CEREBROSPINAL

FLUID

CHANNELS

M. A. Baron,* N. A. and G. F. Dobrovol'skii

DISCOVERY

THE

PIA

MATER UDC 611.819.1-086:612.824.1

Maiorova,

OF BY

OF

THE

THE

CEREBROSPINAL

METHOD

OF

FLUID

CHANNELS

TRACHYSCOPY

In o r d i n a r y m i c r o t o m e sections through the pia m a t e r of the human brain, against the background of the polygonal alveoli filling the subarachnoid space, c e r t a i n large translucent a r e a s differing in the shape of their outline are constantly found. Sometimes they a r e so large that they occupy the whole space between the arachnoid and pia m a t e r . Like the alveoli, these spaces are bounded by m e m b r a n e s of arachnoid endothelium. It is impossible by the o r d i n a r y techniques to distinguish c e r t a i n details which would allow their nature to be determined. At a c u r s o r y glance they give the i m p r e s s i o n of an a r t e f a c t caused by tearing of some of the m e m branes with the joining of s e v e r a l s m a l l alveoli into one large alveolus. However, the careful study of the region of t r a n s l u c e n c y c l e a r l y shows the complete absence of any tear of the m e m b r a n e s in this place. Another suggestion is that the l a r g e translucencies a r e the s a m e alveoli but pathologically enlarged in volume as a r e s u l t of stasis o r other disturbances of the CSF circulation. This is how these spaces a r e seen by some pathologists, who r e g a r d them as the initial stage of formation of subarachnoid cysts. Whatever the case, the large t r a n s l u c e n c i e s among the alveoli have not attracted attention and have not been studied. In this investigation the pia m a t e r of the c e r e b r a l h e m i s p h e r e s f r o m clinically healthy persons dying f r o m acute trauma was studied. The brain with the pia m a t e r was fixed in 10% neutral formalin, Z e n k e r formol, by the methods of Navashin--Krylov and Orth9 and with o s m i u m fixatives. The fixative was injected by the i n t r a v a s c u l a r route and the brain, a f t e r r e m o v a l , was also i m m e r s e d in the fixative. P i e c e s cut f r o m different parts of the brain were embedded in gelatin, celloidin, and paraffin wax, with careful o b s e r v a n c e of the stages involving the c o r r e s p o n d i n g reagents. Absolute alcohol and xylol were not used but were replaced by methyl benzoate and oil of bergamot. T r a n s v e r s e , two-dimensional, and tangential sections of the pia m a t e r , 10-80 ~ thick, were stained with Hansen's iron trioxyhematein and counterstained with aniline blue, with Heidenhain's iron hematoxylin, and by Van Gieson's method and impregnated by the methods of B i e l s c h o w s k y Maresh, Zhukhin, and Gomori. The sections were mounted in Canada balsam. R e g a r d l e s s of the method of fixation, embedding, and staining, in all c a s e s without exception large spaces 'surrounded by alveoli were p r e s e n t in the pia m a t e r . It thus followed that these spaces w e r e n o t artefacts and were not pathologically changed alveoli. They were c r o s s sections through c e r t a i n special types of space, p o s s e s s i n g a normal m e m brane and distinct f r o m the c o m p a r a t i v e l y s m a l l spaces of alveoli (Fig. 1). What a r e these s p a c e s , what is their actual shape and topography in the pin m a t e r , how is the wall of the spaces constructed, and what a r e their relationships with the alveoli? To answer these questions m i c r o t o m e sections, although i r r e p l a c e a b l e f o r the study of individual s t r u c t u r a l elements, are completely unsuitable. They b r e a k up the single a r c h i t e c t u r e of the pia into disconnected f r a g m e n t s , f r o m which it is impossible to r e p r e sent either the shape of the spaces or their relations with other formations of the pin. In the p r e s e n t investigation the decisive role was played by the trachyseopic method, by means of which t h r e e - d i m e n s i o n a l m i c r o s copy of the whole thickness of the pia can be undertaken (Baron, 1949, 1963). Disks 3 to 6 m m in thickness were cut f r o m the fixed brain t r a n s v e r s e l y , parallel with, and tangentially to the surface of the c e r e b r a l hemisphere. The disks included different parts of the cortex with the pia m a t e r covering it. The side of the disk for m i c r o s c o p i c examination was stained with Hansen's trioxyhematein, while the other side remained unstained. The whole disk was then counterstained with Scharlach by H e r x h e i m e r ' s method. The unstained side was stuck with gelatin to a piece of celluloid film and fixed in that position with formalin. The p r e p a r a t i o n thus mounted was cleared in a solution of g l y c e r o l and potassium acetate, the concentrations of which were gradually raised in the c o u r s e of 4 to 6 days to 34% g l y c e r o l and 20% potassium a c e tate. The t r a c h y s c o p i c preparations were studied in a s t e r e o s c o p i c m i c r o s c o p e , with facilities for visual observation and mieromanipulation with fine instruments. L a b o r a t o r y of Experimental Neurohistology, N. N. Burdenko Institute of N e u r o s u r g e r y , Academy of Medical Sciences of the USSR, Moscow. Translated from Arkhiv Anatomii, Gistologii i ]~mbriologii, Vol. 71, No. 7, pp. 10-25, July, 1976. Original article submitted April 23, 1975. 288

0097-0549/78/0903-0288 807.50

9 19 79 Plenum Publishing Corporation

Fig. I

Fig. 2

Fig. i. Cerebrospinal fluid canal in transverse section through pia mater, i) Araehnoid mater; 2) subarachnoid alveoli; 3) CSF canal; 4) artery inside CSF canal; 5) brain. Hansen's iron trioxyhematein. Objective: Neupolar 30 ram. Fig. 2. CSF canal of human pia mater. Trachyscopic brain preparation in tangential section, i) CSF canal in pia mater; 2) artery inside CSF canal; 3) subarachnoid alveoli of pia mater; 4) vein among subarachnoid alveoli; 5) brain. Hansen~s iron trioxyhematein. Objective: Neupolar 60 ram. On f i r s t inspection of such preparations one is struck b y the unexpected picture of a well developed network of canals, running at different levels of the pia m a t e r among the surrounding m a s s e s of alveoli. Iron trioxyhematein stained the walls of the canals and c l e a r l y demonstrated the outlines of the network formed by them (Fig. 2). C o n t r a r y to the widespread belief, the subarachnoid space of the pia m a t e r is not u n i f o r m e v e r y w h e r e , but can be subdivided into two completely different types of spaces: a s y s t e m of canals and a s y s t e m of alveoli. In the t h r e e - d i m e n s i o n a l t r a c h y s c o p i c p r e p a r a t i o n s it can be seen that the canals constitute a well f o r m e d network of tubes, whereas the alveoli a r e c o m p a r a t i v e l y small spaces, s u r p r i s i n g l y r e m i n i s c e n t in shape of honeycombs. In m i c r o t o m e sections the equivalents of the canals a r e large polymorphic s p a c e s , whereas the c r o s s sections of the alveoli c o n s i s t of small and, usually, polygonal spaces (Fig. 1) (Baron and Maiorova, 1958a, b). The s y s t e m of canals was studied experimentally and also examined in autopsy m a t e r i a l f r o m n e u r o s u r g i c a l patients. These investigations, which a r e outside the scope of this paper, d e m o n s t r a t e d conclusively the g r e a t i m p o r t a n c e of the canals both for the n o r m a l CSF circulation and in the pathogenesis of some d i s e a s e s of the CNS. The a l m o s t total absence of any comprehensible r e f e r e n c e s to the existence of a s y s t e m of canals in the c u r r e n t l i t e r a t u r e (morphological, morbid anatomical, and clinical) is therefore e x t r e m e l y s u r prising. HISTORY

OF

THE

DISCOVERY

OF

THE

CSF

CANALS

There is no mention of them in the well-known monographs of Snesarev (1950), Smirnov (1935), Fridman (1957), and Shamburov (1954), in the general articles by Cushing (1914), Dandy (1919), and Weed (1938) or in textbooks specially devoted to the meninges and, in particular, the textbooks by Schaltenbrand and Dorn (1955), Millen andWoollam (1962), Davson (1967), etc. The suggestion made by some workers that they are lymphatics of the pia mater (Iwanow and Romodanowski, 1927; Galkin, 1930; Golman, 1931; Magnus and Jacobi, 1925a, b) has not been confirmed. The present authors in this matter share the critical views of Zhdanov (1948) on the works cited above. The laconic statements of some authors on ~perivaseular ~ (Weed, 1938), ~periadventitial ~ (Magnus and Jacobi, 1925), and ~intra-adventitial" spaces of the pial vessels contradict one another and are too general in character. The view of Kiss (1950) that there are special vessels which drain the CSF and empty directly into the pial veins, and so on, is definitely erroneous. It is, however, unlikely that earlier investigators could have seen this regularly constructed system of canals without having doubts about their nature, and it was therefore necessary to turn to the literature of the 289

Fig. 3. CSF canals of the fissures and gyri of the human pia mater. 1) Arachnoid mater; 2) subarachnoid alveoli; 3) CSF fissure canal; 4) artery inside CSF canal; 5) trabeculae of connective tissue (cords) suspending artery from canal wall; 6) intima piae; 7) brain. CSF fissure canal changes into CSF gyrus canal on left side of figure (3). Magnification 56 x. Drawn under microscope from trachyscopic preparation. 19th century. In fact, in the work of Fohmann and Arnold (cited by Key and Retzius, 1875) and, in particular, of His (1865), who studied what they considered to be pial lymphatics, statements and drawings were found which left no doubt that they were concerned with certain fragments of this canal system. Later, in their unsurpassed investigation, Key and Retzius (1875) showed the fallacy of His' concept of pial lymphatics, but confirmed the existence of pial canals. The discovery of the CSF canals is thus associated with the names of the old anatomists of the 19th century, who mistakenly took them for pial lymphatics. This discovery was subsequently questioned and forgotten, probably because of bias in favor of microtome sections. TOPOGRAPHY

OF

THE

CSF

CANALS

The largest canals arise from the large cisterns at the base of the brain, where they attain a diameter of 4-5 ram. Branching repeatedly, they spread over the surface of the cerebral hemispheres, in which as a rule they lie in the depths of the fissures, and for that reason in future these canals will be called 'fissure canals" (or circulation canals). In the course of branching the diameter of the fissure canals decreases. Examination of a transverse section through a large fissure shows that on three sides (the floor of the fissure, the lower parts of the neighboring gyri) the canal is in contact with brain substance or, more precisely, with the thin layer (intima piae) covering the brain, On the fourth side, however, facing the arachnoid, the canal is bordered by alveoli, arranged in several rows in the superficial part of the subarachnoid space of the fissure. Usually the two lower thirds of such fissures are occupied by canals and only the upper third by alveoli. Corresponding to their position in the depth of the fissure, a cross-section of these canals closely resembles an isosceles triangle, the apex of which points toward the floor of the fissure, and the convex base toward the arachnoid. The small fissures contain canals of smaller diameter, but they occupy a comparatively large part of the subarachnoid space of the fissure. This is because the alveoli covering them are few in number and are arranged i n only a few r o w s . The f i s s u r e c a n a l s give off b r a n c h e s which c l i m b up one side of the g y r u s to its s u m m i t , d e s c e n d down the o t h e r s i d e , and d r a i n into the c a n a l s of the n e i g h b o r i n g f i s s u r e s . As a r e s u l t , the c a n a l s of two n e i g h b o r i n g f i s s u r e s a r e j o i n e d by n u m e r o u s a n a s t o m o s e s : " g y r u s c h a n n e l s " (or s e p a r a t i n g c h a n n e l s ) (Fig. 3). The d i a m e t e r of the g y r u s c h a n n e l s r e m a i n s c o n s t a n t (1-2 mm) t h r o u g h o u t t h e i r c o u r s e . Most g y r u s c h a n n e l s r u n m o r e o r l e s s t r a n s v e r s e l y to the long axis of the g y r u s . At the s u m m i t of the g y r u s s o m e c a n a l s b r e a k up into

290

Fig. 4. Fibrous skeleton of wall of CSF canal; a) wall of CSF canal: 1) lumen of CSF canal; 2) a r t e r y inside CSF canal; 3) wall of CSF canal; 4) subarachnoid alveoli, b) Collagen fibers c r o s s i n g in canal wall: 1) collagen f i b e r s ; 2) nuclei of arachnoid endothelium; 3) granules around nuclei of arachnoid endothelium. Hansen's iron trioxyhematein. Magnification: a) 1 0 0 x , b) 420 x. two thinner b r a n c h e s , like nhorns N (or the letter Y). The c o m m o n unbranched end and the two branches of these gyrus canals empty into different canals in f i s s u r e s between which the gyrus lies. In other c a s e s , only one of these branches empties into a f i s s u r e canal while the second, running along the g y r u s , empties into the neighboring gyrus canal. As a result, the gyrus canals, like the f i s s u r e canals, a n a s t o m o s e with each other. It can be seen in the t r a n s v e r s e section of a gyrus that the canals c r o s s i n g it, unlike the f i s s u r e canals, occupy the m o s t superficial p a r t of the subarachnoid space, in d i r e c t contact and forming v e r y close relations with the araehnoid m a t e r . Along the sides of the canals and also in the depths beneath them lie alveoli. At the s u m m i t of the g y r u s , where the subarachnoid space is g r e a t l y narrowed, the canals occupy all the space between the arachnoid and the intima piae. Here the alveoli lie in a single row.only on the side of the canals. The gyrus canals a r e round in sections. The s m a l l e s t of them attain a diameter of about 200 g. Consequently, f r o m their origin f r o m the l a r g e s t f i s s u r e canals as far as the s m a l l e s t gyrus canals, the d i a m e t e r of their lumen thus d e c r e a s e s continuously f r o m 3-4 m m to 200-300 ~. However, along the c o u r s e of the canals there a r e dilatations many times g r e a t e r than the original d i a m e t e r of the canal. These dilatations a r e found in v e r y c h a r a c t e r i s t i c p l a c e s , where s e v e r a l canals meet. F o r the f i s s u r e canals this is the region of i n t e r a c t i o n of the f i s s u r e s , for the g y r u s canals it is where they break up into branches. In both cases the canals expand suddenly into these dilatations, with a c l e a r l y defined boundary. In t r a c h y s c o p i c p r e p a r a t i o n s the dilatations look like large spaces of widely different shapes, into which three o r m o r e canals empty through c l e a r l y distinguishable round holes. The g r e a t e s t diameter of these dilatations may be f r o m 3 to 10 times g r e a t e r than the d i a m e t e r of the lumen of the canals. STRUCTURE

OF

THE

WALL

OF

THE

CSF

CANALS

Both the canals and the local dilatations formed by them have a well formed wall. Its s t r u c t u r e is distinctive and differs sharply f r o m that of the walls of lymphatics. This fact alone is sufficient to cause the rejection of any attempt to r e g a r d the canals as belonging to the lymphatic s y s t e m . Two components a r e p r e s e n t in the wall of the canals: a fibrous skeleton and the arachnoid endothelium. No muscle fibers a r e p r e s e n t in the wall of the canals, even of the l a r g e s t .

291

The fibrous skeleton of the wall consists mainly of collagen fibers (Fig. 4). These fibers are straight, without undulations. In other words, they have none of the s o - c a l l e d Wreserve folds, Wpermitting lengthening of the collagen fibers, which are virtually unstretchable in vivo. The straight collagen fibers run in the wall of the canal along its axis in the f o r m of two s p i r a l s , one of which has clockwise turns, the other anticlockwise. As a r e s u l t of the c r o s s i n g of the two turns, the collagen fibers are a r r a n g e d r e g u l a r l y in the f o r m of a lattice, which is c l e a r l y distinguishable in impregnated preparations. This fact explains the m e c h a n i s m of the change in lumen of the canals, in which, as has been said, there are no muscle fibers. Variations in the lumen of the canals are passive in c h a r a c t e r and a r e determined by the relative p r e s s u r e s of the CSF in the canals t h e m selves and in the alveoli surrounding them. A change in lumen is produced by rotation of the collagen fibers at the points where they c r o s s , so that during dilatation of the canal the turns of the spirals become less steep and during c o n s t r i c t i o n of the canal they become steeper. A s i m i l a r movement of the fibrous skeletons of hollow organs has been described by many other w o r k e r s (Goerttler, cited by StShr; MSllendorff and Goerttler, 1955; Baron, 1949). Besides collagen fibers, the fibrous skeleton also includes a few argyrophilic fibers. On impregnation by the B i e l s c h o w s k y - M a r e s h method the f o r m e r stain r e d d i s h - v i o l e t whereas the latter stain black. The a r g y r o p h i l i c fibers f o r m a delicate network without any predominant direction. At the s u b m i c r o scopic level the fibrous skeleton of the wail of the CSF canals consists of bundles of collagen fibrils and m i c r o fibrils. Collections of m i c r o f i b r i l s a r e found e v e r y w h e r e among collagen fibrils and close to the p l a s m a m e m branes of the arachnoid endothelial cells. They must probably be r e g a r d e d as p a r t of the morphological subs t r a t e of those fibrous s t r u c t u r e s which can be seen under the light m i c r o s c o p e as argyrophilic fibers. The second component of the wall of the canals (arachnoid endothelium) f o r m s a c y t o p l a s m i c m e m b r a n e in which no i n t e r c e l l u l a r boundaries can be detected with s i l v e r nitrate. Typical nuclei of the a r a c h n o e n d o thelium a r e s c a t t e r e d i r r e g u l a r l y in this m e m b r a n e : large oval nuclei with finely dispersed c h r o m a t i n (pale nuclei) and s m a l l round nuclei r i c h in c h r o m a t i n (dark nuclei). The nuclei show the c h a r a c t e r i s t i c tendency for the arachnoid endothelium to be heaped together. Especially around the nuclei, and less so at a distance f r o m it, there a r e inclusions of various granules and vacuoles, evidence of the active participation of the arachnoid endothelium of the canal wails in exchange p r o c e s s e s with the CSF. In autopsy m a t e r i a l the ability of the arachnoid endothelium of the canals to accumulate colloids, especially hemoglobin, and to decompose it with the formation of hemosiderin (the reaction for iron) was demonstrated. An electron m i c r o s c o p i c investigation revealed that the cytoplasmic m e m b r a n e of the wall of the CSF canals is formed f r o m arachnoid endothelial cells. These cells, with their flattened shape, overlap one another by their p e r i p h e r a l parts where they a r e in contact with neighboring ceils. The intercellular junctions a r e formed by d e s m o s o m e s . The cell nuclei are i r r e g u l a r l y oval in shape. Oval o r round mitochondria and elements of the g r a n u l a r endoplasmic r e t i c u l u m and Golgi apparatus are s c a t t e r e d in the osmiophobic c y t o p l a s m of the ceils. The wall of the CSY canals is lined with arachnoid endothelial cells both on the side of its lumen and on the side of the surrounding alveoli. The relations between these two components can be s u m m a r i z e d by saying that the fibrous skeleton is surrounded by c y t o p l a s m i c m e m b r a n e s of arachnoid endothelial ceils. The easily changing c y t o p l a s m of the arachnoid endothelium r e s t s on its turns, as on a m o r e elastic basis. In His' description the nlymphatic v e s s e l s " of the pia, like o r d i n a r y lymphatics, have continuous walls and do not communicate with the subarachnoid space. Lymph entering f r o m the " p e r i v a s c u l a r s p a c e s " of the brain (now known as spaces of His), c i r c u l a t e s in these v e s s e l s . The subarachnoid space, however, contains CSF which enters it f r o m the c e r e b r a l v e n t r i c l e s . According to His, the lymphatic and CSF systems of the pia m a t e r a r e morphologically completely s e p a r a t e , and functionally they have quite different roles. It was Key and Retzius who f i r s t showed, as the p r e s e n t w r i t e r s now confirm, that the wall of the canals is not in fact continuous. It contains c l e a r l y distinguishable small holes, through which the canals communicate openly with the remaining subarachnoid space. The i n c o r r e c t n e s s of the concepts of His, and of Key and Retzius who m e r e l y stated that the holes in the canal wails a r e s i m i l a r to the c o r r e s p o n d i n g holes in the wails of the alveoli will thus be evident. On the basis of the study of t r a c h y s c o p i c preparations and, in p a r t i c u l a r , of intravital o b s e r v a t i o n of the m o v e m e n t of foreign p a r t i c l e s , p r e v i o u s l y injected into the c i s t e r n a magna of a dog, and their excretion f r o m the channels into the alveoli, the p r e s e n t w r i t e r s obtained a different i m p r e s s i o n (Baron, 1968, 1969). As a rule, the holes in the wall of the canals a r e much s m a l l e r than in the wails of the alveoli. In long segments of the canals there a r e no holes whatsoever. Moreover, the holes in the canals are distinguished by their g r e a t constancy of shape and size. They a r e c i r c u l a r and 15-20 ~ in diameter. Everything said about the holes in the canal wall applies to that p a r t of the wall facing the alveoli and arachnoid. As r e g a r d s the other part, facing the intima pine, no holes a r e p r e s e n t in the wall. Microscopic examination of the isolated intima piae shows that in these regions it is covered with a continuous l a y e r of arachnoid endothelium of the canal wall.

292

Fig. 5

Fig. 6

Fig. 5. Roofof excretory CSF canal on brain gyrus. 1) Nucleus-free zone of arachnoid mater in region of roof of CSF canals; 2) nuclear zones of arachnoid above subarachnoid alveoli. Hansen's iron trioxyhematein, 100 x. Fig. 6. Fibrous skeleton of araehnoid mater above CSF canal. 1) Arachnoid of roof of CSF canal; 2) artery in CSF canal; 3) region of subaraehnoid alveoii. Film preparation. Impregnation by Bielsehowsky-Maresh method.

F i g . 7. R o o f of C S F c a n a l on b r a i n g y r u s . SAS) S u b a r a c h n o i d s p a c e ( l u m e n o f e x c r e t o r y c a n a l ) , IAL) i n n e r a r a c h n o i d e n d o t h e l i a l l a y e r , OAL) o u t e r a r a c h noid e n d o t h e l i a l l a y e r , SDS) s u b d u r a l s p a c e . S u b l a y e r o f d e s q u a m a t e d o s m i o p h i l i c c e l l s of O A L c a n b e s e e n in top p a r t o f f i g u r e s . A r r o w s p o i n t to b u n d l e s of collagen fibrils of reduced eollageno-fibrous b a s i s . O s m i o p h o b i c a r a c h n o i d e n d o t h e l i a l c e l l of OAL c a n be s e e n i n c e n t e r of f i g u r e . E l e c t r o n m i c r o g r a p h , 2500 • On the g y r i of the b r a i n the C S F c a n a l s l i e a g a i n s t the a r a c h n o i d . The a r a c h n o i d a b o v e the C S F c a n a l s f o r m s p a r t o f t h e i r w a l l and c a n b e c a l l e d the " r o o f " of the C S F c a n a l s . The a r a c h n o i d in the r o o f of the C S F c a n a l s i s m u c h t h i n n e r and i t s f i b r o u s s k e l e t o n is r e d u c e d . It c a n b e s e e n in f i l m p r e p a r a t i o n s of the a r a c h n o i d t h a t t h e r e a r e few n u c l e i of the e n d o t h e l i u m in the r o o f . C o n s e q u e n t l y the r o o f of the C S F c a n a l s a r e c l e a r l y d i s t i n g u i s h a b l e a s " n u c l e u s - f r e e " z o n e s o r " t r a c k s " l o c a t e d a b o v e the a r t e r i e s ( F i g s . 5 and 6). E l e c t r o n - m i c r o -

293

Fig. 8. Dilated interceUular spaces in roof of e x c r e t o r y CSF canal in outer arachnoid endothelial layer of arachnoid m a t e r of human c e r e b r a l h e m i s p h e r e s . Top-- boundary between sublayers of desquamated osmiophilic ceils and osmiophobic ceils. Intercellular spaces indicated by a r r o w s . B o t t o m - sublayer of osmiophobic ceils. Dilated i n t e r c e l l u l a r space at boundary between three a r a c h noid endothelial ceils indicated by a r r o w . Magnification: top 7,000; b o t t o m - 20,000. E l e c t r o n m i c r o g r a p h . scopically the roof of the CSF canal is composed f r o m within outward of the inner arachnoid endothelial layer, the reduced collageno-fibrous principal layer, and the outer arachnoid endothelial l a y e r (Fig. 7). The cells of the inner araehnoid endothelial l a y e r of the arachnoid m a t e r are s i m i l a r in u l t r a s t r u c t u r e to the cells lining the CSF canals. In the outer arachnoid endothelial layer a sublayer of osmiophobic cells and a sublayer of des q u a m a t e d o s m i o p h i l i e c e U s , facing the subdural space, can be distinguished (DobrovoPskii, 1969, 1974). Intravital observations on animals (dogs and cats) have shown that the wails of the CSF canals consist of distinctive limiting m e m b r a n e s which propel the CSF along the lumen of the canals in a manner which differs f r o m the slow movement of the CSF in the alveoli. The CSF canals a r e the main trunks for movement of CSF on the surface of the brain. Colloidal solutions and suspensions of particles or ceils, introduced experimentally into the subarachnoid space, spread along the CSF canals. In pathology the CSF canals a r e pathways for the spread of blood, exudates, and tumor m e t a s t a s e s throughout the subarachnoid space (Baron, L y a s s , and M a j o r ova, 1959; Baron, 1957, 1960, 1961). The e x c r e t o r y canals on the s u r f a c e of the gyri a r e the place where CSF drains out of the subaraehnoid space into the subdural space. The excretion of CSF and substances introduced into it takes place through the roofs of the CSF canals on the brain gyri (Baron, L y a s s , and Maiorova, 1964; Maiorova, 1965; DobrovoPskii, 1970, 1974). The universal p e r m e a b i l i t y of the arachnoid m a t e r is based on the network of dilated i n t e r c e l l u l a r spaces which penetrate into the araehnoid and which open both into the subaraehnoid and into the subdural space, and also on the absence of b a s e m e n t m e m b r a n e s in this m e m b r a n e (Fig. 8). The dilated intercellular spaces may attain a size of 500 ,~ or m o r e . Along this network not only CSF, but also h i g h - m o l e c u l a r - w e i g h t substances

294

F i g . 9. ~ T r a n s v e r s e s e c t i o n through s u r f a c e of human b r a i n and its m e n i n g e s . Blood v e s s e l s s u r r o u n d e d by a p a l e b o r d e r - p e r i v a s c u l a r c a n a l s Pv - can be s e e n in the b r a i n s u b s t a n c e G. They e m p t y d i r e c t l y i n t o the e p i c e r e b r a l s p a c e E, l o c a t e d beneath the pia m a t e r P. In s e c t i o n the pia m a t e r 1) a p p e a r s as a thin l a y e r . H e r e and t h e r e in it can be s e e n l a r g e t r a n s l u c e n c i e s (a) in which blood v e s s e l s l i e f r e e l y . T h e s e t r a n s l u c e n c i e s a r e due to l y m p h a t i c c a n a l s of the pia. E x t e r n a l l y the a r a e h n o i d m a t e r A can be s e e n a s a condensed l a y e r . Between i t and the pia l o o s e c o n n e c t i v e t i s s u e and the s u b a r a c h n o i d s p a c e a r e i n t e r p o s e d . F i g u r e and its d e s c r i p t i o n taken f r o m His (1865), Table XI, Fig. 6. M a g nification 50 • and c o l l o i d s ( a l b u m i n s and globulins of the blood) can move. The width of these s p a c e s v a r i e s within wide l i m i t s and a l s o under p a t h o l o g i c a l conditions. F o r e x a m p l e , in s u b a r a c h n o i d h e m o r r h a g e , d u r i n g the p a s s a g e of r e d blood c e l l s through the a r a c h n o i d i t m a y r e a c h m a n y hundreds of A n g s t r o m units ( D o b r o v o l ' s k i i , 1970, 1974). ARRANGEMENT

OF.BLOOD

VESSELS

INSIDE

CSF

CANALS

Between the c a n a l s and the p i a l blood v e s s e l s r e g u l a r t o p o g r a p h i c r e l a t i o n s a r e o b s e r v e d . The v e r y f i r s t i n v e s t i g a t o r s of the p i a l Wlymphatics" - F o h m a n n and A r n o l d - noted that t h e s e v e s s e l s a c c o m p a n y a r t e r i e s and v e i n s . They join t o g e t h e r to f o r m e f f e r e n t t r u n k s which follow the c o u r s e of the l a r g e blood v e s s e l s , e s p e c i a l l y v e i n s , and l e a v e with them through the s a m e openings a t the b a s e of the skull. His i n t r o d u c e d a v e r y i m p o r t a n t c o r r e c t i o n into this d e s c r i p t i o n when he showed that the " l y m p h a t i c s n do not s i m p l y a c c o m p a n y blood v e s s e l s but s u r r o u n d t h e m in the f o r m of wide, continuous s l e e v e s (weite M a n t e l r S h r e n ) . In the f i g u r e {from His) i l l u s t r a t i n g a t r a n s v e r s e s e c t i o n through the pia, r e p r o d u c e d h e r e as F i g . 9, the round l a r g e l u m e n of t h e s e s l e e v e s can be c l e a r l y s e e n , with the injected blood v e s s e l s lying f r e e l y i n s i d e them. The s a m e r e l a t i o n s b e t w e e n the c a n a l s and blood v e s s e l s a r e a l s o d e s c r i b e d by Key and R e t z i u s (Fig. 10). The t r a c h y s e o p i c p r e p a r a t i o n s show c o n c l u s i v e l y that m o s t of the c a n a l s in fact s u r r o u n d blood v e s s e l s like s l e e v e s . H o w e v e r , this is not a r u l e , f o r t h e r e a r e c a n a l s , e s p e c i a l l y in the f i s s u r e s , which have no v e s s e l s w h a t s o e v e r . The two c o m m u n i c a t e with each other and a r e i n d i s t i n g u i s h a b l e in a l l o t h e r r e s e p c t s . T h e r e is t h e r e f o r e no r e a s o n to d e s c r i b e a l l the c a n a l s in g e n e r a l as " p e r i v a s c u l a r . " It has b e e n found that the c a n a l s a l m o s t e n t i r e l y run along the c o u r s e of the p i a l a r t e r i e s and do not continue along its v e i n s . Even w h e r e the a r t e r y and v e i n r u n side by s i d e and p a r a l l e l to each o t h e r it will be s e e n that the outline of the c a n a l s u r r o u n d s the a r t e r y a l o n e , w h e r e a s the vein is l o c a t e d among the a l v e o l i . Only in the l a r g e f i s s u r e c a n a l s a r e veins found t o g e t h e r with the a r t e r i e s . However, unlike the a r t e r i e s , these veins cannot be t r a c e d along the c a n a l but m e r e l y c r o s s it in a s h o r t s e g m e n t , a f t e r which they move a w a y into the a l v e o l i . How does the s y s t e m of c a n a l s p r e s e r v e the c h a r a c t e r of a continuous network if the c a n a l s a r e d i s t r i b u t e d along the a r t e r i e s and do not continue along the v e i n s 7 At f i r s t g l a n c e i t might a p p e a r that under t h e s e c i r c u m s t a n c e s the c a n a l s t e r m i nate b l i n d l y when they r e a c h the s m a l l e s t a r t e r i e s . However, in f a c t no such blind endings e x i s t : l) b e c a u s e of a n a s t o m o s e s b e t w e e n the b r a n c h e s of the s a m e and d i f f e r e n t a r t e r i e s along which the canal of one a r t e r y continues without i n t e r r u p t i o n into the c a n a l of the o t h e r a r t e r y , and 2) s i n c e in the g r e a t e r p a r t of the pia m a t e r w h e r e no such a n a s t o m o s e s e x i s t b e t w e e n the a r t e r i a l r a m i f i c a t i o n s , a t the points of i n t e r s e c t i o n of diff e r e n t b r a n c h e s the c a n a l s c r o s s f r o m one b r a n c h to a n o t h e r .

295

Fig. 10

Fig. 11

Fig. 10. Section through human c e r e b r u m . Section cut obliquely to s u r f a c e to show subarachnoid tissue in f i s s u r e s a between gyri and f i s s u r e s b; c) divided blood v e s s e l s surrounded by their subarachnoid canals. Figure and its description taken f r o m Key and Retzius (1875), Table IV, Fig. 9. Fig. 11. Scheme showing different a r r a n g e m e n t s of a r t e r i e s inside CSF canals in the c e r e b r a l h e m i s p h e r e s . 1) A r t e r y attached to arachnoid m a t e r , 2) a r t e r y located in c e n t e r of CSF canal, 3) a r t e r y adjoins wall of CSF canal. It m u s t not be a s s u m e d that all the pial a r t e r i e s a r e surround6d by canals. There a r e many a r t e r i e s , especially small ones, which run outside the canals and among other s t r u c t u r e s of the pia m a t e r . This happens because an a r t e r y located in a canal gives off branches which run along for a s m a l l distance within the canal and then p e r f o r a t e its wall and continue into the t e r r i t o r y of the alveoli or the intima pine. A r t e r i e s located among the alveoli b e c o m e attached to their m e m b r a n o u s walls and continue to ramify. A r t e r i e s penetrating into the intima piae also ramify, spread in its deep l a y e r s parallel to the b r a i n s u r f a c e , and give off radial a r t e r i e s , which c a n b e traced further into the pial funnels, as Key and Retzius showed. In t r a e h y s c o p i c p r e p parations of the f i s s u r e canals these a r t e r i e s of the intima piae show up by their t r a n s l u c e n c y against the adjacent wall of the canal. In the d i r e c t i o n f r o m the f i s s u r e canals to the gyrus canals their diameter gradually diminishes. As the a r t e r i e s branch, their diameter naturally also d e c r e a s e s , but the changes in size do not take place parallel to each other. In c e r t a i n sections of their path the r a t i o between the d i a m e t e r of the canal and the diameter of the a r t e r y contained in it v a r i e s within v e r y wide limits. For example, in three f i s s u r e canals of the p a r i e t a l lobe of one h e m i s p h e r e with approximately the same s m a l l diameter of 2800 p, the f i r s t canal contained an a r t e r y with a d i a m e t e r of 200 p, the second canal an a r t e r y with a d i a m e t e r of 2200 p, whereas the third canal contained three a r t e r i e s , each 150 p in d i a m e t e r , and one vein 300 p in diameter. In three gyrus canals from the same case, with maximal c r o s s section of about 500 ~, one canal contained an a r t e r y 130 p in d i a m e t e r , the second an a r t e r y 400 ~ in d i a m e t e r , and the third an a r t e r y 75 p in diameter. As r e g a r d s local dilatations of the canals, because of their e x t r e m e l y curious shape and abundance of branches of the v e s s e l s passing through these spaces, it was difficult to determine the c o r r e s p o n d i n g d i a m e t e r s . The relationships o b s e r v e d in this c a s e r e s e m b l e those found in the large c i s t e r n s at the base of the brain. Evidently where the canals dilate the rate of flow in them will exceed the rate of flow in the blood v e s s e l s contained in them by the g r e a t e s t degree. The a r r a n g e m e n t of the a r t e r i e s in the canals is highly distinctive. C r o s s sections through a large canal show that c e r t a i n portions of the a r t e r i e s occupy a central position and a r e surrounded on all sides by the lumen of the canal. In other segments, however, the a r t e r y lies e c c e n t r i c a l l y and adjoins the wall of the canal.

296

Fig. 12. C o n n e c t i v e - t i s s u e t r a b e c u l a in longitudinal section at site of a t t a c h m e n t to a r t e r y . 1) T r a b e c u l a composed of collagen fibers with f i b r o blasts between them, covered by arachnoid endothelium, 2) arachnoid endothelial sheath of the a r t e r y , 3) a r t e r y in lumen of CSF canal, 4) lumen of CSF canal. E h r l i c h ' s hematoxylin-eosin, 100 • Micromanipulation shows that in this case the position of the a r t e r y in the canal is free, and t h e r e is no adhesion between the a r t e r y and the wall of the canal. Similar segments a r e found in small canals, where the a r t e r y lies f r e e l y in the lumen of the canal. However, where the a r t e r y adjoins the wall of the canal, as micromanipulation shows, strong adhesion is found. In gyrus canals running in the m o s t superficial p a r t of the subarachnoid space, this adhesion is localized to the side of the a r t e r y facing the arachnoid, so that the arachnoid m a t e r , the canal wall, and the a r t e r i a l wall a r e all connected together. Because of this adhesion, a section through the lumen of these canals shows the c h a r a c t e r i s t i c semilunar shape, open toward the arachnoid. All these details of the relations between the a r t e r i e s and the canals a r e essential to the understanding of the function Of the canals and of c e r t a i n phenomena o b s e r v a b l e in them during life (Fig. 11). Key and Retzius found yet another s m a l l s t r u c t u r a l element of the canals, namely t r a b e e u l a e suspending the v e s s e l s in them. In their description the t r a b e c u l a e a r e attached by one end to the canal wall and by the other end to the wall of the a r t e r y , and they branch and c r o s s the lumen of the canal in different directions. It is v e r y difficult to distinguish the t r a b e c u l a e of the canals in m i c r o t o m e sections. The r e a s o n is that, so far as is known, nobody since Key and Retzius has succeeded in identifying the s t r u c t u r e s which they saw. However, on examination of hundreds of p r e p a r a t i o n s , in a few c a s e s the longitudinal section through a t r a b e c u l a e ould be seen (Fig. 12). The t r a b e c u l a e a r e composed o f p a r a l l e l collagen fibers, closely opposed to each other, with elongated nuclei of fibrocytes between them, so that they r e s e m b l e a miniature tendon. A f t e r staining with orcein, no elastic fibers could be found either in the trabecula or in the walls of the canals. Such fibers a r e always p r e s e n t in the adventitia of blood v e s s e l s , but they do not spread into the trabeculae. On their s u r f a c e the t r a b e c u l a e a r e covered by a continuous layer of arachnoid endothelium, the pale oval nuclei of which a r e c l e a r l y distinguishable f r o m the elongated nuclei of the fibrocytes. Capillaries and venules, branching in the adventitia of the v e s s e l s , frequently run in the trabeculae. At one end of the t r a becula the arachnoid endothelium covering it c r o s s e s into the arachnoid endothelial sheaths of the v e s s e l s adjacent to the adventitia of the a r t e r y , whereas at the other end of the trabecula the arachnoid endothelium m e r g e s with the arachnoid endothelium of the canal wall. The t r a c h y s c o p i c p r e p a r a t i o n s revealed new features of the attachment and a r r a n g e m e n t of the t r a b e c u lae, and thereby shed light on their functional significance. Three main types of t r a b e c u l a e were found in the canals: 1) attached by one end to the wall of the canals and by the other end to the wall of the a r t e r y , 2) attached by both ends to the canal walls, and 3) attached by both ends to the v e s s e l walls (Arutyunov, Baron, and Maiorova, 1973, 1974). Powerfully developed t r a b e c u l a e in the large canals, both "suspending ~ the a r t e r i e s f r o m the canal walls and, in p a r t i c u l a r , "connecting" their different branching points a r e an important evolutionary adaptation. They stabilize the position of the a r t e r i e s in the canals which, unlike the other a r t e r i e s of the body, a r e entirely contained in an e x t r e m e l y extensive basin of fluid, and they thus provide the conditions essential for the c e r e b r a l circulation. 297

LITERATURE

CITED

Arnold, F., Annotationes Anatomicae de Filamentis Cerebri et Medullae Spinalis, Turici (1938) (cited by Key and Retzius, 1875). Arutiunov, A. J. (Arutyunov, A. I.l, Baron, M. A., and Majorova, N. A. (Maiorova, N. A.), "The role of mechanical factors in the pathogenesis of s h o r t - t e r m and prolonged spasm of the c e r e b r a l a r t e r i e s , w J. Neurosurg., 40, 459 (1974}. Arutyunov, A. I., Baron, M. A., and Maiorova, N. A., WStructure and function of stabilizing constructions of the c e r e b r a l a r t e r i e s in the light of the pathogenesis of a r t e r i a l spasm after rupture of aneurysms, w Vopr. Neirokhir., No. 3, 3 (1973). Baron, M. A., Reactive Structures of the Internal Membranes (Serous, Meninges, Synovial, Endocardium, Amnion) [in Russian], Medgiz, Leningrad (1949). Baron, M. A., WThe role of the CSF canals and subarachnoid alveoli during hemorrhage into subarachnoid space, w Abstracts of Scientific Proceedings of the l l t h Session of the General Assembly of the Academy of Medical Sciences of the USSR, April 15-20, 1957 [in Russian], Medgiz, Moscow (1957), pp. 30-34. Baron, M. A., "Histological and experimental investigation of the membranes (barriers) of the pia mater of the brain," Proceedings of a Conference on Tissue-Blood B a r r i e r s [in Russian], Izd. AN SSSR (1961), pp. 322-340. Baron, M. A., "Trachyscopy,n Great Medical Encyclopedia, Second Edition [in Russian], Vol. 32, Moscow (1963}. Baron, M. A., WMovement of the CSF in the subarachnoid space of the c e r e b r a l hemispheres (intravital o b se rvations), u Byull. l~ksp. Biol. Med., No. 12, 98 (1968). Baron, M. A., "Investigation of the CSF spaces of the brain by injection of actively motile infusorian particles into the CSF," Byull. l~ksp. Biol. Med., No. 9, 115 (1969}. Baron, M. A., and Maiorova, N. A., "The CSF canals of the pia mater of the brain, n Annotations of.Scientific Research of the Academy of Medical Sciences of the USSR for 1956 [in Russian], Book 1, Medgiz (1958), pp. 92-94. Baron, M. A., and Maiorova, N. A., "The role of the CSF canals of the pia mater of the brain in some pathological p r o c e s s e s , " Annotations of Scientific Research of the Academy of Medical Sciences of the USSR for 1956 [in Russian], Book 1, Medgiz (1958), pp. 94-95. Baron, M. A., Lyass, F. M., and Maiorova, N. A., "The phenomenon of 'dew' on the brain surface and its relation to the outflow of CSF along the pial canals of the brain," Vopr. Neirokhir., No. 1, 3 (1959). Baron, M. A., Lyass, F. M., and Maiorova, N. A., "Experimental study of the excretion of colloidal Au 198, Na2Hp3204, Na24C1 and NaITM through the arachnoid mater," Med. Radiol., No. 8, 60 (1964). Cushing, H., "Studies on the cerebrospinal fluid," J. Med. Res., 31, No. 1, 146 (1914). Dandy, W. E., "Experimental hydrocephalus," Ann. Surg., 70, 129 (1919). Davson, H., Physiology of the Cerebrospinal Fluid, Little, Brown and Co., Boston (1967). Dobrovol~skii, G. F., "Ultrastructure of the arachnoid mater of the c e r e b r a l hemispheres and its role in CSF drainage (electron-microscopic investigation)," Vopr. Neirokhir., No. 6, 5 (1969). Dobrovol'skii, G. F., "Electron-microscopic investigation of the excretion of erythrocytes through the a ra c h noid mater during subarachnoid hemorrhage (experimental investigation}," Vopr. Neirokhir., No. 2, 29 (1970). Dobrovol'skii, G. F., "The role of the u l t r a s t r u c t u r e of the arachnoid mater in man in the removal of e r y t h r o cytes from blood escaping into the subarachnoid space (electron-microscopic investigation)," Vopr. Neirokhir., No. 2, 32 (1974). Fohmann, "M~moire sur les vaisseaux lymphatiques," cited in Arnold's "Bemerkungea ~ber den Bau des Hirns und Riickenmarks" (cited by Key and Retzius, 1975). Fridman, A. P., Fundamentals of the Study of the Cerebrospinal Fluid [in Russian], Medgiz, Leningrad (1957). Galkin, W. S., "Uber die Bedeutung der Nasenbahn fiir den Abflus aus dem Subarachnoidalraum," Z. Ges. Exp. Med., 72, Nos. 1-2, 65 (1930). Goerttler, K., cited by P. St~hr, W. V. M~llendorff, and K. Goerttler, Lehrbuch der Histologie und der mikroslopischen Anatomie des Menschen (1955), p. 300. Golmann, S. W., "Beitr~ge zue .normalen und pathologischen Histologie der weichen Hirn ~nd Ruckenmarkshaute des Menschen," Z. Ges. Neurol. Psych., 135, 323 (1931). His, W., "IJber ein perivascul~res Canalsystem in den nerv~sen Centralorganen und i~ber dessen Beziehungen zum Lymphsystem," Z. Wiss. Z.ool., 15, 127 (1865). Iwanow, G., and Romodanowski, K., "Uber den anatomischen Zusammenhang der c e r e b r a l e n und spinalen submeningealen R~iume mit dem Lymphsystem," Z. Ges. Exp. Med., 58, 3 (1927).

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COMPARATIVE RETICULAR

ONTOGENETIC FORMATION

DEVELOPMENT

IN Maeaca

rhesus

V. V. A m u n t s

OF

AND

THE

BRAIN-STEM

MAN

UDC 591.481.1:577.95]-086+611.818:577.95]-086

C o m p a r a t i v e ontogenetic studies of the r e t i c u l a r formation a r e important in o r d e r to r e v e a l the p r i n c i ples of its s t r u c t u r a l and functional organization. The object of the p r e s e n t investigation was to study the r e t i c u l a r formation (RF) of a lower monkey (Macaca rhesus) during p r e n a t a l and postnatal development and to c o m p a r e it with the c o u r s e of ontogeny of the human R F (using data f r o m the l i t e r a t u r e and p e r s o n a l o b s e r v a tions). The b r a i n was investigated in r h e s u s monkeys of the following a g e s : fetuses of 1.5, 2.5, and 3 lunar months, at birth, 0.5 and 3 y e a r s a f t e r birth, and adult animals. Series of 20-p frontal sections through the brain s t e m (medulla, pons, and midbrain) were stained with c r e s y l violet by the method adopted at the Brain Institute, A c a d e m y of Medical Sciences of the USSR. The human brain was investigated in e m b r y o s and fetuses aged 1.5, 2.5, 3, 4.5, and 8 lunar months, at birth, and at the ages of 0.5, 3, and 7 y e a r s and in adults. The cell density in the monkey and human brain was determined in 50 fields of vision p e r cubic m i l l i m e t e r of brain substance by means of Blinkov's (1964) o c u l a r - m i c r o m e t r i c method, with a c o r r e c t i o n for the thickness of the s e c tion and d i a m e t e r of the nucleus o r nucleolus suggested by A b e r c r o m b y (1946), and also allowing for Haug's (1956) rules. Cells of R F were subdivided, in a c c o r d a n c e with Polyakov's (1959) classification of c o r t i c a l neur o n s , into five groups: v e r y small (5-10/5-10 ~), small (11-12/5-10 #), medium (13-22.5/7.5-22.5 p), large (23-30/7.5-30 p), and v e r y large or giant (31-120/7.5-120 p). To determine the volume of RF and the brain stem a planimetric method was used. The volume of the neurons was determined with a nKlassimat" apparatus. The mean volume of the cells was determined for 99 giant and 99 v e r y small and s m a l l R F cells. Volume was calculated by the equation for an ellipsoid, adapted for nerve cells by Geinisman et al. (1969): V = (v a ' b / 6 ) " [(a+b)/3], where V is the volume of a neuron; a, b the two mutually perpendicular d i a m e t e r s of the cell. The results of m e a s u r e m e n t s a r e given in Tables 1-3, in which ~ is the a r i t h m e t i c mean; av the standard deviation; ~v the standard e r r o r of the mean. The investigations showed that R F of the adult lower monkeys (Macaca rhesus) and the adult human brain, when c o m p a r e d , showed c e r t a i n g e n e r a l features of its s t r u c t u r a l organization. Both in the monkey and in man the nuclei of R F f o r m spatially unenclosed cell groups located in the region of the tegmentum of the brain stem. LaboratorY of A r c h i t e c t o n i c s , Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated f r o m Arkhiv Anatomii, Gistologii i Embriologii, Vol. 71, No. 7, pp. 25-29, July, 1976. Original a r t i c l e submitted May 20, 1975.

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