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The pathological basilar artery
Clin. Radiol. (1976) 27, 309-316
THE
PATHOLOGICAL
BASILAR
ARTERY
J. D A N Z I G E R , S. B L O C H and H. P O D L A S
From the Department of Radiology, Princess Nursing Home, Johannesburg, South Africa Vascular anomalies of the basilar artery can mimic m a n y intracranial diseases. Various appearances are discussed as well as the displacements of the artery secondary to mass lesions.
THE basilar artery has an intracranial course, lying on the anterior aspect of the pons. It usually runs in a sagittal plane a few millimetres behind the clivus and joins the posterior cerebral arteries at the level of the posterior clinoid processes. Malformations and variations in position of the basilar artery occur and it is the purpose of this communication to demonstrate some of these changes.
VASCULAR A B N O R M A L I T I E S (a) Aneurysms. - These usually occur at the origin or bifurcation of the basilar artery. The aneurysms may be small or large and therefore the clinical presentation and radiographic appearances will vary depending on the size of the aneurysm. When small, the clinical manifestations are due to subarachnoid haemorrhage and the aneurysm will be
FIG. 1 Vertebral angiogram with subtraction: (A) lateral and (B) antero-posterior projections, demonstrating an aneurysm ( t ) at the origin of the basilar artery. 309
310
C L I N I C A L RADIOLOGY
FIO. 2 Vertebral angiogram (A) antero-posterior and (B) lateral projections, demonstrating an aneurysm at the bifurcation ( 1' ) of the basilar artery.
Fro. 3 Pneumoencephalogram, erect lateral projection, demonstrating posterior displacement of the aqueduct and fourth ventricle ( 1' ).
F~o. 4 Vertebral angiogram: (A) lateral with subtraction and (]3) antero-posterior projections, demonstrating aneurysmal dilatation of the basilar artery.
THE P A T H O L O G I C A L B A S I L A R A R T E R Y
311
FIG. 5
A. Pneumoencephalogram, brow-up hanging head lateral projection, demonstrating encroachment on to the floor of the third ventricle (-I"). 8. Vertebral angiogram with subtraction, showing lengthening of the basilar artery which is producing the indentation into the floor of the third ventricle.
demonstrated on vertebral angiography (Figs. 1, 2). When aneurysms of the basilar artery become giant they encroach on to neighbouring structures and the clinical presentation is then protean and the symptomatology due to the situation of the mass lesion rather than due to bleeding (Pribram et al., 1969; Danziger and Bloch, 1975). In these patients plain roentgenograms of the skull are usually normal although curvilinear calcification behind the clivus may be evident. If pneumoencephalography is performed, posterior displacement of the brainstem will be observed, but will give no indication to the underlying etiology (Fig. 3). Vertebral angiography will define the vascular etiology but may not demonstrate the aneurysm's full extent since it may contain a significant amount of clot (Fig. 4). FIG. 6
Pneumoencephalogram,erect lateral projection, demonstrating posterior displacement of the fourth ventricle (]').
(b) Tortuosity. - This is seen especially in arteriosclerotic patients. As the artery elongates it becomes
312
CLINICAL RADIOLOGY
FIG. 7 Vertebral angiogram: (A) lateral and (B) antero-posterior projections, showing extreme tortuosity of the basilar artery. FIG. 8 Vertebral angiogram: (A) lateral and (B) antero-posterior projections with subtraction in an infant, demonstrating an enlarged basilar artery supplying an arteriovenous malformation.
THE P A T H O L O G I C A L BASILAR ARTERY
313
FIG. 9 Left vertebral angiogram: (A) lateral and (B) antero-posterior projections with subtraction, demonstrating non-visualisation of the basilar artery. The contrast has refluxed down the contralateral vertebral artery. The vermal branch of the posterior inferior cerebellar artery is arrowed ( t' ).
Fio. 10 Carotid angiogram, lateral projection with subtraction, showing reflux of contrast down the basilar artery (I"). This is the same patient as Fig. 9.
Fio. 11 Vertebral angiogram, lateral projection with subtraction, showing the approximation of the basilar artery to the clivus m a child with a brainstem glioma. Note the abnormal appearance of the posterior inferior cerebellar artery (~').
314
CLINICAL RADIOLOGY
F~G. 12 Vertebral angiogram: (A) lateral and (B) antero-posterior projections, demonstrating displacement of the basilar artery backwards and to the left in a patient with a clival meningioma. The situation of the clivus is inked-in in (A). FIG. 13 Vertebral angiogram: (A) lateral and (B) antero-posterior projections in a patient where there is obstruction to the myodil filled posterior end of the third ventricle ( ~"), demonstrating the relationship between it and the terminal portion of the basilar artery.
THE P A T H O L O G I C A L B A S I L A R A R T E R Y
tortuous and may then encroach on to the floor of the third ventricle, or displace the brainstem backwards. The clinical presentation will then vary and be protean, since the manifestations may vary from a hydrocephalus, without the intraventricular pressure being elevated (Hakim and Adams, 1965), to symptoms and signs mimicking a posterior fossa tumour or dementia. Plain roentgenograms of the skull will be normal. Pneumoencephalography may demonstrate features of a normal pressure hydrocephalus. Indentation into the floor of the third ventricle may be seen in the brow-up hanging head lateral projection if the artery has lengthened and is encroaching into the floor of the third ventricle (Fig. 5) (Greitz et al., 1971). With extreme tortuosity of the artery the brainstem is displaced backwards (Fig. 6). Vertebral angiography will indicate the diagnosis by demonstrafing the tortuous appearance of the artery (Fig. 7).
315
In these patients vertebral angiography may demonstrate partial or non-filling of the basilar artery. Carotid angiography may demonstrate retrograde filling of the basilar artery as well as the posterior cerebral and superior cerebellar arteries from the posterior communicating artery and define the situation of the occlusion (Fig. 10). The great majority of occlusion of the basilar artery are due to arteriosclerosis. However, this may result from embolism, clivus fractures or infections (Kubik and Adams, 1946; Loop et al., 1964; Schechter and Zingesser, 1965). (e) Displacements. - Alteration in position of the basilar artery occurs with mass displacements. These displacements may be: (a) Anterior in intra-axial tumours as well as tumours lying posterior to the brainstem (Fig. 11). (b) Posteriorly away from the clivus in extra-axial posterior fossa tumours (Fig. 12).
(c) Arteriovenous Malformations. - When malformations receive an arterial supply from the basilar artery or its branches, this artery becomes enlarged and elongated (Fig. 8).
However, posterior displacement of the brainstem should be interpreted with caution since other pathologies can also displace the basilar artery posteriorly. These include:
(d) Occlusions. - In patients developing occlusion of the basilar artery, rapid coma with death usually
(a) Pathology involving the posterior portion of the third ventricle (Fig. 13). This includes tumours as well as acute dilatation of the third ventricle (Scatliff, 1967). (b) Pontine tumours may extend into the prepontine cistern to envelope the basilar artery and with enlargement of the ventral portion of the tumour, displace the artery dorsally presumably by abutting against the clivus (Glickman and Sholkoff, 1971). (c) Backward displacement of the terminal part of the basilar artery in infants has been observed in aqueduct stenosis (Latorre, 1969).
Occurs.
However, in a certain percentage of patients, an adequate collateral circulation occurs and only transient symptoms with brainstem ischaemia results. There is a direct relationship between the availability of collateral pathways and the ability to survive a basilar artery ischaemia. The site of occlusion is usually distal to the origin of the posterior inferior cerebellar arteries (Fig. 9). However, the occlusion may extend more proximally to involve a vertebral artery and the posterior inferior cerebellar artery arising from it. The distal extension of the occlusion is usually just proximal to the origin of the superior cerebellar arteries. Collaterals may occur via the: (a) Circle of Willis and anastomoses between the branches of the basilar artery. (b) Retrograde flow via partial anastomoses between posterior branches of the middle cerebral artery and posterior branches of the posterior cerebral artery (Moscow and Newton, 1973).
Thus an adequate evaluation of the basilar artery is essential when pathology relating to the posterior fossa is suspected. Acknowledgement. - We wish to thank Mrs J. Sudlow for typing the manuscript.
REFERENCES DANZ1GER, J. t~ BLOCH, S. (1975). Aneurysms acting as mass lesions. Clinical Radiology 26, 267-273. GLICKMAN, M. G. 8z SHOLKOFF, S. D. (1971). Posterior displacement of the basilar artery by intrinsic pontine tumours. American Journal of Roentgenology, 1129 276-280.
316
CLINICAL RADIOLOGY
GREITZ, T., EKBOM,K., KUGELBERG,E. & BREIG, A. (1969). Occult hydrocephalus due to ectasia of the basilar artery. Acta radiologica, 9, 310-316. HAKIM, S. & ADAMS,R. D. (1965). The special clinical problem of symptomatic hydrocephalus with normal cerebrospinal pressure. Journal of Neurological Sciences, 2, 307. KUBIK, C. S. t~ ADAMS, R. D. (1946). Occlusion of basilar artery: clinical and pathological study. Brain, 69, 6-121. LATORRE, E. (1968). The angiographic evaluation in eight post-operative cases of infantile hydrocephalus. Neurobiology, 14, 473-482. LooP, J. W., WHITE, L. E. JR & SHAW,C. M. (1964). Traumatic occlusion of basilar artery within clivus fracture.
Radiology, 83, 36-40. Moscow, N. P. & NEWTON, T. H. (1973). Angiographic implications in diagnosis and prognosis of basilar artery occlusion. American Journal of Roentgenology, 119, 597604. PRIBRAM, H. F. W., HUDSON, J. D. & JOYNT, R. J. (1969). Posterior fossa aneurysms presenting as mass lesions. American Journal of Roentgenology, 105, (2), 334-340. SCATLXFE, J. R. (1967). Terminal basilar artery deformity secondary to suprasellar masses and third ventricle dilatation. American Journal of Roentgenology, 101, 61-67. SCh~EcrrrER, M. M. & ZINGESSER,L. H. (1965). Radiology Of basilar thrombosis. Radiology, 85, 23-32.
THE
PATHOLOGICAL
BASILAR
ARTERY
J. D A N Z I G E R , S. B L O C H and H. P O D L A S
From the Department of Radiology, Princess Nursing Home, Johannesburg, South Africa Vascular anomalies of the basilar artery can mimic m a n y intracranial diseases. Various appearances are discussed as well as the displacements of the artery secondary to mass lesions.
THE basilar artery has an intracranial course, lying on the anterior aspect of the pons. It usually runs in a sagittal plane a few millimetres behind the clivus and joins the posterior cerebral arteries at the level of the posterior clinoid processes. Malformations and variations in position of the basilar artery occur and it is the purpose of this communication to demonstrate some of these changes.
VASCULAR A B N O R M A L I T I E S (a) Aneurysms. - These usually occur at the origin or bifurcation of the basilar artery. The aneurysms may be small or large and therefore the clinical presentation and radiographic appearances will vary depending on the size of the aneurysm. When small, the clinical manifestations are due to subarachnoid haemorrhage and the aneurysm will be
FIG. 1 Vertebral angiogram with subtraction: (A) lateral and (B) antero-posterior projections, demonstrating an aneurysm ( t ) at the origin of the basilar artery. 309
310
C L I N I C A L RADIOLOGY
FIO. 2 Vertebral angiogram (A) antero-posterior and (B) lateral projections, demonstrating an aneurysm at the bifurcation ( 1' ) of the basilar artery.
Fro. 3 Pneumoencephalogram, erect lateral projection, demonstrating posterior displacement of the aqueduct and fourth ventricle ( 1' ).
F~o. 4 Vertebral angiogram: (A) lateral with subtraction and (]3) antero-posterior projections, demonstrating aneurysmal dilatation of the basilar artery.
THE P A T H O L O G I C A L B A S I L A R A R T E R Y
311
FIG. 5
A. Pneumoencephalogram, brow-up hanging head lateral projection, demonstrating encroachment on to the floor of the third ventricle (-I"). 8. Vertebral angiogram with subtraction, showing lengthening of the basilar artery which is producing the indentation into the floor of the third ventricle.
demonstrated on vertebral angiography (Figs. 1, 2). When aneurysms of the basilar artery become giant they encroach on to neighbouring structures and the clinical presentation is then protean and the symptomatology due to the situation of the mass lesion rather than due to bleeding (Pribram et al., 1969; Danziger and Bloch, 1975). In these patients plain roentgenograms of the skull are usually normal although curvilinear calcification behind the clivus may be evident. If pneumoencephalography is performed, posterior displacement of the brainstem will be observed, but will give no indication to the underlying etiology (Fig. 3). Vertebral angiography will define the vascular etiology but may not demonstrate the aneurysm's full extent since it may contain a significant amount of clot (Fig. 4). FIG. 6
Pneumoencephalogram,erect lateral projection, demonstrating posterior displacement of the fourth ventricle (]').
(b) Tortuosity. - This is seen especially in arteriosclerotic patients. As the artery elongates it becomes
312
CLINICAL RADIOLOGY
FIG. 7 Vertebral angiogram: (A) lateral and (B) antero-posterior projections, showing extreme tortuosity of the basilar artery. FIG. 8 Vertebral angiogram: (A) lateral and (B) antero-posterior projections with subtraction in an infant, demonstrating an enlarged basilar artery supplying an arteriovenous malformation.
THE P A T H O L O G I C A L BASILAR ARTERY
313
FIG. 9 Left vertebral angiogram: (A) lateral and (B) antero-posterior projections with subtraction, demonstrating non-visualisation of the basilar artery. The contrast has refluxed down the contralateral vertebral artery. The vermal branch of the posterior inferior cerebellar artery is arrowed ( t' ).
Fio. 10 Carotid angiogram, lateral projection with subtraction, showing reflux of contrast down the basilar artery (I"). This is the same patient as Fig. 9.
Fio. 11 Vertebral angiogram, lateral projection with subtraction, showing the approximation of the basilar artery to the clivus m a child with a brainstem glioma. Note the abnormal appearance of the posterior inferior cerebellar artery (~').
314
CLINICAL RADIOLOGY
F~G. 12 Vertebral angiogram: (A) lateral and (B) antero-posterior projections, demonstrating displacement of the basilar artery backwards and to the left in a patient with a clival meningioma. The situation of the clivus is inked-in in (A). FIG. 13 Vertebral angiogram: (A) lateral and (B) antero-posterior projections in a patient where there is obstruction to the myodil filled posterior end of the third ventricle ( ~"), demonstrating the relationship between it and the terminal portion of the basilar artery.
THE P A T H O L O G I C A L B A S I L A R A R T E R Y
tortuous and may then encroach on to the floor of the third ventricle, or displace the brainstem backwards. The clinical presentation will then vary and be protean, since the manifestations may vary from a hydrocephalus, without the intraventricular pressure being elevated (Hakim and Adams, 1965), to symptoms and signs mimicking a posterior fossa tumour or dementia. Plain roentgenograms of the skull will be normal. Pneumoencephalography may demonstrate features of a normal pressure hydrocephalus. Indentation into the floor of the third ventricle may be seen in the brow-up hanging head lateral projection if the artery has lengthened and is encroaching into the floor of the third ventricle (Fig. 5) (Greitz et al., 1971). With extreme tortuosity of the artery the brainstem is displaced backwards (Fig. 6). Vertebral angiography will indicate the diagnosis by demonstrafing the tortuous appearance of the artery (Fig. 7).
315
In these patients vertebral angiography may demonstrate partial or non-filling of the basilar artery. Carotid angiography may demonstrate retrograde filling of the basilar artery as well as the posterior cerebral and superior cerebellar arteries from the posterior communicating artery and define the situation of the occlusion (Fig. 10). The great majority of occlusion of the basilar artery are due to arteriosclerosis. However, this may result from embolism, clivus fractures or infections (Kubik and Adams, 1946; Loop et al., 1964; Schechter and Zingesser, 1965). (e) Displacements. - Alteration in position of the basilar artery occurs with mass displacements. These displacements may be: (a) Anterior in intra-axial tumours as well as tumours lying posterior to the brainstem (Fig. 11). (b) Posteriorly away from the clivus in extra-axial posterior fossa tumours (Fig. 12).
(c) Arteriovenous Malformations. - When malformations receive an arterial supply from the basilar artery or its branches, this artery becomes enlarged and elongated (Fig. 8).
However, posterior displacement of the brainstem should be interpreted with caution since other pathologies can also displace the basilar artery posteriorly. These include:
(d) Occlusions. - In patients developing occlusion of the basilar artery, rapid coma with death usually
(a) Pathology involving the posterior portion of the third ventricle (Fig. 13). This includes tumours as well as acute dilatation of the third ventricle (Scatliff, 1967). (b) Pontine tumours may extend into the prepontine cistern to envelope the basilar artery and with enlargement of the ventral portion of the tumour, displace the artery dorsally presumably by abutting against the clivus (Glickman and Sholkoff, 1971). (c) Backward displacement of the terminal part of the basilar artery in infants has been observed in aqueduct stenosis (Latorre, 1969).
Occurs.
However, in a certain percentage of patients, an adequate collateral circulation occurs and only transient symptoms with brainstem ischaemia results. There is a direct relationship between the availability of collateral pathways and the ability to survive a basilar artery ischaemia. The site of occlusion is usually distal to the origin of the posterior inferior cerebellar arteries (Fig. 9). However, the occlusion may extend more proximally to involve a vertebral artery and the posterior inferior cerebellar artery arising from it. The distal extension of the occlusion is usually just proximal to the origin of the superior cerebellar arteries. Collaterals may occur via the: (a) Circle of Willis and anastomoses between the branches of the basilar artery. (b) Retrograde flow via partial anastomoses between posterior branches of the middle cerebral artery and posterior branches of the posterior cerebral artery (Moscow and Newton, 1973).
Thus an adequate evaluation of the basilar artery is essential when pathology relating to the posterior fossa is suspected. Acknowledgement. - We wish to thank Mrs J. Sudlow for typing the manuscript.
REFERENCES DANZ1GER, J. t~ BLOCH, S. (1975). Aneurysms acting as mass lesions. Clinical Radiology 26, 267-273. GLICKMAN, M. G. 8z SHOLKOFF, S. D. (1971). Posterior displacement of the basilar artery by intrinsic pontine tumours. American Journal of Roentgenology, 1129 276-280.
316
CLINICAL RADIOLOGY
GREITZ, T., EKBOM,K., KUGELBERG,E. & BREIG, A. (1969). Occult hydrocephalus due to ectasia of the basilar artery. Acta radiologica, 9, 310-316. HAKIM, S. & ADAMS,R. D. (1965). The special clinical problem of symptomatic hydrocephalus with normal cerebrospinal pressure. Journal of Neurological Sciences, 2, 307. KUBIK, C. S. t~ ADAMS, R. D. (1946). Occlusion of basilar artery: clinical and pathological study. Brain, 69, 6-121. LATORRE, E. (1968). The angiographic evaluation in eight post-operative cases of infantile hydrocephalus. Neurobiology, 14, 473-482. LooP, J. W., WHITE, L. E. JR & SHAW,C. M. (1964). Traumatic occlusion of basilar artery within clivus fracture.
Radiology, 83, 36-40. Moscow, N. P. & NEWTON, T. H. (1973). Angiographic implications in diagnosis and prognosis of basilar artery occlusion. American Journal of Roentgenology, 119, 597604. PRIBRAM, H. F. W., HUDSON, J. D. & JOYNT, R. J. (1969). Posterior fossa aneurysms presenting as mass lesions. American Journal of Roentgenology, 105, (2), 334-340. SCATLXFE, J. R. (1967). Terminal basilar artery deformity secondary to suprasellar masses and third ventricle dilatation. American Journal of Roentgenology, 101, 61-67. SCh~EcrrrER, M. M. & ZINGESSER,L. H. (1965). Radiology Of basilar thrombosis. Radiology, 85, 23-32.