Учебники / Otolaryngology - Basic Science and Clinical Review

depressions. The spherical recess directly below the stapedial footplate holds the saccule, and the elliptical recess holds the utricle.The maculae of the saccule and utricle are composed of a field of supporting cells and hair cells that are covered by a gelatinous otolithic membrane that contains many small calcium phosphate crystals (otoconia). These maculae with their otoconial membranes function as both gravity and acceleration receptors, and these two sensory maculae lie at right angles to each other. Posteriorly, the vestibule opens into the semicircular canals. Each semicircular canal contains a semicircular duct that has an ampullated and a nonampullated end as it joins into the utricle.The posterior and superior ducts join together to form a common nonampullated duct called the crus commune.The cristae located within the ampullae are complex sensory receptors that contain secretory cells, supporting cells, and hair cells. The stereociliary bundles of the hair cells are embedded into a gelatinous material called a cupula that is attached to the roof of each ampulla. Angular acceleration results in deflection of the stereocilia, causing a

change in the basal firing rate of the vestibular nerve. The superior canal runs through the floor of the middle fossa making up the arcuate eminence, an important landmark for orientation of the surgeon during middle fossa surgery. The cochlea lies anterior to the vestibule and consists of 21⁄2 turns, with a total average length of 32 mm. Within these bony confines the membranous labyrinth (inner ear) consists of a sac containing a high-potassium, low-sodium fluid (endolymph) and is suspended in and surrounded by a fluid-filled space encased in bone that is low in potassium and high in sodium (perilymph).Within the cochlea there are three fluid-filled spaces called the scala media (filled with endolymph) and the scala tympani and the scala vestibuli (both filled with perilymph).The internal fluid spaces of the saccule, utricle, and semicircular ducts contain endolymph. It is Reissner’s (vestibular) membrane that separates the scala vestibuli from the scala media and the basilar membrane that separates the scala media from the scala tympani (see Fig. 22-5). The round window membrane opens into the basal turn of the scala tympani.

The communication between perilymphatic spaces of the scala vestibuli and scala tympani occurs at the apex of the cochlea; this area of communication is designated the helicotrema of the cochlea.The lateral cochlear wall consists of the stria vascularis and the spiral ligament, which are both metabolically active structures, responsible for maintaining the ionic balance within the cochlea. The organ of Corti is a complex structure consisting of supporting cells, three rows of outer hair cells, and a single row of inner hair cells. The inner hair cells are the actual receptor cells of hearing, whereas the outer hair cells serve as modulators of hearing and fine-tune the area of the basilar membrane that responds to the frequency components of sound via an active electromotile response.Three types of neural elements are found within the cochlea. Rosenthal’s canal contains the spiral ganglion with its afferent auditory neurons.Type I spiral ganglion cells compose 90% of the spiral ganglion neurons and innervate the inner hair cells, with multiple neurons projecting to and innervating a single inner hair cell.Type II spiral ganglion cells make up 10% of the spiral ganglion’s neuronal population; each type II neuron innervates multiple outer hair cells. The endolymphatic sac connects to the endolymph-filled portion of the inner ear via the endolymphatic duct.The sac is a complex structure that lies intercalated within the dura of the posterior fossa. An imaginary line drawn through the horizontal semicircular canal and the outline of the posterior semicircular canal approximates the position of the sac.The cochlear aqueduct connects the scala tympani via an opening on the petrous pyramid in the posterior fossa. In most humans this duct has been obliterated by connective tissue, but it forms a potential communication for bacteria to and/or from the labyrinth to the cerebrospinal fluid of the cranial cavity.

Three nerves innervate the sensory receptors of the inner ear: the cochlear nerve and the superior and inferior divisions of the vestibular nerve (see Fig. 22-3). The superior vestibular nerve supplies part of the saccule (via Voit’s nerve), the utricle, and the superior and lateral semicircular canal ampullae.The inferior vestibular nerve innervates the posterior canal ampulla and the remainder of the saccule.

VASCULAR SUPPLY

The blood supply of the pinna is supplied by the posterior auricular artery (external carotid), the anterior auricular artery (superficial temporal), and a branch of the occipital artery.Venous drainage is supplied by the corresponding

veins as well as by the mastoid emissary vein. Lymphatic drainage is to the anterior auricular nodes and then to the superficial parotid nodes anteriorly, or to the retroauricular nodes, and from there to the upper deep cervical nodes posteriorly or inferiorly. Within the temporal bone the internal carotid crosses under the eustachian tube and then turns upward and inward anterior to the cochlea. The major venous structure within the temporal bone is the sigmoid sinus. The sigmoid sinus runs from the lateral sinus to the jugular bulb that then becomes the jugular vein.The position of the jugular bulb is variable, and it may be dehiscent in the floor of the middle ear.The superior petrosal sinus connects the transverse sinus with the cavernous sinus. The inferior petrosal sinus connects the jugular bulb with the cavernous sinus. The middle ear is supplied by several different arteries derived from both the internal and external carotid as well as the basilar arteries. Vascular perfusion of the inner ear is supplied by the labyrinthine artery that is a branch of the anteroinferior cerebellar artery (AICA).

NERVES RUNNING THROUGH THE TEMPORAL BONE

The anatomy of the facial nerve is presented in detail in Chapter 35. However the facial nerve deserves a special comment in this chapter because of its complicated route through the temporal bone. The knowledge of its anatomy is a prerequisite for any surgery of the middle ear and the mastoid.The facial nerve enters the temporal bone by the internal auditory canal (IAC). Within the IAC the facial nerve is superior to the cochlear nerve and anterior to the superior vestibular nerve. At the lateral end of the IAC, the nerve passes superior to a ridge called the transverse crest and anterior to a wedge called Bill’s bar. Lateral to this is the labyrinthine segment of the facial nerve. The nerve travels slightly anterior between the basal turn of the cochlea and the ampulla of the superior semicircular canal. The geniculate ganglion lies at the lateral end of the labyrinthine segment. Here the facial nerve turns posterior (first genu) to become the horizontal or tympanic segment, and the greater petrosal nerve exits the geniculate ganglion anteriorly and exits the temporal bone through the facial hiatus. The main trunk of the facial nerve passes along the medial wall of the tympanic cavity superior to the oval window niche and then bends around the oval window (second genu) to travel in an inferior direction as the vertical or mastoid segment begins. The facial nerve gives off

Figure 22-6 A temporal bone after dissection of facial recess.AU, auricular branch of facial nerve; CT, chorda tympani; EAC, external auditory canal; FN, facial nerve; IN, incus; LSCC, lateral semicircular canal; PR, promontory; ST, stapes;TE, tegmen.

three branches during its descent through the mastoid cavity: (1) the nerve to the stapedius muscle, (2) the sensory auricular branch of the facial nerve that innervates the EAC, and (3) the chorda tympani. These last two branches of the facial nerve are useful anatomical landmarks during surgery. Transmastoid surgical procedures often require a progressive thinning of the posterior wall of the EAC to identify the descending segment of the facial nerve and to access middle ear from the mastoid through the facial recess. The facial recess makes up the space between the chorda tympani, the main trunk of the facial nerve, and the incus (Fig. 22-6).

Jacobson’s nerve or the inferior tympanic nerve is a branch of CN IX that enters the middle ear through the inferior tympanic canaliculus.This nerve then forms the tympanic plexus and may arborize to the promontory, where it may be submucosal, located within a sulcus on the promontory, or within a complete canal. The branches reunite if they have arborized close to the cochleariform process forming the lesser petrosal nerve; this nerve then passes in a canal beneath the tensor tympani muscle and into the middle cranial fossa, where it is medial to the greater superficial petrosal nerve.

Arnold’s nerve is a composite structure, formed by the auricular branch of the vagus nerve, the glossopharyngeal nerve, and the facial nerve. The auricular branch of the vagus nerve courses from the superior ganglion of the vagus nerve and passes posteriorly over the dome of the jugular bulb to enter the anterior aspect of the fallopian canal just proximal to the chorda tympani nerve. At this point the sensory

contribution from the facial nerve fuses with the sensory contribution of the vagus nerve to form a single nerve, which exits the sheath of the main trunk of the facial nerve as the auricular branch or exits the temporal bone as a single auricular branch of the facial nerve from stylomastoid foramen providing sensation to the EAC and the auricle. Glomus tumors arise from the collection of chemoreceptor tissue, which is found in high concentration associated with the parasympathetic fibers carried in CN IX and X. Similar collections of chemoreceptor tissue (i.e., glomus bodies) are found along the course of Arnold’s and Jacobson’s nerves in the tympanic canaliculus, over the promontory, in the retrofacial air cell tracts, and around the geniculate ganglion.

EPONYMS AND ANATOMICAL PEARLS

•Citelli’s angle sinodural angle.

•Dorello’s canal: The VI nerve canal running between the tip of the petrous bone and the sphenoid bone.This is the anatomical basis for the triad of VI palsy, pain, and the draining of the ear observed in infections of the petrous apex.

•Huguier’s canal: The exit point of the chorda tympani from the middle ear.

•Huschke’s foramen: Found in the anteroinferior external auditory canal and connects to the preauricular area

•Hyrtl’s fissure: An embryological connection between the hypotympanum and the subarachnoid space. It is usually obliterated in adults.

•Meckel’s cave: A bony depression housing the CNV ganglion.

•Santorini’s fissure: Lymphatics found in anteroinferior aspect of the external canal that allow for the spread of disease from the ear canal into the preauricular area and the skull base.

•Trautmann’s triangle:The area between the sigmoid sinus, superior petrosal sinus, and lateral canal.

SUGGESTED READINGS

Donaldson JA, Duckert LG, Lambert PM, Rubel EW. Surgical Anatomy of the Temporal Bone. 4th ed. New York: Raven Press; 1992

Proctor B. Surgical Anatomy of the Ear and Temporal Bone. New York:Thieme Medical Publishers; 1989

Schuknecht HR,Gulya AJ. Anatomy of the Temporal Bone with Surgical Implications. Philadelphia: Lea & Febiger; 1986

SELF-TEST QUESTIONS

For each question select the correct answer from the lettered alternatives that follow.To check your answers, see Answers to Self-Tests on page 716.

1.The chorda tympani nerve is a branch of which cranial nerve?

A.IX

B.X

C.VIII

D.VII

2.The tensor tympani muscle is innervated by which cranial nerve?

A.X

B.VII

C.V

D.IX

3.The muscle responsible for eustachian tube closure is the

A.Tensor tympani

B.Tensor vela palatini

C.Salpingopharyngeal

D.None of the above

4.Gradenigo’s syndrome is due to the anatomical relationships of

A.The petrous apex to the CN VI nerve

B.The mastoid to the sphenoid bone

C.The facial nerve to the middle ear

D.The cavernous sinus to the carotid

A working knowledge of the normal microscopic anatomy of the human temporal bone and the histopathology of disorders that affect hearing, balance, and facial nerve function is essential for practicing otolaryngologists as well as subspecialists in the area of otology and neurotology. This knowledge is helpful as a basis for understanding disease processes that will be encountered in the clinical setting, to evaluate the efficacy of medical management of disorders of the ear, and finally in perfecting or modifying surgical technique.The purpose of this chapter is to introduce the trainee to conventional light microscopic anatomy and to provide examples of common histopathology in a variety of disease categories. Although light microscopy of the human temporal bone has been done for over 100 years, progress in understanding the pathogenesis and treatment of otologic disorders requires renewed attention to this form of scientific inquiry. For example, cochlear implantation for the rehabilitation of the profoundly deaf using multichannel implants has been done on a routine basis for20 years. However, the biological consequences of implanting an electrode array in the human can most directly be answered by study of postmortem specimens from individuals who in life had undergone implantation. Furthermore, the current revolution in molecular genetics and molecular biology requires renewed attention to the collection and study of human specimens for several reasons. For example, much of what we know about the molecular genetics of hearing loss is based on homologous mutants or genetically engineered deletions in the mouse. However, comparison of the histopathology in these animal models with human disease is essential to verify the validity of the model. Furthermore, in addition to light microscopy, human specimens may be studied by a variety of techniques, including electron microscopy immunohistochemistry and retrieval and amplification of nucleic acid sequences, both from archivally collected and newly acquired temporal bone.

The purpose of this chapter will be to introduce the reader to the normal light microscopic anatomy of the human temporal bone and to provide a representative example of the pathology of the ear. For a more complete reference, the reader is referred to the classic text of Schuknecht (1993).

TECHNIQUES FOR RETRIEVAL AND STUDY OF THE HUMAN TEMPORAL BONE

The details concerning retrieval of temporal bones have been published elsewhere.The National Temporal Bone Hearing and Balance Pathology Resource Registry of the

National Institute on Deafness and Other Communication Disorders provides an excellent resource for retrieval and study techniques, a national database of currently available temporal bone sections, and recent research publications in the area of temporal bone histopathology (Merchant et al, 1993).The registry may be accessed by a 24-hour telephone number (800–822–1327) or by e-mail (tbregistry@meei.harvard.edu).

PLANE OF SECTION

Although human temporal bone specimens may be sectioned in any anatomical plane, as depicted in the following examples, the most conventional plane of section is horizontal or axial, which corresponds to the axial plane in computed tomographic (CT) scanning. As in the following examples, the tissue has been embedded in celloidin, sectioned at 20 , and stained with hemotoxylin and eosin.

HISTOLOGY OF THE NORMAL TEMPORAL BONE

The 14 photomicrographs depicted in Figs. 23-1A-K are representative examples of serial horizontal sections through the left temporal bone of a male who died at age 77.The series of photomicrographs begin superiorly, near the floor of the middle cranial fossa, and pass inferiorly to the cranial base.

HISTOPATHOLOGY

DEVELOPMENTAL DEFECTS

The following are examples of common phenotypes of developmental defects in the temporal bone. They include anomalies of the cochlear capsule (Mondini’s deformity), anomaly of the membranous labyrinth (Scheibe’s dysplasia), congenital aural atresia, and the persistent stapedial artery.

Mondini’s Anomaly (Fig. 23-2)

This dysplasia is characterized by anomalies of the bony capsule of the cochlea and vestibule as well as dysplasia of the membranous labyrinth. The degree of dysplasia and functional abnormality can vary widely. The length of the cochlear duct is shorter than the normal 32 to 34 mm, and in general the vestibule is large, with anomalies of the semicircular canals, including variations in size and number of canals. Mondini’s dysplasia may occur with no other recognized genetic or nongenetic abnormalities,

Malleus

Incus

Facial Nerve

Lateral Canal

Superior Canal Ampulla

Antrum

Petrous Apex

Non-ampullated End

of the Superior Canal

Posteriosuperior

Cell Tract

A

B

C

Figure 23-1 Selected horizontal (axial) serial sections from a normal left adult human temporal bone. (A, left) Section at the level of the epitympanum,the head of the malleus and body of the incus, and through the arch of the superior semicircular canal, crista ampullaris of the superior semicircular canal, and geniculate ganglion. Pneumatized spaces include the antrum and the posterior superior cell tract (magnification X4).(A,right) Detail of the crista ampullaris of the superior semicircular canal (magnification X55).

Neuroepithelium

Cupula

Crista

Utricular Macula

Otolithic Membrane

Malleus

Incus

Facial Nerve

Lateral Canal

Superior Canal Ampulla

Antrum

Petrous Apex

Non-ampullated End

of the Superior Canal

Posteriosuperior

Cell Tract

D

(B, left) Section at the level of the crista of the lateral semicircular canal, superior aspect of the internal auditory canal, and macula utriculi (magnification X4). (B, right) The macula utriculi and utricular division of the superior vestibular nerve (magnification X59). (C) Section at the level of the basal turn of the cochlea and the internal auditory canal (magnification X4). (D) Section at the level of the stapes footplate and tendon of the tensor tympani muscle (magnification X4).

Posterior Canal

Endolymphatic Duct

F

Eustachian Tube

Tensor

Tympani

Muscle

Stapedius Muscle

Ampullated End of the

Posterior Canal

Singular Nerve

H

Stapedius Muscle

Descending

Segment of the Cochlear Aqueduct

Facial Nerve

J

Figure 23-1 (Continued) (E,left) Section through the modiolus of the cochlea (magnification X4). (E, right) Normal anatomy of the cochlea (magnification X57.8). (F) Section at the level of the macula sacculi (magnification X4). (G) Section at the level of the tendon of the stapedius muscle and descending segment of the facial nerve (magnification X4). (H) Section at the level of the ampullated end of the posterior semicircular canal and the singular nerve

G

Ampulla of the

Posterior Canal

I

Cochlea

Facial Nerve

Sigmoid Sulcus

K

(magnification X4). (I) Section at the level of the round window membrane. The proximity of the eustachian tube to the petrous portion of the internal carotid artery is shown (magnification X4).

(J) Section at the level of the cochlear aqueduct between the scala tympani of the basal turn and the subarachnoid space (magnification X4). (K) Section through the inferior aspect of the basal turn inferior to the round window (magnification X4).

Cochleariform Process

Facial Nerve

Cochlea

Vestibule

Internal Auditory Canal

Figure 23-2 Mondini’s dysplasia of the left inner ear.This 85-year-old female was congenitally deaf, and severe Mondini’s dysplasia was found in both inner ears.An enlarged and malformed vestibule and a cochlea consisting of a rounded compartment and malformed modiolus were seen (magnification X12).

or it may be associated with known genetic disorders such as Klippel-Feil syndrome, Pendred’s syndrome, and trisomies. Alternately, it may occur as the result of exposure to teratogenic insults in the fetus, such as diphenylhydantoin and isotretinoin. This dysplasia may be unilateral or bilateral and can be diagnosed on CT scan.

Scheibe’s Dysplasia of the Membranous

Labyrinth (Fig. 23–3)

In Scheibe’s dysplasia, the bony capsule of the inner ear is normal. However, there is dysplastic development of the pars inferior (cochlea and saccule). Like Mondini’s dysplasia, Scheibe’s dysplasia is the phenotypic expression of a wide variety of genetically determined disorders of the inner ear.The dysgenesis may be seen in animals such as the Dalmatian dog.

Congenital Aural Atresia (Fig. 23–4)

This congenital anomaly is characterized by maldevelopment of the external auditory canal, resulting in either a narrowed canal or a true total atresia. It is commonly associated with anomalies of the auricle and both middle and inner ear. Congenital aural atresia may be seen as one manifestation of a genetically determined syndrome such as Treacher Collins, Crouzon’s, branchio-oto-renal syndrome, or Goldenhar’s syndrome, or in disorders with a questionable genetic basis such as the CHARGE syndrome (coloboma of the eye, heart anomaly, choanal atresia, retardation, and genital and ear anomalies), or as

a consequence of intrauterine exposure to teratogenic substances.

Persistent Stapedial Artery (Fig. 23–5)

The embryonic circulation includes the stapedial branch of the hyoid artery. In the transition to the adult circulation, the stapedial artery atrophies, and the hyoid portion becomes the caroticotympanic arteries. However, in some cases the stapedial artery persists as a branch of the internal carotid system and supplies blood either to the distribution of the normal middle meningeal artery or to the distribution of the superorbital, infraorbital, and mandibular arteries. A persistent stapedial artery can be encountered during middle ear surgery as it passes through the obturator foramen of the stapes. Because this vessel may substitute for part of the intracranial blood supply, it should not be interrupted.

GENETICALLY DETERMINED DISORDERS OF THE INNER EAR

There is a burgeoning list of recognized genetic disorders of the inner ear. An excellent reference is the text by Gorlin et al (1995). This chapter presents only four representative examples: Usher’s syndrome, Alport’s syndrome, Waardenburg’s syndrome, and the nonsyndromic dominantly inherited disorder DFNA-9.

USHER’S SYNDROME (FIG. 23-6)

Usher’s syndrome is inherited as an autosomal recessive disorder and is characterized by sensorineural hearing