FROM THE DEPARTMENT OF DIAGNOSTIC RADIOLOGY, AKADEMISKA SJUKHUSET, UNIVERSITY OF UPPSALA, S-750 14 UPPSALA, AND THE DEPARTMENT OF OTOLARYNGOLOGY, REGIONSJUKHUSET, UNIVERSITY OF LINKOPING, S-581 85 LINKOPING, SWEDEN.
MULTIDIRECTIONAL TOMOGRAPHY IN RECONSTRUCTIVE MIDDLE EAR SURGERY H. F.
WILBRAND
and L.
EKVALL
The planning and prognosis of reconstructive surgery of the middle ear require detailed information about the functional and anatomic status of the tympanic cavity and mastoid cells. This is also of particular importance in the occasional occurrence of secondary postoperative hearing impairment. Clinical and audiologic data extended by a detailed roentgenographic evaluation afford the best possibility of arriving at a reliable diagnosis. Tomography has proved its usefulness in the demonstration ofthe ossicles (BRUNNER et coll. 1961, DULAC 1961, FREY 1964, WRIGHT et colI. 1969, SANDSTROM & WILBRAND 1971, JENSEN et coll. 1973). Conventional roentgenography of the temporal bone, even with a variety of special positioning, is unable to provide similar information. The tomographic appearance of various pathologic conditions which give reason for surgical reconstruction of the ossicular chain has been described extensively in otoradiologic literature (AGAZZI et coll. 1958, MUNDNICH & FREY 1959, VALVASSORI 1963, 1965, 1967 PORTMANN & GUILLEN 1967, ANDRE et coll, 1968, JENSEN & ROVSING 1971). LANGFELDT (1960, 1963) reported on tomography of the middle ear in columella operations (HALL & RYTZNER 1957, 1959). Submitted for publication 11 January 1974.
436
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MULTIDIRECTIONAL TOMOGRAPHY IN RECONSTRUCTIVE MIDDLE EAR SURGERY 437 The present investigation deals with the use of pre- and postoperative tomography in reconstructive surgery of the ossicular chain. In middle ear surgery the intention is usually to reconstruct the sound transmitting mechanism directly after cleaning measures have been undertaken. If this is not feasible, it may be done in a second stage operation. Preservation or reconstruction of the bony external acoustic meatus is essential for the anatomic and functional result. In cases with a previous radical mastoidectomy the bony meatus can be reconstructed with cortical bone autograft. The operation cavity in the present series of operations was usually obliterated with bone chips and muscle tissue. There are two fundamental types of ossicular reconstruction with auto- or homotransplants, based on the primary defect (Fig. 1): (1) In the first type of procedure (the A type), the stapes is intact. The lesion is often located to the long process of the incus (Fig. I a). The gap between the stapes and the malleus or the drum can be bridged with the body of the incus-incus transposition (Fig. 1 b)-or by using a boot-shaped transplant prepared from an incudal auto- or homograft or from cortical bone (Fig. 1 c). (2) In the second type of procedure (the B type), only the stapedial footplate remains (Fig. 1 d), and the columella (cortical bone) acquires a boomerang-like shape with its long, gracile wing resting on the footplate and its wider shaft attached to the reconstructed tympanic membrane-myringoplasty (Fig. 1 e). This type is often combined with extensive reconstruction of parts of the osseous external meatus after previous radical mastoidectomy (Fig. 1 d, e, f, g). The present investigation is limited to the tomographic appearances of reconstructed middle ears with osseous transplants. The intention is to elucidate the possibilities of tomography to provide information in pre- and postoperative examination of patients with middle ear diseases. Material and Methods
Experience was gained from 65 selected, operated cases from the period 1967 to 1970. The patients were primarily examined by conventional roentgenography and also underwent preoperative and postoperative tomography with the Poly tome in some of the five routine projections, the true lateral, antero-posterior, halfaxial, axial-pyramidal and Stenvers' projections (MUNDNICH & FREY 1959, JENSEN & ROVSING 1971). Exposure data: 55-75 kV, 50 rnA, 11.6 s (double hypocycloid movement), 0.3 mm focal spot, magnification factor 1.3. The radiographic system consisted of universal film (processed in a 3.5 min Pakorol machine) and high definition screens (Siemens Rubin). The tomograms (4- or 6-seriograms, each tomogram 5 cm in diameter) were evaluated in an ordinary viewing box with a mask with a density of 1.5-1.8. The tomograms were harmonized by means of an electromechanical dodger (courtesy Rikets Allmanna Kartverk; Geographical Survey Office of Sweden, Stockholm).
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H. F. WILBRAND AND L. EKVALL
Abbreviations used in the figures (they correspond to those applied by K. W. Frey, J. Jensen, H. Rovsing and K. Terrahe) 1 2 2a 2b 2c 3a 3b 3c 5 VII VIla VII b VII c VIId VII e VIIf 8
8a 9
9a 9b 10 11 11a
external acoustic meatus tympanic cavity epitympanic recess mesotympanic cavity hypo tympanic recess malleus incus stapes mastoid process facial canal facial canal, labyrinthine part facial canal, 1st bend facial canal, tympanic part facial canal, 'lateral knee', 2nd bend facial canal, mastoid part stylomastoid foramen cochlea cochlea, basal turn vestibulum oval window round window lateral semicircular canal superior semicircular canal superior semicircular canal, ampullary region
12 12 a
posterior semicircular canal posterior semicircular canal, ampullary region 13 internal acoustic meatus temporal squama 17 18 sigmoid sinus jugular fossa 19 20 tympanic temporal bone mandible 22 zygomatic process 23 28, e.p. pyramidal eminence bone transplant RTr. (bone chips or cortical transplants mastoid cells c.m. C.Sk. canal skin Citr, cortical transplant columella Col. fascial tissue F I.c.m. middle cranial fossa f.c.p. posterior cranial fossa muscle tissue M.T. operation defect Op. Op.c. operation cavity Pr. promontorium
The indication for postoperative tomography after reconstructive procedures for chronic otitis was to establish the appearance and position of the osseous auto- or homotransplant or in some cases to find an explanation for failure of hearing improvement or a secondary hearing reduction.
Roentgenography Conventional roentgenography. The evaluation of the temporal bone on these films is restricted to an appraisal of the air cells, the range of pneumatization (distance between the sigmoid sinus and the posterior wall of the external auditory meatus and the peri-labyrinthine pneumatization) as well as changes of an inflammatory, cholesteatomatous, or other nature. Conventional roentgenography allows a survey of the middle ear and inner ear structures, but finer details such as alterations for example in the ossicular chain, the optic capsule and the facial canal or the boundaries of the jugular fossa cannot be satisfactorily demonstrated. Such structural details may be demonstrated however, by multidirectional tomography (hypocloid, spiral).
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MULTIDIRECTIONAL TOMOGRAPHY IN RECONSTRUCTIVE MIDDLE EAR SURGERY 30
439
30b
Col------_
9b
b
a 3 a be
MT
c Op C
90
Col
8T'
, ,,
·····r'
OpC
c:k~l
.ii·····
d
e
Fig. 1. Defects in the ossicular chain and corresponding reconstruction types, schematic. a) Disrupted ossicular chain (defect in the long process of the incus). b) A-reconstruction (incus transposition). The remainder of the incus interposed between manubrium of malleus and intact stapes. c) Atransplant interposed between tympanic membrane and intact stapes. d) State efter radical mastoidectomy with operation cavity and total lack of ossicular chain; only the stapedial footplate left. e) B-reconstruction with the boomerang-shaped columella; its tip placed on the footplate and the wider shaft attached to reconstructed tympanic membrane (myringoplasty). f) Lateral view of preoperative situation for B-columella reconstruction. g) B-reconstruction. Position of boomerang-shaped columella. (Abbreviations on opposite page.)
f
.,,
Col
g
Preoperative tomography yields essential information in: (1) Chronic otitis. The condition of the mastoid cells and their septa, the extent of destruction and of the air content of the cells and of the tympanic space can be evaluated in detail. The extent of destruction of the individual ossicles can be established. In cholesteatoma destruction of the bony septa in the epitympanum and
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H. F. WILBRAND AND L. EKVALL
VIlc 11
Col
OP ColVIlclla
9a
3.1 10
9.1
Op 13
3a
3.1
,;'A.
2a
13
VIId
20
1
Sa
8.1
~~
Vile
~~
Pr
2c
19 a
Col
2c
19
b
c
Fig. 2. A-type reconstruction (incus transposition). a) A.p. projection. The remainder of the incus is interposed between the stapedial head and the manubrium mallei. Operation defects in the periantral region. b) Halfaxial projection. The interposed incus between the head of the stapes and the manubrium mallei is seen in its relation to the tympanic part of the facial canal in the aerated tympanic space. c) Lateral projection. Appearance of the transposed incus in relation to the lateral aspect of the facial canal.
aditus ad antrum can be revealed. In extensive cholesteatoma tegmental erosions may be detected, as well as destructions in the otic capsule (labyrinthine fistula). Preoperative knowledge of spontaneous or pathologic defects of the facial canal increases the safety of the surgical procedure. (2) Trauma. It is essential that the dislocations in the ossicular chain (luxation) and the detailed course of fractures be outlined. In traumatic facial palsies the appearance of the facial canal must be established. (3) Malformations of the middle ear. The extent and configuration of the air spaces as well as of the osseous atresia of the external acoustic meatus and the shape of the ossicular chain need to be clearly revealed. Fig. 3. A-reconstruction (boot-shaped columella). a) A.p, projection shows a bevelled section of the boot-shaped A columella and its relationship to the stapes and the tympanic part of the facial canal. b) Halfaxial projection. The relationship of the boot-shaped columella to surrounding structures is better revealed by this projection than by a.p. The Aerated tympanic space in a) and b). c) Axial-pyramidal projection shows the inclination and relationship of the columella to the structures near the oval window. d) Lateral projection. The tomographic plane is at the junction of the boot-shaped columella to the stapedial head. Relationship to the facial canal and the pyramidal eminence.
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MULTIDIRECTIONAL TOMOGRAPHY IN RECONSTRUCTIVE MIDDLE EAR SURGERY
a
b
c
d
Fig. 3. (For legend see opposite page.)
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441
442
H. F. WILBRAND AND L. EKVALL
VIIe
3e
Col
9
\\:. 2
8a
5
Pr 2e
a
b
c
Fig. 4. Boomerang-shaped B columella inserted in the middle ear in order to restore hearing. a) Halfaxial projection. The boomerang-columella is seen resting with its tip on the stapedial foot plate and its free position in the aerated tympanic space. Small defect of the tympanic part of the facial canal. b) Axial-pyramidal projection. c) Lateral projection. The inclination of the B columella is seen to be free from contact with its bony surrounding (the tympanic part of the facial canal and the pyramidal eminence of the posterior tympanic wall).
In malformation as well as in acquired pathologic conditions information concerning the oval and round windows is important in planning of the operation. The facial canal has to be outlined since its course may be abnormal. Postoperative tomography. The main interest is concentrated on the long-term appearance and position of the bony transplants in the middle ear. (1) In an A type reconstruction using the incus transposition method the ossicular situation is demonstrated in the a.p., halfaxial and lateral projections (Fig. 2). In the present version a boot-like A-transplant (Fig. I c) is well demonstrated in the a.p. view and even more favourably in the halfaxial or axial-pyramidal as we as in the true lateral projection (Fig. 3). (2) The boomerang-shaped columella (8 type) (Fig. I e) will be used after previous radical mastoidectomy in cases in which the external meatus often also has to be reconstructed (Fig. I d, e, f, g). The halfaxial and true lateral projections usually give the best information but may be complemented by the axial-pyramidal and a.p. projections for judging the site of the columella, the tip of which is located on the
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MUJ,-TIDIRECTIONAL TOMOGRAPHY IN RECONSTRUCTIVE MIDDLE EAR SURGERY
a
443
b
Fig. 5. Boomerang-shaped columella of cortical bone inserted in a previously radically operated ear. a) In the halfaxial projection the gracile tip of the columella is placed in the center of the stapedial footplate. b) Lateral projection; (tomographic plane lateral to the tympanic space) bony reconstruction of the upper and posterior part of the external meatus.
footplate of the stapes (Figs 4, 5). The appearance of the external meatus reconstructed by bone transplants is best demonstrated in the true lateral projection. (3) In cases of unattained hearing improvement or recurrence of hearing impairment the same projections will be used. By tomography, dislocation or abnormal inclination of the columella may be detected. A case of secondary hearing impairment is illustrated in Fig. 6. Tomography revealed that the columella was abnormally located in relation to the boundaries of the oval window, and to the tympanic part of the facial canal, thus possibly fixed to this structure. This conclusion was confirmed at reoperation. Such complications may be more often expected in a B type than in an A type operation. In the latter, detachment of the columella from the stapes head might be expected. Another mechanical cause of postoperative hearing loss, detected by tomography in one case, is penetration of the columella through the stapedial footplate (Fig. 7). Defective postoperative aeration of the middle ear is another cause of hearing impairment discernible tomographically.
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444
a
b
c
Fig. 6. Dislocation of a B-columella causing postoperative hearing loss. a) A.p. projection. High position of the columella in the oval window. b) Halfaxial projection. Dislocated columella tip at the footplate and the intimate relationship of the columella with the tympanic part of the facial canal. c) Lateral projection, tomogram at the level of the oval window.
Discussion
Preoperative middle ear tomography is extensively discussed in the literature. The positioning is guided by the clinical demands for information and is dependent upon the results of the previous clinical examination. There is always a request for detailed information about the ossicular chain, which is best demonstrated in the halfaxial, axial-pyramidal and sometimes in Stenvers' projection; but the true lateral projection must always be applied in preoperative tomography. Many authors consider that for a preoperative analysis, the a.p. and the lateral projections give sufficient information (LANGFELDT 1960,1963, BRUNNER 1964, FREY 1965, 1967, VALVASSORI 1967, WRIGHT et coil. 1969, HULSE et coil. 1972, JENSEN 1973). The halfaxial projection (DANIC et coli. 1965, VIGNAUD et coil. 1965), however, is to be preferred together with the true lateral projection in the appraisal of the long process of the incus and the incudo-stapedial joint. All these projections combined give essential information about the presence of the stapes and the dimension of the oval window together with the tympanic part of the facial canal. Further, the dimensions and the aeration of the tympanum,
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MULTIDIRECTIONAL TOMOGRAPHY IN RECONSTRUCTIVE MIDDLE EAR SURGERY
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Fig. 7. Penetration of the B columella through the stapedial footplate, causing a postoperative secondary hearing loss of the purely conductive type. a) A.p. projection. The situation is not fully demonstrable. b) Halfaxial projection, The tip of the columella is seen to penetrate through the boundaries of the oval window into the vestibule. Inclination of the boomerang-shaped columella medially and downwards towards the hypotympanic space.
a
b
the attic and the mastoid and the peri-labyrinthine cells can be appraised. The other parts of the facial canal as well as the appearance of the external acoustic meatus and the protympanic space might also be examined. Information concerning the existence of gaps in the tegmen and the posterior wall of the mastoid cavity, as well as of defects of the facial canal and otic capsule, are necessary in order not to vulverate structures deprived of their osseous protection in the procedure of deepithelializing the cavity and the middle ear before reconstruction. Defects in the bony wall may be detected down to dimensions of I mm and less, provided that they are located at a favourable angle to the tomographic plane. Small tegmental defects may remain undetected but can be regarded as unessential. The jugular fossa and the carotid canal in some cases have a very thin bony wall or might even lack an osseous wall against the tympanum. Otosclerotic changes in the oval window or in its direct neighbourhood can be recognized preoperatively. In cases of middle ear malformation the outline of the facial canal is of cardinal importance. In these respects clinical examinations give no information and even with an excellent technique such conditions cannot be demonstrated adequately by conventional radiography. Minor defects are often not observed in a single tomographic projection, however, and the use of at least two projections is therefore needed. Before reconstruction in cases previously operated upon (radical mastoidectomy)
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L.
EKVALL
(Fig. 1 d, e, f, g) the temporal bone is examined for information of possible residual cells and of the osseous continuity of the tegmen.
Postoperative tomography in columella operations with bone grafts has not been discussed in the literature since the report of LANGFELDT. The halfaxial view combined with the true lateral may be sufficient for the information required, in some cases complemented with the axial-pyramidal or the axial projection; the latter causes discomfort to the patient, however. In an A or a B type reconstruction, the halfaxial projection is preferred to the a.p. because of the good discernment of the topographic relationship of the transplant to its environment. In successful reconstruction, attention is paid to the long-term appearance of the transplant. Since small cavities in ossicles are discernible in tomograms (SANDSTROM & WILBRAND 1971), it may be expected that long-term changes in the osseous transplant can be detected. A great risk of resorption or fixation of the cortical bone columella has been reported (STEINBACH 1972, PULEC & SHEEHY 1973) but this does not correspond to the experience of KLEY & DRAF (1965) or EKVALL (1973). Postoperative hearing impairment or unattained hearing improvement without clinically evident cause may be explained by tomography. A secondary hearing loss may be due to malposition of the B type columella tip on the stapedial footplate. Undue incliniation of the graft, contact of the graft with environmental structures, or penetration of the columella through the footplate may comprise other mechanical causes. Also minute penetrations may be disclosed when the tomographic plane is at a right angle to the plane of the oval window and the footplate. Viewing conditions are of special importance in evaluation of the tomograms as we are concerned here with visual perception of fine structural details, the image contrast of which lies at a low level of the characteristic curve. Any dazzling effect should be avoided.
SUMMARY The tomographic demonstration of essential structural details before reconstructive middle ear surgery with osseous auto- and homografts is described, and the preoperative information requirements are briefly discussed. The tomographic appearance of the different types of reconstruction is presented. The halfaxial and true lateral projections are to be preferred, if necessary complemented by the axial-pyramidal projection. Tomography may disclose obvious morphologic causes of absence of postoperative hearing improvement or secondary hearing impairment.
ZUSAMMENFASSUNG Die tomographische Darstellung wichtiger Detailstrukturen vor einer rekonstruktiven Operation des Mittelohresmit knochernen Auto- und Homotransplantaten wird beschrieben.
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MULTIDIRECTIONAL TOMOGRAPHY IN RECONSTRUCTIVE MIDDLE EAR SURGERY
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Gleichzeitig wird die Frage des praoperativen Informationsbediirfnisses erortert, Das tomographische Erscheinungsbild der verschiedenen Rekonstruktionstypen wird besprochen. Die semiaxiale und laterale Projektion sollten vorgezogen und wenn notig mit der pyramidaxialen Einstellung vervollstandigt werden. Mit der Tomographie konnen wahrscheinlich vorliegende morphologische Ursachen einer postoperativ nicht eingetretenen Gehorverbesserung oder eine sekundaren Gehorverschlechterung geklart werden.
RESUME Les auteurs decrivent la mise en evidence tomographique de details structuraux essentiels avant la chirurgie reconstructrice de l'oreiIle moyenne par des auto- et des hornogreffes osseuses, et ils examinent brievement quelles sont les informations preoperatoires necessaires, lIs presentent les aspects tomographiques des differents types de reconstruction. II faut preferer les incidences semi-axiales et Ie prom strict qui sont completes si necessaire par l'incidence axiale de la pyramide. La tomographie peut decouvrir des causes morphologiques evidentes qui expliquent I'absence d'arnelioration post-operatoire de l'audition ou une diminution secondaire de l'acuite auditive.
REFERENCES AGAZZI C., COVA P. L. e SENALDI M.: Serneiotica stratigrafica dell' osso temporale. (In Italian.) Relazione al XVI raduno del gruppo Alta Italia della Soc. Ital. Otolaringologica, Milano 1958. ANDRE P., PIALOUX P., PONSET E., DULAC G.-L. et FRANCOIS J.: La tomographie en otorhino-laryngologie. Librairie Arnette, Paris 1968. BRUNNER S.: Radiological examination of temporal bone in infants and children. Radiology 82 (1964), 401. - PETERSEN 0. and STOKSTED P.: Tomography of the auditory ossicles, Acta radial. 56 (1961),20. DANIC J., VIGNAUD J., SUDAKA J. et LICHTENBERG R.: Visibilite radiographique de l'etrier et de la Ienetre ovale. Interet dans l'otospongiose. Ann. Oto-Iaryng. (Paris) 82 (1965), 681. DULAC G.-L.: Incidences analytiques dans la tomographie des osselets de l'oreille moyenne. J. Radiol. Electrol. 42 (1961), 85. EKVALL L.: Total middle ear reconstruction. Acta Oto-laryng, (Stockh.) 75 (1973), 279. FREY K. W.: Die Tomographie zur Diagnostik der Gehorknochelchen, Rontgen-Bl, 12 (1964), 527. - Die Tomographie zur Diagnostik der kleinen Ohrmissbildungen, Missbildungen der Gehorknochelchen bei offenem Gehorgang und vorhandenem Trommelfell. Rontgen-Bl, 18 (1965), 346. - Die Tomographie bei Luxationen und Frakturen der Gehorknochelchen. Z. Laryng Rhinol. 46 (1967), 765. HALL A. and RYTZNER c.: Stapedectomy and autotransplantation of ossicles. Acta otolaryng. (Stockh.) 47 (1957), 318. - - Malleus-stapes transposition. Pract. oto-rhino-Iaryng. (Basel) 21 (1959), 316. HULSE R., REISNER K. und GOSEPATH J.: Experimentelle Untersuchung zur tomographischen Darstellbarkeit der Labyrinthfenster im Rontgenschichtbild. Fortschr. Rontgenstr. 117 (1972),179.
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JENSEN J. and ROVSING H.: Fundamentals of ear tomography. Charles C. Thomas Publisher Springfield, Illinois, 1971. - and THOMSEN J.: Dislocation of the incus. The reliability of tomography. Arch. Ohr.-, Nas.- u. Kehlk.-Heilk. 204 (1973), 143. KLEY W. und DRAF W.: Histologische Untersuchungen tiber autotransplantierte Gehorknochelchen und Knochenstiickchen im Mittelohr beim Menschen. Acta oto-laryng. (Stockh.) 59 (1965), 593. LANGFELDT B.: Tomography in the middle ear in columella operations. Acta radiol. 53 (1960), 129. - Tomography in the middle ear in sound-transmission disturbances. Acta radiol. Diagnosis 1 (1963), 133. MONDNICH K. und FREY K. W.: Das Rontgenschichtbild des Ohres. Georg Thieme, Stuttgart 1959. PORTMANN M. et GUILLEN G.: Radiodiagnostic en otologie. Masson & Cie, Paris 1967. PULEC J. L. and SHEEHY J. L.: Tympanoplasty: ossicular chain reconstruction. Laryngoscope (St. Louis) 83 (1973), 448. SANDSTROM B. and WILBRAND H. F.: Anatomic cause for intraossicular cavities in temporal bone tomography. Acta radiol. Diagnosis 11 (1971), 225. STEINBACH E.: Vergleichende Untersuchungen an Gehorknochelchen- und Knochentransplantaten beim Kaninchen und Menschen. Habilationsschrift, Tiibingen 1972. VALVASSORI G. E.: Laminagraphy of the ear. Amer. J. Roentgenol. 89 (1963),1155. - Otosclerosis: a new challenge to roentgenology. Amer. J. Roentgenol, 94 (1965), 566. - Tomography of the temporal bone. In: Surgery of the ear, p. 137. W. B. Saunders Company, Philadelphia and London 1967. VIGNAUD J., DANIC J., LICHTENBERG R. et SUDAKA J.: Nouvelles recherches en radiootologie. I. Radiographie de l'etrier, II. Aspect tomographique de la Ienetre ovale dans l'otospongiose. J. Radiol. Electrol. 46 (1965), 129. WRIGHT W., TAYLOR C. E. and BIZAL J. A.: Tomography and the vulnerable incus. Ann. Oto-laryng, 78 (1969), 263,
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MULTIDIRECTIONAL TOMOGRAPHY IN RECONSTRUCTIVE MIDDLE EAR SURGERY H. F.
WILBRAND
and L.
EKVALL
The planning and prognosis of reconstructive surgery of the middle ear require detailed information about the functional and anatomic status of the tympanic cavity and mastoid cells. This is also of particular importance in the occasional occurrence of secondary postoperative hearing impairment. Clinical and audiologic data extended by a detailed roentgenographic evaluation afford the best possibility of arriving at a reliable diagnosis. Tomography has proved its usefulness in the demonstration ofthe ossicles (BRUNNER et coll. 1961, DULAC 1961, FREY 1964, WRIGHT et colI. 1969, SANDSTROM & WILBRAND 1971, JENSEN et coll. 1973). Conventional roentgenography of the temporal bone, even with a variety of special positioning, is unable to provide similar information. The tomographic appearance of various pathologic conditions which give reason for surgical reconstruction of the ossicular chain has been described extensively in otoradiologic literature (AGAZZI et coll. 1958, MUNDNICH & FREY 1959, VALVASSORI 1963, 1965, 1967 PORTMANN & GUILLEN 1967, ANDRE et coll, 1968, JENSEN & ROVSING 1971). LANGFELDT (1960, 1963) reported on tomography of the middle ear in columella operations (HALL & RYTZNER 1957, 1959). Submitted for publication 11 January 1974.
436
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MULTIDIRECTIONAL TOMOGRAPHY IN RECONSTRUCTIVE MIDDLE EAR SURGERY 437 The present investigation deals with the use of pre- and postoperative tomography in reconstructive surgery of the ossicular chain. In middle ear surgery the intention is usually to reconstruct the sound transmitting mechanism directly after cleaning measures have been undertaken. If this is not feasible, it may be done in a second stage operation. Preservation or reconstruction of the bony external acoustic meatus is essential for the anatomic and functional result. In cases with a previous radical mastoidectomy the bony meatus can be reconstructed with cortical bone autograft. The operation cavity in the present series of operations was usually obliterated with bone chips and muscle tissue. There are two fundamental types of ossicular reconstruction with auto- or homotransplants, based on the primary defect (Fig. 1): (1) In the first type of procedure (the A type), the stapes is intact. The lesion is often located to the long process of the incus (Fig. I a). The gap between the stapes and the malleus or the drum can be bridged with the body of the incus-incus transposition (Fig. 1 b)-or by using a boot-shaped transplant prepared from an incudal auto- or homograft or from cortical bone (Fig. 1 c). (2) In the second type of procedure (the B type), only the stapedial footplate remains (Fig. 1 d), and the columella (cortical bone) acquires a boomerang-like shape with its long, gracile wing resting on the footplate and its wider shaft attached to the reconstructed tympanic membrane-myringoplasty (Fig. 1 e). This type is often combined with extensive reconstruction of parts of the osseous external meatus after previous radical mastoidectomy (Fig. 1 d, e, f, g). The present investigation is limited to the tomographic appearances of reconstructed middle ears with osseous transplants. The intention is to elucidate the possibilities of tomography to provide information in pre- and postoperative examination of patients with middle ear diseases. Material and Methods
Experience was gained from 65 selected, operated cases from the period 1967 to 1970. The patients were primarily examined by conventional roentgenography and also underwent preoperative and postoperative tomography with the Poly tome in some of the five routine projections, the true lateral, antero-posterior, halfaxial, axial-pyramidal and Stenvers' projections (MUNDNICH & FREY 1959, JENSEN & ROVSING 1971). Exposure data: 55-75 kV, 50 rnA, 11.6 s (double hypocycloid movement), 0.3 mm focal spot, magnification factor 1.3. The radiographic system consisted of universal film (processed in a 3.5 min Pakorol machine) and high definition screens (Siemens Rubin). The tomograms (4- or 6-seriograms, each tomogram 5 cm in diameter) were evaluated in an ordinary viewing box with a mask with a density of 1.5-1.8. The tomograms were harmonized by means of an electromechanical dodger (courtesy Rikets Allmanna Kartverk; Geographical Survey Office of Sweden, Stockholm).
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Abbreviations used in the figures (they correspond to those applied by K. W. Frey, J. Jensen, H. Rovsing and K. Terrahe) 1 2 2a 2b 2c 3a 3b 3c 5 VII VIla VII b VII c VIId VII e VIIf 8
8a 9
9a 9b 10 11 11a
external acoustic meatus tympanic cavity epitympanic recess mesotympanic cavity hypo tympanic recess malleus incus stapes mastoid process facial canal facial canal, labyrinthine part facial canal, 1st bend facial canal, tympanic part facial canal, 'lateral knee', 2nd bend facial canal, mastoid part stylomastoid foramen cochlea cochlea, basal turn vestibulum oval window round window lateral semicircular canal superior semicircular canal superior semicircular canal, ampullary region
12 12 a
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The indication for postoperative tomography after reconstructive procedures for chronic otitis was to establish the appearance and position of the osseous auto- or homotransplant or in some cases to find an explanation for failure of hearing improvement or a secondary hearing reduction.
Roentgenography Conventional roentgenography. The evaluation of the temporal bone on these films is restricted to an appraisal of the air cells, the range of pneumatization (distance between the sigmoid sinus and the posterior wall of the external auditory meatus and the peri-labyrinthine pneumatization) as well as changes of an inflammatory, cholesteatomatous, or other nature. Conventional roentgenography allows a survey of the middle ear and inner ear structures, but finer details such as alterations for example in the ossicular chain, the optic capsule and the facial canal or the boundaries of the jugular fossa cannot be satisfactorily demonstrated. Such structural details may be demonstrated however, by multidirectional tomography (hypocloid, spiral).
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Preoperative tomography yields essential information in: (1) Chronic otitis. The condition of the mastoid cells and their septa, the extent of destruction and of the air content of the cells and of the tympanic space can be evaluated in detail. The extent of destruction of the individual ossicles can be established. In cholesteatoma destruction of the bony septa in the epitympanum and
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aditus ad antrum can be revealed. In extensive cholesteatoma tegmental erosions may be detected, as well as destructions in the otic capsule (labyrinthine fistula). Preoperative knowledge of spontaneous or pathologic defects of the facial canal increases the safety of the surgical procedure. (2) Trauma. It is essential that the dislocations in the ossicular chain (luxation) and the detailed course of fractures be outlined. In traumatic facial palsies the appearance of the facial canal must be established. (3) Malformations of the middle ear. The extent and configuration of the air spaces as well as of the osseous atresia of the external acoustic meatus and the shape of the ossicular chain need to be clearly revealed. Fig. 3. A-reconstruction (boot-shaped columella). a) A.p, projection shows a bevelled section of the boot-shaped A columella and its relationship to the stapes and the tympanic part of the facial canal. b) Halfaxial projection. The relationship of the boot-shaped columella to surrounding structures is better revealed by this projection than by a.p. The Aerated tympanic space in a) and b). c) Axial-pyramidal projection shows the inclination and relationship of the columella to the structures near the oval window. d) Lateral projection. The tomographic plane is at the junction of the boot-shaped columella to the stapedial head. Relationship to the facial canal and the pyramidal eminence.
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Fig. 4. Boomerang-shaped B columella inserted in the middle ear in order to restore hearing. a) Halfaxial projection. The boomerang-columella is seen resting with its tip on the stapedial foot plate and its free position in the aerated tympanic space. Small defect of the tympanic part of the facial canal. b) Axial-pyramidal projection. c) Lateral projection. The inclination of the B columella is seen to be free from contact with its bony surrounding (the tympanic part of the facial canal and the pyramidal eminence of the posterior tympanic wall).
In malformation as well as in acquired pathologic conditions information concerning the oval and round windows is important in planning of the operation. The facial canal has to be outlined since its course may be abnormal. Postoperative tomography. The main interest is concentrated on the long-term appearance and position of the bony transplants in the middle ear. (1) In an A type reconstruction using the incus transposition method the ossicular situation is demonstrated in the a.p., halfaxial and lateral projections (Fig. 2). In the present version a boot-like A-transplant (Fig. I c) is well demonstrated in the a.p. view and even more favourably in the halfaxial or axial-pyramidal as we as in the true lateral projection (Fig. 3). (2) The boomerang-shaped columella (8 type) (Fig. I e) will be used after previous radical mastoidectomy in cases in which the external meatus often also has to be reconstructed (Fig. I d, e, f, g). The halfaxial and true lateral projections usually give the best information but may be complemented by the axial-pyramidal and a.p. projections for judging the site of the columella, the tip of which is located on the
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MUJ,-TIDIRECTIONAL TOMOGRAPHY IN RECONSTRUCTIVE MIDDLE EAR SURGERY
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Fig. 5. Boomerang-shaped columella of cortical bone inserted in a previously radically operated ear. a) In the halfaxial projection the gracile tip of the columella is placed in the center of the stapedial footplate. b) Lateral projection; (tomographic plane lateral to the tympanic space) bony reconstruction of the upper and posterior part of the external meatus.
footplate of the stapes (Figs 4, 5). The appearance of the external meatus reconstructed by bone transplants is best demonstrated in the true lateral projection. (3) In cases of unattained hearing improvement or recurrence of hearing impairment the same projections will be used. By tomography, dislocation or abnormal inclination of the columella may be detected. A case of secondary hearing impairment is illustrated in Fig. 6. Tomography revealed that the columella was abnormally located in relation to the boundaries of the oval window, and to the tympanic part of the facial canal, thus possibly fixed to this structure. This conclusion was confirmed at reoperation. Such complications may be more often expected in a B type than in an A type operation. In the latter, detachment of the columella from the stapes head might be expected. Another mechanical cause of postoperative hearing loss, detected by tomography in one case, is penetration of the columella through the stapedial footplate (Fig. 7). Defective postoperative aeration of the middle ear is another cause of hearing impairment discernible tomographically.
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Fig. 6. Dislocation of a B-columella causing postoperative hearing loss. a) A.p. projection. High position of the columella in the oval window. b) Halfaxial projection. Dislocated columella tip at the footplate and the intimate relationship of the columella with the tympanic part of the facial canal. c) Lateral projection, tomogram at the level of the oval window.
Discussion
Preoperative middle ear tomography is extensively discussed in the literature. The positioning is guided by the clinical demands for information and is dependent upon the results of the previous clinical examination. There is always a request for detailed information about the ossicular chain, which is best demonstrated in the halfaxial, axial-pyramidal and sometimes in Stenvers' projection; but the true lateral projection must always be applied in preoperative tomography. Many authors consider that for a preoperative analysis, the a.p. and the lateral projections give sufficient information (LANGFELDT 1960,1963, BRUNNER 1964, FREY 1965, 1967, VALVASSORI 1967, WRIGHT et coil. 1969, HULSE et coil. 1972, JENSEN 1973). The halfaxial projection (DANIC et coli. 1965, VIGNAUD et coil. 1965), however, is to be preferred together with the true lateral projection in the appraisal of the long process of the incus and the incudo-stapedial joint. All these projections combined give essential information about the presence of the stapes and the dimension of the oval window together with the tympanic part of the facial canal. Further, the dimensions and the aeration of the tympanum,
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Fig. 7. Penetration of the B columella through the stapedial footplate, causing a postoperative secondary hearing loss of the purely conductive type. a) A.p. projection. The situation is not fully demonstrable. b) Halfaxial projection, The tip of the columella is seen to penetrate through the boundaries of the oval window into the vestibule. Inclination of the boomerang-shaped columella medially and downwards towards the hypotympanic space.
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the attic and the mastoid and the peri-labyrinthine cells can be appraised. The other parts of the facial canal as well as the appearance of the external acoustic meatus and the protympanic space might also be examined. Information concerning the existence of gaps in the tegmen and the posterior wall of the mastoid cavity, as well as of defects of the facial canal and otic capsule, are necessary in order not to vulverate structures deprived of their osseous protection in the procedure of deepithelializing the cavity and the middle ear before reconstruction. Defects in the bony wall may be detected down to dimensions of I mm and less, provided that they are located at a favourable angle to the tomographic plane. Small tegmental defects may remain undetected but can be regarded as unessential. The jugular fossa and the carotid canal in some cases have a very thin bony wall or might even lack an osseous wall against the tympanum. Otosclerotic changes in the oval window or in its direct neighbourhood can be recognized preoperatively. In cases of middle ear malformation the outline of the facial canal is of cardinal importance. In these respects clinical examinations give no information and even with an excellent technique such conditions cannot be demonstrated adequately by conventional radiography. Minor defects are often not observed in a single tomographic projection, however, and the use of at least two projections is therefore needed. Before reconstruction in cases previously operated upon (radical mastoidectomy)
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(Fig. 1 d, e, f, g) the temporal bone is examined for information of possible residual cells and of the osseous continuity of the tegmen.
Postoperative tomography in columella operations with bone grafts has not been discussed in the literature since the report of LANGFELDT. The halfaxial view combined with the true lateral may be sufficient for the information required, in some cases complemented with the axial-pyramidal or the axial projection; the latter causes discomfort to the patient, however. In an A or a B type reconstruction, the halfaxial projection is preferred to the a.p. because of the good discernment of the topographic relationship of the transplant to its environment. In successful reconstruction, attention is paid to the long-term appearance of the transplant. Since small cavities in ossicles are discernible in tomograms (SANDSTROM & WILBRAND 1971), it may be expected that long-term changes in the osseous transplant can be detected. A great risk of resorption or fixation of the cortical bone columella has been reported (STEINBACH 1972, PULEC & SHEEHY 1973) but this does not correspond to the experience of KLEY & DRAF (1965) or EKVALL (1973). Postoperative hearing impairment or unattained hearing improvement without clinically evident cause may be explained by tomography. A secondary hearing loss may be due to malposition of the B type columella tip on the stapedial footplate. Undue incliniation of the graft, contact of the graft with environmental structures, or penetration of the columella through the footplate may comprise other mechanical causes. Also minute penetrations may be disclosed when the tomographic plane is at a right angle to the plane of the oval window and the footplate. Viewing conditions are of special importance in evaluation of the tomograms as we are concerned here with visual perception of fine structural details, the image contrast of which lies at a low level of the characteristic curve. Any dazzling effect should be avoided.
SUMMARY The tomographic demonstration of essential structural details before reconstructive middle ear surgery with osseous auto- and homografts is described, and the preoperative information requirements are briefly discussed. The tomographic appearance of the different types of reconstruction is presented. The halfaxial and true lateral projections are to be preferred, if necessary complemented by the axial-pyramidal projection. Tomography may disclose obvious morphologic causes of absence of postoperative hearing improvement or secondary hearing impairment.
ZUSAMMENFASSUNG Die tomographische Darstellung wichtiger Detailstrukturen vor einer rekonstruktiven Operation des Mittelohresmit knochernen Auto- und Homotransplantaten wird beschrieben.
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Gleichzeitig wird die Frage des praoperativen Informationsbediirfnisses erortert, Das tomographische Erscheinungsbild der verschiedenen Rekonstruktionstypen wird besprochen. Die semiaxiale und laterale Projektion sollten vorgezogen und wenn notig mit der pyramidaxialen Einstellung vervollstandigt werden. Mit der Tomographie konnen wahrscheinlich vorliegende morphologische Ursachen einer postoperativ nicht eingetretenen Gehorverbesserung oder eine sekundaren Gehorverschlechterung geklart werden.
RESUME Les auteurs decrivent la mise en evidence tomographique de details structuraux essentiels avant la chirurgie reconstructrice de l'oreiIle moyenne par des auto- et des hornogreffes osseuses, et ils examinent brievement quelles sont les informations preoperatoires necessaires, lIs presentent les aspects tomographiques des differents types de reconstruction. II faut preferer les incidences semi-axiales et Ie prom strict qui sont completes si necessaire par l'incidence axiale de la pyramide. La tomographie peut decouvrir des causes morphologiques evidentes qui expliquent I'absence d'arnelioration post-operatoire de l'audition ou une diminution secondaire de l'acuite auditive.
REFERENCES AGAZZI C., COVA P. L. e SENALDI M.: Serneiotica stratigrafica dell' osso temporale. (In Italian.) Relazione al XVI raduno del gruppo Alta Italia della Soc. Ital. Otolaringologica, Milano 1958. ANDRE P., PIALOUX P., PONSET E., DULAC G.-L. et FRANCOIS J.: La tomographie en otorhino-laryngologie. Librairie Arnette, Paris 1968. BRUNNER S.: Radiological examination of temporal bone in infants and children. Radiology 82 (1964), 401. - PETERSEN 0. and STOKSTED P.: Tomography of the auditory ossicles, Acta radial. 56 (1961),20. DANIC J., VIGNAUD J., SUDAKA J. et LICHTENBERG R.: Visibilite radiographique de l'etrier et de la Ienetre ovale. Interet dans l'otospongiose. Ann. Oto-Iaryng. (Paris) 82 (1965), 681. DULAC G.-L.: Incidences analytiques dans la tomographie des osselets de l'oreille moyenne. J. Radiol. Electrol. 42 (1961), 85. EKVALL L.: Total middle ear reconstruction. Acta Oto-laryng, (Stockh.) 75 (1973), 279. FREY K. W.: Die Tomographie zur Diagnostik der Gehorknochelchen, Rontgen-Bl, 12 (1964), 527. - Die Tomographie zur Diagnostik der kleinen Ohrmissbildungen, Missbildungen der Gehorknochelchen bei offenem Gehorgang und vorhandenem Trommelfell. Rontgen-Bl, 18 (1965), 346. - Die Tomographie bei Luxationen und Frakturen der Gehorknochelchen. Z. Laryng Rhinol. 46 (1967), 765. HALL A. and RYTZNER c.: Stapedectomy and autotransplantation of ossicles. Acta otolaryng. (Stockh.) 47 (1957), 318. - - Malleus-stapes transposition. Pract. oto-rhino-Iaryng. (Basel) 21 (1959), 316. HULSE R., REISNER K. und GOSEPATH J.: Experimentelle Untersuchung zur tomographischen Darstellbarkeit der Labyrinthfenster im Rontgenschichtbild. Fortschr. Rontgenstr. 117 (1972),179.
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JENSEN J. and ROVSING H.: Fundamentals of ear tomography. Charles C. Thomas Publisher Springfield, Illinois, 1971. - and THOMSEN J.: Dislocation of the incus. The reliability of tomography. Arch. Ohr.-, Nas.- u. Kehlk.-Heilk. 204 (1973), 143. KLEY W. und DRAF W.: Histologische Untersuchungen tiber autotransplantierte Gehorknochelchen und Knochenstiickchen im Mittelohr beim Menschen. Acta oto-laryng. (Stockh.) 59 (1965), 593. LANGFELDT B.: Tomography in the middle ear in columella operations. Acta radiol. 53 (1960), 129. - Tomography in the middle ear in sound-transmission disturbances. Acta radiol. Diagnosis 1 (1963), 133. MONDNICH K. und FREY K. W.: Das Rontgenschichtbild des Ohres. Georg Thieme, Stuttgart 1959. PORTMANN M. et GUILLEN G.: Radiodiagnostic en otologie. Masson & Cie, Paris 1967. PULEC J. L. and SHEEHY J. L.: Tympanoplasty: ossicular chain reconstruction. Laryngoscope (St. Louis) 83 (1973), 448. SANDSTROM B. and WILBRAND H. F.: Anatomic cause for intraossicular cavities in temporal bone tomography. Acta radiol. Diagnosis 11 (1971), 225. STEINBACH E.: Vergleichende Untersuchungen an Gehorknochelchen- und Knochentransplantaten beim Kaninchen und Menschen. Habilationsschrift, Tiibingen 1972. VALVASSORI G. E.: Laminagraphy of the ear. Amer. J. Roentgenol. 89 (1963),1155. - Otosclerosis: a new challenge to roentgenology. Amer. J. Roentgenol, 94 (1965), 566. - Tomography of the temporal bone. In: Surgery of the ear, p. 137. W. B. Saunders Company, Philadelphia and London 1967. VIGNAUD J., DANIC J., LICHTENBERG R. et SUDAKA J.: Nouvelles recherches en radiootologie. I. Radiographie de l'etrier, II. Aspect tomographique de la Ienetre ovale dans l'otospongiose. J. Radiol. Electrol. 46 (1965), 129. WRIGHT W., TAYLOR C. E. and BIZAL J. A.: Tomography and the vulnerable incus. Ann. Oto-laryng, 78 (1969), 263,
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