Acta Oto-Laryngologica
ISSN: 0001-6489 (Print) 1651-2251 (Online) Journal homepage: http://www.tandfonline.com/loi/ioto20
Landmark Structures to Approach the Internal Auditory Canal: A Dimensional Study Related to the Middle Cranial Fossa Approach Tatsuo Matsunaga, Makoto Igarashi & Jin Kanzaki To cite this article: Tatsuo Matsunaga, Makoto Igarashi & Jin Kanzaki (1991) Landmark Structures to Approach the Internal Auditory Canal: A Dimensional Study Related to the Middle Cranial Fossa Approach, Acta Oto-Laryngologica, 111:sup487, 48-53 To link to this article: http://dx.doi.org/10.3109/00016489109130445
Published online: 08 Jul 2009.
Submit your article to this journal
Article views: 12
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ioto20 Download by: [New York University]
Date: 13 February 2016, At: 05:58
Acta Otolaryngol (Stockh) 1991; Suppl. 487:48-53
Landmark Structures to Approach the Internal Auditory Canal: A Dimensional Study Related to the Middle Cranial Fossa Approach TATSUO MATSUNAGA,' MAKOTO IGARASH12 and JIN KANZAKI' From the 'Department of Otolaryngology, School of Medicine, Keio University, and the 'University Research Center, Nihon University, Tokyo, Japan
Downloaded by [New York University] at 05:58 13 February 2016
Matsunaga T, Igarashi M, Kanzaki J. Landmark structures to approach the internal auditory canal: A dimensional study related to the middle cranial fossa approach. Acta Otolaryngol (Stockh) 1991; Suppl 487: 48-53. For the purpose of assisting the accurate topological identification of the internal auditory canal (IAC) during surgery through the middle cranial fossa, we conducted a dimensional study around the IAC using histologically prepared temporal bones. The anterior margin of the porus acousticus, the posterior margin of the porus acousticus, and the center of the fundus were located 19.7 mm, 16.8 mm, and 8.2 mm from the center of the malleus head, respectively. The angles formed by lines connecting those three points of the IAC and the ossicles were also measured. These values could be of help to identify the accurate localization of the IAC using the ossicles as surgical landmarks, when available. The common crus, i.e. a critical inner ear structure for hearing preservation, was also studied. The distance from the medial side of the common crus to the posterior wall of the IAC was relatively constant. However, the distance from the medial side of the common crus to the surface of the posterior cranial fossa was variable. Measurements in the vertical sections showed that the thickness of the superior bony wall of the IAC was similar to that of the cochlear otic capsule which should be kept unexposed for hearing preservation. Key words: surgical anatomy, acoustic neurinoma, ossicles.
INTRODUCTION Identifying the correct location of the IAC is the most critical point of the middle cranial fossa surgery toward successful acoustic neurinoma removel. Portmann (1) summarized the following four ways of localizing the IAC through the middle cranial fossa: 1) To expose the superficial petrosal nerve proximally until it gets into the IAC; 2) To expose the axis of the IAC which is 60" to the blue line of the superior semicircular canal (3); 3) To expose the posterior wall of the IAC which locates lOmm anterior to the center of the same blue line (4);and 4)To expose the 28 mm or more medial area from the outer surface of the squamous temporal bone on the biauricular line (5). Method 1) has the risk of inadvertant incursion into the facial nerve. The landmark of method 2) and 3) is the blue line of the superior semicircular canal, which is often difficult to find. In our hospital the biauricular line is routinely used as the landmark to localize the IAC in cases with useful hearing. In cases without useful hearing, the ossicles are always used as the other landmark to localize the IAC without any damage to the facial nerve. Using CT target imaging, Tsuchihashi et al. ( 6 ) recently reported a dimensional study on the topographic relationships between the biauricular line and the IAC. In the present study, we measured various distances and angles between the ossicles and the IAC. In addition, some other measurements between the IAC and the inner ear were conducted for the purpose of not exposing the membranous labyrinth during hearing preservation surgery.
Landmark structures to approach the internal auditory canal 49 MATERIAL AND METHODS The material was selected from the temporal bone collection of Baylor College of Medicine, Department of Otorhinolaryngology. Temporal bones from patients with post-operative ear, metastatic malignant disease, anomaly, bone disease, severe inflammation, and acoustic neurinoma were excluded. Temporal bones from children (under 15 years old) were also excluded. Selected horizontal or vertical sections (stained in hematoxylin-eosin) were projected onto trace papers with a calibrated magnification ( x 13.5). Manual drawings were made and the distances and angles were measured.
Downloaded by [New York University] at 05:58 13 February 2016
RESULTS AND DISCUSSION 1) The distances and angles between the ossicles and the IAC (Fig. 1) The selection criteria of the sections were as follows; a) Horizontal sections containing the incudo-malleolar articulation and the short process of the incus; b) Horizontal sections in which the ossicles are fixed with ligaments and mucous membranes in proper expected positions; c) Horizontal sections which contain the widest horizontal dimension of the porus acousticus. Thirty-three out of 368 ears examined had sections that met these criteria. The distances were measured from the center of the malleus head (0)to the anterior margin of the porus acousticus (A), posterior margin of the porus acousticus (B) and the center of the fundus (C). Then angles were measured in the following way. Firstly, the lines X and Y were drawn. The line X is the pivoting axis of the malleus-incus. The line Y makes a right angle against the line X at the point 0. Secondly, the angles LA, LB, and L C were measured. The angles LA, L B, and L C are the angles which are formed between the lines OA, OB or OC and the line Y, respectively. The means and the standard deviations of OA, OB, OC, LA, L B, and LC are presented in the Table I. Basically, the ossicles should be used as the landmark in cases without useful hearing. By using this landmark in combination with the biauricular line, accurate identification of the IAC is possible.
2 ) The distance between the common crus and the IAC (Fig.1) The selection criteria of the sections were criterion 1.c). and the horizontal sections containing the medial side of the common crus. Fifteen out of 84 ears examined had sections
Fig. 1. The distances and an-
gles between the ossicles the IAC. The distance tween the common crus the IAC. The distance tween the common crus the pyramidal edge.
and beand beand
50
T. Matsunaga et al.
Table I. The distances and angles between the ossicles and the IAC No.
Mean
S.D.
From the center of the malleus head to the anterior margin of the porus acousticus
33
19.7 mm
2.1 mm
From the center of the malleus head to the posterior margin of the porus acousticus
33
16.8 mm
1.7 mm
From the center of the malleus head to the center of the fundus
33
8.2 mm
0.8 mm
LA:
Between OA and the line Y
33
23.8"
7.3"
L B:
Between OB and the line Y
33
4.9"
6.9'
L C:
Between OC and the line Y
33
7.8"
6.8"
OA:
OB:
Downloaded by [New York University] at 05:58 13 February 2016
oc:
that met these criteria. The distance ( L l ) was measured from the medial side of the common crus (D) to the posterior wall of the IAC. The mean and the standard deviation of L1 are presented in Table 11. For total removal of the tumor inside the IAC, the posterior wall of the IAC has to be drilled out. In this process, the medial side of the common crus is the most critical area for preservation of hearing. The extent of the drilling in the posterior area of the IAC must be within this distance (LI).
3 ) The distance between the common crus and the pyramidal edge (Fig. 1) The selection criteria and the number of the ears used for this measurement were the same as those of L1. The distance (L2) was measured from the point D to the surface of the posterior cranial fossa. The mean and the standard deviation of L2 are presented in Table 11. The standard deviation of L2 is twice as large as that of LI. The reason of this discrepancy is that the degree of pneumatization between the common crus and the pyramidal edge is highly variable in contrast to the inconsiderable pneumatization between the common crus and the IAC in most of the cases. In the cases of little pneumatization, the common crus and posterior semicircular canal sometimes locate very close to the posterior cranial fossa. Though drilling is not made from the pyramidal edge but from the posterior wall of the IAC in the middle cranial fossa approach, surgeons have to be careful when operating in this area in hearing preservation surgery. Table 11. The distance between the common crus and the IAC. The distance between the common crus and the pyramidal edge
L1:
L2:
No.
Mean
S.D.
From the medial side of the common crus to the posterior wall of the I A C
15
4.5mm
0.7 mm
From the medial side of the common crus to the surface of the posterior cranial fossa
15
3.4mm
1.4 mm
Landmark structures to approach the internal auditory canal
Downloaded by [New York University] at 05:58 13 February 2016
Fig. 2. The depth of the porus acousticus.
4) The depth of the porus acousticus f r o m the middle cranial fossa (Fig. 2) The selection criterion in the vertical sections (perpendicular to the long axis of the petrous bone) was to contain the widest vertical dimension of the porus acousticus. Nine out of 14 ears exaimined had sections that met this criterion. The distance (L3) was measured from the surface of the middle cranial fossa to the superior margin of the porus acousticus. The mean and the standard deviation of L3 are presented in Table 111. The superior wall of the porus acousticus has a variety of shapes so its standard deviation is large. The superior wall of the IAC is first removed at the medial part in hearing preservation surgery, then the exposure is extended toward the porus acousticus and the fundus. The vertical measurement was conducted to assist the exposure of the facial nerve in the IAC without any damage on it. 5 ) The depth of the IAC and the cochlea f r o m the middle cranial fossa (Fig. 3)
The selection criterion in the vertical sections (perpendicular to the long axis of the petrous bone) was that it contains the midmodiolar section of the cochlea. Ten out of 14 ears examined had sections that met this criterion. The following distances were measured near the fundus. L4 and L5 are the distances from the surface of the middle cranial fossa to the Table 111. The depth of the porus acousticus. The depth of the IAC and the cochlea at the fundus No. L3:
L4:
L5:
L6:
Mean
S.D.
From the surface of the middle cranial fossa to the superior margin of the porus acousticus
9
5.0 mm
1.6 mm
From the surface of the middle cranial fossa to the superior wall of the IAC near the fundus
9
2.9mm
0.8 mm
10
2.1 mm
0.6 mm
10
5.2 mm
0.7 mm
From the surface of the middle cranial fossa to the superior margin of the cochlear spiral The vertical diameter of the I A C
51
52
T. Matsunaga et al.
Downloaded by [New York University] at 05:58 13 February 2016
Fig. 3. The depth of the IAC and the cochlea at the fundus.
superior wall of the IAC and the superior margin of the cochlear spiral. L6 is the vertical diameter of the IAC; extension of L4. The means and the standard deviations of L4, L5 and L6 are presented in Table 111. Due to an artifact, a total of 9 ears could be used for the measurement of L4. It should be emphasized that both distances from the surface of the middle cranial fossa to the IAC and the cochlea were relatively short. Careful manipulation is necessary not to expose the cochlea near the fundus. 6) Correlation with the measurements reported in the past Although most of the dimensional studies of the IAC were focused on the diameter, length, and shape (7- 17), some studies carried useful information for surgery through middle cranial fossa (6, 18, 19). Our present study belongs to this latter group and adds data for achievement of more accurate identification of the IAC. As material for the measurement, dry or wet tomporal bones, histologically prepared temporal bones, X-ray films, and CT films were used. In the process of celloidin embedding histological preparations, which we used for the study, it was reported that bone shrinks by about 9%)(20). So the shrinkage rate must be taken into consideration. However, the merit of this method is that we had a clear outline of the ossicles, the IAC and the inner ear structures, and that enabled us to perform accurate measurements. ACKNOWLEDGEMENTS The authors are grateful to Dr. S. Ikeda for this help with the statistical analysis.
REFERENCES 1. Portman M. Sterkers JM, Charachon R, Chouard CH. Surgical approaches and technique. In: Portmann M, Sterkers JM, Charachon R, Chouard CH, eds. The internal auditory meatus. Edinburgh, London and New York: Churchill Livingstone, 1975: 99- 182. 2. House WF. Surgical exposure of the internal auditory canal and its contents through the middle cranial fossa. Laryngoscope 1961; 71: 1363-85. 3. Fisch U. Transtemporal surgery of the internal auditory canal. Reports of 92 cases, technique, indications and results. Adv Otorhinolaryngol 1970; 17: 203-40. 4. Cohadon F, Castel JP, Lemann P, Portmann M . Variations anatomiques et rapports intrapetreux du conduit auditif interne-applications a I’aboord otoneurochirurgigal. C R Assoc Anat 1968; 140. 5. Pialoux P, Freyss G , Nancy P, Saint-Macary M, Davine F. Contribution a I’anatomie stereotaxique du conduit auditif interne et de la premiere portion du facial. Ann Otolaryng 1972; 89: 141-2.
Downloaded by [New York University] at 05:58 13 February 2016
Landmark structures to approach the internal auditory canal 6. Tsuchihashi N, 0-uchi T, Ogawa K, Kunihiro T, Ogawa S, Inoue T, Kanzaki J. Dimensional measurements of internal auditory canal and middle ear structures by CT target imaging. Clin Otol Jpn 1989; 16: 38-42. 7. Ebenius B. The results of examination of the petrous bone in auditory nerve tumors. Acta Radio1 (Stockh) 1934; 15: 284-90. 8. Camp JD, Cilley EIL. The significance of asymmetry of the pori acoustic as an aid in diagnosis of eighth nerve tumors. Am J Roentogenol 1939; 41: 713-8. 9. Graf K. Geschwulste des Ohres und des Kleinhirnbrunkenwinkels. Stuttgart: Georg Thieme Verlag, 1952 238. 10. Valvassori GE, Pierce RH. The normal internal auditory canal. Am J Roentogenol 1964; 92: I232 -4 I . 11. Amjad AH, Scheer AA, Rosenthal J. Human internal auditory canal. Arch Otolaryngol 1969; 89: 709- 14. 12. Cordova M. Anatomie du conduit auditif interne. Rev Laryngol Otol Rhino1 (Bord) 1972; 93: 727-36. 13. Papangelou L. Study of the human auditory canal. Laryngoscope 1972; 82: 617-24. 14. Oliverse FP, Schuknecht HF. Width of the internal auditory canal. Ann Otol 1979; 88: 316-23. 15. Thomsen J, Reiter S, Borum P, Tos M. Tomography of the internal acoustic meatus. J Laryngol Otol 1981; 95: 1191-200. 16. 0-uchi T, Kanzaki J, Okada T. Dimensional measurements of inner ear structures by CT target imaging. Otologia Fukuoka 1982; 28: 959-68. 17. Nakamura M. Evaluation of temporal bone pneumatization on high resolution CT (HRCT). Measurements of the temporal bone in normal and otitis media group and their correlation to measurements of internal auditory meatus, vestibular or cochlear duct. J Otolaryngol Jpn 1988; 91: 1002-11. 18. Lang J. Anatomy of the brain stem and the lower cranial nerves, vessels and surrounding structures. Am J Otol 1985; Suppl 1-19. 19. Parisier SC The middle cranial fossa approach to the internal auditory canal. An anatomical study stressing critical distances between surgical landmarks. Laryngoscope 1977; 87: 1-20. 20. Igarashi M, 0-uchi T, Alford BR. Volumetric and dimensional measurements of vestibular structures in the squirrel monkey. Acta Otolaryngol (Stockh) 1981; 91: 437-44. Address for correspondence: Tatsuo Matsunaga, Department of Otolaryngology, School of Medicine, Keio University, Shinanomachi 35, Shinjuku-ku, Tokyo 160, Japan
53
ISSN: 0001-6489 (Print) 1651-2251 (Online) Journal homepage: http://www.tandfonline.com/loi/ioto20
Landmark Structures to Approach the Internal Auditory Canal: A Dimensional Study Related to the Middle Cranial Fossa Approach Tatsuo Matsunaga, Makoto Igarashi & Jin Kanzaki To cite this article: Tatsuo Matsunaga, Makoto Igarashi & Jin Kanzaki (1991) Landmark Structures to Approach the Internal Auditory Canal: A Dimensional Study Related to the Middle Cranial Fossa Approach, Acta Oto-Laryngologica, 111:sup487, 48-53 To link to this article: http://dx.doi.org/10.3109/00016489109130445
Published online: 08 Jul 2009.
Submit your article to this journal
Article views: 12
View related articles
Full Terms & Conditions of access and use can be found at http://www.tandfonline.com/action/journalInformation?journalCode=ioto20 Download by: [New York University]
Date: 13 February 2016, At: 05:58
Acta Otolaryngol (Stockh) 1991; Suppl. 487:48-53
Landmark Structures to Approach the Internal Auditory Canal: A Dimensional Study Related to the Middle Cranial Fossa Approach TATSUO MATSUNAGA,' MAKOTO IGARASH12 and JIN KANZAKI' From the 'Department of Otolaryngology, School of Medicine, Keio University, and the 'University Research Center, Nihon University, Tokyo, Japan
Downloaded by [New York University] at 05:58 13 February 2016
Matsunaga T, Igarashi M, Kanzaki J. Landmark structures to approach the internal auditory canal: A dimensional study related to the middle cranial fossa approach. Acta Otolaryngol (Stockh) 1991; Suppl 487: 48-53. For the purpose of assisting the accurate topological identification of the internal auditory canal (IAC) during surgery through the middle cranial fossa, we conducted a dimensional study around the IAC using histologically prepared temporal bones. The anterior margin of the porus acousticus, the posterior margin of the porus acousticus, and the center of the fundus were located 19.7 mm, 16.8 mm, and 8.2 mm from the center of the malleus head, respectively. The angles formed by lines connecting those three points of the IAC and the ossicles were also measured. These values could be of help to identify the accurate localization of the IAC using the ossicles as surgical landmarks, when available. The common crus, i.e. a critical inner ear structure for hearing preservation, was also studied. The distance from the medial side of the common crus to the posterior wall of the IAC was relatively constant. However, the distance from the medial side of the common crus to the surface of the posterior cranial fossa was variable. Measurements in the vertical sections showed that the thickness of the superior bony wall of the IAC was similar to that of the cochlear otic capsule which should be kept unexposed for hearing preservation. Key words: surgical anatomy, acoustic neurinoma, ossicles.
INTRODUCTION Identifying the correct location of the IAC is the most critical point of the middle cranial fossa surgery toward successful acoustic neurinoma removel. Portmann (1) summarized the following four ways of localizing the IAC through the middle cranial fossa: 1) To expose the superficial petrosal nerve proximally until it gets into the IAC; 2) To expose the axis of the IAC which is 60" to the blue line of the superior semicircular canal (3); 3) To expose the posterior wall of the IAC which locates lOmm anterior to the center of the same blue line (4);and 4)To expose the 28 mm or more medial area from the outer surface of the squamous temporal bone on the biauricular line (5). Method 1) has the risk of inadvertant incursion into the facial nerve. The landmark of method 2) and 3) is the blue line of the superior semicircular canal, which is often difficult to find. In our hospital the biauricular line is routinely used as the landmark to localize the IAC in cases with useful hearing. In cases without useful hearing, the ossicles are always used as the other landmark to localize the IAC without any damage to the facial nerve. Using CT target imaging, Tsuchihashi et al. ( 6 ) recently reported a dimensional study on the topographic relationships between the biauricular line and the IAC. In the present study, we measured various distances and angles between the ossicles and the IAC. In addition, some other measurements between the IAC and the inner ear were conducted for the purpose of not exposing the membranous labyrinth during hearing preservation surgery.
Landmark structures to approach the internal auditory canal 49 MATERIAL AND METHODS The material was selected from the temporal bone collection of Baylor College of Medicine, Department of Otorhinolaryngology. Temporal bones from patients with post-operative ear, metastatic malignant disease, anomaly, bone disease, severe inflammation, and acoustic neurinoma were excluded. Temporal bones from children (under 15 years old) were also excluded. Selected horizontal or vertical sections (stained in hematoxylin-eosin) were projected onto trace papers with a calibrated magnification ( x 13.5). Manual drawings were made and the distances and angles were measured.
Downloaded by [New York University] at 05:58 13 February 2016
RESULTS AND DISCUSSION 1) The distances and angles between the ossicles and the IAC (Fig. 1) The selection criteria of the sections were as follows; a) Horizontal sections containing the incudo-malleolar articulation and the short process of the incus; b) Horizontal sections in which the ossicles are fixed with ligaments and mucous membranes in proper expected positions; c) Horizontal sections which contain the widest horizontal dimension of the porus acousticus. Thirty-three out of 368 ears examined had sections that met these criteria. The distances were measured from the center of the malleus head (0)to the anterior margin of the porus acousticus (A), posterior margin of the porus acousticus (B) and the center of the fundus (C). Then angles were measured in the following way. Firstly, the lines X and Y were drawn. The line X is the pivoting axis of the malleus-incus. The line Y makes a right angle against the line X at the point 0. Secondly, the angles LA, LB, and L C were measured. The angles LA, L B, and L C are the angles which are formed between the lines OA, OB or OC and the line Y, respectively. The means and the standard deviations of OA, OB, OC, LA, L B, and LC are presented in the Table I. Basically, the ossicles should be used as the landmark in cases without useful hearing. By using this landmark in combination with the biauricular line, accurate identification of the IAC is possible.
2 ) The distance between the common crus and the IAC (Fig.1) The selection criteria of the sections were criterion 1.c). and the horizontal sections containing the medial side of the common crus. Fifteen out of 84 ears examined had sections
Fig. 1. The distances and an-
gles between the ossicles the IAC. The distance tween the common crus the IAC. The distance tween the common crus the pyramidal edge.
and beand beand
50
T. Matsunaga et al.
Table I. The distances and angles between the ossicles and the IAC No.
Mean
S.D.
From the center of the malleus head to the anterior margin of the porus acousticus
33
19.7 mm
2.1 mm
From the center of the malleus head to the posterior margin of the porus acousticus
33
16.8 mm
1.7 mm
From the center of the malleus head to the center of the fundus
33
8.2 mm
0.8 mm
LA:
Between OA and the line Y
33
23.8"
7.3"
L B:
Between OB and the line Y
33
4.9"
6.9'
L C:
Between OC and the line Y
33
7.8"
6.8"
OA:
OB:
Downloaded by [New York University] at 05:58 13 February 2016
oc:
that met these criteria. The distance ( L l ) was measured from the medial side of the common crus (D) to the posterior wall of the IAC. The mean and the standard deviation of L1 are presented in Table 11. For total removal of the tumor inside the IAC, the posterior wall of the IAC has to be drilled out. In this process, the medial side of the common crus is the most critical area for preservation of hearing. The extent of the drilling in the posterior area of the IAC must be within this distance (LI).
3 ) The distance between the common crus and the pyramidal edge (Fig. 1) The selection criteria and the number of the ears used for this measurement were the same as those of L1. The distance (L2) was measured from the point D to the surface of the posterior cranial fossa. The mean and the standard deviation of L2 are presented in Table 11. The standard deviation of L2 is twice as large as that of LI. The reason of this discrepancy is that the degree of pneumatization between the common crus and the pyramidal edge is highly variable in contrast to the inconsiderable pneumatization between the common crus and the IAC in most of the cases. In the cases of little pneumatization, the common crus and posterior semicircular canal sometimes locate very close to the posterior cranial fossa. Though drilling is not made from the pyramidal edge but from the posterior wall of the IAC in the middle cranial fossa approach, surgeons have to be careful when operating in this area in hearing preservation surgery. Table 11. The distance between the common crus and the IAC. The distance between the common crus and the pyramidal edge
L1:
L2:
No.
Mean
S.D.
From the medial side of the common crus to the posterior wall of the I A C
15
4.5mm
0.7 mm
From the medial side of the common crus to the surface of the posterior cranial fossa
15
3.4mm
1.4 mm
Landmark structures to approach the internal auditory canal
Downloaded by [New York University] at 05:58 13 February 2016
Fig. 2. The depth of the porus acousticus.
4) The depth of the porus acousticus f r o m the middle cranial fossa (Fig. 2) The selection criterion in the vertical sections (perpendicular to the long axis of the petrous bone) was to contain the widest vertical dimension of the porus acousticus. Nine out of 14 ears exaimined had sections that met this criterion. The distance (L3) was measured from the surface of the middle cranial fossa to the superior margin of the porus acousticus. The mean and the standard deviation of L3 are presented in Table 111. The superior wall of the porus acousticus has a variety of shapes so its standard deviation is large. The superior wall of the IAC is first removed at the medial part in hearing preservation surgery, then the exposure is extended toward the porus acousticus and the fundus. The vertical measurement was conducted to assist the exposure of the facial nerve in the IAC without any damage on it. 5 ) The depth of the IAC and the cochlea f r o m the middle cranial fossa (Fig. 3)
The selection criterion in the vertical sections (perpendicular to the long axis of the petrous bone) was that it contains the midmodiolar section of the cochlea. Ten out of 14 ears examined had sections that met this criterion. The following distances were measured near the fundus. L4 and L5 are the distances from the surface of the middle cranial fossa to the Table 111. The depth of the porus acousticus. The depth of the IAC and the cochlea at the fundus No. L3:
L4:
L5:
L6:
Mean
S.D.
From the surface of the middle cranial fossa to the superior margin of the porus acousticus
9
5.0 mm
1.6 mm
From the surface of the middle cranial fossa to the superior wall of the IAC near the fundus
9
2.9mm
0.8 mm
10
2.1 mm
0.6 mm
10
5.2 mm
0.7 mm
From the surface of the middle cranial fossa to the superior margin of the cochlear spiral The vertical diameter of the I A C
51
52
T. Matsunaga et al.
Downloaded by [New York University] at 05:58 13 February 2016
Fig. 3. The depth of the IAC and the cochlea at the fundus.
superior wall of the IAC and the superior margin of the cochlear spiral. L6 is the vertical diameter of the IAC; extension of L4. The means and the standard deviations of L4, L5 and L6 are presented in Table 111. Due to an artifact, a total of 9 ears could be used for the measurement of L4. It should be emphasized that both distances from the surface of the middle cranial fossa to the IAC and the cochlea were relatively short. Careful manipulation is necessary not to expose the cochlea near the fundus. 6) Correlation with the measurements reported in the past Although most of the dimensional studies of the IAC were focused on the diameter, length, and shape (7- 17), some studies carried useful information for surgery through middle cranial fossa (6, 18, 19). Our present study belongs to this latter group and adds data for achievement of more accurate identification of the IAC. As material for the measurement, dry or wet tomporal bones, histologically prepared temporal bones, X-ray films, and CT films were used. In the process of celloidin embedding histological preparations, which we used for the study, it was reported that bone shrinks by about 9%)(20). So the shrinkage rate must be taken into consideration. However, the merit of this method is that we had a clear outline of the ossicles, the IAC and the inner ear structures, and that enabled us to perform accurate measurements. ACKNOWLEDGEMENTS The authors are grateful to Dr. S. Ikeda for this help with the statistical analysis.
REFERENCES 1. Portman M. Sterkers JM, Charachon R, Chouard CH. Surgical approaches and technique. In: Portmann M, Sterkers JM, Charachon R, Chouard CH, eds. The internal auditory meatus. Edinburgh, London and New York: Churchill Livingstone, 1975: 99- 182. 2. House WF. Surgical exposure of the internal auditory canal and its contents through the middle cranial fossa. Laryngoscope 1961; 71: 1363-85. 3. Fisch U. Transtemporal surgery of the internal auditory canal. Reports of 92 cases, technique, indications and results. Adv Otorhinolaryngol 1970; 17: 203-40. 4. Cohadon F, Castel JP, Lemann P, Portmann M . Variations anatomiques et rapports intrapetreux du conduit auditif interne-applications a I’aboord otoneurochirurgigal. C R Assoc Anat 1968; 140. 5. Pialoux P, Freyss G , Nancy P, Saint-Macary M, Davine F. Contribution a I’anatomie stereotaxique du conduit auditif interne et de la premiere portion du facial. Ann Otolaryng 1972; 89: 141-2.
Downloaded by [New York University] at 05:58 13 February 2016
Landmark structures to approach the internal auditory canal 6. Tsuchihashi N, 0-uchi T, Ogawa K, Kunihiro T, Ogawa S, Inoue T, Kanzaki J. Dimensional measurements of internal auditory canal and middle ear structures by CT target imaging. Clin Otol Jpn 1989; 16: 38-42. 7. Ebenius B. The results of examination of the petrous bone in auditory nerve tumors. Acta Radio1 (Stockh) 1934; 15: 284-90. 8. Camp JD, Cilley EIL. The significance of asymmetry of the pori acoustic as an aid in diagnosis of eighth nerve tumors. Am J Roentogenol 1939; 41: 713-8. 9. Graf K. Geschwulste des Ohres und des Kleinhirnbrunkenwinkels. Stuttgart: Georg Thieme Verlag, 1952 238. 10. Valvassori GE, Pierce RH. The normal internal auditory canal. Am J Roentogenol 1964; 92: I232 -4 I . 11. Amjad AH, Scheer AA, Rosenthal J. Human internal auditory canal. Arch Otolaryngol 1969; 89: 709- 14. 12. Cordova M. Anatomie du conduit auditif interne. Rev Laryngol Otol Rhino1 (Bord) 1972; 93: 727-36. 13. Papangelou L. Study of the human auditory canal. Laryngoscope 1972; 82: 617-24. 14. Oliverse FP, Schuknecht HF. Width of the internal auditory canal. Ann Otol 1979; 88: 316-23. 15. Thomsen J, Reiter S, Borum P, Tos M. Tomography of the internal acoustic meatus. J Laryngol Otol 1981; 95: 1191-200. 16. 0-uchi T, Kanzaki J, Okada T. Dimensional measurements of inner ear structures by CT target imaging. Otologia Fukuoka 1982; 28: 959-68. 17. Nakamura M. Evaluation of temporal bone pneumatization on high resolution CT (HRCT). Measurements of the temporal bone in normal and otitis media group and their correlation to measurements of internal auditory meatus, vestibular or cochlear duct. J Otolaryngol Jpn 1988; 91: 1002-11. 18. Lang J. Anatomy of the brain stem and the lower cranial nerves, vessels and surrounding structures. Am J Otol 1985; Suppl 1-19. 19. Parisier SC The middle cranial fossa approach to the internal auditory canal. An anatomical study stressing critical distances between surgical landmarks. Laryngoscope 1977; 87: 1-20. 20. Igarashi M, 0-uchi T, Alford BR. Volumetric and dimensional measurements of vestibular structures in the squirrel monkey. Acta Otolaryngol (Stockh) 1981; 91: 437-44. Address for correspondence: Tatsuo Matsunaga, Department of Otolaryngology, School of Medicine, Keio University, Shinanomachi 35, Shinjuku-ku, Tokyo 160, Japan
53
