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Neuroradiology 14, 101-105 (1977)
© by Springer-Verlag 1977
ORIGINALS
Descending Tentorial Herniation: Findings on Computed Tomography J. Stovring University of New Mexico, Department of Radiology School of Medicine, Albuquerque, New Mexiko, USA
Summary. Descending tentorial herniation (DTH) can be diagnosed by computed tomography. Encroachment upon the lateral aspect of the suprasellar cistern is an early sign of impending tentorial herniation. Actual herniation is evidenced by rotation and shift of the brain stem with consequent widening of the crural and ambient cisterns on the side of the space-occupying lesion. In a more advanced stage of herniation, obliteration of cisternal spaces at the tentorial level will occur. Aqueductal compression secondary to the herniation will cause increased intraventricular pressure with widening of those parts of the lateral ventricles that are not exposed to the compression by the mass; a characteristic finding is widening of the temporal horn on the side opposite the space-occupying lesion. Infarction in the territory of the posterior cerebral artery may complicate DTH.
Key words: Computed tomography, cranial - Tentorial herniation - Aqueductal obstruction - Hydrocephalus - Cerebral infarct.
Herniation of part of the temporal lobe down into the tentorial hiatus as a distant effect of supratentorial mass lesions was first reported as a pathological entity by Meyer [1] in 1920. Since then, an extensive literature has appeared on the gross pathological findings [2, 3, 4] with descending tentorial herniation (DTH) and the characteristic changes that can be observed on pneumoencephalograms [5, 6] and cerebral angiograms [7]. Computed tomography (CT) has increasingly replaced these noxious procedures as the definitive neuroradiological diagnostic procedure for most in-
tracranial disease processes. Consequently, it is important to be aware of the changes that descending tentorial herniation produces on CT of the brain. The purpose of this paper is to analyze these findings. So far, few publications have appeared on this topic [8, 9, 10] and no previous paper has covered all the known aspects of CT findings with this entity.
Normal and Pathological Anatomy The dural septa, the falx cerebri and the tentorium cerebelli act as incomplete walls which divide the cranial cavity into three compartments: the right and left supratentorial hemicrania and the posterior fossa. An opening in the tentorium cerebelli, the tentorial incisura, provides a communication between the supratentorial space and the posterior fossa. Naidich et al [11] give an excellent analysis of the normal anatomy of the tentorial incisura. A small supratentorial mass may initially be accommodated by compression of adjacent subarachnoid spaces with displacement of cerebrospinal fluid (CSF). With continued expansion, this reservoir will no longer be sufficient and brain structures will become displaced toward other regions where additional space for expansion is available. This displacement can take place within the involved hemisphere or across the midline under the falx or in a descending direction through the tentorial incisura. The most common type of cerebral herniation is subfalcial herniation which is very easy to recognize on CT due to the characteristic shift of midline structures. The second most common type is descending transtentorial herniation; the demonstration of this type is, due to its potentially lifethreatening consequences, of great prognostic sig-
102
Fig. 1. Right cerebral hemisphere seen from the medial aspect demonstrating gyri that may participate in DTH: (1) uncus, the anterior medial extension of hippocampal gyrus; (2) hippocampal gyrus proper; (3) lingual gyrus; (4) isthmus of fornicate gyms. (1) and (2) constitute the most medial part of the temporal lobe, while (3) is part of the occipital lobe and (4) belongs to the parietal lobe
J. Stovring: Descending Tentorial Herniation
Azambuja et al [5] divided descending tentorial herniation into three subtypes: anterior, posterior and complete herniations. With the anterior type the uncus only (the hook-shaped anterior extremity of the hippocampal gyrus) is involved, and is herniated down into the ipsilateral crural cistern (Figs. 1 and 2) causing the brain stem to become shifted and rotated. This anterior (uncal) herniation is the initial event in most cases of tentorial herniation, usually followed by herniation of more posteriorly located structures later, at a more advanced stage of the herniation. However, the distribution and sequence of the herniation will also depend on such factors as the location of the space-occupying lesion and the size and configuration of the incisura [4, 12]. A posterior herniation is present when the hippocampal gyrus (behind the uncus) has herniated down into the posterolateral part of the tentorial hiatus (Figs. 1 and 2). Larger posterior hernias may also include the isthmus of the fornical gyrus and the anterior part of the lingual gyrus (Fig. 1). The posterior herniations encroach upon the lateral part of the quadrigeminal plate cistern and will cause a displacement, rotation and compression of the brain stem. When both anterior and posterior herniations are present and join each other, the result is a socalled complete herniation.
Fig. 2. Anatomy of region of tentorial incisura: (1) diaphragma sellae, (2) anterior clinoid process, (3) clinotentorial ligament, (4) free edge of tentorial hiatus, (5) cross-section of mesencephalon with cerebral aqueduct, (6) crural cistern where uncus will descend with anterior tentorial herniation, (7) posterolateral part of tentorial hiatus where hippocampal gyrus will descend with posterior herniation, (8) relatively narrow anterior part of falx cerebri, (9) wider posterior part of falx
nificance to the patient. Other types of herniation, which are beyond the scope of this article, include ascending tentorial herniation, herniations across the sphenoid ridge (transalar herniation), herniation of the gyrus rectus behind the tuberculum sellae, herniation of adjacent structures into a large empty sella and tonsillar herniation through the foramen magnum.
While a left sided anterior (uncal) herniation will produce a counterclockwise rotation of the mesencephalon (Fig. 3 C), a posterior herniation on the same side will tend to produce a clockwise rotation (Fig. 4). As a consequence, the net rotational effect may be small or nil when combined anterior and posterior herniations are present on the same side, forming a complete herniation (Fig. 5 A). However, the brain stem will be markedly shifted and will be compressed against the free tentorial edge of the opposite side. With bilateral complete herniations, which are less common, a horseshoe-shaped hernia will result, compressing the brain stem from both sides. This sideways compression will cause the midbrain to become elongated in the anteroposterior direction. Bilateral descending tentorial herniations, which correspond to the axial pressure cone syndrome of Liliequist [6], occur mostly with frontal and central tumors, while lesions that are temporal or parietal in location tend to produce unilateral herniations or, at least, herniations that are considerably larger on one side than on the other. In all instances of D T H there will be an axial caudal displacement of the midbrain and pons.
J. Stovring: Descending Tentorial Herniation
103
Fig.3A-C. A 46year old woman in coma two weeks after head injury with large left subacute subdural hematoma (small arrows). A Note subfalcial herniation with marked shift of septum pellucidum. B Section through a lower level. Tentorial herniation is evidenced by dilatation of contralateral temporal horn (vertical arrow) and by complete effacement of cisternal spaces. Midbrain rotation cannot be assessed on this precontrast CT since adjacent cisterns are obliterated by the herniation. C On postcontrast CT through same level, opacified perimesencephalic vessels clearly outline the shifted and rotated midbrain
Fig. 4. A 41year old man with left temporoparietal glioma. Slight widening of contralateral temporal horn (vertical arrow) indicates that DTH is present. Note tilted quadrigeminal plate indicating rotation of mesencephalon, another sign of herniation (small arrows)
Fig.5 A and B. A 38year old man with drowsiness, decerebrate posturing and dilated right pupil after acute head injury with acute right subdural hematoma combined with right temporo-occipital contusion (low density). There is marked subfalcial herniation with compression of both frontal horns from mass effect (horizontal arrows). But there is paradoxical widening of opposite ventricular atrium and temporal horn indicating that DTH is present. Marked shift of brain stem (small arrows in Fig. 5 A) is further evidence of herniation
Findings On Computed Tomography
2. Widening of the Crural, Ambient and Lateral Pontine Cisterns on the Same Side as the Expanding Lesion, Usually with Associated Rotation of the Brain Stem (Fig. 7)
1. Encroachment Upon the Lateral Aspect of the Suprasellar Cistern (Fig. 6 A ) This is a v e r y e a r l y sign which is c a u s e d b y a m e d i a l d i s l o c a t i o n of t h e u n c u s a n d u s u a l l y will i n d i c a t e i m p e n d i n g t e n t o r i a l h e r n i a t i o n , a l t h o u g h this sign m a y also b e c a u s e d b y m o r e local c h a n g e s such as an exp a n d i n g l e s i o n o f t h e t e m p o r a l l o b e [8].
T h e s e findings i n d i c a t e t h a t a c t u a l h e r n i a t i o n is p r e sent a n d t h a t t h e d e s c e n d i n g t e m p o r a l l o b e has shifted t h e b r a i n s t e m to t h e o p p o s i t e side. S o m e t i m e s t h e r o t a t i o n of t h e m e s e n c e p h a l o n is m o r e easily a p p r e c i a t e d a f t e r c o n t r a s t e n h a n c e m e n t w h e n
104
Fig. 6 A and B. Traumatic left temporal intracerebral hematoma in a 50 year old woman found stuporous outside a bar with skull fracture and slightly dilated left pupil, right herniparesis and right visual field defect. A There are signs of early tentorial herniation with medially shifted uncus encroaching slightly upon lateral aspect of five cornered star of suprasellar cistern with resulting amputation of lateral point of the star on that side. B Early medial shift of hippocampal gyrus which is pushing slightly on quadrigeminal plate. Uncal herniation with medial shift of the anterior choroidal artery was angiographically verified
J. Stovring: Descending Tentorial Herniation
Fig. 8 A and B. Large acute left subdural hematoma with small traumatic right frontal intracerebral bleed in a 37 year old man with skull fracture, coma and dilated, unresponsive pupils following head injury. A Slice through dorsum sellae demonstrates effacement of all cisternal spaces at this level secondary to DTH. Widening of right temporal horn is further evidence of herniation (vertical arrow). B Widening of entire lateral ventricle on side opposite main mass. Vague reduction of density in left occipital area (small arrowheads) is consistent with ischemia in territory of left posterior cerebral artery. Unproved. The patient died a few hours after the CT. Autopsy could not be obtained
pear as the basal hypothalamus is displaced ventrally. The perimesencephalic cisterns (interpeduncular, crural, ambient and quadrigeminal plate cistern) will also become effaced as the tentorial hiatus is crowded with displaced caudal hypothalamus, herniated temporal lobe and compressed midbrain. Even the cistern of the great vein of Galen may become narrowed when the splenium of the corpus callosum is displaced inferiorly.
Fig. 7 A and B. Large right chronic or subacute subdural hematoma (main part of the subdural collection not shown on these slices) in a 74 year old unconscious and decerebrate man. The presence of DTH is indicated by shift of brain stem with consequent widening of right ambient and lateral pontine cisterns (horizontal arrows). Dilatation of temporal horn (vertical arrow) on side opposite subdural collection is further evidence of herniation
the circummesencephalic vessels are opacified (Fig. 3C). On non-contrasted CT, a tilted quadrigeminal plate cistern will indicate rotation of the midbrain (Fig. 4). 3. Effacement of Cisternal Spaces at the Tentorial Level (Fig. 3 B) There will be a tendency to obliteration of cisternal spaces at the level of the tentorial hiatus with a more advanced stage of herniation [9]. The suprasellar cistern, which is visible on 85% of routine CT scans with 13 mm scanning slices [8], will disap-
4. Downward Axial Displacement of the Brain Stem The author of this article has found it difficult to assess this phenomenon on CT. Osborn [9] found that visualization of the basilar artery at a lower level than usual can be seen as a sign of caudal displacement of the brain stem. In the future, with coronal and sagittal computed tomograms, the phenomenon of caudal displacement of the brain stem will probably be more easily appreciated. 5. Partial Hydrocephalus as an Effect of DTH When herniation of sufficient severity is present, an obstruction of the aqueduct will result from the compression of the mesencephalon [3, 6, 10]. This will cause increased intraventricular pressure. Narrowing of the subarachnoid space overlying the supratentorial mass and narrowing of cisterns at the tentorial incisura by herniated brain structures will also adversely affect the CSF circulation and the ventricular pressure. Ordinarily, elevation of in-
105
J. Stovring: Descending Tentorial Herniation
traventricular pressure will cause a generalized hydrocephalus. However, in the presence of a large supratentorial mass this cannot occur; only those parts of the ventricular system that are somehow shielded from the pressure effect of the mass will be able to dilate. With a unilateral mass, the bony midline massif, which consists of the body of the sphenoid with the sella turcica, will shield the contralateral temporal horn very effectively from the pressure effect of the mass, so that contralateral widening of the temporal horn will be a constant finding with tentorial herniation which is of sufficient severity to cause aqueductal compression (Figs. 3, 4, 5 and 7). Similarly, the falx will have a shielding effect, especially the wider posterior part of the falx, so that dilatation of the contralateral atrium and occipital horn will be another frequent finding with unilateral masses causing tentorial herniation (Figs. 3 and 5). Occasionally, apparently when the opening in the falx is unusually small, the falx will have so much shielding effect that the entire contralateral ventricle may be dilated (Fig. 8). Consequently, partial hydrocephalus, most often involving the temporal horn on the side opposite the mass, should be considered an important diagnostic sign of DTH with unilateral supratentorial mass lesions unless there are signs of direct ventricular blocking by the mass or signs of pre-existing hydrocephalus or atrophy that could explain the widening. However, ve,ntricular widening may occur unrelated to tentorial herniation when there is blood in the ventricles. Contralateral widening of the temporal horn will be a constant finding with acute supratentorial mass lesions, traumatic or apoplectic, in patients with a dilated, fixed pupil or other clinical signs of acute tentorial herniation [10]. More slowly enlarging tumors will allow the various brain structures more time for adaptation. In such cases, the more dramatic acute clinical signs of DTH will be absent, but papilledema will invariably be present when dilatation of a contralateral temporal horn indicates that tentorial herniation has caused increased intraventricular pressure.
Conclusion
Descending tentorial herniation produces characteristic changes on CT. These changes should be carefully looked for in all cases of larger supratentorial space-occupying lesions because of the important clinical implications of herniation.
References 1. Meyer, A.: Herniation of the brain. Arch. Neurol. Psychiatry 4, 387-400 (1920) 2. Lindenberg, R.: Compression of brain arteries as pathogenetic factor for tissue necroses and their areas of predilection. J. Neuropathol. Exp. Neurol. 14, 223-243 (1955) 3. Sunderland, S.: The tentorial notch and complications produced by herniation of the brain through that aperture. Br. J. Surg. 45, 422-438 (1958) 4. Mastri, A. R.: Brain herniations: I. Pathology. (In) Radiology of the Skull and Brain, vol. 2, book 4, pp. 2659-2670. Ed. by Newton, T.H., Potts, D.G. St. Louis: Mosby 1974 5. Azambuja, N., Lindgren, E., Sjogren, S.E.: Tentorial herniations: II. Pneumography. Acta Radiol. 46, 224-231 (1956) 6. Liliequist, B.: Encephalographic changes in the axial pressure cone syndrome. Acta Radiol. 54, 369-378 (1960) 7. Perret, L.V., Margolis, M.T.: Brain herniations: II. Angiography. (In) Radiology of the Skull and Brain, vol. 2, book 4, pp. 2671-2699 Ed. by Newton, T.H., Potts, D.G. St. Louis: Mosby 1974 8. Naidich, T.P., Pinto, R.S., Kushner, M.J., Lin, J.P., Kricheff, I.I., Leeds, N.E., Chase, N.E.: Evaluation of sellar and parasellar masses by computed tomography. Radiology 120, 91-99 (1976) 9. Osborn, A.G.: Diagnosis of descending transtentorial herniation by cranial computed tomography. Radiology 123, 93-96 (1977) 10. Stovring, J.: Contralateral temporal horn widening in unilateral supratentorial mass lesion: A diagnostic sign indicating tentorial herniation. J. Computer Assisted Tomogr. (Computed Tomogr.) 1, 319-323 (1977) 1l. Naidich, T.P., Leeds, N.E., Kricheff, I.I., Pudlowski, R.M., Naidich, J.B., Zimmerman, R. D.: The tentorium in axial section. I. Normal CY appearance and non-neoplastic pathology. Radiology 123, 631-638 (1977) 12. Plant, H.F.: Size of tentorial incisura related to cerebral herniation. Acta Radiol. (Diagn.) 1, 916-928 (1963) Received: July 1, 1977
6. Infarction in the Territory of the Posterior Cerebral Artery An important complication that occurs in some cases [2] of DTH is infarction of the occipital lobe secondary to kinking of a depressed posterior cerebral artery over the free margin of the tentorial hiatus on the same side as the descending herniation (Fig. 8 B).
J. Stovring, M.D. Department of Radiology University of New Mexico School of Medicine Albuquerque, New Mexico 87131, USA
Neuroradiology 14, 101-105 (1977)
© by Springer-Verlag 1977
ORIGINALS
Descending Tentorial Herniation: Findings on Computed Tomography J. Stovring University of New Mexico, Department of Radiology School of Medicine, Albuquerque, New Mexiko, USA
Summary. Descending tentorial herniation (DTH) can be diagnosed by computed tomography. Encroachment upon the lateral aspect of the suprasellar cistern is an early sign of impending tentorial herniation. Actual herniation is evidenced by rotation and shift of the brain stem with consequent widening of the crural and ambient cisterns on the side of the space-occupying lesion. In a more advanced stage of herniation, obliteration of cisternal spaces at the tentorial level will occur. Aqueductal compression secondary to the herniation will cause increased intraventricular pressure with widening of those parts of the lateral ventricles that are not exposed to the compression by the mass; a characteristic finding is widening of the temporal horn on the side opposite the space-occupying lesion. Infarction in the territory of the posterior cerebral artery may complicate DTH.
Key words: Computed tomography, cranial - Tentorial herniation - Aqueductal obstruction - Hydrocephalus - Cerebral infarct.
Herniation of part of the temporal lobe down into the tentorial hiatus as a distant effect of supratentorial mass lesions was first reported as a pathological entity by Meyer [1] in 1920. Since then, an extensive literature has appeared on the gross pathological findings [2, 3, 4] with descending tentorial herniation (DTH) and the characteristic changes that can be observed on pneumoencephalograms [5, 6] and cerebral angiograms [7]. Computed tomography (CT) has increasingly replaced these noxious procedures as the definitive neuroradiological diagnostic procedure for most in-
tracranial disease processes. Consequently, it is important to be aware of the changes that descending tentorial herniation produces on CT of the brain. The purpose of this paper is to analyze these findings. So far, few publications have appeared on this topic [8, 9, 10] and no previous paper has covered all the known aspects of CT findings with this entity.
Normal and Pathological Anatomy The dural septa, the falx cerebri and the tentorium cerebelli act as incomplete walls which divide the cranial cavity into three compartments: the right and left supratentorial hemicrania and the posterior fossa. An opening in the tentorium cerebelli, the tentorial incisura, provides a communication between the supratentorial space and the posterior fossa. Naidich et al [11] give an excellent analysis of the normal anatomy of the tentorial incisura. A small supratentorial mass may initially be accommodated by compression of adjacent subarachnoid spaces with displacement of cerebrospinal fluid (CSF). With continued expansion, this reservoir will no longer be sufficient and brain structures will become displaced toward other regions where additional space for expansion is available. This displacement can take place within the involved hemisphere or across the midline under the falx or in a descending direction through the tentorial incisura. The most common type of cerebral herniation is subfalcial herniation which is very easy to recognize on CT due to the characteristic shift of midline structures. The second most common type is descending transtentorial herniation; the demonstration of this type is, due to its potentially lifethreatening consequences, of great prognostic sig-
102
Fig. 1. Right cerebral hemisphere seen from the medial aspect demonstrating gyri that may participate in DTH: (1) uncus, the anterior medial extension of hippocampal gyrus; (2) hippocampal gyrus proper; (3) lingual gyrus; (4) isthmus of fornicate gyms. (1) and (2) constitute the most medial part of the temporal lobe, while (3) is part of the occipital lobe and (4) belongs to the parietal lobe
J. Stovring: Descending Tentorial Herniation
Azambuja et al [5] divided descending tentorial herniation into three subtypes: anterior, posterior and complete herniations. With the anterior type the uncus only (the hook-shaped anterior extremity of the hippocampal gyrus) is involved, and is herniated down into the ipsilateral crural cistern (Figs. 1 and 2) causing the brain stem to become shifted and rotated. This anterior (uncal) herniation is the initial event in most cases of tentorial herniation, usually followed by herniation of more posteriorly located structures later, at a more advanced stage of the herniation. However, the distribution and sequence of the herniation will also depend on such factors as the location of the space-occupying lesion and the size and configuration of the incisura [4, 12]. A posterior herniation is present when the hippocampal gyrus (behind the uncus) has herniated down into the posterolateral part of the tentorial hiatus (Figs. 1 and 2). Larger posterior hernias may also include the isthmus of the fornical gyrus and the anterior part of the lingual gyrus (Fig. 1). The posterior herniations encroach upon the lateral part of the quadrigeminal plate cistern and will cause a displacement, rotation and compression of the brain stem. When both anterior and posterior herniations are present and join each other, the result is a socalled complete herniation.
Fig. 2. Anatomy of region of tentorial incisura: (1) diaphragma sellae, (2) anterior clinoid process, (3) clinotentorial ligament, (4) free edge of tentorial hiatus, (5) cross-section of mesencephalon with cerebral aqueduct, (6) crural cistern where uncus will descend with anterior tentorial herniation, (7) posterolateral part of tentorial hiatus where hippocampal gyrus will descend with posterior herniation, (8) relatively narrow anterior part of falx cerebri, (9) wider posterior part of falx
nificance to the patient. Other types of herniation, which are beyond the scope of this article, include ascending tentorial herniation, herniations across the sphenoid ridge (transalar herniation), herniation of the gyrus rectus behind the tuberculum sellae, herniation of adjacent structures into a large empty sella and tonsillar herniation through the foramen magnum.
While a left sided anterior (uncal) herniation will produce a counterclockwise rotation of the mesencephalon (Fig. 3 C), a posterior herniation on the same side will tend to produce a clockwise rotation (Fig. 4). As a consequence, the net rotational effect may be small or nil when combined anterior and posterior herniations are present on the same side, forming a complete herniation (Fig. 5 A). However, the brain stem will be markedly shifted and will be compressed against the free tentorial edge of the opposite side. With bilateral complete herniations, which are less common, a horseshoe-shaped hernia will result, compressing the brain stem from both sides. This sideways compression will cause the midbrain to become elongated in the anteroposterior direction. Bilateral descending tentorial herniations, which correspond to the axial pressure cone syndrome of Liliequist [6], occur mostly with frontal and central tumors, while lesions that are temporal or parietal in location tend to produce unilateral herniations or, at least, herniations that are considerably larger on one side than on the other. In all instances of D T H there will be an axial caudal displacement of the midbrain and pons.
J. Stovring: Descending Tentorial Herniation
103
Fig.3A-C. A 46year old woman in coma two weeks after head injury with large left subacute subdural hematoma (small arrows). A Note subfalcial herniation with marked shift of septum pellucidum. B Section through a lower level. Tentorial herniation is evidenced by dilatation of contralateral temporal horn (vertical arrow) and by complete effacement of cisternal spaces. Midbrain rotation cannot be assessed on this precontrast CT since adjacent cisterns are obliterated by the herniation. C On postcontrast CT through same level, opacified perimesencephalic vessels clearly outline the shifted and rotated midbrain
Fig. 4. A 41year old man with left temporoparietal glioma. Slight widening of contralateral temporal horn (vertical arrow) indicates that DTH is present. Note tilted quadrigeminal plate indicating rotation of mesencephalon, another sign of herniation (small arrows)
Fig.5 A and B. A 38year old man with drowsiness, decerebrate posturing and dilated right pupil after acute head injury with acute right subdural hematoma combined with right temporo-occipital contusion (low density). There is marked subfalcial herniation with compression of both frontal horns from mass effect (horizontal arrows). But there is paradoxical widening of opposite ventricular atrium and temporal horn indicating that DTH is present. Marked shift of brain stem (small arrows in Fig. 5 A) is further evidence of herniation
Findings On Computed Tomography
2. Widening of the Crural, Ambient and Lateral Pontine Cisterns on the Same Side as the Expanding Lesion, Usually with Associated Rotation of the Brain Stem (Fig. 7)
1. Encroachment Upon the Lateral Aspect of the Suprasellar Cistern (Fig. 6 A ) This is a v e r y e a r l y sign which is c a u s e d b y a m e d i a l d i s l o c a t i o n of t h e u n c u s a n d u s u a l l y will i n d i c a t e i m p e n d i n g t e n t o r i a l h e r n i a t i o n , a l t h o u g h this sign m a y also b e c a u s e d b y m o r e local c h a n g e s such as an exp a n d i n g l e s i o n o f t h e t e m p o r a l l o b e [8].
T h e s e findings i n d i c a t e t h a t a c t u a l h e r n i a t i o n is p r e sent a n d t h a t t h e d e s c e n d i n g t e m p o r a l l o b e has shifted t h e b r a i n s t e m to t h e o p p o s i t e side. S o m e t i m e s t h e r o t a t i o n of t h e m e s e n c e p h a l o n is m o r e easily a p p r e c i a t e d a f t e r c o n t r a s t e n h a n c e m e n t w h e n
104
Fig. 6 A and B. Traumatic left temporal intracerebral hematoma in a 50 year old woman found stuporous outside a bar with skull fracture and slightly dilated left pupil, right herniparesis and right visual field defect. A There are signs of early tentorial herniation with medially shifted uncus encroaching slightly upon lateral aspect of five cornered star of suprasellar cistern with resulting amputation of lateral point of the star on that side. B Early medial shift of hippocampal gyrus which is pushing slightly on quadrigeminal plate. Uncal herniation with medial shift of the anterior choroidal artery was angiographically verified
J. Stovring: Descending Tentorial Herniation
Fig. 8 A and B. Large acute left subdural hematoma with small traumatic right frontal intracerebral bleed in a 37 year old man with skull fracture, coma and dilated, unresponsive pupils following head injury. A Slice through dorsum sellae demonstrates effacement of all cisternal spaces at this level secondary to DTH. Widening of right temporal horn is further evidence of herniation (vertical arrow). B Widening of entire lateral ventricle on side opposite main mass. Vague reduction of density in left occipital area (small arrowheads) is consistent with ischemia in territory of left posterior cerebral artery. Unproved. The patient died a few hours after the CT. Autopsy could not be obtained
pear as the basal hypothalamus is displaced ventrally. The perimesencephalic cisterns (interpeduncular, crural, ambient and quadrigeminal plate cistern) will also become effaced as the tentorial hiatus is crowded with displaced caudal hypothalamus, herniated temporal lobe and compressed midbrain. Even the cistern of the great vein of Galen may become narrowed when the splenium of the corpus callosum is displaced inferiorly.
Fig. 7 A and B. Large right chronic or subacute subdural hematoma (main part of the subdural collection not shown on these slices) in a 74 year old unconscious and decerebrate man. The presence of DTH is indicated by shift of brain stem with consequent widening of right ambient and lateral pontine cisterns (horizontal arrows). Dilatation of temporal horn (vertical arrow) on side opposite subdural collection is further evidence of herniation
the circummesencephalic vessels are opacified (Fig. 3C). On non-contrasted CT, a tilted quadrigeminal plate cistern will indicate rotation of the midbrain (Fig. 4). 3. Effacement of Cisternal Spaces at the Tentorial Level (Fig. 3 B) There will be a tendency to obliteration of cisternal spaces at the level of the tentorial hiatus with a more advanced stage of herniation [9]. The suprasellar cistern, which is visible on 85% of routine CT scans with 13 mm scanning slices [8], will disap-
4. Downward Axial Displacement of the Brain Stem The author of this article has found it difficult to assess this phenomenon on CT. Osborn [9] found that visualization of the basilar artery at a lower level than usual can be seen as a sign of caudal displacement of the brain stem. In the future, with coronal and sagittal computed tomograms, the phenomenon of caudal displacement of the brain stem will probably be more easily appreciated. 5. Partial Hydrocephalus as an Effect of DTH When herniation of sufficient severity is present, an obstruction of the aqueduct will result from the compression of the mesencephalon [3, 6, 10]. This will cause increased intraventricular pressure. Narrowing of the subarachnoid space overlying the supratentorial mass and narrowing of cisterns at the tentorial incisura by herniated brain structures will also adversely affect the CSF circulation and the ventricular pressure. Ordinarily, elevation of in-
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J. Stovring: Descending Tentorial Herniation
traventricular pressure will cause a generalized hydrocephalus. However, in the presence of a large supratentorial mass this cannot occur; only those parts of the ventricular system that are somehow shielded from the pressure effect of the mass will be able to dilate. With a unilateral mass, the bony midline massif, which consists of the body of the sphenoid with the sella turcica, will shield the contralateral temporal horn very effectively from the pressure effect of the mass, so that contralateral widening of the temporal horn will be a constant finding with tentorial herniation which is of sufficient severity to cause aqueductal compression (Figs. 3, 4, 5 and 7). Similarly, the falx will have a shielding effect, especially the wider posterior part of the falx, so that dilatation of the contralateral atrium and occipital horn will be another frequent finding with unilateral masses causing tentorial herniation (Figs. 3 and 5). Occasionally, apparently when the opening in the falx is unusually small, the falx will have so much shielding effect that the entire contralateral ventricle may be dilated (Fig. 8). Consequently, partial hydrocephalus, most often involving the temporal horn on the side opposite the mass, should be considered an important diagnostic sign of DTH with unilateral supratentorial mass lesions unless there are signs of direct ventricular blocking by the mass or signs of pre-existing hydrocephalus or atrophy that could explain the widening. However, ve,ntricular widening may occur unrelated to tentorial herniation when there is blood in the ventricles. Contralateral widening of the temporal horn will be a constant finding with acute supratentorial mass lesions, traumatic or apoplectic, in patients with a dilated, fixed pupil or other clinical signs of acute tentorial herniation [10]. More slowly enlarging tumors will allow the various brain structures more time for adaptation. In such cases, the more dramatic acute clinical signs of DTH will be absent, but papilledema will invariably be present when dilatation of a contralateral temporal horn indicates that tentorial herniation has caused increased intraventricular pressure.
Conclusion
Descending tentorial herniation produces characteristic changes on CT. These changes should be carefully looked for in all cases of larger supratentorial space-occupying lesions because of the important clinical implications of herniation.
References 1. Meyer, A.: Herniation of the brain. Arch. Neurol. Psychiatry 4, 387-400 (1920) 2. Lindenberg, R.: Compression of brain arteries as pathogenetic factor for tissue necroses and their areas of predilection. J. Neuropathol. Exp. Neurol. 14, 223-243 (1955) 3. Sunderland, S.: The tentorial notch and complications produced by herniation of the brain through that aperture. Br. J. Surg. 45, 422-438 (1958) 4. Mastri, A. R.: Brain herniations: I. Pathology. (In) Radiology of the Skull and Brain, vol. 2, book 4, pp. 2659-2670. Ed. by Newton, T.H., Potts, D.G. St. Louis: Mosby 1974 5. Azambuja, N., Lindgren, E., Sjogren, S.E.: Tentorial herniations: II. Pneumography. Acta Radiol. 46, 224-231 (1956) 6. Liliequist, B.: Encephalographic changes in the axial pressure cone syndrome. Acta Radiol. 54, 369-378 (1960) 7. Perret, L.V., Margolis, M.T.: Brain herniations: II. Angiography. (In) Radiology of the Skull and Brain, vol. 2, book 4, pp. 2671-2699 Ed. by Newton, T.H., Potts, D.G. St. Louis: Mosby 1974 8. Naidich, T.P., Pinto, R.S., Kushner, M.J., Lin, J.P., Kricheff, I.I., Leeds, N.E., Chase, N.E.: Evaluation of sellar and parasellar masses by computed tomography. Radiology 120, 91-99 (1976) 9. Osborn, A.G.: Diagnosis of descending transtentorial herniation by cranial computed tomography. Radiology 123, 93-96 (1977) 10. Stovring, J.: Contralateral temporal horn widening in unilateral supratentorial mass lesion: A diagnostic sign indicating tentorial herniation. J. Computer Assisted Tomogr. (Computed Tomogr.) 1, 319-323 (1977) 1l. Naidich, T.P., Leeds, N.E., Kricheff, I.I., Pudlowski, R.M., Naidich, J.B., Zimmerman, R. D.: The tentorium in axial section. I. Normal CY appearance and non-neoplastic pathology. Radiology 123, 631-638 (1977) 12. Plant, H.F.: Size of tentorial incisura related to cerebral herniation. Acta Radiol. (Diagn.) 1, 916-928 (1963) Received: July 1, 1977
6. Infarction in the Territory of the Posterior Cerebral Artery An important complication that occurs in some cases [2] of DTH is infarction of the occipital lobe secondary to kinking of a depressed posterior cerebral artery over the free margin of the tentorial hiatus on the same side as the descending herniation (Fig. 8 B).
J. Stovring, M.D. Department of Radiology University of New Mexico School of Medicine Albuquerque, New Mexico 87131, USA
