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=The Form And Structure Of The Endolymphatic And Associated Ducts In The Child=

Barry J. Anson And J. Gordon Wilson


Departments of Anatomy and Otolaryngology, Northrwestern. University Medical School


Twenty- Six Figures (1936)

==Introduction==

In anatomical and otological textbooks those portions of the membranous labyrinth which subserve a sensory function have been, for decades, painstakingly ﬁgured and minutely described; experimentation concerning these parts has been elaborately prosecuted. Yet, except for relatively few investigations, mainly of recent date, the non—nervous portions of the epithelial canal system in mammals have been neglected; as a result students and practitioners must depend upon highly stylized diagrams of the endolymphatic duct and its connections——diagrams which are not matched in their inadequacy by illustrations of any other important structure in the human body.


Recent investigations upon the endolymphatic duct system serve to strengthen the earlier opinion of Boettcher (1869 a, b) that in mammals the constituent ducts are not simple quill-like tubes, lined uniformly with a smooth layer of epithelium, but are characterized by regional specialization which affects the wall. of the duct, the cells of Which it is composed, and the underlying stroma.


‘ Contribution no. 149 from the anatomical laboratory of Northwestern University Medical School. Investigation conducted under the auspices of the Central Bureau of Research of the American Otological Society.


Guild '( ’27 a) directed attention anew to the epithelial projections which invade the lumen of the distal por_tion of the endolymphatic duct in the guinea pig, and proposed terms for the subdivisions of the duct, . based upon the form and abundance of. these projections and upon the caliber of the duct itself; upon experimental evidence Guild (-’27 b) assigned to the projections, with their subjacent vascular connective tissue, the function of resorbing the endolymph.

The proximal end of the endolymphatie duct also differs in shape from the conventional picture of it,-as has been pointed out by Bast (’28) and by others.

Our observations upon endolymphatie and associated ducts in man corroborate the opinions of these investigators.

MATERIAL

The serial sections upon which this study was chieﬂy carried out, were made from the ear of a child 2 years old who died of sinus-thrombosis after scarlet fever. The bone was excised 2 hours after death and fixed immediately in 10% formalin, then decalciﬁed in a 3% solution of nitric acid in 10% formalin. Celloidin sections were cut 25 p in thickness, in the plane indicated in ﬁgure 4, and stained with haematoxylin and eosin. The general topography of the area is shown in ﬁgures 1 to 3. In order to display effectively the shape of the ducts, re constructions representing their lumens were prepared by the Born method.’ ‘The reconstruction shown in ﬁgure 5 was prepared by the Born wax-plate

method from tracings made with an Edinger apparatus at a magniﬁcation of 400 diameters, reduced to & in the drawings; it includes the area of eighty-eight sections; ﬁgures 20 to 22 and 24 represent parts of the reconstruction shown in ﬁgure 1, reduced -5- in drawing. Figures 1 to 3 were prepared by Edinger projection apparatus at a magniﬁcation of 18 diameters; between ﬁgures 1 and ,2, seventeen sections intervene; between 2 and 3, twenty-two sections. Figures 11 to 19, 25 and 26, were prepared by the same method at magniﬁcation of 240 diameters; between ﬁgures 11 and 12, two sections intervene; between 12 and 13, twenty; 13 and 14, three; 14 and 15, nine; 15 and 16, ﬁve; 16 and 17, eleven; 17 and 18, twenty; between 18 and 19, thirty-eight. Figures 7 and S were redrawn from a reconstruction in Wilson and Anson, 1929; ﬁgures 9 and 10 were adapted from diagrams in current textbooks. ENDOLYMPHATIC DUCT 487

DESCRIPTION AND DISCUSSION

According to the conventional accounts and illustrations (ﬁg. 9) the endolymphatic duct is a blindly ending process from the saccule which, upon leaving the posterior surface of the latter, extends through the vestibular aqueduct to end as a subdural sac on the posterior surface of the petrous portion of the temporal bone; the endolymphatic duet, near its saccular origin is joined by a short canal, the utrieulosaecular duct, which arises from the anterior Wall of the utricle.


Figs. 1 to 4 Figures 1 to 3, sections through temporal bone of a child 2 years of age. X 6; ﬁgure 1, level of utricular fold and superior part of endo-lymphatic sinus; ﬁgure 2, inferior portion of sinus; ﬁgure 3, narrowed intraosseous, part of endolymphatic duct ; ﬁgure 4, plane of section of series and level of section in ﬁgure 1. Arrow M directed medialward, A anteriorly.

We ﬁnd, however, that the endolymphatic and utriculosaccular ducts possess features and a complex form, which not only require special description, but also render the use of more descriptive terms advisable. The endolymphatic duct, for example, as it leaves the inferior constricted portion of the saccule is at ﬁrst markedly thinned, (fig. 5). As it continues

posteriorly, the duct widensrapidly to form an elongate dilatation (ﬁgs. 5 and 6, Sinus I). This primary dilatation is situated medial to the utricle, from which it receives the narrow utriculosaccular (or utricular) duct. ‘ Continuing at ﬁrst in approximately horizontal plane, the sinus parallels the course of the common duct of origin of the superior and posterior semicircular ducts (ﬁgs. 1 and 2); at the oriﬁce of the vestibular aqueduct, the sinus becomes constricted (ﬁg. 3). Here the narrowing is exaggerated by the impushings of the epithelial wall which encroach prominently upon the lumen of the tube. While still within the aqueduct, the duct expands again into a second enlargement (ﬁg. 5, Sinus II), whose walls are also deeply rugose. Once more the duct narrows, then expands for a third time as it nears the cranial aperture of the aqueduct; this distal expansion includes the endolym— phatic sac of the familiar descriptions. ‘ The utricular duct is also of special form, being compressed in the horizontal plane at its utricular extremity, where the oriﬁce is guarded medially by a valve-like fold formed by the approximated walls of utricle and endolymphatic duct; the oriﬁce beneath the fold is not a rounded foramen but an elliptical slit (ﬁgs. 7 and 8). Brieﬂy, conventional diagrammatic illustrations (ﬁgs. 9 and 10) fail to record the true form of the duct and its communications (ﬁg. 6) or even the positions of the sinuses and of the utricular fold (ﬁg. 10, dotted lines). The several portions of the canal system may now be described in greater detail.

The saccular extremity of the endolymphatic duct (or saccular duct) is found to be relatively deep in the crani0 caudal direction, compressed mediolaterally (ﬁg. 5). In a

Figs.5to 10 Figure 5, infero-lateral view of reconstruction of the space enclosed by endolymphatic duct and its communications in the child of 2 years; distal enlargement, saccule, utricle only partially shown; site of vestibular oriﬁce of aqueduct indicated by ring. X 50. Figure 6, drawing prepared from reconstruction in ﬁgure 5; lumen cross-hatched. Figure 7, semi-diagrammatic drawing of canal system in region of utricular duct, halved in horizontal plane. Figure 8, same, entire, from utricular aspect; showing the slit-like communication, beneath the pedal portion of ‘valve,’ between the uricle and endolymphatic duct. Figures 9 and 10, conventional ﬁgures of areas shown in ﬁgures 5 to 8; compare 6 with 10, 7 and 8 with 9. Dotted lines in ﬁgure 10 indicate diagrammatically the chief changes needed to convert a conventional into correct diagram.




section cut at right angle to its long axis, it would have the form of a greatly ﬂattened ellipse, being but 1.87 to 2.33 [.1 in Width (as measured from the sections) and 200 p in depth (estimated from its presence in successive sections). It is paralleled in its course for a distance of 0.29 mm. by a ﬁngerlike diverticulum of the saccule (fig. 5). The dilation or sinus begins early in the course of the duct and the transition from thin to wide portions is rapid (ﬁg. 11). Near the point of communication with the duct from the utricle it has attained its maximum proportions (ﬁgs. 20 to 22). The expansion as a Whole is approximately 2.2 mm. long and 0.625 mm. deep (latter measurement estimated).

The utriculosaccular, (or utricular) duct leaves the anteromedial aspect of the utricle to join the sinus-like enlargement of the endolymphatic duct. The adjacent walls of utricle and sinus are approximated to each other in such a Way that, when viewed in horizontal sections the two epithelial walls, with onclosed core of areolar tissue, form a fold or ‘valve’ for the duct by which utricle and sinus communicate (ﬁgs. 6, 7). The ‘valve’ was ﬁrst described by Bast (’28) as seen in the human embryo; its constancy of form and regularity of occurrence in man were- established by the investigations of the present authors (Anson and Wilson, ’29; Wilson and Anson, ’29; twelve cases), and in mammals generally by the work of HOEman and Bast ( ’30; eleven species), and of Roberts (’32; one species, sixty series); that it is a deﬁnite feature of the embryonic mammalian ear has been shown by Anson (’34) in a study of 205 series, comprising twelve species. In sections it possesses the -form of an elongate shank ending in a more bulky free extremity (ﬁgs. 11, 12), an appearance which suggests that it may be a curtain—like fold between two chambers; but when seen in reconstruction (ﬁgs. 7, 8) it is found to be free only along a. (vertical) line. Since it ends in a free extremity which follows the curve of the anterior utricular wall against which it lies, the ‘fold really constitutes the posterior boundary of the utricular duet (ﬁgs. 7, 8) ; in the series of the 2-year-old child, and in many other series, the ENDOLYMPHATIC DUCT 491

Figs. 11 to 19 Drawings (Edinger) of endolymphatic and associated ducts, arranged in distal progression from utricle toward endolymphatic sac. X 60. Figures 11 and 12, through proximal dilatation (Sinus I) of endolymphatic duet, utricular fold, and communication (ﬁg. 12) beneath the latter (fig. 1 passes through the same level, as does also the cut surface of the reconstruction in ﬁg. 7). Figure 13, Iluct at beginning of the vestibular aqueduct, at the junction of the dilated with the proximal constricted portion (compare ﬁgs. 26 and 24) ; ﬁgures 14, 15, 16, through constricted portion, showing epithelial bridges and rugae; ﬁgure 17, through beginning of intermediate dilatation or Sinus II (compare ﬁgs. 25 and 24); ﬁgure 18, through wider portion of the same; the level is that of the extremity of the reconstruction in ﬁgure 24 and top of that in ﬁgure 5; ﬁgure 19, through distal portion of the dilatation.

utricular extremity of the duct thus formed is a compressed ellipse whose long axis is the craniocaudal plane (ﬁgs. 20 to 22 and-23 c). As the utricular duct extends medialward to join the endolymphatic duct; the sidewise compression becomes less" marked (ﬁgs. 21, 22 and 23b) and it ﬁnally assumes the form of an oval whose long axis is in the horizontal plane (ﬁgs. 20, 21, 23a). The utricular joins the endolymphatic duct at an acute angle (ﬁg. 12; compare ﬁg. 21). _

The utricular fold, which forms the inner wall of the utricular duct,‘ is a stouter structure than the outer wall against which it may be applied (ﬁgs. 7, 12); the fold is not only a double structure, but is supported posteriorly by bone and a tongue of periosteal tissue; the outer wall, on the contrary is a single epithelial layer overlaying a slight substratum of connective tissue. We therefore believe that, were the movements of endolymph strong enough to produce a marked change in the shape of the duct, it would be the outer wall and not the inner or ‘valvular’ wall whose contour would be appreciably altered——and changed so that its utricular oriﬁce would assume a lenticular rather than circular form. Bast (’34) found evidence of its function in two cases with ruptured saccule; from. the observation that the cochlear duct and saccule may be disturbed to the extent of collapse without damage or collapse of the utricle and semicircular ducts, he concluded that the ‘utriculo-endolymphatic valve’ is responsible for the maintenance of normal pressure in the utricle and semicircular ducts when that in the saccule and cochlear duct is suddenly reduced.

The elongate sinus-like part of the endolymphatic duct, at the internal aperture of the vestibular aqueduct, becomes continuous with a portion of the canal system which is compressed and rugose (ﬁgs. 5, 6, 13). These rugosities as seen in sections were ﬁgured by Sterzi (’10) and by Boettcher earlier (1869). In our series the ﬁrst prominent fold, as Well as several others less pronounced, appear on the inferior and medial surfaces. The site of the ﬁrst folds marks the region of junction of the dilated and constricted portions, and the commencement of the ENDOLYMPHATIG DUCT 493

intraosseous course of the endolymphatic duct. At this point the duct undergoes a marked change in direction, turning rather sharply downward. It acquires a compressed form being ﬂattened from side—to—side (figs. 14 to 16, 26 and 24).



Figs. 20 to 23 Three views of utrieular, and related portions of the reconstruction shown in ﬁgure 5; showing the utrieular duct adjacent parts of the utriele and of the proximal dilatation (Sinus I); X 66. Figures 21, 22. Figure 20, infero-medial view; ﬁgure 21, inferior view; ﬁgure 22, anteroinferior view.

Mediolateral ﬂattening continues to be a feature of the duct through much of its intraosseous part (ﬁg. 16, 17). The rugosities present in the narrowed transitional portion between sinus and constriction (ﬁg. 13) become more prominent 494 B. J. ANSON AND J. G. WILSON

as constriction is succeeded by dilatation. (ﬁgs. 17, 18); an unusually deep ridge is found on the antero—medial aspect which almost segregates a medially directed wing of the duct (ﬁgs. 16, 26); this one decreases in prominence distally, and is replaced by several smaller ridges (ﬁgs. 17, 25); on the lateral surface, two deep ridges are present (ﬁgs. 24, at level of 25), and near the distal extremity of the duct in our series, others appear (ﬁgs. 18,. left end of 24). Smaller subsidiaries of this scheme of plication are numerous. Not infre 2.5



Figs. 24 to 26 Reconstruction, and sections of the rugose constricted portion (right), and intermediate dilated portion (left) of endolymphatic duct (compare ﬁgs. 16, 17). Rugae (ﬁg. 25) appear as elongate excavations, epithelial bridges (fig. 26) as open areas. X 66.

quently apposed ridges, even when shallow, stretch across the lumen, meet and fuse at intervals, and thus, in some sections subdivide the lumen into two or more parts (ﬁgs. 14 to 16, 19); such bridges may be stand—like, consisting only of ﬂattened epithelium or somewhat bulkier with a core of connective tissue. Within the same category belong the numerous clumps of epithelial cells which, in a single section, appear and disappear with focusing (ﬁgs. 15, 16).

The greater portion of the lining of the ducts consists of a cuboidal epithelium with spherical nuclei; these cells possess a very deﬁnite cuticular border, intercellular substance, and ENDOLYMPHATIC nucr 495

usually a deﬁnite basement membrane. The commonest variation of this type of epithelium is a somewhat ﬂattened form, rarely so depressed, however, as to be described as squamous. When so ﬂattened the free border of the cell may be elevated in its middle part so as to appear humped, and lend to the Whole layer a scalloped appearance. The ﬂattened cells are found most abundantly in the saccular and the utricular ducts; the cuboidal cells predominate in the larger vesicles—the utricle, saccule, and the sinus of the endolymphatic duct. This relatively simple epithelium is found also in the rugose distal parts of theendolymphatic duct, sometimes in association with cells resembling those ﬁgured by Guild as observed in the guinea pig——cells With rounded free borders and short basal processes. The epithelial tufts consist of cells, slightly taller than neighboring cuboidal ones, with rounded borders. The bridges which extend entirely across the lumen possess markedly ﬂattened epithelium. Beneath the epithelium of the endolymphatic duct, throughout the length of the vestibular aqueduct, is situated a vascular connective tissue———forming an arrangement of tissues which meets the histological requirements of an organ for resorption.

Terminology. According to the conventional accounts and illustrations the endolymphatic duct is a smooth-walled, tubular, extension from the saccule Which, after traversing the Vestibular aqueduct, terminates as a subdural or intradural sac on the posterior surface of the petrous portion of the temporal bone; the endolymphatic duct is joined at an acute angle by a short canal, the so-called utriculo-saccular duct which arises from the adjacent anterior wall of the utricle. In these descriptions a duct which does not communicate directly with the saccule is termed ultriculosaccular, while the duct which does so communicate, being regarded as part of the endolymphatic duct, receives no distinguishing name. Apparently such an inept combination of established terms has arisen out of a failure to apply a special name to that part of the endolymphatic duct which extends from the saccule to the point where the former receives the duct from the utricle; when logically regarded as a saccular duct, as it was by Boettcher, the common duct, formed by the junction of the

channel from the utricle with that from the saccule was then considered the endolymphatic duct. Were the canal system as simple in form as is conventionally pictured (ﬁgs. 9 to 10) Boettcher’s terminology would be entirely acceptable; there would be a utricular duct (not utriculo-saccular) and a saccular duct, joining, like the arms of a Y inverted, an_d originating from utricle and saccule, respectively. Obv_1ously these could- correctly be termed utriculo-endolymphatic duct and sacculo-endolymphatic duct. The form of the canals in this proximal portion is not, however, as simple as familiar diagrams would lead one to suppose. We ﬁnd that in man, as in the guinea pig (Guild), that part of the endolymphatic duct (using the term in customary way) which lies adjacent to the utricle is greatly dilated (ﬁgs. 5 to 6); in man, this expansion extends through almost the entire distance from the saccule to the internal aperture of the vestibular aqueduct; into it open the duct from the utricle and the. one from the saccule; the latter duct in man, although, short (ﬁgs. 5, 11), is still distinctive enough to warrant separated designation by the term seccular duct. The expanded region intervening between the termination of the saccular duct and oriﬁce of the aqueduct, requires a descriptive- term. Guild (’27 a), wishing to emphasize its close relation to the saccule, supplied the term sinus posterior sacculi. Considering it advisable to set it off from the saccule, and to record its position in relation to the other two dilatations in the course of the endolymphatic duct we have provisionally termed it Sinus I (ﬁgs. 5, 11 to 12), recognizing that "sinus proximalis might be preferable; since the term ‘sinus’ has been loosely used clinically for diverticular processes, ‘ampulla’ would be preferred were it not for the fact that the term is already applied to the enlarged endings of the semicircular ducts. Into Sinus I opens the duct from the utricle, commonly termed utriculo-saccular; were one to regard the sinus as belonging with the saccule, as does Guild, then the use of this term would be warranted; on the contrary it would not be a reasonable term were one considering, as is customary, that the endolymphatic duct extends to the saccule; in that case the term utricular (or utriculo-endolymphatic) duct would be preferred.

In choosing between the terms fold and valve, for the struc ture "separating utricle and sinus it might be borne in mind

that in BNA terminology the term plica, or fold, refers to a permanent crest or elevation of a lining membrane which encroaches but little upon the space from whose wall it projects, as, for example, the aryepiglottic folds of the pharynx, the transverse folds of the rectum, or the circular ones of the small intestines——all of which project into the lumen without contact of their free margins. The term valvula, or valve, on the contrary is restricted in application to those projections into hollow organs which unquestionably possess the physiological function of temporarily closing the lumen of the tube itself or the oriﬁce of a smaller communicating channel; it includes such morphologically different structures as the ileocolic valve, the valves in the aorta, and those in the pulmanary artery. In anatomical form, the utricular ‘fold’ bears a resemblance to the ﬁrst named; but, Whereas, the oriﬁce at the ileocolie junction is closed by two ﬂaps which come into contact with each other, in the case of the utricular duct a single ﬂap exists, the opposing smooth wall completing the boundary of the elliptical communication; but in spite of the general resemblance of the fold within the membranous labyrinth to a labium of the valvula coli, one hesitates to employ for the former the term ‘valve ’— since the implied action has not deﬁnitely been proved to occur.

The portion of the duct system within the vestibular aqueduct is usually termed the endolymphatic duct, its blind subdural enlargement being the endolymphatic sac. In the guinea pig Guild found the ﬁrst part within the aqueduct constricted; he called it the ductus endolymphaticus proprius to distinguish it from the succeeding dilated part, the saccus endolymphaticus proprius (in which he distinguished proximal intermediate, and distal portions). But in man the arrangement is more complex, in that two intraosseous dilatations occur, for which, provisionally again, we have used the terms Sinus II, Sinus III, (for which sinus intermedius, sinus distalis might be more appropriate); Sinus III is the endolymphatic sac of the familiar descriptions, and in man, as in the guinea pig, it is situated largely within the aqueduct; for the constricted portions between Sinuses I—II, II—III, the term isthmus might prove suitable. It must ﬁrst be determined, however, by further reconstructions, whether the succession of enlargements and constrictions within the aqueduct is constant. Should it be found that usually only one expansion occurs as theduct traverses the vestibular aqueduct then the authors would accept, unaltered, Guild’s suggested terms for the parts described.“

‘ In man Guild later found corresponding regions in the epithelial tube system,

for which he believed “the terminology suggested for the several morphologically diﬂerentiated parts” in the guinea. pig would be quite applicable (Guild, abstract Anat. Rec., vol. 38, no. 1 (Supp1.), pp. 12-13).


LITERATURE CITED

ANSON, B. J. 1934 The early development of the membranous labyrinth in mammalian embryos, with special reference to the endolymphatic duct and utriculo-cndolymphatic duct. Anat. Rec.,'vo1. 59, pp. 15-25.

ANSON, B. J. m J. G. Wmsou 1929 The utricular fold in the adult human ear. Anat. Rem, vol. 43, pp. 251-255.

BAST, T. H. 1928 The utriculo-endolylnphatic valve. Anat. Rec., vol. 40, pp. 61-65.

1934 Function of the ntriculo-endolymphatic valve. Two cases of ruptured saccule in children. Arch. of OtoIaryng., vol. 15, pp. 537-550.

BOETTCIIER; A. 18693. Ueber Entwickelung und Ban des Behﬁrlabyrinths nach Untersuchungen an Siiugethfiex-en. Verh. d. Kais. Leop. Carol. c. Adad. d. Naturforscher, Bd. 35, S. 1-203.

1869 b Ueber den Aquaeductus vestibuli bei Katzen und Menschen. Arch. f. Anat. u. Physiol. J9.hrg., s. 372-380.

GrU11.n, S. R. 1927 3. Observations upon the structure and normal contents of the ductus and eaccus endolymphatieus in the guinea. pig. (Cavia cobaya). Am. J. Anat., vol- 39, pp. 1-56.

1927b The circulation of the endolymph. Am. J. Anat., vol. 39, pp. 57-81. .

H01-‘mun, E. F. AND T. H. B'As-1' 1930 A- comparative study of the ‘utriculoendolymphatic valve’ in some common mammals. Anat. Rec, vol. 46, pp. 333—347. '

Rosters, J. T. 1932 On the utrienlo-endolymphatic valve in the albino rat. Anat. Rec, vol. 53, pp. 255-264.

STERZI, G. 1910 I1 sacco endolinfatico. Ricerche anatomiselre ed embryiologiche. Gegembauer ’s Morph. J ahrb., Bd. 39, S. 446-496.

WILSON, J. G. AND B. J. Anson 1929 The ‘utriculo-endolmphatic valve’ (East) in a two-year-old child. Anat. Rec, vol. 43, pp. 145-153.

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