Ann Otol 88 :1979
VEIN OF THE VESTIBULAR AQUEDUCT ANTONIO MAZZONI, MD BERGAMO, ITALY
The vein of the vestibular aqueduct (VVA) was investigated in a series of 40 human temporal bones. The processing included vascular injection with a colored medium, decalcification and cutting in serial, thick sections, which were put in a clear fluid and studied with a stereomicroscope. The labyrinthine roots of the VVA are the single veins of the ampulla and simple limbs of the semicircular canals and of the posterior wall of the utricle. They drain the rich capillary bed of the simple endolymphatic walls of the canals and the utricle, as well as a small peripheral area of the cristae and the utricular macula. The VVA leaves the vestibule through an individual bone canal running parallel to the vestibular aqueduct up to the dura of the posterior side of the petrosa in the area of the endolymphatic sac. It then opens in the inferior petrosal sinus or the jugular bulb. The vein receives other branches from the bone, dura and sac. Correct information on the course of this vein appears to be lacking in contemporary textbooks and articles, although it has been correctly described since the last century.
The vestibular aqueduct was recently the object of anatomical and clinical reports in relation to the diagnosis as well as the pathophysiological mechanisms of of Meniere's disease. The interpretation of the findings concerning the vestibular aqueduct and its content, the endolymphatic duct and the vein of the vestibular aqueduct (VVA), as well as the newly-discovered paravestibular canaliculus, was inaccurate because of a lack of objective anatomical information and a misreading of the literature. The object of this paper is to review the literature on the VVA and to report our findings on this vein and its paravestibular osseous course.
and sac were found in patients with Meniere's disease." Histopathological studies of patients with Meniere's disease demonstrated avascular fibrosis of the perisaccular connective tissue":" and exotosis-Iike buds of lamellar bone on the walls of the aqueduct," In 1968 Clemis and Valvassori" reported an exceptionally high correlation between sensorineural hearing loss and an abnormal or absent radiological visualization of the vestibular aqueduct. This correlation was later restricted to Meniere's disease.I-" Yuen and Schuknecht," however, found no abnormal caliber of the aqueduct in temporal bones from patients with Meniere's disease.
LITERATURE REVIEW
Studies on the gross anatomy of the aqueduct and related structures were stimulated by clinical experience." Ogura and Clemis!' examined the vestibular aqueduct by means of microdissection of osmic-acid-stained temporal bones. A structure was identified near the aqueduct and called the paravestibular canaliculus. It began from the vestibule, superior and a little medial to the opening of the aqueduct; it ran in a bony channel of its own, parallel to the aqueduct, and terminated distally by branching into the substance of the posterior fossa dura in the region of the endolymphatic sac. The canaliculus contained loose connective tissue with an
This review will first consider recent clinical studies which focus on the role of the vestibular aqueduct in inner ear disorders, then it will discuss the normal anatomy of the aqueduct and its vein in relationship to these studies.
Clinical Aspects. The current interest in the vestibular aqueduct arose in connection with Meniere's disease. A normal endolymphatic duct and sac are considered essential for labyrinthine function. Experimental ablation of the endolymphatic sac caused endolymphatic hydrops in animals,' while structural abnormalities of the endolymphatic duct
From the Department of Otolaryngology. University of Ferrara. Ferrara, Italy. and the Instltut of Anatomy, University of Odense, Odense, Denmark.
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artery and a vein. The canaliculus was believed by the authors to carry the blood supply of the endolymphatic sac and to fulfill a pressure-regulating function between the posterior fossa and the perilymphatic space. Similar findings were obtained by Stahle and Wilbrands and Wilbrand et al 12 with tomography and microdissection of human petrous bones. Minute vascular connections between the canaliculus and the aqueduct were also shown and, within a contextual concept of a reduced visibility of the aqueduct at tomography, were felt "to contribute to the complexity of the morphological factors which with all probability are linked to the pathogenesis of Meniere's disease." In conclusion, the authors cited refer to a picture of vascular anatomy in which the VVA runs with the endolymphatic duct in the aqueduct and terminates in the sigmoid sinus. Veins from the endolymphatic sac either drain into the VVA or go directly into the sigmoid sinus. The paravestibular canaliculus begins at the vestibule, closely follows the aqueduct and ramifies in proximity to the sac. An artery and a vein of unknown origin and destination are contained in the canaliculus. Normal Aruztomy. In 1761, Cotunnius'" first described the cochlear and the vestibular aqueducts and their adjacent channels. A vein collecting all the venous branches of the tympanic scalae of the cochlea and a vestibular branch follows the cochlear aqueduct in a channel of its own and ends in the jugular vein. The VVA has a similar course. It collects the blood from the vestibule and the semicircular canals and courses in a bone canal adjacent to the vestibular aqueduct. It then descends along the outer layer of the dura mater and opens into the lateral sinus. This precise description was disregarded and practically lost for at least a century. Eichler," in 1892, reviewed the works of contemporary authors who were aPfarently unaware of the contribution 0 Contunnius and either did not mention any vein or described a single element of the whole picture. With Siebenmann'v-" the description of Contunnius regained its original clari-
ty. Canalis accessorius aqueducts cochleae, (accessory canal of the cochlear aqueduct) and canalis accessorius aqueducti vestibuli, (accessory canal of the vestibular aqueduct) lie parallel to and separate from their respective aqueducts. The VVA, collecting branches from the utricle and the six crura (limbs) of the semicircular canals, begins near the inner aperture of the vestibular aqueduct and enters its own osseous channel, that is, the accessory canal of the vestibular aqueduct. Since the organic description by Siebenmann, the course, autonomous or not, and the destination of the VVA have been described differently in textbooks as well as in specialty studies. Few textbooks carried the correct description; commonly the vein was described as running within the aqueduct itself, or it was not mentioned. Its termination was sometimes reported in the inferior petrosal sinus or the sigmoid sinus, but more often in the superior petrosal sinus. According to Bast and Anson17 the vein runs with the endolymphatic duct through the vestibular aqueduct up to the dura and opens into the lateral sinus. Anson et apo pointed out the small veins running close to the aqueduct and opening into the vein of the aqueduct. METHODS AND MATERIALS Forty petrous bones from adults with no disease of the ear or temporal bone, both in the history and clinical examination, were submitted to the investigation. The essential goal of the processing consisted of obtaining a series of 1 mm thick, cleared sections from temporal bones previously submitted to vascular injection of the internal auditory artery and to osmic-acid staining of the membranous labyrinth. The method of removal, injection and staining of the specimens was as described by Hansen" and reported in detail elsewhere":" with the processing of the thick sections. The findings on the course of the VVA were also verified in several series of histological sections of temporal bones used as controls.
RESULTS
The VVA drains the major portion of the semicircular canals and a part of the utricle. This is the general picture of the confluence of the tributary veins and the course of the VVA. Each semicircular canal has two veins, one for the ampullar crus and one for the simple crus (crus with its plural, crura, belongs to
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a
sse
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b
Fig. 1. Vein of the vestibular aqueduct (WA) in the dorsal wall of the vestibule. Arrow points to the vein of the ampullar crus of the lateral canal which receives the other veins according to different patterns in a, b & c (see text). ED - Endolymphatic duct and vestibular aqueduct; Lse - Lateral semicircular canal; pse - Posterior semicircular canal; sse - Superior semicircular canal.
Latin anatomical terminology and means the limb, ampullar or simple, of the semicircular canal). As each canal opens into the vestibule, the veins lie on its posterior wall where they begin to run in a medial direction (Fig. Ia ). While some veins join to form the stem of the VVA, others proceed individually up to the medial wall of the vestibule. Here, both the VVA and the single veins make a sharp dorsal tum and enter a bone channel where they merge to form the complete VVA. The opening of this channel lies just cranially to the beginning of the vestibular aqueduct. The VVA proceeds in its bone channel up to the jugular bulb or the inferior petrosal sinus (Fig. 2). TRIBUTARY VEINS OF TIIE VVA
These will be described in the order
in which they merge to give rise to the VVA (Fig. la).
Vein of the Ampullar Crus of the Lateral Canal (vACLC). From the convex wall of the canal the vein runs on the posteromedial wall of the endosteal ampulla to the posterior wall of the vestibule, where it is joined by the posterior utricular vein. It drains the venous blood from the membranous canal and from the periphery of the lateral crista. Vein of the Simple Crus of the Lateral Canal (vSCLC). This enters the vestibule and courses medially and slightly superiorly passing cranially to the opening of the common crus and then joining the VVA. Posterior Utricular Vein (PUv). This is formed by several branches draining the
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Fig. 2. The course of the vein of the vestibular aqueduct (VV A) seen from the posterior side of the temporal bone. The insert shows the relative situation of the vein and the vestibular aqueduct in their first segment, as well as the intraosseous course of the last branch to the VVA. ED - Endolymphatic duct; IPS - Inferior petrosal sinus; JB Jugular bulb.
posterior wall of the utricle and by small branches draining the periphery of the macula along the inferior aspect of the utricle. The vein crosses over to the posterior wall of the vestibule where it meets the preceding veins (Fig. 3.) Vein of the Simple Crus of the Superior Canal (vSCSC). This passes from the simple crus of the superior canal to the common crus and up to the vestibule. Here, the vein turns around the upper margin of the crus opening and joins the vACLC. Occasionally, the vSCSC joins the vein of the simple crus of the posterior canal and the common stem proceeds to the vACLC (Fig. 3).
Vein of the Simple Crus of the Posterior Canal (vSCPC). This may join the vSCSC (see above) or it may individually pass to the vestibule, where it joins the VVA. Vein of the Ampullar Crus of the Superior Canal (vACSC). This runs in a caudomedial direction from the posterior wall of the endosteal ampulla to the medial wall of the vestibule. Here it joins the VVA just prior to its entrance into the bone channel, or it enters the bone independently and joins the VVA in its canal (Fig. Ib),
In one quarter of the cases the VVA receives one or two veins which are nor-
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Fig. 3. Thick, cleared section in horizontal plane. The stem of the vein of the vestibular aqueduct (VVA) receives the vein of the common crus (vCC) and the posterior utricular vein (PUv). The drainage of the utricular macula (U) into the VVA can be appreciated. The vCC is here formed by the vein of the simple crus of the posterior canal and by the vein of the simple crus of the superior canal. ED - Capillaries of the isthmic portion of the endolymphatic duct. (x16)
mally tributaries of the posterior vestibular vein. They are the vein of the ampullar crus of the posterior canal and the vein of the crista of the posterior canal (Fig. Ia).
completed before the bone canal. The vACLC receives in the following order the vSCLC, the PUv, the vSCSC, the vSCPC and the vACSC (Fig. Ic).
CONFLUENCE OF THE TRIBUTARIES OF THE VVA
AQUEDUcr
The tributaries meet along the posterior and the medial walls of the vestibule with various patterns, which may be described by taking the vACLC as the peripheral root of the VVA. Pattern 1. The vACLC running lateromedially on the posterior wall receives, in this order, the vSCLC, the PUv and the vein of the common crus (vSCSC and vSCPC). The stem of the VVA is then joined by the vACSC either in its osseous canal or just prior to the entrance of the canal (Fig. Ia). Pattern 2. The vACLC receives the vSCLC and the PUv, their common stem enters the main osseous channel where it is joined by the common stem of the vein of the common crus and the vACSC (Fig. Ib). Pattern 3. The stem of the VVA is
COURSE OF THE VEIN OF THE VESTIBULAR
The extralabyrinthine COurse (Fig. 2) of the VVA is in an osseous canal separated from and parallel to the vestibular aqueduct up to the dura of the endolymphatic sac area. Therefore, the vein follows the dura up to the inferior petrosal sinus or the jugular bulb (Fig. 2). In order to simplify the description, the course may be divided into three segments. The VVA enters its osseous canal at a point on the medial wall of the vestibule just cranially and dorsally to the entrance of the vestibular aqueduct. In the first segment, the VVA has a dorsal direction, almost parallel to the vestibule, and lies cranially to the aqueduct from which it is separated by bone. The confluence of the last tributaries occurs in this tract (Fig. 2, insert). In its second segment, the vein makes a wide dorsal and inferior tum so as to
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Fig. 4. Histological section in horizontal plane. The vein of the vestibular aqueduct (arrow) leaves the bone and enters the dura close to the endolymphatic sac (ES). (H & E, xIS)
leave the labyrinthine capsule and run through the retrolabyrinthine cells. It thus gradually approaches the posterior side of the petrosa, and there it arrives on the periosteal aspect of the dura at a point medial to the emergence of the endolymphatic duct (Fig. 4). While parallel to the aqueduct, this second segment is first superior, then medioinferior and eventually anteromedial to the aqueduct (Fig. 2). In its third and final segment, the VVA runs vertically and caudally within the dura and contiguous to the endolymphatic sac. The vein thus joins the inferior petrosal sinus just prior to the latter's termination in the jugular bulb, or it enters the bulb itself. The relationships of the VVA to the endolymphatic sac are as follows. The vein initially corresponds to the anterior side of the first narrow portion of the sac. Then, as the expanding sac acquires an inferolateral direction, the still-vertical vein faces the medial margin of the sac (Fig. 2). On its dural route, the VVA receives several veins coming from the endolymphatic sac, the dura adjacent to the sac, the petrous bone and the mucosa of the retrolabyrinthine cells. The veins of the sac run parallel and in
a lateromedial direction up to the VVA, where they end either individually or after joining in a larger stem on the anterior side of the sac (Figs. 5 and 6). These veins are joined by branches from the bone deep to the posterior wall of the petrosa and from retrolabyrinthine cells. The course of the VVA presented this variation in one case. In the second portion of its course, the vein turns inferolaterally, passing within the arch of the posterior semicircular canal and reaches the infralabyrinthine area. Here it becomes vertical and, running medially and dorsally to the fallopian canal, joins the jugular bulb. DISCUSSION
A most notable aspect of the literature on the VVA is the recurrent regression from a rational and correct description to an inaccurate and contradictory picture. Despite the various contexts in which this occurred, there appears to be a common semantic factor that deserves consideration. This is the name itself of "the vein of the vestibular aqueduct," which is a literal misnomer leading to the assumption that the vein lies within the aqueduct. In view of this, a more
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Fig. 5. Thick, cleared section in horizontal plane. The vein of the vestibular aqueduct (VV A) is joined by a large vein of the endolymphatic sac (ES) (arrow). (x16)
strictly descriptive terminology should be adopted for the vein and its bone canal, and, for the sake of symmetry, also for "the vein of the cochlear aqueduct." The anatomical features of the VVA are peculiar. The vein collects blood from the rich network of the thin endolymphatic wall of the semicircular canals and a small peripheral area of the cristae and the utricle macula. The major portion of the cristae and the maculae drains into the vein of the cochlear aqueduct through the anterior and the posterior vestibular veins. The VVA is formed on the posterior vestibular wall, where no other vessel lies, and enters the pores of the medial wall of the vestibule as a single or double stem. It presents more variations than any other labyrinthine vessel both in the patterns of fusion and in the number of its tributaries. A typical feature of its morphology is that the final fusion of the tributaries may occur deep to the medial wall of the vestibule and beyond the endosteum. The course of the VVA with its close connection to the endolymphatic duct and sac, as well as its termination into the inferior petrosal sinus or the jugular bulb, appears to be in agreement with
the embryology and the functional anatomy of the inner ear. Also the tributary veins from the network of the sac correspond to the same concept. On the other hand, the tributary branches from the dura, the petrous bone and the mucosa of the retrolabyrinthine cells fit the theory of partial connections between the inner ear circulation and the adjacent circulatory districts." Several of the morphological features mentioned above have been reported, although in less detail, by previous authors. Discussions of the course of the vein/3.15.16 its tributary branches," and the venous drainage of the endolymphatic sac in the VVA appear in the literature." Cussen'" correctly reported the course of the vein. The data of the present investigation were made possible by modern optical equipment as well as the method of specimen preparation, which afforded a study in stereomicroscopy of the vascular bed from the capillary district to the large bone vessels without losing the continuity of the vessels. A number of points, however, remain obscure. The tributary veins from the bone to the VVA were incompletely visualized due to the low pressure build-up in the venous regimen, as commonly occurs with arterial injection of an insulated speci-
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men. The small artery running with the VVA in the bone channel'! was not seen in our specimens. One may infer from this that the artery is not a branch of the internal auditory artery and the subarcuate artery, which are directly supplied with this technique of injection. As a matter of analogy, it is worth mentioning that a similar artery pairing the vein of the cochlear aqueduct is present in human embryos and disappears in later fetal life.23 Vascular connections between the vein and the vestibular aqueduct, which were evidenced in plastic molds of the inner ear,S,12 were not seen, perhaps due to a technical failure. However, the plastic molding technique may not discriminate vessels from nonvascular spaces. The reciprocal position of the vestibular aqueduct and the VVA were found rather consistently, the vein lying first caudally then substantially ventromedially to the duct. This does not agree completely with the data by Wilbrand et a}12 who found a paravestibular canal lateral to the aqueduct in 9 of 35 dissected specimens. The clinical relevance of these anatomical findings may deserve a few observations. The recently described "paravestibular canaliculus" corresponds to the bony course of the VVA, that is, to the accessory vestibular duct also known, in medical dictionaries, as "aqueductus Cotunnii," the aqueduct of Cotugno. Its role in pathological conditions apparently needs more investigation. The close relationship between the VVA and the endolymphatic sac may be of importance in surgery of the sac for Meniere's disease. Operations on the sac may damage the vein, thus producing a permanent or a transient disturbance of the venous drainage of the inner ear. The capillary network on the endolymphatic walls of the semicircular canals could be effected, while the periphery of the cristae can as well drain through their central veins to the vein of the cochlear aqueduct.v--" A similar problem relates to experimental otopa-
thology. A vein similar to the human VVA is present in the rabbit and the monkey while it is lacking in the guinea pig and the cat." Surgical obliteration of the endolymphatic sac and duct in these animals produced endolymphatic hydrops. Concomitant damage of the VVA may have occurred in rabbits and monkeys thus creating an additional factor in the experiment." CONCLUSIONS
A correct and rational description of the VVA was given by Cotugno" in 1761 and by Siebenmann'" in 1894, but later it was repeatedly lost to the advantage of an incomplete or wholly incorrect picture. The later description of the paravestibular canaliculus, that is, the unrecognized bony course of the VVA, is an example of this occurrence. The present study adds some details to the basic picture of the cited authors. The VVA is the route of venous drainage of a part of the vestibular labyrinth: the three semicircular canals and a small area of the cristae of the canals and the utricular macula. Most of the cristae and the macula drain to the vein of the cochlear aqueduct. This separation of venous routes between sensorial and nonsensorial areas in the vestibule escapes a functional interpretation. The VVA takes an individual bony course parallel to the vestibular aqueduct and reaches the dura mater of the posterior side of the petrous bone, where it runs up to the inferior petrosal sinus or the jugular bulb. In its course, the vein receives further tributary branches from the bone, the dura and the endolymphatic sac. These connections, which need quantitative evaluation, suggest a complex picture which includes the blood supply of the membranous labyrinth, the petrous bone and the dura mater. The information presented on normal anatomy should promote interest in this neglected vein in histopathological studies of temporal bones as well as in experimental pathology.
REFERENCES 1. Kimura RS, Schuknecht HF: Membraneous hydrops in the inner ear of the guinea pig after obliteration of the endolym-
phatic sac. Pract Oto-Rhino-LaryngoI 27: 343354, 1965 2. Shambaugh GE, Clemis JD, Arenberg
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VEIN OF VESTIBULAR AQUEDUCT IK: Endolymphatic duct and sac in Meniere's disease. Arch Otolaryngol 89:816-825, 1969 3. Hallpike CS, Cairns H: Observations on the pathology of Meinere's syndrome. J Laryngol Otol 53:625-654, 1938 4. Zechner G, Altmann F: Histological studies on the human endolymphatic duct and sac. Pract Oto-Hhino-Laryngol 31:65-83, 1969 5. Zechner G: Zur Pathohistologie des Ductus und Saccus Endolymphaticus. Acta Otolaryngol (Stockh) 75:232-238, 1973 6. Clemis GD, Valvassori GE: Recent radiographic and clinical observations on the vestibular aqueduct. Otolaryngol Clin North Am October: 339-346, 1968 7. Brunner S, Pedersen CB: Experimental roengen examination of the vestibular aqueduct. Acta Radiol Diagn 11:443-448, 1971 8. Stahle J, Wilbrand H: The vestibular aqueduct in patients with Meniere's disease. Acta Otolaryngol (Stockh) 78:36-48, 1974 9. Yuen SS Schuknecht HF: Vestibular aqueduct and endolymphatic duct in Meniere's disease. Arch Otoladyngol 96:553-555, 1972 10. Anson BJ, Donaldson JA, Warpeha RL, et al: The vestibular and cochlear aqueducts: Their variational anatomy in the adult human ear. Laryngoscope 75:1023-1223, 1965 11. Ogura Y, Clernis JD: A study of the gross anatomy of the human vestibular aqueduct. Ann Otol Rhinol Laryngol 80:813-825, 1971 12. Wilbrand HF, Rask-Anderson H, Gilstring D: The vestibular aqueduct and the paravestibular canal. An anatomic and roentgenologic investigation. Acta Radiol Diagn 15: 337-355, 1974 13. Cotunnius: De aqueductibus auris humanae mternae anatomica dissertatio, Neapoli 1761
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14. Eichler 0: Anatomische Untersuchungen tiber die Wege des Blutstromes im Menschlichen Ohrlabyrinth. Abh Math Phys Klasaechs Akad Wiss 5:311-349, 1892 15. Siebenmann F: Ueber die Injection der Knochenkanaele des Aqueductus vestibuli et cochleae mit Woodschen Metall. Mittheilungen aus dem anatom. Institut im Vesalianum zu Basel, 1889 16. Siebenmann F: Die Blutgeiaesse im Labyrinth des menschlichen Ohres. Wiesbaden, Bergmann, 1894 17. Bast HT, Anson BJ: The Temporal Bone and the Ear. Springfield, Thomas, 1949 18. Hansen CC: Vascular anatomy of the human temporal bone. Ann Otol Rhinol Laryngol 79:269-276, 1970 19. Mazzoni A: Internal auditory canal. Arterial relations at the porus acusticus. Ann Otol Rhinol Laryngol 78:797-814, 1969 20. Mazzoni A: Internal auditory artery supply to the petrous bone. Ann Otol Rhinol Laryngol 81:13-21, 1972 21. Nabeya D: A study in comparative anatomy of the blood vascular system of the internal ear in mammalia and homo. Acta Sch Med Univ Imp Kioto 4:1-132, 1923
22. Gussen R: Meniere's syndrome. Compensatory collateral venous drainage with endolymphatic sac fibrosis. Arch Otolaryngol 99: 414-418, 1974 23. Kellner G, Richter OB: Ueber die Entwicklung der Gefaesse des Innerohres beim Menschen. Monatsschr Ohrenheik LaryngoRhinol 96:187-209, 1962 24. Scuderi R, Del Bo M: La vascolarizzazione del labirinto umano. Arch Ital Otol Rhinol Laryngol 63 (Suppl 11) 1952 25. Mazzoni A: The blood supply of the vestibular labyrinth in man. 1979, in press
REPRINTS - Antonio Mazzoni, MD, Divisione Otorinolaringoiatrica, Ospedale Maggiore, 24100 Bergamo, Italy.
AMERICAN DIOPTER AND DECIBEL SOCIETY "1980 Guideposts in Ophthalmology and Otolaryngology" is the theme of the American Diopter-Decibel Society spring seminar. Sessions will be held at Lake Buena Vista, Florida, March 16-22, 1980. For details contact: E. A. Rittenhouse, MD, 522 Walnut Street, McKeesport, PA 15132.
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VEIN OF THE VESTIBULAR AQUEDUCT ANTONIO MAZZONI, MD BERGAMO, ITALY
The vein of the vestibular aqueduct (VVA) was investigated in a series of 40 human temporal bones. The processing included vascular injection with a colored medium, decalcification and cutting in serial, thick sections, which were put in a clear fluid and studied with a stereomicroscope. The labyrinthine roots of the VVA are the single veins of the ampulla and simple limbs of the semicircular canals and of the posterior wall of the utricle. They drain the rich capillary bed of the simple endolymphatic walls of the canals and the utricle, as well as a small peripheral area of the cristae and the utricular macula. The VVA leaves the vestibule through an individual bone canal running parallel to the vestibular aqueduct up to the dura of the posterior side of the petrosa in the area of the endolymphatic sac. It then opens in the inferior petrosal sinus or the jugular bulb. The vein receives other branches from the bone, dura and sac. Correct information on the course of this vein appears to be lacking in contemporary textbooks and articles, although it has been correctly described since the last century.
The vestibular aqueduct was recently the object of anatomical and clinical reports in relation to the diagnosis as well as the pathophysiological mechanisms of of Meniere's disease. The interpretation of the findings concerning the vestibular aqueduct and its content, the endolymphatic duct and the vein of the vestibular aqueduct (VVA), as well as the newly-discovered paravestibular canaliculus, was inaccurate because of a lack of objective anatomical information and a misreading of the literature. The object of this paper is to review the literature on the VVA and to report our findings on this vein and its paravestibular osseous course.
and sac were found in patients with Meniere's disease." Histopathological studies of patients with Meniere's disease demonstrated avascular fibrosis of the perisaccular connective tissue":" and exotosis-Iike buds of lamellar bone on the walls of the aqueduct," In 1968 Clemis and Valvassori" reported an exceptionally high correlation between sensorineural hearing loss and an abnormal or absent radiological visualization of the vestibular aqueduct. This correlation was later restricted to Meniere's disease.I-" Yuen and Schuknecht," however, found no abnormal caliber of the aqueduct in temporal bones from patients with Meniere's disease.
LITERATURE REVIEW
Studies on the gross anatomy of the aqueduct and related structures were stimulated by clinical experience." Ogura and Clemis!' examined the vestibular aqueduct by means of microdissection of osmic-acid-stained temporal bones. A structure was identified near the aqueduct and called the paravestibular canaliculus. It began from the vestibule, superior and a little medial to the opening of the aqueduct; it ran in a bony channel of its own, parallel to the aqueduct, and terminated distally by branching into the substance of the posterior fossa dura in the region of the endolymphatic sac. The canaliculus contained loose connective tissue with an
This review will first consider recent clinical studies which focus on the role of the vestibular aqueduct in inner ear disorders, then it will discuss the normal anatomy of the aqueduct and its vein in relationship to these studies.
Clinical Aspects. The current interest in the vestibular aqueduct arose in connection with Meniere's disease. A normal endolymphatic duct and sac are considered essential for labyrinthine function. Experimental ablation of the endolymphatic sac caused endolymphatic hydrops in animals,' while structural abnormalities of the endolymphatic duct
From the Department of Otolaryngology. University of Ferrara. Ferrara, Italy. and the Instltut of Anatomy, University of Odense, Odense, Denmark.
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artery and a vein. The canaliculus was believed by the authors to carry the blood supply of the endolymphatic sac and to fulfill a pressure-regulating function between the posterior fossa and the perilymphatic space. Similar findings were obtained by Stahle and Wilbrands and Wilbrand et al 12 with tomography and microdissection of human petrous bones. Minute vascular connections between the canaliculus and the aqueduct were also shown and, within a contextual concept of a reduced visibility of the aqueduct at tomography, were felt "to contribute to the complexity of the morphological factors which with all probability are linked to the pathogenesis of Meniere's disease." In conclusion, the authors cited refer to a picture of vascular anatomy in which the VVA runs with the endolymphatic duct in the aqueduct and terminates in the sigmoid sinus. Veins from the endolymphatic sac either drain into the VVA or go directly into the sigmoid sinus. The paravestibular canaliculus begins at the vestibule, closely follows the aqueduct and ramifies in proximity to the sac. An artery and a vein of unknown origin and destination are contained in the canaliculus. Normal Aruztomy. In 1761, Cotunnius'" first described the cochlear and the vestibular aqueducts and their adjacent channels. A vein collecting all the venous branches of the tympanic scalae of the cochlea and a vestibular branch follows the cochlear aqueduct in a channel of its own and ends in the jugular vein. The VVA has a similar course. It collects the blood from the vestibule and the semicircular canals and courses in a bone canal adjacent to the vestibular aqueduct. It then descends along the outer layer of the dura mater and opens into the lateral sinus. This precise description was disregarded and practically lost for at least a century. Eichler," in 1892, reviewed the works of contemporary authors who were aPfarently unaware of the contribution 0 Contunnius and either did not mention any vein or described a single element of the whole picture. With Siebenmann'v-" the description of Contunnius regained its original clari-
ty. Canalis accessorius aqueducts cochleae, (accessory canal of the cochlear aqueduct) and canalis accessorius aqueducti vestibuli, (accessory canal of the vestibular aqueduct) lie parallel to and separate from their respective aqueducts. The VVA, collecting branches from the utricle and the six crura (limbs) of the semicircular canals, begins near the inner aperture of the vestibular aqueduct and enters its own osseous channel, that is, the accessory canal of the vestibular aqueduct. Since the organic description by Siebenmann, the course, autonomous or not, and the destination of the VVA have been described differently in textbooks as well as in specialty studies. Few textbooks carried the correct description; commonly the vein was described as running within the aqueduct itself, or it was not mentioned. Its termination was sometimes reported in the inferior petrosal sinus or the sigmoid sinus, but more often in the superior petrosal sinus. According to Bast and Anson17 the vein runs with the endolymphatic duct through the vestibular aqueduct up to the dura and opens into the lateral sinus. Anson et apo pointed out the small veins running close to the aqueduct and opening into the vein of the aqueduct. METHODS AND MATERIALS Forty petrous bones from adults with no disease of the ear or temporal bone, both in the history and clinical examination, were submitted to the investigation. The essential goal of the processing consisted of obtaining a series of 1 mm thick, cleared sections from temporal bones previously submitted to vascular injection of the internal auditory artery and to osmic-acid staining of the membranous labyrinth. The method of removal, injection and staining of the specimens was as described by Hansen" and reported in detail elsewhere":" with the processing of the thick sections. The findings on the course of the VVA were also verified in several series of histological sections of temporal bones used as controls.
RESULTS
The VVA drains the major portion of the semicircular canals and a part of the utricle. This is the general picture of the confluence of the tributary veins and the course of the VVA. Each semicircular canal has two veins, one for the ampullar crus and one for the simple crus (crus with its plural, crura, belongs to
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a
sse
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b
Fig. 1. Vein of the vestibular aqueduct (WA) in the dorsal wall of the vestibule. Arrow points to the vein of the ampullar crus of the lateral canal which receives the other veins according to different patterns in a, b & c (see text). ED - Endolymphatic duct and vestibular aqueduct; Lse - Lateral semicircular canal; pse - Posterior semicircular canal; sse - Superior semicircular canal.
Latin anatomical terminology and means the limb, ampullar or simple, of the semicircular canal). As each canal opens into the vestibule, the veins lie on its posterior wall where they begin to run in a medial direction (Fig. Ia ). While some veins join to form the stem of the VVA, others proceed individually up to the medial wall of the vestibule. Here, both the VVA and the single veins make a sharp dorsal tum and enter a bone channel where they merge to form the complete VVA. The opening of this channel lies just cranially to the beginning of the vestibular aqueduct. The VVA proceeds in its bone channel up to the jugular bulb or the inferior petrosal sinus (Fig. 2). TRIBUTARY VEINS OF TIIE VVA
These will be described in the order
in which they merge to give rise to the VVA (Fig. la).
Vein of the Ampullar Crus of the Lateral Canal (vACLC). From the convex wall of the canal the vein runs on the posteromedial wall of the endosteal ampulla to the posterior wall of the vestibule, where it is joined by the posterior utricular vein. It drains the venous blood from the membranous canal and from the periphery of the lateral crista. Vein of the Simple Crus of the Lateral Canal (vSCLC). This enters the vestibule and courses medially and slightly superiorly passing cranially to the opening of the common crus and then joining the VVA. Posterior Utricular Vein (PUv). This is formed by several branches draining the
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Fig. 2. The course of the vein of the vestibular aqueduct (VV A) seen from the posterior side of the temporal bone. The insert shows the relative situation of the vein and the vestibular aqueduct in their first segment, as well as the intraosseous course of the last branch to the VVA. ED - Endolymphatic duct; IPS - Inferior petrosal sinus; JB Jugular bulb.
posterior wall of the utricle and by small branches draining the periphery of the macula along the inferior aspect of the utricle. The vein crosses over to the posterior wall of the vestibule where it meets the preceding veins (Fig. 3.) Vein of the Simple Crus of the Superior Canal (vSCSC). This passes from the simple crus of the superior canal to the common crus and up to the vestibule. Here, the vein turns around the upper margin of the crus opening and joins the vACLC. Occasionally, the vSCSC joins the vein of the simple crus of the posterior canal and the common stem proceeds to the vACLC (Fig. 3).
Vein of the Simple Crus of the Posterior Canal (vSCPC). This may join the vSCSC (see above) or it may individually pass to the vestibule, where it joins the VVA. Vein of the Ampullar Crus of the Superior Canal (vACSC). This runs in a caudomedial direction from the posterior wall of the endosteal ampulla to the medial wall of the vestibule. Here it joins the VVA just prior to its entrance into the bone channel, or it enters the bone independently and joins the VVA in its canal (Fig. Ib),
In one quarter of the cases the VVA receives one or two veins which are nor-
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Fig. 3. Thick, cleared section in horizontal plane. The stem of the vein of the vestibular aqueduct (VVA) receives the vein of the common crus (vCC) and the posterior utricular vein (PUv). The drainage of the utricular macula (U) into the VVA can be appreciated. The vCC is here formed by the vein of the simple crus of the posterior canal and by the vein of the simple crus of the superior canal. ED - Capillaries of the isthmic portion of the endolymphatic duct. (x16)
mally tributaries of the posterior vestibular vein. They are the vein of the ampullar crus of the posterior canal and the vein of the crista of the posterior canal (Fig. Ia).
completed before the bone canal. The vACLC receives in the following order the vSCLC, the PUv, the vSCSC, the vSCPC and the vACSC (Fig. Ic).
CONFLUENCE OF THE TRIBUTARIES OF THE VVA
AQUEDUcr
The tributaries meet along the posterior and the medial walls of the vestibule with various patterns, which may be described by taking the vACLC as the peripheral root of the VVA. Pattern 1. The vACLC running lateromedially on the posterior wall receives, in this order, the vSCLC, the PUv and the vein of the common crus (vSCSC and vSCPC). The stem of the VVA is then joined by the vACSC either in its osseous canal or just prior to the entrance of the canal (Fig. Ia). Pattern 2. The vACLC receives the vSCLC and the PUv, their common stem enters the main osseous channel where it is joined by the common stem of the vein of the common crus and the vACSC (Fig. Ib). Pattern 3. The stem of the VVA is
COURSE OF THE VEIN OF THE VESTIBULAR
The extralabyrinthine COurse (Fig. 2) of the VVA is in an osseous canal separated from and parallel to the vestibular aqueduct up to the dura of the endolymphatic sac area. Therefore, the vein follows the dura up to the inferior petrosal sinus or the jugular bulb (Fig. 2). In order to simplify the description, the course may be divided into three segments. The VVA enters its osseous canal at a point on the medial wall of the vestibule just cranially and dorsally to the entrance of the vestibular aqueduct. In the first segment, the VVA has a dorsal direction, almost parallel to the vestibule, and lies cranially to the aqueduct from which it is separated by bone. The confluence of the last tributaries occurs in this tract (Fig. 2, insert). In its second segment, the vein makes a wide dorsal and inferior tum so as to
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Fig. 4. Histological section in horizontal plane. The vein of the vestibular aqueduct (arrow) leaves the bone and enters the dura close to the endolymphatic sac (ES). (H & E, xIS)
leave the labyrinthine capsule and run through the retrolabyrinthine cells. It thus gradually approaches the posterior side of the petrosa, and there it arrives on the periosteal aspect of the dura at a point medial to the emergence of the endolymphatic duct (Fig. 4). While parallel to the aqueduct, this second segment is first superior, then medioinferior and eventually anteromedial to the aqueduct (Fig. 2). In its third and final segment, the VVA runs vertically and caudally within the dura and contiguous to the endolymphatic sac. The vein thus joins the inferior petrosal sinus just prior to the latter's termination in the jugular bulb, or it enters the bulb itself. The relationships of the VVA to the endolymphatic sac are as follows. The vein initially corresponds to the anterior side of the first narrow portion of the sac. Then, as the expanding sac acquires an inferolateral direction, the still-vertical vein faces the medial margin of the sac (Fig. 2). On its dural route, the VVA receives several veins coming from the endolymphatic sac, the dura adjacent to the sac, the petrous bone and the mucosa of the retrolabyrinthine cells. The veins of the sac run parallel and in
a lateromedial direction up to the VVA, where they end either individually or after joining in a larger stem on the anterior side of the sac (Figs. 5 and 6). These veins are joined by branches from the bone deep to the posterior wall of the petrosa and from retrolabyrinthine cells. The course of the VVA presented this variation in one case. In the second portion of its course, the vein turns inferolaterally, passing within the arch of the posterior semicircular canal and reaches the infralabyrinthine area. Here it becomes vertical and, running medially and dorsally to the fallopian canal, joins the jugular bulb. DISCUSSION
A most notable aspect of the literature on the VVA is the recurrent regression from a rational and correct description to an inaccurate and contradictory picture. Despite the various contexts in which this occurred, there appears to be a common semantic factor that deserves consideration. This is the name itself of "the vein of the vestibular aqueduct," which is a literal misnomer leading to the assumption that the vein lies within the aqueduct. In view of this, a more
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Fig. 5. Thick, cleared section in horizontal plane. The vein of the vestibular aqueduct (VV A) is joined by a large vein of the endolymphatic sac (ES) (arrow). (x16)
strictly descriptive terminology should be adopted for the vein and its bone canal, and, for the sake of symmetry, also for "the vein of the cochlear aqueduct." The anatomical features of the VVA are peculiar. The vein collects blood from the rich network of the thin endolymphatic wall of the semicircular canals and a small peripheral area of the cristae and the utricle macula. The major portion of the cristae and the maculae drains into the vein of the cochlear aqueduct through the anterior and the posterior vestibular veins. The VVA is formed on the posterior vestibular wall, where no other vessel lies, and enters the pores of the medial wall of the vestibule as a single or double stem. It presents more variations than any other labyrinthine vessel both in the patterns of fusion and in the number of its tributaries. A typical feature of its morphology is that the final fusion of the tributaries may occur deep to the medial wall of the vestibule and beyond the endosteum. The course of the VVA with its close connection to the endolymphatic duct and sac, as well as its termination into the inferior petrosal sinus or the jugular bulb, appears to be in agreement with
the embryology and the functional anatomy of the inner ear. Also the tributary veins from the network of the sac correspond to the same concept. On the other hand, the tributary branches from the dura, the petrous bone and the mucosa of the retrolabyrinthine cells fit the theory of partial connections between the inner ear circulation and the adjacent circulatory districts." Several of the morphological features mentioned above have been reported, although in less detail, by previous authors. Discussions of the course of the vein/3.15.16 its tributary branches," and the venous drainage of the endolymphatic sac in the VVA appear in the literature." Cussen'" correctly reported the course of the vein. The data of the present investigation were made possible by modern optical equipment as well as the method of specimen preparation, which afforded a study in stereomicroscopy of the vascular bed from the capillary district to the large bone vessels without losing the continuity of the vessels. A number of points, however, remain obscure. The tributary veins from the bone to the VVA were incompletely visualized due to the low pressure build-up in the venous regimen, as commonly occurs with arterial injection of an insulated speci-
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men. The small artery running with the VVA in the bone channel'! was not seen in our specimens. One may infer from this that the artery is not a branch of the internal auditory artery and the subarcuate artery, which are directly supplied with this technique of injection. As a matter of analogy, it is worth mentioning that a similar artery pairing the vein of the cochlear aqueduct is present in human embryos and disappears in later fetal life.23 Vascular connections between the vein and the vestibular aqueduct, which were evidenced in plastic molds of the inner ear,S,12 were not seen, perhaps due to a technical failure. However, the plastic molding technique may not discriminate vessels from nonvascular spaces. The reciprocal position of the vestibular aqueduct and the VVA were found rather consistently, the vein lying first caudally then substantially ventromedially to the duct. This does not agree completely with the data by Wilbrand et a}12 who found a paravestibular canal lateral to the aqueduct in 9 of 35 dissected specimens. The clinical relevance of these anatomical findings may deserve a few observations. The recently described "paravestibular canaliculus" corresponds to the bony course of the VVA, that is, to the accessory vestibular duct also known, in medical dictionaries, as "aqueductus Cotunnii," the aqueduct of Cotugno. Its role in pathological conditions apparently needs more investigation. The close relationship between the VVA and the endolymphatic sac may be of importance in surgery of the sac for Meniere's disease. Operations on the sac may damage the vein, thus producing a permanent or a transient disturbance of the venous drainage of the inner ear. The capillary network on the endolymphatic walls of the semicircular canals could be effected, while the periphery of the cristae can as well drain through their central veins to the vein of the cochlear aqueduct.v--" A similar problem relates to experimental otopa-
thology. A vein similar to the human VVA is present in the rabbit and the monkey while it is lacking in the guinea pig and the cat." Surgical obliteration of the endolymphatic sac and duct in these animals produced endolymphatic hydrops. Concomitant damage of the VVA may have occurred in rabbits and monkeys thus creating an additional factor in the experiment." CONCLUSIONS
A correct and rational description of the VVA was given by Cotugno" in 1761 and by Siebenmann'" in 1894, but later it was repeatedly lost to the advantage of an incomplete or wholly incorrect picture. The later description of the paravestibular canaliculus, that is, the unrecognized bony course of the VVA, is an example of this occurrence. The present study adds some details to the basic picture of the cited authors. The VVA is the route of venous drainage of a part of the vestibular labyrinth: the three semicircular canals and a small area of the cristae of the canals and the utricular macula. Most of the cristae and the macula drain to the vein of the cochlear aqueduct. This separation of venous routes between sensorial and nonsensorial areas in the vestibule escapes a functional interpretation. The VVA takes an individual bony course parallel to the vestibular aqueduct and reaches the dura mater of the posterior side of the petrous bone, where it runs up to the inferior petrosal sinus or the jugular bulb. In its course, the vein receives further tributary branches from the bone, the dura and the endolymphatic sac. These connections, which need quantitative evaluation, suggest a complex picture which includes the blood supply of the membranous labyrinth, the petrous bone and the dura mater. The information presented on normal anatomy should promote interest in this neglected vein in histopathological studies of temporal bones as well as in experimental pathology.
REFERENCES 1. Kimura RS, Schuknecht HF: Membraneous hydrops in the inner ear of the guinea pig after obliteration of the endolym-
phatic sac. Pract Oto-Rhino-LaryngoI 27: 343354, 1965 2. Shambaugh GE, Clemis JD, Arenberg
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VEIN OF VESTIBULAR AQUEDUCT IK: Endolymphatic duct and sac in Meniere's disease. Arch Otolaryngol 89:816-825, 1969 3. Hallpike CS, Cairns H: Observations on the pathology of Meinere's syndrome. J Laryngol Otol 53:625-654, 1938 4. Zechner G, Altmann F: Histological studies on the human endolymphatic duct and sac. Pract Oto-Hhino-Laryngol 31:65-83, 1969 5. Zechner G: Zur Pathohistologie des Ductus und Saccus Endolymphaticus. Acta Otolaryngol (Stockh) 75:232-238, 1973 6. Clemis GD, Valvassori GE: Recent radiographic and clinical observations on the vestibular aqueduct. Otolaryngol Clin North Am October: 339-346, 1968 7. Brunner S, Pedersen CB: Experimental roengen examination of the vestibular aqueduct. Acta Radiol Diagn 11:443-448, 1971 8. Stahle J, Wilbrand H: The vestibular aqueduct in patients with Meniere's disease. Acta Otolaryngol (Stockh) 78:36-48, 1974 9. Yuen SS Schuknecht HF: Vestibular aqueduct and endolymphatic duct in Meniere's disease. Arch Otoladyngol 96:553-555, 1972 10. Anson BJ, Donaldson JA, Warpeha RL, et al: The vestibular and cochlear aqueducts: Their variational anatomy in the adult human ear. Laryngoscope 75:1023-1223, 1965 11. Ogura Y, Clernis JD: A study of the gross anatomy of the human vestibular aqueduct. Ann Otol Rhinol Laryngol 80:813-825, 1971 12. Wilbrand HF, Rask-Anderson H, Gilstring D: The vestibular aqueduct and the paravestibular canal. An anatomic and roentgenologic investigation. Acta Radiol Diagn 15: 337-355, 1974 13. Cotunnius: De aqueductibus auris humanae mternae anatomica dissertatio, Neapoli 1761
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14. Eichler 0: Anatomische Untersuchungen tiber die Wege des Blutstromes im Menschlichen Ohrlabyrinth. Abh Math Phys Klasaechs Akad Wiss 5:311-349, 1892 15. Siebenmann F: Ueber die Injection der Knochenkanaele des Aqueductus vestibuli et cochleae mit Woodschen Metall. Mittheilungen aus dem anatom. Institut im Vesalianum zu Basel, 1889 16. Siebenmann F: Die Blutgeiaesse im Labyrinth des menschlichen Ohres. Wiesbaden, Bergmann, 1894 17. Bast HT, Anson BJ: The Temporal Bone and the Ear. Springfield, Thomas, 1949 18. Hansen CC: Vascular anatomy of the human temporal bone. Ann Otol Rhinol Laryngol 79:269-276, 1970 19. Mazzoni A: Internal auditory canal. Arterial relations at the porus acusticus. Ann Otol Rhinol Laryngol 78:797-814, 1969 20. Mazzoni A: Internal auditory artery supply to the petrous bone. Ann Otol Rhinol Laryngol 81:13-21, 1972 21. Nabeya D: A study in comparative anatomy of the blood vascular system of the internal ear in mammalia and homo. Acta Sch Med Univ Imp Kioto 4:1-132, 1923
22. Gussen R: Meniere's syndrome. Compensatory collateral venous drainage with endolymphatic sac fibrosis. Arch Otolaryngol 99: 414-418, 1974 23. Kellner G, Richter OB: Ueber die Entwicklung der Gefaesse des Innerohres beim Menschen. Monatsschr Ohrenheik LaryngoRhinol 96:187-209, 1962 24. Scuderi R, Del Bo M: La vascolarizzazione del labirinto umano. Arch Ital Otol Rhinol Laryngol 63 (Suppl 11) 1952 25. Mazzoni A: The blood supply of the vestibular labyrinth in man. 1979, in press
REPRINTS - Antonio Mazzoni, MD, Divisione Otorinolaringoiatrica, Ospedale Maggiore, 24100 Bergamo, Italy.
AMERICAN DIOPTER AND DECIBEL SOCIETY "1980 Guideposts in Ophthalmology and Otolaryngology" is the theme of the American Diopter-Decibel Society spring seminar. Sessions will be held at Lake Buena Vista, Florida, March 16-22, 1980. For details contact: E. A. Rittenhouse, MD, 522 Walnut Street, McKeesport, PA 15132.
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