The anatomy of the subarachnoid cisterns

Transcription

1 Acta Radiologica ISSN: (Print) (Online) Journal homepage: The anatomy of the subarachnoid cisterns B. Liliequist To cite this article: B. Liliequist (1956) The anatomy of the subarachnoid cisterns, Acta Radiologica, 46:1-2, 61-71, DOI: / To link to this article: Published online: 14 Dec Submit your article to this journal Article views: 657 View related articles Citing articles: 34 View citing articles Full Terms & Conditions of access and use can be found at

2 FROM THE ROENTGEN DEPARTMENT (DIRECTOR: PROF. ERIK LTNDOREN), RERAFIMERLASARETTET, STOCKHOLM, SWEDEN THE ANATOMY OF THE SUBARACHNOID CISTERNS by B. Liliequist Encephalography has become more and more widely used in recent years. As a result of this development, we have learned that the investigation of the subarachnoid cisterns is often just as important as that of the ventricula,r system. Encephalography gives more information than ventriculography, and examinations of the latter type have therefore decreased in number at Serafimerlasarettet. The anatomy and roentgenographic appearances of the cisterns are not as well known as those of the ventricular system. The anatomy has, to be sure, been described in the anatomic literature, but the descriptions have been written in such a manner that they are not immediately useful when it comes to the orientation of the structures in the roentgen film. We have also found the roentgenologic descriptions of the cisterns, available in the literature, to be incomplete and partly incorrect, Comparative studies of their appearances in anatomic specimens and in roentgen films have therefore been carried out. The brains used for the anatomic investigations were previously fixed with formaldehyde injected intra-arterially. A solution of gelatine in water, into which barium sulphate had been stirred, was used as contrast medium and was injected either into the cerebello-medullary cistern or into the subarachnoid space above the quadrigeminal plate. The injection was made and the roentgen films were exposed before the cranial vault was opened. The brain was then removed and additional films were obtained, mainly in the projections common in encephalography. At this stage, tomography was also used. The appearances of the cisterns in these films and in dissections of the specimens have been compared with a large number of normal encephalographies. The following report refers only to the appearances of the cisterns in adults.

3 62 B. LILIEQUIST Fig. 1. Air in nirdullary cistern, and extensions from cerebello-medullary cistern delimiting the medulla oblongata. The trigeminal nerve is seen as a round soft tissue formation in medial part of cerebellopontine cisterns. The cerebello-medullary cistern is situated in the angle between the medulla oblongata and the cerebellum. The subarachnoid space in front of the medulla oblongata constitutes the medullary cistern. The pontine cistern lies in front of the pons, and is continued superiorly in the intercrural cistern and anteriorly in the chiasmatic cistern. The cistern of the lamina terminalis is in front of the third ventricle and merges into the cistern of the corpus callosum. The quadrigeminal plate gives the cistern above its characteristic radiologic appearances, and we therefore call it the quadrigeminal cistern; it is also known as the cistern of the great vein of Galen. The cerebello-medullary cistern merges above the vermis into the subarachnoid space, which is very narrow.'the cistern continues forwards into the vallecula, situated between the tonsils into which the foramen of Magendie also opens. Anteriorly, the cerebello-medullary cistern communicates on each side with the medullary cistern; these communications appear in frontal views taken with a beam direction approximately parallel to the chis as two oblique rather narrow bands of air (Fig. 1). The air in these situations together with the air in the medullary cistern delimits the medulla oblongata in the roentgenogram. Around the tonsils the cerebello-medullary cistern also communicates antero-superiorly with the pontine cistern, opening into it approximately at the point where it merges into the cerebello-pontine cistern. On both sides of the pons, the pontine cistern communicates through a broad passage with the cerebello-pontine cistern, situated in the angle between the pons and the cerebellum. Anteriorly, it is limited by the posterior surface of the pyramid, posteriorly by the anterior surface of the cerebellum, and superiorly by the tentorium (Fig. 2). The contour between the air in the cerebello-pontine cistern and the surface of the cerebellum is always irregular. Medially and antero-inferiorly, the cistern is delimited by the convex lateral surface of the pons. A round, soft tissue formation surrounded by air may be seen in the cistern in films taken with less tilt of the tube than employed for the usual half-axial view; this is caused by the trigeminal nerve. It is highly im-

4 THE ANATOMY OF THE SUBARACHNOID CISTERNS 63 portant that radiologists should be familiar with the normal appearance of these cisterns, since tumours situated in the pontine angle often deform the cisterns before they affect the appearances of the ventricular system. A large subarachnoid space is situated between the anterior surface of the pons and the medial portions of the posterior surface of the frontal lobes. Its lateral limits consist of the medial surfaces of the temporal lobes- The Fig. 2. Bariuni contrast in pontinr and rere- Sylvian fissure issues laterally bellopontinc cisterns showing the broad p h - from both sides of its anterior sage between them. part. This subarachnoid space is generally divided into two cisterns, one lying postero-superiorly - the intercrural cistern - and the other antero-inferiorly - the chiasmatic cistern. There is no commonly accepted limit between the two; DAVIDOFF and DYKE described it as follows: The interpeduncular cistern extends as far anteriorly as the caudal margin of the optic chiasm and the internal carotid arteries. There is, however, a thin araclinoidal membrane in this subarachnoid space. This membrane is often seen in the encephalogram as a fine line with a convexity forwards, extending from the tip of the Fig. 3. Membrane separating intercrural and chiasmatic cisterns (left). Air arrested against the membrane (right).

5 64 T3. LTLIEQUIST Fig. 4. Crurd cisterns of characteristic a1)peararice. dorsum of the sella to tlie anterior edge of the mamillary bodies (Fig. 3). In our opinion, this membrane is probably the reason why often during encephalography the air at first remains in tlie intercrural cistern, and only gradually fills the chiasmatic cistern. It seems appropriate to accept this membrane as the line of demarcation between the chiasmatic and the intercrural cisterns, possessing as it does the advantages of a definite anatomic structure. If the membrane cannot be seen, the limit may be denoted by a line from the tip of the dorsum of the sella to the anterior edge of the mamillary bodies, or, in other words, approximately a straight line from the tip"of the dorsum of the sella perpendicular to the upper border of the cistern. The intercrural cistern covers the intercrural fossa and continues below and laterally to the cerebral peduncles. Its lateral extensions, from a practical point of view, should have their own name, since they may cause certain diagnostic difficulties. We call them the crural cisterns (Fig. 4). A small part of the uncus is situated in the cistern medially to the edge of the tentorium. Fig. 5. The optic chiasm can be located either in front of and on the same level as the anterior clinoid processes (left), or behind them (right).

6 THE ANATOMY OF THE SUHARACHKOII) CISTERSS 65 The intercrural cistern communicates anteriorly with the chiasmatic cistern, which is largelyfilled by the optic chiasm and the two internal carotid arteries, and antero-laterally merges into the Sylvian fissure. If these two cisterns are observed from the side in a specimen, they will present an almost square appearance. Anteriorly, the chiasmatic cistern is in relation to the posterior edge of the gyriis rectus on the lower surface of the frontal lobe, except in the midline where the cistern communicates with the cistern of the lamina terminalis. The anterior contour of the chiasmatic cistern is generally softly rounded with a convexity backwards. The roof of the cistern is roughly straight. Sometimes Fig. 6. The basilar artery in a 1'. a. film the cistern inlfro"nt of tyie chiasm is not filled with air, the air remaining instead against the posterior surface of the chiasm. This must not be confused with the situation which develops when the air is arrested by the membrane separating the chiasmatic and the intercrural cisterns. The posterior surface of the chiasm is straight whereas the membrane always is slightly curved. The relation between the position of the chiasm and the Fig. 7. The olfactory cisterns (left) are situated closer to the midline than the crural cisterns (right) Actic Riidiologicn. Vol. 46.

7 66 B. LILIEQUIST Fig. 8. Specimen with contrast medium surrounding the pericallosal artery which passes across the gyri arid sulci (left). Air around the pericallosal artery simulating a subfrontal tumour (right). anterior clinoid processes differs. The lower forward part of the chiasm is either situated in front of the tip of the anterior clinoid processes, on a level with them, or behind them above the sella (Fig. 5). Furthermore, the infundibulum, the tuber cinereum, and the mamillary bodies, are visible in the cistern. The posterior limit for the air in the intercrural cistern consists of the anterior surface of the pons. In the posterior part of the cistern the basilary artery is always visible; it may be seen in frontal views (Fig. 6). The intercrural cistern is situated between the cerebral peduncles and the crural cistern on both sides of the peduncles. The latter have a charac- teristic appearance, and can always be identified... They are.. Fig. 9. Cistern of corpus callosum. pointed, _. and diverge superiorly and laterally. The limits of the crural cistern consist laterally of the uncus, medially of the cerebral peduncles, and superiorly of the optic tract. Postero-inferiorly, they merge into the ambient cistern. The air in the crud cistern is situated on a level which lies more anteriorly and higher up than the air around the rest of the brain stem. that is, in the ambient cistern.

8 THE ANATOMY OF THE SUBARACHNOIU CISTERNS 67 Fig. 10. Specimen with contrast medium in the quadrigeminal cistern, aqueduct and fourth ventricle. Pig. 11. The quadrigeminal plate is easily discernible on a lateral view. These two levels of air may therefore always be seen to cross in such a view. The appearances of the crural cistern are such that they might be confused with a cerebello-pontine cistern displaced upwards. This may occur particularly if the crural cistern is filled without filling of the cerebello-pontine cistern. One may thus make the mistake that there is a soft tissue mass displacing the cerebello-pontine cistern. The two cisterns are situated on two different levels and may thus be separated in films exposed with different beam directions. From the most anterior part of the chiasmatic cistern, extensions of the subarachnoid space - the olfactory cisterns - continue on each side of the midline into the olfactory sulcus. The best filling is obtained with the patient in the supine position. In an a. p. film they look somewhat like the crural cisterns, but diverge less and are situated closer to the midline. In a half-axial a. p. film the crural cisterns, but not the olfactory cisterns, may be seen (Fig. 7). There should thus be no difficulty in practice to differentiate between the two cisterns. The chiasmatic cistern continues an- Fig. 12. The quadrigeminal plate in a 1). a. film.

9 68 B. LILIEQUIST Fig. 13. The ambient wings end against uncus. Contrast medium in the wings (left); air in the wings (right). tero-superiorly along the midline as the cistern of the lamina terminalis. It merges above into the cistern of the corpus callosum at the point where the genu of the corpus callosum commences. This provides an otherwise lacking, sharply defined anatomic limit between the cistern of the lamina terminalis and the cistern of the corpus callosum. Air is often present also in the other sulci on the medial surface of the frontal lobes. The first part of the pericallosal artery conimonly passes right across the sulci and gyri in a slight curve, and air may then be present in the subarachnoid space surrounding the artery. This string of air then has the same form, that is, concave antero-inferiorly, and may appear similar to the air surrounding a subfrontal extracerebral tumour (Pig. 8). Tha cistern of the corpus callosum surrounds the corpus callosum, and may be divided into three parts - the anterior part surrounding the genu, the middle or upper part above the corpus, and the posterior part around the splenium. Like the pericallosal artery, the posterior portion of the latter sometimes describes an arc with a slight downward convexity (Fig. 9). Around the splenium the posterior part conimunicates with the quadrigeminal cistern. The quadrigeminal cistern is situated in the posterior part of the tentorial notch (Fig. 10). The colliculate bodies, the anterior medullary velum, and the lingula cerebelli, form its inferior relations and the vermis, the anterior edge of which is slightly convex, its posterior relation; the main part of the roof consists of the splenium. The pineal body bulges into the anterior part of the cistern, and the great vein of Galen is situated in its upper part. Its width is the same as that of the quadrigeminal plate. It merges laterally into the ambient cistern. The cistern communicates anteriorly with the subarachnoid space above the third ventricle and posteriorly with the subarachnoid space surrounding the vermis of the cerebellum.

10 THE ANATOMY OF THE SUBARACHNOID CISTERNS 69 Fig. 14. The ambient wings above thalamus filled with contrast mcdiuni (left) and with air (right). The appearance of the quadrigeminal plate is so characteristic that it is easy to recognize, and this gives us also the position of the cistern (Fig. 11). Below the splenium the cistern is largely filled by the great vein of Galen. When the aqueduct and the fourth ventricle also are filled with air, it is possible to estimate the form and thickness of the quadrigeminal plate, the anterior medullary velum, and the lingula cerebelli. The quadrigeminal plate is easily discernible against the air in a frontal view (Fig. 12). A rounded formation may often be seen in the cistern between the colliculate bodies; it consists of the pineal body and the great vein of Galen projected on top of each other. The ambient cistern is a twofold cistern surrounding the Ixainstem. It issues posteriorly from the quadrigeminal cistern, turns round the brainstem, and communicates anteriorly with the pontine and crural cisterns. It is thus much narrower posteriorly and extends forward in a fan-like manner; its greatest extension is in the sagittal plane. The larger part of the cistern is situated below the tentorium and the smaller part above it. Two arched bands of air crossing the quadrigeminal plate are often seen in lateral films. They either cross the anterior or the mid-section of the quadrigeminal plate, but never behind it. These arcs have been thought by most authors to indicate the ambient cistern. Anatomic investigation shows, however, that this part of the subarachnoid space is situated around the thalamus, is perpendicular to the ambient cistern proper, and extends from its antero-superior edge; a good name for it would be the wing of the ambient cistern. These wings are situated in the frontal plane. They continue above the thalamus and below the for-

11 70 B. LILIEQIJIYT Fig. 15. Appearance of ambient wings in a p. a. film, filled with contrast medium (left), and with air (right). nicis as far as the foramen of Monroe. Laterally the wings extend to the attachment of the chorioid plexus. There is thus a narrow subarachnoid space stretching laterally to the medial wall of the temporal horn and separated from it only by a thin layer of pia and ependyma. The wings communicate above the roof of the third ventricle with each other, and behind the thalamus with the quadrigeminal cistern. The walls consist on the anterior concave aspect of the thalamus, on the posterior convex aspect of the fornix, and inferiorly of the hippocampal gyrus. The wing terminates anteriorly against the posterior edge of the uncus (Fig. 13). In frontal projections the layer of air in the wings is narrow and they are therefore difficult to observe; the air lying around the top of the thalamus is, however, often seen in the form of the two narrow bands (Fig. 14). In a specimen with contrast medium in the cisterns, these wings have a characteristic appearance. Sometimes, when the subarachnoid space in the wings is wider than usual, it is possible to see the wings air-filled in a p.-a. film (Fig. 15). It will be evident from this description that different parts are seen in lateral and frontal views. This is due to the position of the ambient cistern proper and its extensions, the ambient wings. The former can thus only be seen in frontal projections, and the ambient wings essentially only in lateral views. The investigation of the subarachnoid space has achieved great importance and in the future, probably, it will become even more valuable in the early diagnosis of intracranial expanding lesions. This, however, presupposes an exact knowledge of its normal anatomy.

12 THE ANATOMY OF THE SUBARAC!HNOID CISTERNS 71 SUMMARY The anatorriic and roentgenologic appearances of the subarachnoid cisterns, based upon comparative studies, are described. Z U S AM M E N F A S S U N (4 Das anatornische und roritgenologische Aussehen der subarachnoidalen Cisternen wird beschrieben; der Verfasser stiitet sich hierbei auf komparativen Studien. RESUMe 8e basant sur des Qtudes comparatives, l'auteur d6crit les aspects anatomiques et radiologiquev des citernes sous-arachnofdiennes.