naidich TP, Kricheff II, George AE, et al: The normal anterior inferior cerebellar artery. Anatomic-radiographic correlation with emphasis on the lateral projection. Radiology 119:355-373, May 1976 11. Naidich TP, Kricheff II, George AE, et al: The anterior inferior cerebellar artery in mass lesions. Radiology 119:375-383, May 1976 12. Takahashi M, Wilson G, Hanafee W: The anterior inferior cerebellar artery: its radiographic anatomy and significance in the diagnosis of extraaxial tumors of the posterior fossa. Radiology 90: 281-287, Feb 1968 13. Takahashi M, Okudera T, Tomanaga M, et al: Angiographic diagnosisof acoustic neurinomas: analysisof 30 lesions.Neuroradiology 2:191-200, 1971 14. Mello LR, Tanzer A: Some aspects of trigeminal neurinomas. Neuroradiology 4:215-221, 1972 15. Wullenweber R, Traupe H, Schwarz G: Angiographic demonstration of a trigeminal neurinoma. Neuroradiology 10:225-229, 1976
The Base View in Vertebral Angiography An Aid in the Diagnosis of Extraaxial Cerebellopontine Angle Tumors 1 Richard S. Pinto, M.D., Ajax E. George, M.D., Irvin I. Kricheff, M.D., Thomas P. Naidich, M.D.,2 and Allan Fox, M.D.3 Though the advent of computed tomography has improved the detection of posterior fossa lesions, there are times when it can not be used to differentiate between an intra- and extraaxial lesion, particularly when the mass is anteriorly located. Base view angiography can be used to make this distinction, accurately localize the lesion, and demonstrate involvement or compression of vital adjoining structures. INDEX TERMS: Posterior fossa, angiography • Posterior fossa, neoplasms • (Vertebral, basilar artery, angiography, 1[75] .1243) • (Vertebral, basilar artery, special nonroutine projection,
1[75].125) Radiology 124: 157-164, July 1977
neurosurgeon in the preoperative assessment of the cerebellar vasculature, since accidental occlusion or laceration of vital arterial or venous structures may lead to irreparable neurological damage. In cerebellopontine angle surgery, the anterior inferior cerebellar artery (AICA) is the most important artery encountered by the surgeon. An acoustic neuroma with its origin at or adjacent to the
HOUGH THE ADVENT of computed tomography (CT) has aided in the detection of posterior fossa lesions, the CT scan will not always disclose whether a mass is intraor extraaxial. Angiography, though now less important in the detection of a mass, must take on a greater role in the precise localization of lesions, with definition of origin and demonstration of involvement or compression of adjacent vital structures. Angiography is also important to the
T
Fig. 1. A and B. Injected cerebellar specimen with corresponding radiograph. A normal PICA is demonstrated in the base view, with its anterior (AM), lateral (LM) and posterior medullary segments (PM) encircling the medulla oblongata. Foreshortening of the anterior and posterior medullary segments also occurs on the base view projection. The supratonsillar segment (ST) has a medial convexity on the base view as it courses over the cerebellar tonsil. The vermian branches (V) of the PICA are observed in paramedian locations, with hemispheric branches (H) noted to course laterally. A right common AICA-PICA trunk vessel is observed dividing in its cisternal portion into caudomedial (CM) and rostrolateral (RL) branches. Note the anterior convexity of the prepontine segment (PS) of the AICA on the base view, which changes to a posterior convexity in its cisternal segment, distal to the division of the AICA into RL and CM branches. There is an anterior convexity as the AICA reaches the floccular surface of the cerebellum (floccular segment = FS). 1 From the Department of Radiology, Section of Neuroradiology, New York University Medical Center, New York, N. Y. Presented at the Fourteenth Annual Meeting of the American Society of Neuroradiology, Atlanta, Geo., May 19, 1976. ss 2 Present address: Montefiore Hospital and Medical Center, Department of Radiology, New York, N. Y. 10467. 3 Present address: University Hospital, Department of Radiology, London 72, Ontario, Canada.
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porus acousticus will initially displace the AICA posteriorly. As the AICA may normally either pass superiorly or inferiorly to the seventh and eighth cranial nerves, it may be either elevated or depressed as seen on the straight anteroposterior projection, but it will always be displaced in an arcuate fashion posteriorly away from the petrous bone. This displacement, a key sign in differentiating between intra- and extraaxial lesions, is best evaluated by a base view angiogram (BVA). The frontal angiogram leaves much to be desired in determining brain stem compression by an extraaxial tumor, or extension of the tumor to the tentorial notch, information which, if known preoperatively, will frequently change the planned surgical approach from one of total excision of the tumor to that of a subtotal intracapsular removal. The BVA can provide this information; it will accurately demonstrate medial displacement of either the prepontine portion of the AICA or the circum-mesencephalic segment of the superior cerebellar artery (SCA). This is indicative of brain stem compression, with its im-
July 1977
plied adherence by tumor and extension to the tentorial notch. By determining the primary vascular displacement as seen on the BVA, differentiation between a low and high cerebellopontine angle mass may be made. BASE VIEW ANATOMY
Forty-six injected brain specimens and 18 normal vertebral base view angiograms were evaluated for the "typical" configuration of the posterior fossa vasculature. Our findings are summarized relative to the anatomic courses of the posterior inferior cerebellar artery (PICA), the anterior inferior cerebellar artery (AICA), and the superior cerebellar artery (SCA). The PICA supplies the inferior posterior quarter of the cerebellar hemisphere, including the cerebellar tonsil, the inferior portion of the vermis, and the choroid plexus of the fourth ventricle. One of its subdivisions is the anterior medullary segment, which is related to the medulla oblongata and courses inferoposteriorly to the medullary ridge
Fig. 2. Normal base view vertebral angiograms. A. Normal base view anatomy of the PICA and the SCA. Both PICAs are filled. The segments of the PICA are labelled (see legend to Figure 1).Note that the supratonsillar segments of both PICAs, which course superomedially over the cerebellar tonsils, come together in the midline (arrowheads). The normal course of the SCA is seen circling the mesencephalon. The crural (arrow), perimesencephalic (crossed arrow), and quadrigeminal segments of the SCA (double crossed arrow) are clearly observed outlining the normal midbrain. Note that the crural segment has an anterior convexity, the perimesencephalic segment has a lateral convexity, and the superior vermian branches of the SCA arise at the termination of the SCA at its quadrigeminal segment. These vermian arteries have a paramedian course. B. Normal base view anatomy of the AICA. Bilateral common AICA-PICA trunks are observed (arrows) with smaller accessory AICAs (arrowheads). The 3 segments of AICA are labelled (see legend to Figure 1). The normal sigmoid-shaped course of the AICA on the baseview angiogram is noted, and easily compared to the contralateral side.
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of the biventral lobule. This segment is foreshortened in the base projection, and is frequently projected as a loop; it occasionally may be absent (Figs. 1, A and S, and 2, A). The second segment of the PICA, the lateral medullary segment, is related to the IcHeral aspect of the medulla as the artery runs posteriorly in the, cerebellomedullary fissure. This segment is seen in its entirety on the base projection, having initially a stnooth curvature, laterally around the medulla, then returning to a paramedian position at the posterolateral aspect of the medulla. The vessel then abruptly turns superiorly adjacent to the medial aspect of the tonsil as the posterior medullary segment, which occasionally may be medial or lateral to the tonsil (7), and is closely related to the roof of the lower part of the fourth ventricle. This segment i~ foreshortened and is frequently observed as a sigmoid.:.shaped loop on the base view projection. The artery courses over the tonsil (supratonsillar segment) and reaches the posterior margin of the tonsil, runs downward in the retrotonsillar fissure (where it is the superior retrotonsillar segment) and finally terminates as the verrnlan branches (2, 5, 6). The normal AlGA may be divided into three segments: (a) the prepontine segment, related to the anterior margin of the pons; (b) the Cisternal segment, where the artery divides into rostrolateral and caudomedial branches; and (c) the floccular segment, which is related to the anterior surface of the cerebellum. In 30 % of the cases, accessory arteries may be present (9). The rostrolateral artery (RL) is larger than the caudomedial (GM) artery, except when the PICA is hypoplastic or absent. The entire course of the
AlGA and its major divisions is clearly observed on the base view (Figs. 1, A and B, and 2, B). The prepontine segment is anteriorly convex on a properly angled base projection. The cisternal portion of the AICA frequently demonstrates a slight posterior convexity immediately distal to its division into RL and CM branches. The RL reaches the seventh and eighth cranial nerves anterior to the flocculus; this portion is tethered and may not be displaced by extraaxial cerebellopontine angle masses. On the BV A, the RL is anteriorly convex distal to its origin within the cerebellopontine angle cistern, and describes a single or double arterial loop anterior to the flocculus. The RL then continues posterolaterally to enter the great horizontal fissure. The CM, in the base projection, has a slight posterior convexity in its cisternal portion distal to the sixth nerve. It continues anteriorly to lie beneath the flocculus and on the petrosal surface of the biventral lobule. The CM then turns posteromedially, coursing on the lateral aspect of the biventral lobule, and finally reaches the posteroinferior surface of the cerebellum (2, 3, 8, 10-13). The SCA originates from the basilar artery and passes anterior to the cerebral peduncles (crural segment), then courses laterally and posteriorly around the midbrain. This portion of the SCA has been termed the circum-mesencephalic segment. The marginal artery is a branch of this portion of the SCA; it supplies the anterior and superior surfaces of the cerebellum. The SCA approaches the midline posterior to the quadrigeminal plate (quadrigeminal segment), and terminates as the superior vermian
INPIUIlOA O ...ITOMEATAL LINE
A
Neuroradiology
B
ANTERIOR
PCA--m-n-"-"""""~""""
SCA'"--"JrN-~'--,~ '~I--~~:o....:------t-t\--AICA eup.rlor
poe'.rlor
POSTERIOR
Fig. 3. A. Schematic diagram demonstrating the 80-85° angulation of the central ray of the x-ray beam to the inferior orbitomeatalline to obtain a base view during vertebral angiography. This angulation was chosen to visualize the entire course of the AlGA without the superimposition of the crural segments of the SCA which occurs with greater angUlation,and to prevent flattening of the anterior convexity of the prepontine portion of the AlGA which is seen with a lesser degree of angulation. B. Schematic diagram of the base of skull with the "normal" vasculature superimposed. Note that the prepontine and cisternal segments of the AlGA are not obscured by overlying branches of the SCA and PCA, whereas the floccular segment is partially hidden. This is a frequent occurrence ih vertebral base view angiography, but does not hinder the angiographic interpretation of an extraaxial cerebellopontine mass, which depends primarily on the posteromedial displacement of the proximal segments of the AICA (PCA = posterior cerebral artery; SCA = superior anterior inferior cerebellar artery). cerebellar artery; AICA
=
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Table I:
S.
PINTO AND OTHERS
Diagnoses
Extraaxial Acoustic Neuromas Meningiomas Cholesteatoma 5th Nerve Neuromas* Craniopharyngioma Arachnoidal Cysts Subdural Hematoma Paraganglioma Intraaxial Brain Stem GI ioma/Metasteses** Cerebellar Hemispheric Metastases Medulloblastoma Hemangioblastoma Cerebellar Hemispheric Astrocytoma Diffuse Cerebellar Swelling*** Intraventricular (IV Ventricle) Cholesteatoma Glioma* Vascular AVM with Cerebellar Hematoma Aneurysms Supratentorial Thalamic Astrocytoma Falcine Meningioma Normal Total * 1 Case not pathologically proved. **4 Cases not pathologically proved. ***Not pathologically proved.
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branches (2, 4, 8, 9). The BVA delineates all 3 segments of the SeA in their entirety (Fig. 2, B). 6 5 1 3 2 2 1
1 5 2 3 2 1
1
1 4 1 1 18
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MATERIAL AND METHODS
The Schonander serial changer base was modified to permit a 25° angulation of the film plane. This complemented head extension so that the x-ray beam had an 80-85° angulation to the interior orbitomeatal line (Fig. 3, A). This degree of angulation is best for observing the entire course of the AlGA, particularly the prepontine segment, which would be hidden by superimposition of the crural portions of the SGA if a greater degree of angulation was used. With a lesser degree of angulation the prepontine segment of AlGA loses its typical anterior convexity, and the posterior convexity of the cisternal segment of the AlGA is accentuated (Fig. 3, B). RESULTS
In all cases, a routine 2X magnification lateral angiogram, half-axial frontal angiogram, and/or a straight anteroposterior frontal projection were obtained in addition to the base view angiogram. Sixty-two lesions were
Fig. 4. Base view angiogram and straight anteroposterior projections in a patient with a right acoustic neuroma. A. BVA: Two AICAs (main AICA, arrowheads; accessory AICA, crossed arrows) on the right are bowed posteriorly in arcuate fashion away from the petrous bone, a sign of the extraaxial origin of the tumor. The prepontine segment of the AICA is medially displaced, a sign of tumor impingement upon the lateral surface of the pons. The cisternal and floccular segments of the AICA (the lateral two arrowheads) indicate a tumor within the cerebellopontine angle cistern displacing the anterior surface of the cerebellum away from the petrous pyramid. Note the contralateral displacement of the ST segment of the PICA (arrows), indicative of an ipsilateral posterior fossa mass. B. Straight anteroposterior view demonstrates both main (arrowheads) and accessory AICAs (crossed arrows) displaced inferiorly. The crural segment of the SCA may be elevated. The ST segment of the PICA is obscured. When the AICA is depressed, one is unable to conclusively differentiate an intra- from an extraaxial mass.
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evaluated, including 14 intraaxial tumors, 21 extraaxial tumors (17 involving the cerebellopontine angle and/or cural cisterns), 2 intraventricular lesions, 5 vascular anomalies, and 2 supratentorial tumors; 18 normal studies were also evaluated (TABLE I). Of the extraaxial lesions that involved the cerebellopontine angle, there were 6 acoustic neuromas, 3 fifth nerve neuromas, 3 meningiomas, 1 primary cholesteatoma, 1 paraganglioma (from the jugular fossa involving the 9, 10 and 11th cranial nerves), 2 craniopharyngiomas (impinging upon the crural cistern), and a basilar artery aneurysm with a prepontine clot. The frontal angiograms revealed the AlGA to be elevated in 7 extraaxial cerebellopontine angle tumors, depressed in 5, and not displaced in 5 (TABLE II). In all 12 cases where the AlGA was displaced, the BVA demonstrated the AlGA to be stretched in an arcuate fashion away from the petrous bone, an infallible sign of the extraaxial origin of the lesion (Figs. 4, A and B; 5, A and B; 6, A and B). Of the 15 extraaxial tumors which involved the cerebellopontine angle, the cisternal portion of the AICA was displaced in 12, with the prepontine segment of the AlGA displaced medially in 11 (Figs. 4, A, 5, A, 6, A). At surgery, all 11 tumors were found to be adherent to the lateral or anterolateral aspect of the pons. Only the tumor that did not displace the prepontine segment, an acoustic neuroma measuring 2 X 2 X 3 em, was found at surgery to be separate from the lateral aspect of the pons.
Table II:
Neuroradiology
AICA Configuration on the Anteroposterior Projection Cases
Diagnoses
Elevated
7
Depressed
5
No Displacement
5
2 Acoustic Neuromas 2 CP Angle Meningiomas Paraganglioma Basilar Artery Aneurysm with Hematoma Clival Cholesteatoma 4 Acoustic Neuromas 1 CP Angle Meningioma 3 Fifth Nerve Neuromas 2 Craniopharyngiomas
--------
In our series of 6 acoustic neuromas, 4 demonstrated medial displacement of the circum-mesencephalic portion of the SGA; this finding correlated with the operative finding of extension of the tumor into the incisura. Two cerebellopontine angle meningiomas also produced similar SGA displacement (Fig. 6, A and B). All 6 cerebellopontine angle lesions with extension into the incisura were so diagnosed preoperatively on BV A. In only 2 of these cases was it possible to make this diagnosis from routine projections. Three fifth nerve neuromas were studied, 2 of which were histologically verified. The SeA was the primary vessel displaced by high cerebellopontine angle masses, with no displacement of the AlGA (Fig. 7, A and B). This
Fig. 5. Vascular acoustic neuroma, right cerebellopontine angle. A. BVA reveals the right AICA posteriorly displaced in arcuate fashion away from the petrous bone (arrowheads). An inferior accessory AICA is also arcuately displaced around the posterior margin of the tumor (arrows). The PICA is noted to be shifted posteriorly and across the midline (crossed arrows). The medial displacement of the prepontine segment of the AICA indicates brain stem impingement, with its implied adherence by tumor. The neovascularity of the tumor appears to originate from the inferior accessory AICA. B. Straight anteroposterior view demonstrates a confusing picture of the AICA because of the increased vascularity of the tumor. It is not clear on this view whether elevation or depression of AICA has occurred. A determination of the displacement of the PICA can not be determined on this view.
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pattern eliminates an acoustic neuroma from consideration. DISCUSSION
It is generally accepted that the half-axial or Towne projection is suboptimal for visualtzation of the total course of the AlGA, primarily because of superimposition of the prepontine and cisternal portions of the AICA by the posterior medullary segment and other branches of the PICA. Takahashi (12, 13) has recommended the routine use of the straight anteroposterior projection to best demonstrate the full course of the AICA. In a series of 14 cerebellopontine angle tumors he noted displacement of the AlGA in 9. Two lesions were intraaxial tumors with exophytic extension into the cerebellopontlne angle. Six lesions, all extraaxial in origin, displaced the AICA superiorly. Downward displacement was observed in 2: a meningioma and an astrocytoma with exophytic extension. By comparison, in a group of 24 intraaxial tumors cited by the same author (12), the AlGA was slightly depressed by 3 pontine tumors, a cerebellar hemisphere metastasis, and a cerebellar epidermoid tumor. Takahashi therefore concluded that elevation of the AlGA is strongly indicative of an expanding extraaxial lesion of the cerebellopontine
July 1977
angle, a finding which our results have fully corroberated. He further concluded that depression of the AlGA is unreliable in differentiating between an, intraaxial and an extraaxiallesion of the cerebellopontlne angle. From its origin, the AlGA passes anterior to the belly of the pons and dips slightly inferiorly while coursing laterally in the cerebellopontlne angle cistern anterior to the sixth cranial nerve. It then passes either superior or inferior to the seventh and eighth cranial nerves; this relationship determines whether an acoustic neuroma either elevates or depresses the cisternal portion of the AlGA (8). A certain number of extraaxial cerebellopontine angle tumors will therefore depress the AlGA on the frontal projection and difficulty may arise in differentiating an extraaxial lesion from an intraaxial mass. In our series of 12 extraaxial tumors of the cerebellopontine angle (exclusive of the 3 fifth nerve neuromas), the BV A demonstrated stretching of the AlGA in an arcuate fashion away from the petrous bone, a sign of the extraaxial origin of the lesion (Figs. 4, A; 5, A; 6, A). Thus in the 5 cases with depression of the AICA on the frontal projections, the BV A was more reliable than the anteroposterior projection in determining the origin of the mass (Figs. 4, A and B~ 5, A and B; 6, A and B). The radiological literature has not dealt with the medial
Fig. 6. Left acoustic neuroma with anterior incisural extension. A. The BVA demonstrates an extraaxial configuration of the AlGA, with medial displacement of the prepontine segment (arrow), indicative of brain stem involvement and its implied adherence by tumor. Medial displacement of a branch of the superior cerebellar artery (arrowhead) indicates extension of tumor to the incisura, with implied tumor adherence to the lateral aspect of the mesencephalon. Posterior displacement of the ipsilateral posterior medullary segment of PIGA is also noted (crossed arrow). B. Straight anteroposterior view reveals depression of the left AlGA. This projection is inconclusive regarding the occurrence of tumor extension into the tentorial notch and brain stem impingement.
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VERTEBRAL
growth of extraaxial tumors to involve the brain stem, a phenomenon frequently associated with tumors greater than 2.5 cm in diameter. It is our feeling that neither the half-axial nor the anteroposterior projection gives any clear delineation of brain stem involvement. On the BVA, medial displacement of the prepontine segment of the AlGA indicates brain stem impingement and implies significant adherence by the tumor to the anterolateral aspect of the brain stem, which may render total excision impossible (Figs. 4, A and B; 5, A and B; 6, A and B). Growth of the tumor to and above the tentorial notch may preclude total removal of the tumor, or may require variations in the surgical approach. No angiographic signs of this extension, except in very massive lesions, are described in the radiographic literature. Keiffer (8) states the one may suspect extension of an extraaxial cerebellopontine angle mass which has grown upward anterior to the brain stem and through the tentorial notch on the basis of upward and posterior displacement of the proximal portions of the posterior cerebral and superior cerebellar arteries. He further suggests that these findings strongly favor a diagnosis of meningioma. We feel that these vascular displacements indicate only a very large lesion. Medial deviation of the circum-mesencephalic portion of the SGA, or posterior displacement of the crural segment of the SGA as demonstrated on the BVA, is a strong indication that the tumor has extended to the tentorial
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notch, and will be present with relatively small tumors in the area. Adherence of the tumor to the lateral aspect of the mesencephalon is frequent when these vascular displacements are present. The BVA may be used to differentiate between a low or high cerebellopontine angle mass. In cases of low cerebellopontine angle lesions with tentorial extension there is arcuate posterior displacement of the AlGA and medial displacement of the circum-mesencephalic segment of the SGA. This pattern is most frequently ~een with acoustic neuromas and low petrosal meningiomas. In high cerebellopontine angle lesions, marked medial displacement of the crural and circum-mesencephalic segments of the SGA is observed, with no displacement of the AlGA, which essentially eliminates an acoustic neuroma from the differential diagnosis (Fig. 7, A and B). We have observed this pattern in 3 cases of fifth nerve neuroma and also in a case of tentorial meningioma (14, 15). CONCLUSIONS
The BVA is helpful in differentiating intraaxial from extraaxial tumors, particularly when the frontal anteroposterior projection is inconclusive, by demonstrating posterior arcuate displacement of the AlGA. Medial displacement of either the prepontine segment of the AlGA or the circum-mesencephalic segment of the SGAindicates brain stem involvement, with its implied adherence by the
Fig. 7. Right fifth nerve neuroma with extension into the superior portion of the cerebellopontine angle cistern. A. BVA demonstrates marked medial displacement of the right superior cerebellar artery (arrow), indicative of "high" brain stem compression. The ipsilateral AICA is normal (arrowheads), which eliminates an acoustic neuroma from the differential diagnosis. This pattern of displacement of the superior cerebellar artery and a normal AICA is indicative of a high cerebellopontine angle, anterior incisural mass. B. Towne's projection, vertebral angiogram: medial displacement of the superior cerebellar artery is demonstrated. The course of the AICA, obscured by the PICA, cannot be evaluated.
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tumor. Medial displacement of the circum-mesencephalic segment of the SCA is highly suggestive of tumor extension into the incisura. Predominent displacement of the AICA with minimal displacement of the SCA indicates a low cerebellopontine angle lesion, which is most frequently an acoustic neuroma. Marked displacement of the SCA with little or no displacement of the AICA is seen with high cerebellopontine angle masses (at the anterior aspect of the incisura), and observed primarily with fifth nerve neuromas and petrosal and/or tentorial meningiomas. ACKNOWLEDGEMENTS: We sincerely wish to thank Ms LindaMichaels for her devotion to the preparation of this manscript, and Mr. George Ozaki and Brian Zietlow for their excellent photo-reproductions. Department of Radiology New York University Medical Center New York, N. Y. 10016
REFERENCES 1. Atkinson WJ: The anterior inferior cerebellar artery: its variations, pontine distribution, and significance in the surgery of cerebello-pontine angle tumors. J Neurol NeurosurgPsychiatr 12:137-151, May 1949 2. George AE: A systematic approach to the interpretation of posterior fossa angiography. Radiol Clin North Am 12:371-400, Aug 1974 3. Gerald B, Wolpert SM, Haimovici H: Angiographic anatomy of the anterior inferior cerebellar artery. Am J Roentgenol 118:617-621, Jul 1973 4. HoffmanHB, Margolis Mr, Newton TH: The superior cerebellar
July 1977
artery. Section 1. Normal gross and radiologicanatomy. [In]: Radiology of the Skull and Brain, ed by TH Newton and OGPotts. S1. Louis, Mosby, vol 2, book 2,1974, pp 1,809-1,830 5. Greitz T, Sjogren SE: The posterior inferior cerebellar artery. Acta Radiol (Diag) 1:284-297, 1963 6. HuangYP, Wolf BS: Angiographic features of fourth ventricle tumors with special reference to the posterior inferior cerebellar artery. Am J RoentgenoI107:543-564, Nov 1969 7. Huang,YP, Wolf BS: Differential diagnosis of fourth ventricle tumors. Neuroradiology 1:4-19, 1970 8. Kieffer SA, Binet EF, Gold LHA: Angiographic diagnosis of intra- and extraaxial tumors in the cerebellopontine angle. Am J RoentgenoI124:297-309, Jun 1975 9. Mani RL, Newton TH, Glickman MG: The superior cerebellar artery: an anatomic-roentgenographic correlation. Radiology 91: 1,102-1,108, Dec 1968 10. Naidich TP, Kricheff II, George AE, et al: The normal anterior inferior cerebellar artery. Anatomic-radiographic correlation with emphasis on the lateral projection. Radiology 119:355-373, May 1976 11. Naidich TP, Kricheff II, George AE, et al: The anterior inferior cerebellar artery in mass lesions. Radiology 119:375-383, May 1976 12. Takahashi M, Wilson G, Hanafee W: The anterior inferior cerebellar artery: its radiographic anatomy and significance in the diagnosis of extraaxial tumors of the posterior fossa. Radiology 90: 281-287, Feb 1968 13. Takahashi M, Okudera T, Tomanaga M, et al: Angiographic diagnosisof acoustic neurinomas: analysisof 30 lesions.Neuroradiology 2:191-200, 1971 14. Mello LR, Tanzer A: Some aspects of trigeminal neurinomas. Neuroradiology 4:215-221, 1972 15. Wullenweber R, Traupe H, Schwarz G: Angiographic demonstration of a trigeminal neurinoma. Neuroradiology 10:225-229, 1976
