A Study of the Junction Between the Straight Sinus and the Great Cerebral Vein*

Home , Sinus (anatomy), Straight sinus

J. Anat. (1989), 164, pp. 49-54 49 With 4 figures Printed in Great Britain A study of the junction between the straight sinus and the great cerebral vein*

W. M. GHALI, M. F. M. RAFLA, E. Y. EKLADIOUS AND K. A. IBRAHIM Anatomy Department, Faculty of Medicine, Ain-Shams University, Cairo, Egypt (Accepted 10 August 1988)

INTRODUCTION The presence of a small body projecting into the floor of the straight sinus at its junction with the great cerebral vein, and the nature of such a body have been the subject of controversy. Clark (1940) named it the suprapineal arachnoid body and described it as being formed of arachnoid granulation tissue filled with a sinusoidal plexus of blood vessels. He claimed that this body seemed to provide a ball valve mechanism whereby the venous return from the third and lateral ventricles might be impeded and this, in turn, would exert a direct effect on the secretion of the cerebrospinal fluid. Similar observations have been mentioned by Williams & Warwick (1980). On the other hand, Balo (1950) denied the role played by that body in the regulation of secretion of the cerebrospinal fluid. Thus the aim of the present work was to verify the presence of such a body and to investigate its nature and the possible role it might play in haemodynamic regulation in that strategic area.

MATERIAL AND METHODS Twenty brains (15 from the dissecting room and 5 from the postmortem room of Ain-Shams University, Faculty of Medicine) were used for this study. They were of both sexes (12 males and 8 females) and their ages ranged from 40-60 years. The skull was opened and the brain, with its intact dura, was carefully dissected free and extracted from the cranial cavity. The brains from the dissecting room were divided into three groups, each composed of 5 brains. In the first group, a median sagittal section was cut so that the straight sinus was opened. In the second group, parasagittal sections were cut 1 cm from the median plane. Thorough dissection was carried out to study the pattern ofthejunction between the inferior sagittal sinus and the great cerebral vein to form the straight sinus. Moreover, the angle between the great cerebral vein and the straight sinus was measured. In the third group, the cerebellum was removed to examine the inferior surface of tentorium cerebelli with its contained straight sinus. The brains from the postmortem room were dissected to expose the junction between the great cerebral vein, the inferior sagittal and the straight sinuses. That junction was carefully excised intact, fixed in 10 % formal saline, orientated in paraffin blocks and 12 /cm sections were cut. Sections were stained with haematoxylin and eosin and Masson's trichrome stains. * Reprint requests to Dr Wagdy Mahmoud Ghali, 16 El-Shahied Mahmoud El-Ashry, off El-Amal Street, Triumph Square, Heliopolis, Cairo, Egypt. so W. M. GHALI AND OTHERS RESULTS Macroscopic study The great cerebral vein was seen to begin below the splenium of the corpus callosum by the union of two internal cerebral veins. It passed upwards behind the posterior aspect of the splenium of the corpus callosum where it received the right and left basal veins. Then it joined the inferior sagittal sinus to drain into the straight sinus. The wall of the great cerebral vein was found to form a smooth curve with that of the inferior sagittal sinus, while the inferior sagittal sinus was in line with the straight sinus. The angle ofjunction between the great cerebral vein and the straight sinus was an acute one, ranging from 60-80 °C (Fig. 1). Examination of the opened straight sinus revealed the presence of a small elevation in its floor at its junction with the great cerebral vein. The elevation had a smooth surface, convex upwards. Its dimensions ranged between 3 5-4 5 mm in length and 2 5-3 mm in width at its basal part (Fig. 2). Examination of the inferior aspect of the tentorium cerebelli at the straight sinus, showed the presence of a hollow cavity at its junction with the great cerebral vein. This cavity formed the lumen of the elevation described above at the anterior end of the floor of the straight sinus (Fig. 3). Microscopic study Histological sections of the anterior end of the straight sinus revealed the presence of a smooth elevation with an empty cavity underlying it (Figs. 2, 3). The wall ofthe straight sinus was formed ofdense fibrous tissue arranged in laminae of collagen bundles that ran parallel to each other and was lined by vascular endothelium The elevation consisted of more or less interwoven bundles of collagen fibres which were again lined with vascular endothelium continuous with that of the straight sinus. DISCUSSION The present study has demonstrated the presence of an elevation bulging into the floor of the straight sinus at its junction with the great cerebral vein. Such an elevation corresponds to the 'body' described by Clark (1940), Balo (1950) and Williams & Warwick (1980). Clark named the elevation, the 'suprapineal arachnoid body' and explained it as a much enlarged arachnoid granulation bulging through the floor of the straight sinus. A similar description is given by Williams & Warwick. Furthermore, Clark mentioned that the body was attached to the superior vermis of the cerebellum. In the present study, however, the presence of such an enlarged arachnoid granulation could not be detected since the elevation was merely a hollow bulge from the floor of the straight sinus at its junction with the great cerebral vein. The present study has demonstrated that the great cerebral vein receives the right and left basal veins before opening into the straight sinus as described by Peele (1954), Last (1972), Williams & Warwick (1980) and Chusid (1982). Peele added that such basal veins constitute an important anastomotic channel between the superficial and deep venous systems of the brain. Furthermore, many intracerebral anastomoses exist between the terminal tributaries of the superficial and deep veins of the brain, and this provides a system ofshunting ofblood in cases of blockage ofeither system (Carpenter & Sutin, 1983). Thus, regulation of cerebrospinal fluid secretion by a ball valve mechanism as described by Clark cannot be accepted for, even with complete obstruction of the great Straight sinus and great cerebral vein 51

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Fig. 1. A photograph showing the great cerebral vein (V), inferior sagittal sinus (1) and the straight sinus (S) with a cannula inserted into it.

Fig. 2. A photograph of opened straight sinus (S). Note the elevation (arrows) at the anterior end of the floor of the sinus. 52 W. M. GHALI AND OTHERS

Fig. 3. A photomicrograph of the elevation (E) which consists of a hollow vesicle (arrow) with a wall of collagenous tissue. Haematoxylin and eosin. x 14.

Tube 3

Tube 1 Tube 2

Fig. 4. A diagram showing the junction between the inferior sagittal sinus (Tube 1), great cerebral vein (Tube 2) and the straight sinus (Tube 3). See text for description. Straight sinus and great cerebral vein 53 cerebral vein, the blood would be diverted to the superficial venous system of the brain according to Peele (1954) and Carpenter & Sutin (1983). Furthermore, 50% of the cerebrospinal fluid is formed by the choroid plexus (Ganong, 1983), while the remainder is formed around the cerebral vessels and along the ventricular walls. As the great cerebral vein represents the venous drainage of the choroid plexuses of the third and lateral ventricles, its obstruction would affect only 50 % of the cerebrospinal fluid secretion. Moreover, it is considered that the formation of the cerebrospinal fluid is an active process (Cserr, 1971; Snell, 1980; Guyton, 1982). As this elevation occupies a strategic point between two streams of blood, namely those from the great cerebral vein and from the inferior sagittal sinus into the straight sinus, it is important to study the possible functional role played by such an elevation vis-a'-vis the haemodynamics of the region. The junction of the inferior sagittal sinus, great cerebral vein and straight sinus may be considered as being formed of three tubes (Tube 1 = inferior sagittal sinus; Tube 2 = great cerebral vein and Tube 3 = straight sinus) (Fig. 4). In Tube 2, according to the kinematics of fluid flow, the boundary streamlines A and B cannot be deflected to Tube 3 without turbulence owing to the acute angle between the tubes. It must therefore be deflected to form a curve as is shown in Figure 4, for the boundary streamline A must leave the inner wall of Tube 3. The zone between the deflected streamline A and the inner wall of Tube 3 is called Dead Zone I. This dead zone contains fluid which forms vortices as shown by El-Ansary (1972a, b). The flow from Tube 1 is represented in Figure 4 by two boundary streamlines C and D. The streamline C passes uninterruptedly along Tube 3 while the streamline D will take the course as shown in Figure 4. Another dead zone, II, will be formed as a result. The surface area and location of Dead Zone II will depend on the ratios Q1/Q2 and D1/D2, where Q, = flow rate from the inferior sagittal sinus (Tube 1), Q2 = flow rate from the great cerebral vein (Tube 2), D1 = diameter of the inferior sagittal sinus (Tube 1) and D2 = diameter of the great cerebral vein (Tube 2). The inferior sagittal sinus is smaller in diameter than the great cerebral vein so that Q1 will be smaller than Q2; thus the effect of Dead Zone II on the wall of the sinus can be neglected. In Tube 3, it can be observed that at level a, the stream is narrow, while at Level b the stream is wider, El-Ansary (1972) and Daugherty, Franzini & Finnemore (1985) have stated that, according to Bernoulli's equation and the equation of continuity, the narrower the stream, the faster the flow and the lower the pressure. This suggests that the pressure in the vicinity of Dead Zone I will be less than the pressure in the remainder of Tube 3. Consequently, the inner wall of Tube 3, in the vicinity of the dead zone will be exposed to some inward deflection. El-Ansary (1972) has stated that, in such a tube system, vortex formation will be prevented by filling in the dead zone to form an elevation projecting into the lumen and such an elevation is provided by the formation described in this paper. Thus, it seems that the presence of such an elevation at this strategic point is to prevent vortex formation with its harmful effects on the entrance of the straight sinus at its junction with the great cerebral vein. The elevation has no role in the control of the cerebrospinal fluid secretion. Whether this elevation is present from birth or whether it is the result of the continuous inward deflection is a matter for further investigation. 54 W. M. GHALI AND OTHERS

SUMMARY In the present study 20 human brains were used to verify the presence of a small body projecting into the floor of the straight sinus at its junction with the great cerebral vein. The elevation could be identified at the anterior end of the floor of the straight sinus with an empty cavity underlying it. Histologically, the elevation was found to consist of interwoven bundles of collagen fibres covered by vascular endothelium continuous with that of the straight sinus. The importance of such an elevation in the regulation of blood flow from the great cerebral vein to the straight sinus is discussed from a hydrodynamic point of view. The authors are grateful to Professor Dr Ahmed El-Ansary, Head of the Department of Hydraulics and Irrigation, Faculty of Engineering, Alexandria University, for his helpful and generous comments regarding the hydrodynamic part of the study.

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