The Facial Nerve Coursing Inferior to the Oval Window Toby G. Mayer, MD,
James A.
Crabtree, MD
anomalies of the facial of great concern to the otologic surgeon. Nine cases from the literature are reviewed and three of our own are reported in which the facial nerve coursed inferior to the oval window. All cases were explored for congenital conductive hearing impairments and were accompanied by severe stapes abnormalities.
The
\s=b\ Congenital
nerve are
(Arch Otolaryngol 102:744-746, 1976)
Though
abnormalities of the course of the facial nerve are rare, they are of grave concern to the otologie surgeon. Three cases in which the facial nerve passed inferior to the oval window are reported. In these cases, the nerve was dehiscent, and a deformed stapes was present as well. EMBRYOLOGY While the origin of the ossicular tissue of the middle ear is controver¬ sial, the explanation forwarded by Anson and associates13 is briefly reviewed. The ossicles are derived from the mesenchyme of the first and second pharyngeal arches. The clas¬ sical theory stated that the malleus and incus originated from the first arch (Meckel cartilage) and that the stapes was derived from the second arch (Reichert cartilage). According to the modern theory of development, the first arch forms the head of the malleus and the body and short crus of the incus, while the manubrium of the malleus, the long crus of the incus, and the stapes arch with the outer layer of the foot plate are derived from the second arch. The anterior process of the malleus originates by independent ossification. Accepted for publication June 1, 1976. From the Department of Otolaryngology, University of Southern California, Los Angeles. Read before the Los Angeles Society of Otolaryngology, Los Angeles, November, 1974. Reprint requests to 1300 N Vermont Ave, suite 508, Los Angeles, CA 90027 (Dr Crabtree).
cartilaginous
(labyrinthine
layer) of the foot plate is derived from the otic capsule. The annular ligament is formed by the thinning out of the otic capsule in the foot plate area and the differentiation of precartilaginous cells to fibrous tissue. The facial nerve develops lateral to the blastema and grooves it so as to divide the blastema into the stapes, the interhyale (the future stapedial muscle and tendon), and the laterohyale (the future pyramidal eminence and anterior wall of the facial canal). As suggested by Durcan et al,' should part of Reichert cartilage fail to develop normally, the facial canal might be partially or totally absent in its middle ear portion. Thus, the facial nerve could advance anteroinferiorly as far as the stapes. If there were failure or delay of union between the branchial part of the stapes and the otic capsule, or failure of that part of the stapes derived from the second arch to develop, this would permit an even further progression of the facial nerve to the area below the oval window. REPORT OF CASES
5'/2-year-old girl, when congenital ophthalmologic
Case 1.—A seen, had
first and abnormali¬
renal anomalies. There were no ties of the pinnae, external canals,
or
tympanic membranes, except accessory cartilages anterior to the tragus bilater¬ ally. The audiogram showed a bilateral 50dB slightly ascending conductive loss with a
normal bone level and discrimination.
Radiologie studies revealed normal find¬ ings. The diagnosis of congenital conduc¬ tive hearing loss was made. Exploration of the right ear revealed a normal malleus and incus. The stapes was monopolar without an identifiable foot plate. The facial nerve was in a normal position but was dehiscent. No repair was attempted. Ten years later, the left
ear
was
Downloaded From: http://archotol.jamanetwork.com/ by a University of Iowa User on 05/27/2015
and malleus were short manubrium. The stapes was monopolar and not attached to the foot plate, which was not clearly demarcated from the surrounding bone. An annular ligament could not be identi¬ fied. The facial nerve was dehiscent and inferior to the oval window. A Shea drill was used to fenestrate the foot plate area, and reconstruction was performed using a perichondrial graft and a 4-mm wire loop. Six months postoperatively, the initial 30dB gain was lost, and this ear was reexplored. There was bony closure of the oval window, and a similar reconstruction was
explored. The incus normal except for
a
1.—Left ear in case 1. Malleus in its lower portion is not attached to tympanic membrane. Incus was slightly stubby and monopolar crus has been removed from foot plate. Facial nerve can be seen cours¬ ing between foot plate and round win¬ dow.
Fig
Fig 2.—Line drawing of structures de¬ scribed in Fig 1.
Fig 3.—Right ear in case 3. Stubby incus, no stapes superstructure, and window with the facial nerve coursing beneath are seen.
performed using a 4.5-mm loop. The initial gain had slipped to a 12-dB improvement after 3V2 months. Bone levels and discrimi¬ nation remained unchanged postoperative¬ ly (Fig 1 and 2). Case 2.—A 7'/2-year-old girl was found to have the following: a complete absence of the right pinna and external canal; a total atresia of the left external auditory canal ending in a small blind pouch; short palate; hypoplasia of the mandible and facial bones on the right; minimal right facial weakness; an extra right thumb. The audiogram showed a bilateral slightly ascending 70-dB air level with a flat bone level of 10 dB. Discrimination was normal bilaterally. Polytome x-ray films revealed deformed malleus and incus, which ap¬ peared to be fused on both sides. The right ear was explored to reconstruct an external auditory canal with the following findings. The malleus and incus were a fused mass, and a deformed stapes remnant was not attached to the foot plate. The foot plate was barely identifiable from surrounding bone, with no annulus present. Bone was chipped from the foot plate area and covered with perichondrium. A cartilage strut to the tympanic membrane was used to reconstruct the ossicular chain. At six weeks, there was a 30-dB gain, but this regressed to 15 dB after 17 months. Discrimination and bone levels remained
unchanged.
Two years later, the left ear was explored. A deformed malleus with absence of the long process was found, and the
deformed incus
was
attached to the stapes
area
of oval
Fig 4.—Line drawing of Fig 3.
Fig 5.—Polytomogram revealing short, slightly dilated horizontal greatly dilated vestibule (arrow).
head by a fibrous strand. The anterior crus of the stapes was absent and the posterior crus inserted into a dehiscent facial nerve, which was below the oval window area. The stapes head and tendon were normal. The foot plate was poorly demarcated, with no annulus present. A fasciai graft was placed over a tympanic membrane remnant, and no reconstruction of the ossicular chain was
Downloaded From: http://archotol.jamanetwork.com/ by a University of Iowa User on 05/27/2015
attempted
semicircular canal with
due to the presence of severe ossicular abnormalities. Case 3.—A 17-year-old boy had had repeated excisions of a right preauricular cyst. In addition, he had bilateral cupshaped ears and a mild right facial weak¬ ness of unknown duration. The external canals and tympanic membranes were normal. The audiogram showed bilateral,
ascending air levels of 65 dB
and flat bone levels of 25 dB, with normal discrimination. Polytome x-ray films revealed greatly dilated horizontal semicircular canals that formed a large cavity with the vestibule bilaterally. Surgical exploration of the right ear demonstrated a normal malleus and a tapered long process of the incus, without a lenticular process. No stapes superstructure was present, and the foot plate was poorly defined without a recog¬ nizable annular ligament. A dehiscent facial nerve passed below the oval window. The foot plate was fenestrated with a Shea drill, and a fasciai graft with a 4-mm wire loop was used to reconstruct the ossicular chain. Six months postoperatively, the patient has maintained a 20-dB improve¬ ment with no change in the bone conduc¬ tion or discrimination. Five months later, the left ear was explored. There was a normal malleus but a markedly shortened long process of the incus. No stapes superstructure was found. A stapes niche was in the usual position below a normal facial nerve. The foot plate was without an annular ligament. The foot plate was fenestrated using the Shea drill and covered with a perichondrial graft. A cartilage strut from the foot plate to the tympanic membrane was used to recon¬ struct the ossicular chain. Four months postoperatively, the patient has main¬ tained a 20-dB improvement with no change in bone conduction or discrimina¬ tion (Fig 3 and 4).
REVIEW OF THE LITERATURE
With the advent of microsurgery and surgical repair of the hearing mechanism, an anomalous course of the facial nerve within the middle ear is of vast importance. If this variant is not recognized, serious consequences may occur. Dehiscence of the tympanic facial canal is the most common anomaly, occurring in 57% of 211 temporal bones, according to Dietzel (cited by Kettel'1). Bifurcation of the facial nerve around the stapedial crura has been reported by Caparosa and Klas¬ sen" and by Durcan et al.4 Only nine other cases could be found in which the facial nerve coursed inferior to the oval window. Hough7 describes a single case, as do Sham¬ baugh and Clemis," in which the nerve ran below the oval window, with no additional information other than that the latter had otosclerosis. Leek" reports a case in which the patient had an abnormal-appearing facial nerve below the oval window that was not recognized at a routine stapedectomy.
A
patient
with bilateral
stapes fixation and
congenital
facial nerve inferior to the oval window in one ear was described by Fowler.10 Henner11 describes a patient with this anomaly bilaterally in whom there was stapes deformity, a poorly defined foot plate, and the nerve described as a boggy mass. Finally, Durcan et al4 report three cases in which the nerve ran below the oval window, was dehiscent, and was associated with marked a
stapes superstructure abnormality a fixed, poorly defined foot
with
plate.
COMMENT Can we recognize these cases preoperatively? At surgery, what are the clues that allow us to identify an anomalous course of the facial nerve? There is no question that every otologie surgeon would suspect possi¬ ble middle ear anomalies in a patient with congenital atretic ears and multi¬ ple anomalies. However, this condition was present in only 1 of the 12
reported patients. The majority had
normal pinnae, external canals, and tympanic mem¬ branes. Several did have minor anom¬ alies such as preauricular cysts, extra digits, and accessory cartilages, as well as anomalies of other systems (renal, eye, etc). These findings should make one more alert for variation at the time of surgery. All of the cases reported herein and all those reviewed with history avail¬ able were diagnosed as congenital conductive hearing losses. These pa¬ tients, therefore, should be differen¬ tiated from those with otosclerosis. House12 has stated that the following characteristics will help to establish a diagnosis of congenital conductive hearing loss: (1) marked conductive deafness in early childhood that is greater than could be due to any other acquired pathological process; (2) lack of progression of the hearing impair¬ ment; and (3) rather typical audiomet¬ rie findings of a flat air conduction loss at the 50- to 60-dB level associated with a flat bone curve approximating the zero level. However, some of these patients have had a slight sensori¬ neural hearing loss or a conductive loss less than 50 to 60 dB. Polytome x-ray films are indicated not only in those patients with con¬ genital atretic ears, but also in those
Downloaded From: http://archotol.jamanetwork.com/ by a University of Iowa User on 05/27/2015
patients with congenital conductive hearing loss. Although polytomography failed in these patients to
demonstrate an abnormal course of the facial nerve, they did reveal an unsuspected bilateral anomalous hori¬ zontal canal with a dilated vestibule
(Fig 5). All
nerves
dehiscent and with three excep¬
were
appeared normal,
tions in which the nerve appeared as a "boggy mass." Ten of 12 cases were associated with marked stapedial ab¬ normalities and absent annular liga¬ ments of the foot plates. In two of the cases from the literature, a facial weakness followed surgery. This dem¬ onstrates the need for identifying the nerve prior to ossicular reconstruc¬ tion. In the first case reported, some
improvement (15 dB) was attained, though two procedures were neces¬ sary. In the third case, there
was a
20-
improvement bilaterally. In both cases, there was no change in the bone dB
conduction or discrimination scores. Finally, if this anomaly is suspected and identified, the surgical repair should carry no greater risk than other stapes procedures, although the results are not as satisfactory. References 1. Anson BJ, Harper DG, Warpeha RL: The surgical anatomy of the facial canal and facial nerve. Ann Otol Rhinol Laryngol 72:713-734, 1963. 2. Hanson
JR, Anson BJ, Strickland EM: Branchial sources of the auditory ossicles in man. Arch
Otolaryngol 76:200-215,
1962. 3. Bast JH, Anson BJ, Tichany SF: The development of the second brachian arch (Reichert's cartilage), facial canal and associated structures in man. Q Bull Northwestern Univ Med School 30:235-249, 1956. 4. Durcan DJ, Shea JJ, Sleeckx JP: Bifurcation of the facial nerve. Arch Otolaryngol 86:619-631, 1967. 5. Kettel K: Surgery of the facial nerve. Arch Otolaryngol 77:327-341, 1963. 6. Caparosa RJ, Klassen D: Congenital anomalies of the stapes and facial nerve. Arch Otolaryngol 83:420-421, 1966. 7. Hough JVD: Congenital malformations of the middle ear. Arch Otolaryngol 78:335-344, 1963. 8. Shambaugh GE Jr, Clemis JD: Facial nerve paralysis, in Paparella MM, Shumrick DA (eds): Otolaryngology. Philadelphia, WB Saunders Co, 1973, vol 2, pp 263-282. 9. Leek JH: An anomalous facial nerve: The otologist's albatross. Laryngoscope 84:1535-1544, 1974. 10. Fowler EP: Variations of the facial nerve. Laryngoscope 71:937-946, 1961. 11. Henner B: Congenital middle ear malformations. Arch Otolaryngol 71:454-461, 1960. 12. House HP: Diagnostic aspects of congenital ossicular fixation. Trans Am Acad Ophthalmol Otolaryngol 60:787-790, 1956.
James A.
Crabtree, MD
anomalies of the facial of great concern to the otologic surgeon. Nine cases from the literature are reviewed and three of our own are reported in which the facial nerve coursed inferior to the oval window. All cases were explored for congenital conductive hearing impairments and were accompanied by severe stapes abnormalities.
The
\s=b\ Congenital
nerve are
(Arch Otolaryngol 102:744-746, 1976)
Though
abnormalities of the course of the facial nerve are rare, they are of grave concern to the otologie surgeon. Three cases in which the facial nerve passed inferior to the oval window are reported. In these cases, the nerve was dehiscent, and a deformed stapes was present as well. EMBRYOLOGY While the origin of the ossicular tissue of the middle ear is controver¬ sial, the explanation forwarded by Anson and associates13 is briefly reviewed. The ossicles are derived from the mesenchyme of the first and second pharyngeal arches. The clas¬ sical theory stated that the malleus and incus originated from the first arch (Meckel cartilage) and that the stapes was derived from the second arch (Reichert cartilage). According to the modern theory of development, the first arch forms the head of the malleus and the body and short crus of the incus, while the manubrium of the malleus, the long crus of the incus, and the stapes arch with the outer layer of the foot plate are derived from the second arch. The anterior process of the malleus originates by independent ossification. Accepted for publication June 1, 1976. From the Department of Otolaryngology, University of Southern California, Los Angeles. Read before the Los Angeles Society of Otolaryngology, Los Angeles, November, 1974. Reprint requests to 1300 N Vermont Ave, suite 508, Los Angeles, CA 90027 (Dr Crabtree).
cartilaginous
(labyrinthine
layer) of the foot plate is derived from the otic capsule. The annular ligament is formed by the thinning out of the otic capsule in the foot plate area and the differentiation of precartilaginous cells to fibrous tissue. The facial nerve develops lateral to the blastema and grooves it so as to divide the blastema into the stapes, the interhyale (the future stapedial muscle and tendon), and the laterohyale (the future pyramidal eminence and anterior wall of the facial canal). As suggested by Durcan et al,' should part of Reichert cartilage fail to develop normally, the facial canal might be partially or totally absent in its middle ear portion. Thus, the facial nerve could advance anteroinferiorly as far as the stapes. If there were failure or delay of union between the branchial part of the stapes and the otic capsule, or failure of that part of the stapes derived from the second arch to develop, this would permit an even further progression of the facial nerve to the area below the oval window. REPORT OF CASES
5'/2-year-old girl, when congenital ophthalmologic
Case 1.—A seen, had
first and abnormali¬
renal anomalies. There were no ties of the pinnae, external canals,
or
tympanic membranes, except accessory cartilages anterior to the tragus bilater¬ ally. The audiogram showed a bilateral 50dB slightly ascending conductive loss with a
normal bone level and discrimination.
Radiologie studies revealed normal find¬ ings. The diagnosis of congenital conduc¬ tive hearing loss was made. Exploration of the right ear revealed a normal malleus and incus. The stapes was monopolar without an identifiable foot plate. The facial nerve was in a normal position but was dehiscent. No repair was attempted. Ten years later, the left
ear
was
Downloaded From: http://archotol.jamanetwork.com/ by a University of Iowa User on 05/27/2015
and malleus were short manubrium. The stapes was monopolar and not attached to the foot plate, which was not clearly demarcated from the surrounding bone. An annular ligament could not be identi¬ fied. The facial nerve was dehiscent and inferior to the oval window. A Shea drill was used to fenestrate the foot plate area, and reconstruction was performed using a perichondrial graft and a 4-mm wire loop. Six months postoperatively, the initial 30dB gain was lost, and this ear was reexplored. There was bony closure of the oval window, and a similar reconstruction was
explored. The incus normal except for
a
1.—Left ear in case 1. Malleus in its lower portion is not attached to tympanic membrane. Incus was slightly stubby and monopolar crus has been removed from foot plate. Facial nerve can be seen cours¬ ing between foot plate and round win¬ dow.
Fig
Fig 2.—Line drawing of structures de¬ scribed in Fig 1.
Fig 3.—Right ear in case 3. Stubby incus, no stapes superstructure, and window with the facial nerve coursing beneath are seen.
performed using a 4.5-mm loop. The initial gain had slipped to a 12-dB improvement after 3V2 months. Bone levels and discrimi¬ nation remained unchanged postoperative¬ ly (Fig 1 and 2). Case 2.—A 7'/2-year-old girl was found to have the following: a complete absence of the right pinna and external canal; a total atresia of the left external auditory canal ending in a small blind pouch; short palate; hypoplasia of the mandible and facial bones on the right; minimal right facial weakness; an extra right thumb. The audiogram showed a bilateral slightly ascending 70-dB air level with a flat bone level of 10 dB. Discrimination was normal bilaterally. Polytome x-ray films revealed deformed malleus and incus, which ap¬ peared to be fused on both sides. The right ear was explored to reconstruct an external auditory canal with the following findings. The malleus and incus were a fused mass, and a deformed stapes remnant was not attached to the foot plate. The foot plate was barely identifiable from surrounding bone, with no annulus present. Bone was chipped from the foot plate area and covered with perichondrium. A cartilage strut to the tympanic membrane was used to reconstruct the ossicular chain. At six weeks, there was a 30-dB gain, but this regressed to 15 dB after 17 months. Discrimination and bone levels remained
unchanged.
Two years later, the left ear was explored. A deformed malleus with absence of the long process was found, and the
deformed incus
was
attached to the stapes
area
of oval
Fig 4.—Line drawing of Fig 3.
Fig 5.—Polytomogram revealing short, slightly dilated horizontal greatly dilated vestibule (arrow).
head by a fibrous strand. The anterior crus of the stapes was absent and the posterior crus inserted into a dehiscent facial nerve, which was below the oval window area. The stapes head and tendon were normal. The foot plate was poorly demarcated, with no annulus present. A fasciai graft was placed over a tympanic membrane remnant, and no reconstruction of the ossicular chain was
Downloaded From: http://archotol.jamanetwork.com/ by a University of Iowa User on 05/27/2015
attempted
semicircular canal with
due to the presence of severe ossicular abnormalities. Case 3.—A 17-year-old boy had had repeated excisions of a right preauricular cyst. In addition, he had bilateral cupshaped ears and a mild right facial weak¬ ness of unknown duration. The external canals and tympanic membranes were normal. The audiogram showed bilateral,
ascending air levels of 65 dB
and flat bone levels of 25 dB, with normal discrimination. Polytome x-ray films revealed greatly dilated horizontal semicircular canals that formed a large cavity with the vestibule bilaterally. Surgical exploration of the right ear demonstrated a normal malleus and a tapered long process of the incus, without a lenticular process. No stapes superstructure was present, and the foot plate was poorly defined without a recog¬ nizable annular ligament. A dehiscent facial nerve passed below the oval window. The foot plate was fenestrated with a Shea drill, and a fasciai graft with a 4-mm wire loop was used to reconstruct the ossicular chain. Six months postoperatively, the patient has maintained a 20-dB improve¬ ment with no change in the bone conduc¬ tion or discrimination. Five months later, the left ear was explored. There was a normal malleus but a markedly shortened long process of the incus. No stapes superstructure was found. A stapes niche was in the usual position below a normal facial nerve. The foot plate was without an annular ligament. The foot plate was fenestrated using the Shea drill and covered with a perichondrial graft. A cartilage strut from the foot plate to the tympanic membrane was used to recon¬ struct the ossicular chain. Four months postoperatively, the patient has main¬ tained a 20-dB improvement with no change in bone conduction or discrimina¬ tion (Fig 3 and 4).
REVIEW OF THE LITERATURE
With the advent of microsurgery and surgical repair of the hearing mechanism, an anomalous course of the facial nerve within the middle ear is of vast importance. If this variant is not recognized, serious consequences may occur. Dehiscence of the tympanic facial canal is the most common anomaly, occurring in 57% of 211 temporal bones, according to Dietzel (cited by Kettel'1). Bifurcation of the facial nerve around the stapedial crura has been reported by Caparosa and Klas¬ sen" and by Durcan et al.4 Only nine other cases could be found in which the facial nerve coursed inferior to the oval window. Hough7 describes a single case, as do Sham¬ baugh and Clemis," in which the nerve ran below the oval window, with no additional information other than that the latter had otosclerosis. Leek" reports a case in which the patient had an abnormal-appearing facial nerve below the oval window that was not recognized at a routine stapedectomy.
A
patient
with bilateral
stapes fixation and
congenital
facial nerve inferior to the oval window in one ear was described by Fowler.10 Henner11 describes a patient with this anomaly bilaterally in whom there was stapes deformity, a poorly defined foot plate, and the nerve described as a boggy mass. Finally, Durcan et al4 report three cases in which the nerve ran below the oval window, was dehiscent, and was associated with marked a
stapes superstructure abnormality a fixed, poorly defined foot
with
plate.
COMMENT Can we recognize these cases preoperatively? At surgery, what are the clues that allow us to identify an anomalous course of the facial nerve? There is no question that every otologie surgeon would suspect possi¬ ble middle ear anomalies in a patient with congenital atretic ears and multi¬ ple anomalies. However, this condition was present in only 1 of the 12
reported patients. The majority had
normal pinnae, external canals, and tympanic mem¬ branes. Several did have minor anom¬ alies such as preauricular cysts, extra digits, and accessory cartilages, as well as anomalies of other systems (renal, eye, etc). These findings should make one more alert for variation at the time of surgery. All of the cases reported herein and all those reviewed with history avail¬ able were diagnosed as congenital conductive hearing losses. These pa¬ tients, therefore, should be differen¬ tiated from those with otosclerosis. House12 has stated that the following characteristics will help to establish a diagnosis of congenital conductive hearing loss: (1) marked conductive deafness in early childhood that is greater than could be due to any other acquired pathological process; (2) lack of progression of the hearing impair¬ ment; and (3) rather typical audiomet¬ rie findings of a flat air conduction loss at the 50- to 60-dB level associated with a flat bone curve approximating the zero level. However, some of these patients have had a slight sensori¬ neural hearing loss or a conductive loss less than 50 to 60 dB. Polytome x-ray films are indicated not only in those patients with con¬ genital atretic ears, but also in those
Downloaded From: http://archotol.jamanetwork.com/ by a University of Iowa User on 05/27/2015
patients with congenital conductive hearing loss. Although polytomography failed in these patients to
demonstrate an abnormal course of the facial nerve, they did reveal an unsuspected bilateral anomalous hori¬ zontal canal with a dilated vestibule
(Fig 5). All
nerves
dehiscent and with three excep¬
were
appeared normal,
tions in which the nerve appeared as a "boggy mass." Ten of 12 cases were associated with marked stapedial ab¬ normalities and absent annular liga¬ ments of the foot plates. In two of the cases from the literature, a facial weakness followed surgery. This dem¬ onstrates the need for identifying the nerve prior to ossicular reconstruc¬ tion. In the first case reported, some
improvement (15 dB) was attained, though two procedures were neces¬ sary. In the third case, there
was a
20-
improvement bilaterally. In both cases, there was no change in the bone dB
conduction or discrimination scores. Finally, if this anomaly is suspected and identified, the surgical repair should carry no greater risk than other stapes procedures, although the results are not as satisfactory. References 1. Anson BJ, Harper DG, Warpeha RL: The surgical anatomy of the facial canal and facial nerve. Ann Otol Rhinol Laryngol 72:713-734, 1963. 2. Hanson
JR, Anson BJ, Strickland EM: Branchial sources of the auditory ossicles in man. Arch
Otolaryngol 76:200-215,
1962. 3. Bast JH, Anson BJ, Tichany SF: The development of the second brachian arch (Reichert's cartilage), facial canal and associated structures in man. Q Bull Northwestern Univ Med School 30:235-249, 1956. 4. Durcan DJ, Shea JJ, Sleeckx JP: Bifurcation of the facial nerve. Arch Otolaryngol 86:619-631, 1967. 5. Kettel K: Surgery of the facial nerve. Arch Otolaryngol 77:327-341, 1963. 6. Caparosa RJ, Klassen D: Congenital anomalies of the stapes and facial nerve. Arch Otolaryngol 83:420-421, 1966. 7. Hough JVD: Congenital malformations of the middle ear. Arch Otolaryngol 78:335-344, 1963. 8. Shambaugh GE Jr, Clemis JD: Facial nerve paralysis, in Paparella MM, Shumrick DA (eds): Otolaryngology. Philadelphia, WB Saunders Co, 1973, vol 2, pp 263-282. 9. Leek JH: An anomalous facial nerve: The otologist's albatross. Laryngoscope 84:1535-1544, 1974. 10. Fowler EP: Variations of the facial nerve. Laryngoscope 71:937-946, 1961. 11. Henner B: Congenital middle ear malformations. Arch Otolaryngol 71:454-461, 1960. 12. House HP: Diagnostic aspects of congenital ossicular fixation. Trans Am Acad Ophthalmol Otolaryngol 60:787-790, 1956.
