Further observations on the blood supply of the hypophysis cerebri of the rhesus monkey.код для вставкиСкачать
FURTHER OBSERVATIONS ON THE BLOOD SUPPLY O F THE HPPOPHYSIS CEREBRI O F THE RIIESUS MONKEY GEORGE B. WISLOCKI Uepurtment of Anatomy, Harvurd Medical Scliool, Boston, Xassachusrfts SIX I'IGURES Two previous papers dealt with the blood supply of the hypophysis of the rhesus monkey, as investigated in thick serial sections of injected pituitaries (Wislocki and King, '36 j PJislocki, '36). The present contribution, which concludes these studies, employs instead, a technique of actual dissection of the hypophysis. By this method it has been possible to confirm, correct, or amplify certain of tlie observations made with tlie previous technique. MATERIAL AND METHOD The blood vessels of the head of an adult rhesus monkey were injected with India ink through the heart. The calvariurn was removed arid the head fixed in 10% formalin. :% trichloracetic The skull was decalcified by placing it in 4 acid. After decalcification, the specimen was washed and carried over into 70% alcohol. With rongeurs and scissors the base of the skull was then removed, exposing the liypophysis in situ in the meninges at the base of the brain. The filial dissectioii of the pituitary, blocked o u t in situ, was carried o a t in 70% alcohol under a binocular dissecting microscope, utilizing iris scissors, fine jeweler's forceps and a cataract knife as instruments. The specimen under the microscope was illuminated by direct light from a Spencer spot-lamp. 137 138 GEORGE B. WIGLOCK1 ORXERVATIOSS The results of the study of the rliesus monkey's pituitary by the technique outlined above are presented in the form of six drawings illustrating various phases of the dissection. Prom examination of these figures many of the essential characteristics of the topography of the pituitary circul at'ion can be clearly visualized. Figure 1 shows the initial step in the dissection of the hypophysis. The bony sclla and the dura (clu) have been removed showing the base of the gland. I n the wall of the dural cavernous sinuses (cs) the inferior hypophyseal arteries (iha) can be seen skirting the posterior border of the neural lobe, and giving off a nuniber of small branches which, piercing the dura, penetrate the irifuridibular process. I n addition to the inferior hypophyseal arteries, veins can be seen in the dissection. On the surface of the gland and emanating from its substance small venulcs arc visible. These are derived both from the anterior lobe and from the neural lobe. They pass laterally to enter the cavernous sinuses as a series of minute lateral veins (lhv). Figure 2 represents a continuation of the dissection, obtaincd by carefully plucking away the infundibular process and pars intermedia, revealing a deeper set of venules (lhv) arising from the anterior lobe and tlie irifundibuJum. These also collect laterally into minute venous stems which enter the cavernous sinuses. Besides the superficial veins shown in the previous figure and tlie deeper veins seen here, a few similar venules were encountered, but destroyed, while removing the neural lobe. These were also directed toward the lateral border of the gland, excepting two o r three which emerged independently from the posterior pole of the neural lobe. These latter venulcs appeared to be derived exclusively from the neural tissue and pars intermedia. Further dissection of the hypophysis reveals the region of the stalk as shown in figure 3. This drawing illustrates the derivation of the superior hypophyseal arteries (sha) from the carotid arteries a t their junction with the vessels forming BLOOD S'CIPPT,Y O F T I I E H Y P O P H Y S I S 139 BBBREV JATlONS art, minute branching arteriole passing f r o m pituitary stalk into hgpothal aiiius b h ~ branch , of basilar Teiii hv, basilar veins c b , ear ernous sinus ctu, edge of duru reflected froni hy- pophysis PI?, emissary vein from hypothalamus iha, inferior hypoph) scal iirterics 1115, 1atei:rl hypophyseal veins me, iiiedian eminmce of tuher ciuereum up, optic chiasma p b , portal venules IJ\ 11, para\ ciitricular nucleus sha, superior hyophyseai :irteries r, x esscl connecting pituitary stalk and l ~ ~ p o t l i a l a m u s Fig. 1 Dissection of the base of the pituitary g1:rnd showing the inferior hgpophyseal arteiies ( i h e ) skirting the neural lobe and giving off penetrating branchus. Lateral hvpophysral wnnlcs ( 1 h ) arc seen collecting on t h e surfare of the gland and passiiig laterallg ab uiiriute rrswls which enter the caver~ious sinuses (cs). 'J'IIE ANATOMICAL RECORD, V U L. 73, N O . 2 140 GEORGE B. WISLOCKI the circle of Willis. Xotrworthy is that the superior hypopliyseal arterics anastornose abundantly to form an arterial plexus arouiid thc stalk, a iiiniiber of arterioles filially penetrating the substance of the stalk. Clear also is the rich plexiform layer of capillaries lying in the mantle of pars tuberalis covering the stalk. Tliis plexus is coextensive wilh Fig. '7 Further divsection of t h e body of the pituitary gland, obtained h 1 rcIrioval of the neural lobe, showing lateral hypopllpseal vcnules (lhv) clraming the interior of the h ~ p o p h p s i s . the pars tuheralis and does not exteiid onto or into the surrouiidirig tuber cinerenm adjoining the attachment of the stalk to the base of the brain. Inrleed tlie liorder of this plexus is conspicuously sharp. From the plesus small vessels ( p v ) , apparently venulcs, arise which pass along the surface of the stalk toward the bod? of the hypophpsis. These vessels are intcrpwted as being portal vciiules, arising from a plexus in the pars tubcralis and appearing t o low themselves in the sinusoidal capillaries of the anterior lobe o r in the dreper cupil la r y p lexu s sur r ouriclirig the i nf undihula r y r oce 8::. Fig. 3 Dissection f tlic hypophgseal stalk showing supcrior hypophysenl arteries (slrx) deiivcd from tlic carotid arterics, anastoniosing aiict srnding twigs t o the h ~ p o l ~ h ~ s stalk. eal On t h e surface of tlic stalk lodgcd in the mantle of pars tuhertilis a, rich iietnork o f ~ e s s e l s can t)r secii ill n h i c h crrinll portal r(nules ( p v ) are rccognizablc. Figure 4 i-cpreseiits a solliewhat further. claboration of the dissection showing the complete set of super.ior hypophyseal arteries (shv) and their numerous anastomoses. The truiilcs of the carotid arterics and of the circle of Willis haye been in the main cut away. The termiiial twigs of the arborizing hypophyseal arttliaies penetrate the siallr of the glanld, or 142 GEORGE B. JVIHLOC rn the neck betwecn the stalk and the body of the gland. The body of the hypophysis has actually been cut away in the dissection, excepting a stump of 1)ars anterior surrounding the oval infundibnlum. On tlie cut suri'acc of the pars anterior numerous minute vessels are seen, tlie larger consisting of tiny arterioles or rennles, the smaller represelltirig Pig. 4 The hypirph)-seal s h l k disxrcted sn as t,o s h o w a11 of tlie supcrjor hypopliyscal arteries ( sh x ) fornriiig anastomoses a n d giving off IiI1mPI'ous twigs t o the stalk from all sidcs. sinusoids. Bctwem tlie anterior lohe a n d the oval outliiie of the infuiidihulum the cut links of a delicate plexus of capillaries a r e visiblc. The interior of the iiifuiidibnlurn is relatively a\Tascular in this zoiie 1)etwccn stalk and infnndihular 1)rocess. At irregular intervals short delicate tufts of capillaries j m c t r a t e the infuntlibnlum as indicated in figures 4 a i d 5. These tufts coniicct >i-itli tlie plexus of capillaries surrounding the iiifundihulnm ; they pierce the inf uridibiilum anteriorly arid are frcquciitly bilaterally situated as at the two levels shown in figures 4 and 5. Figure 5 is a co~npanioripiece to the prececling (1ir;sectioii. It is similar to figure 4,excepting that the arteries Iiavcl heen almost completely rcmoved, rwealing the dirtribation, course, Fig. 5 A further tlissectioii of s t d k ohtairicvl by rernoring thc superior Ii;ypopli>-swI arteries. Beneath t h e arterics i s now rcvcnled the s~ stem of haailsr wins (bv) arising f r o m vcnules emerging f r o m t,he h s u of the braiii, h u t rceeiving no tributary vcnules or capillaries from th e surface of the hppop1iysiu. A tributary vrnule ( ~ J ~ J vi )s a h o n n emerging froin t h e h ~ p o t h a l n m u s ;t h e origin of t,his venulr can be seeu in thc ricxt fipurc. and character of the basilar veins (bv) on the surface of the lippothalamus. 111 the preceding figure the basilar veins (fig. 4, bv) c a n be seen only faintly uiiclerneatIi the artericls at a deeper level. Soteworthy regarding thcse veins is that they do not arise from the h ~ p o p h y s e a lstalk. They a r e formed b y veins emerging from the substance of the brain aild rcachiiig the surface some distance from the stalk. These emissary veiiules bend at right angles 011 reaching the surface of the tubcr cinereurn and proceed, by uniting, t o form the basilar veins. These circumstances account for the blunt, sudden way in whicli the basilar veins malie their appearance, well removed f r o m the hy yophysis. Chnsequently there appears to be little, if any, possihle venous drainage from the pituitary directly into the nearby basilar veins on the surface of the Iiypothalamus. The iiidcpeiidcnce of tlie pituitary complcx, as far a s surface connections wit11 these reins are coilcerned, is cleui=lyseen i n the figure. The final dissection of the pituitary is slionn i n figure 6. The dissection is derived from tlie specimen p o r t r a y d in figure 5 by splitting it open in thc mid-sagittal plane. Each of the resulting halves of the hypophysis reveals the interior of the third ventricle and the adjacent wall of tlip hypothalamus arid pituitary stalk. The wall of tlie ventricle has been pai*tially ilisscctcvl away by removal of its most snpcrficial substance. This brings the hloocl vessels in tlie subjacent tissue and their relationship to the 1)lood vessels in the pituitary stalk m o i prominently ~ into view. By delicate dissection the junction of the pituitary stalk and the tuhcr cinercum was suhseqneiitly completely dissected, iii both halves, so that a survey could be made of all of the vascular connections existing hetiwen t l ~ epituitary and the hypothalamus. Figure G reveals a number of interesting features regarcliiig the vascular relationsliips of the pituitary and hypothalamus. First of all the characteristic plexiform tufts of siausoidal capillaries call be seen penetrating the substance o€ the jnfundiliular stalk and the niedian eminence ( i i ~ ) of thc tubcr P,T,OOT, S I T P L Y O F T H E HYPOPHYSIS Fig. 6 The dissrc,ted hppuphyseal stalk and h~-pot.halai~ius split in the iuidsagittal plane, revealing the vascuhr plcsuses within the 111-popliyseal stalk. The transitional vessels lietween t h e median eininenw (nip) of the Iiypophyseal stalk arid the hypothalamus arc shown. T h e largest, of these (1:) is B vessel of undeterrniiied character. d Iiiinut,e arteriole ( a r t ) traversing t h e boundary of the st,alk and hypothalamus is also visible. Ba hypothalamic rein ( e v ) is seen; i t passes t o the surfape and drains int,o a branrh (i)lw) of one of the lrasilar veins. This branch is the same vessel seen from the surfact? in figure 5 ( h h v ) . It is clear from study of thc blood vessels in the transition zone hrtwwn hppophyseal stalk and brain proper, shown in this figure, that there are no significant vascular links bctweeri t,he pituitary and the more important nuclear centers of the hypothalamus, f o r example, t h e paraventricular nucleus ( p n ) . 146 GEORGE B. \VlSLOCKI cinereurn from the mantle of blood vessels and capillaries located in the pars tuberalis which encloses the hypophyseal stalk. The larger of tliese tufts a r c supplied with afferent arterioles. Secondly, i t can be seen that at the border of the rriecliaii eminence many of the siniisoidztl tufts connect by mini1t e ve s sel s mi t 11 char a c:t e ri stic sl end cia capillaries of the brain. These anastomoses, although fairly nuincrons, appear in the main to bc of the calibcr of capillaries, only a very €ew of them appearing t o be of tlie magnitude of small arterioles or vcnulcs. The second largest of all such coiiricctioiis hetmeen the pituitary stalk aiicl the hypotlialamus, discovered in the present spccimcii, is shown in figure 6 ( a r t ) . It is seen to be EL delicate bi.aiiclliug vessel which emerges from the limits of the stalk ancl passes for a short distance into ilie liypothalarnus hefore it breaks up into capillaries. It is regarded a s being an arteriole for two reasons. It appears t o arise from thc central arteriole of a vascular tuft in the hypopliyseal stalk arid it breaks up into capillaries which can he traced quite definitely t o the nearby li>-pothalaiiiic: veiiules ( e r ) shown in the figurc. Only o m vessel of any considerahle size and extent was discoverahle upon complete dissection of thc entire zone of traiisi tion hetween the pituitary stalk and the hypothalamus proper. This vessel, \\liicli arises near the anterior border of the hypopliyseal stalk, is slio~viiin tlie figiire (v). It emerges from a typical plexiis in the median eiiiinencc of tlie tiilner cinereurn and follows a course skirting the optic chiasma. Whethei. it is to be regartlecl a s a r t w i a l or renous in character rcmains uriclctcrmincd f o r the iiature of its origin is ohscurecl by the complexity of the tuft from ~ h i c hit arises, arid its ultimate dcstinatioii caiinot be accurate17 traced. T t is the oiily cxtcnsive connection between the stalk region iilld the hypothalamus encountered i n the Course of the snrvey of all possible transitional vessels. Consequently it must be coilsidered as being of exceptional occurrence. Another noteworthy feature of the dissection shown in figure 6 is thc demonstratioii of the complete course of an BLOOD SUPPLY O F TIUC HYPOPHPSIS 147 emissary vein (cv) in the wall 01 the third ventricle. This veiri can be traced from the interior of the brain through the wall of the tuber cinereum, adjacent to the median eminence, to its connection with a branch of one of the basilar (bbv) veins on the brain surface. This same branch can be identified in the previous dissection (fig. 5, bbv). Thus we are able to trace a branch of oiie of the basilar veins from its entire source in the substance of the hypotlialamus. Of interest regarding this typical vein is that, although it skirts the pituitary, it receives no vessels of the caliber of venules from the hy-pophyseal territory. Its connections with the pituitary, insofar as they exist, appear t o be of capillary size only. Regarding the possibility of sizable vascular connections between the hypophyseal stalk and the hypothalamusespecially the existence of vessels of the nature of portal veins-the present dissection of the monkey affords no convincing evidence. The anastomoses between the vessels of the two regions appear to be relatively small and quite local in character, certainly not involving any important vascular linkage between the pituitary stalk and such distantly situated hypothalamic structures as the paraventricular and supraoptic nuclei. I n figure 6 part of the paraventricular nucleus (pvn) can be seen in the upper right hand corner of the field, identifiable by its pronounced capillarity. The unlikelihood of this nuclear mass receiving vessels of any size directly from the region of the pituitary stalk is apparent at a glance. And indeed this impression has been checked by careful and complete dissection of the intervening territory with the failure to locate any possible significant vascular connections whatsoever. The same negative results were obtained upon searching for possible portal venules or other direct vascular coriricciions between the pituitary stalk and the supraoptic nuclei which lie some distance laterally to the median eminence and are not shown in the figure. THPI A N A T O M I C I L B E C O E D , VOI.. 72, X O . 2 148 GEOKGE R. WISLOCKI nISCUSSION The results of dissection of the pituitary complex by the technique adopted confirm in the main the conclusions reached in the previous studies of the pituitary of the rhesus monkey based on examination of cleared, thick, serial sections. Little doubt remains concerning the nature and distribution of the arteries which reach the pituitary as two groups: one the inferior hypophyseal arteries ; and two, the superior hypophyseal arteries. The former are distributed in the infundibular process ; the latter enter the hypophyseal stalk, from which branches pass to the anterior lobe. Further evidence is gained regarding the existence of venules passing between the hypophyseal stalk and the body of the gland. Conriected at either end with capillaries, these are probably correctly interpreted as constituting a system of portal vessels. Regarding the systemic veins, draining the hypophyseal complex, the present study reveals a series of small venules emanating from the body of the gland which enter the cavernous sinuses. These arise more especially, but nevertheless not exclusively, from the neural lobe. The stalk region appeam to possess no venous connections of importance, excepting the system of portal venules connecting the stalk with the body of the gland. Direct systemic veins appear to be totally lacking. First, there is no evidence of capillaries or venules draining from the surface of the stalk into the nearby basilar veins. Secondly, direct systemic venous coniiections with the veins of the hypothalamus proper do not appear to exist. With the exception of one larger vessel of undetermined nature, encountered in the present specimen, and a few minute channels which are probably arterial, the vascular connections between the stalk and the hypothalamus arc of capilliform size. It is apparent, moreover, that the relatively minute anastomoses between the vessels of the brain and those of the hypophyseal stalk are restricted to quite local territory, involving only the immediate border zone hetween stalk and brain. No significant vascular pathways exist between the pituitary and such structures, lying at a distance, BLOOD SUPPLY O F T H E HYPOPHPSIS 149 as the paraventricular and snpraoptic nuclei. These possess quite independent vascular supplies. Thus it follows that in the rhesus monkey the main efferent vascular channels are those extending from the body of the gland to empty into the cavernous sinuses. Drainage by capillaries o r venules connecting the stalk and the brain, if it occurs at all, must be quite subsidiary. Eflerents represented by either venules or capillaries leading directly from the surface of the stalk into the adjacent basilar veins on1 the brain surface are completely lacking. The monkey differs in this respect from the cat in which it has recently been shown (Wislocki, '37) that a certain number of capillaries pass from the circumference of the hypophyseal stalk to the surface o i the hypothalamus to become small venules tributary to the basilar veins. I n spite of these efferents, the venules leading from the body of the gland into the cavernous sinuses are regarded in the cat also as being the most sizable and important pathways for venous drainage. SUMMARY An account is given of the dissection, under a binocular microscope, of a pituitary gland of a rhesus monkey in which the blood vessels have been completely injected with India ink. Superior and inferior hypophyseal arteries are traced into the gland. Small venules of portal character are observed on the pituitary stall;, connecting the stalk with the body of the gland. Systemic venules are described passing from the body of the gland into the cavernous sinuses. Systemic venules running from the hypophyseal stalk to the nearby basilar veins on the surface of the tuber cinereum are lacking. Connections greater than capillary caliber between the stalk and the hypothalamus are relatively few in nnmber and slight in extent. The largest such connections, whether they be interpreted as venules or arterioles, are too restricted in caliber, extent, o r number t o be regarded as playing any significant role in conveying blood from the pituitary complex to the hypothalamic centers. 150 GEORGE B. WISLOCKI LITERA4TURK CITED WIsLorxI, G. B. 1936 The vascular supply o f the hypop1i~sis cerebri of the rhesus monkey and man. Proc. Assn. f o r &search in Nervous and Mcntal Disease, vol. 17, pp. 48-68. - 1937 The vascular supply of the hypopohysis cerebri of the eat. Anat. Rrc., vol. 69, pp. 361-387. WISLOCKI,G. B., AND L. S. KINQ 1936 The permeability of the hypophysis and hypothalamus to vital dyes, with a study of the hypophyseal vascular supply. Am. J. Anat., vol. 58, pp. 4 2 1 4 7 2 .