However, in view of the possibility of human error by the authors, editors or publisher of the work herein or changes in medical knowledge, neither the authors, editors or publisher, nor any other party involved in the preparation of this work, guarantees that the information contained herein is accurate or complete in every respect, and they are not responsible for any errors or omissions or for the results obtained from the use of such information. Some of the product names, patents and registered designs referred to in this book are in fact registered trademarks or proprietary names, although this fact is not always specifically referred to in the text.
PREFACE
Acknowledgment
Embryology
Squamous Portion
Tympanic Portion
Styloid Portion
In addition, the styloglossus, stylohyoideus, and stylopharyngeus muscles also originate in the distal portion of the styloid process. The stylohyoid ligament extends from the apex of the process to the lesser cornu of the hyoid bone.
Mastoid Portion
Petrous Portion
The first branchial fissure or first groove is derived from the ectoderm and contributes to the formation of the EAC, the cuticular layer of the tympanic membrane, and the tympanic annulus. During embryogenesis, the dorsal part of the first branchial cleft continues to form the EAC, while the ventral part disappears.
Anatomy
Ectoderm of the first gill slit gives rise to the EAC, which develops as an invagination at the site of the future auricle in the fourth week of pregnancy. Defective ossification of the anteroinferior EAC may result in a persistent defect (foramen of Huschke).
Exte
In neonates, the EAC is almost straight and the floor of the bony canal is only partially ossified. The roof and the rest of the posterior wall arise from the squamous temporal bone.
Anatomy of the Middle Ear
- PL FPI:LP
- LPFISP
The tensor tympani semicanal lies superior to the tympanic opening of the Eustachian tube. At the back of the promontory, under the oval window, is the round window niche.
Facia
The tympanic segment (12.0 mm) extends from the geniculate ganglion to the second genus of the facial nerve. Figure 4-6 (A) Axial CT and (B) contrast-enhanced fat-suppressed MR obtained at similar levels through the mastoid bone show the descending portion of the facial nerve (arrow.
Clinical Features
The development of the sensory epithelium within the membranous labyrinth occurs simultaneously with growth and ossification (weeks 8 to 24). Ossification of the eye capsule takes place between the 16th and 24th week via 14 ossification centers.
Inne
The cochlea is the last part of the membranous labyrinth to undergo maturation and is therefore more subject to developmental malformations than the vestibular system. Once the membranous labyrinth reaches maturity (6 to 7 months of fetal age), no further growth occurs for the remaining lifespan of the individual.
Anatomy of the Inner Ear
Figure 5–2 (A) Axial computed tomography (CT) and (B) balanced T2-driven pulse sequence (T2 DRIVE) image through the superior aspect of the epitympanum shows the core of the superior semicircular canal (arrows.
The Vestibule
The Cochlea
MTISS
ISS MT
Consequently, the sound waves are transmitted directly to the perilymph of the cochlea as liquid waves. These fluid waves are transmitted through the Reissner membrane to the endolymph of the cochlear duct.
BT RWN
The perilymphatic waves are transmitted via the apex of the cochlea from the scala vestibuli (helicotrema) to the scala tympani and finally propagated through the round fenestra, which has a flexible diaphragm (Fig. 5–8 and Fig. 5–9). different parts of the membrane respond to different auditory frequencies: higher frequencies closer to the base, lower frequencies closer to the apex.
Vestibular Aqueduct and Endolymphatic Duct System
Endolymphatic Duct System
Ultrastructural organization of the epithelial lining of the endolymphatic duct and sac in the guinea pig. The histogenesis and growth of the ear capsule and its contained periotic tissue space in the human embryo.
Epidemiology
In type C atresias, the course of the facial nerve is more anterior and may occasionally overlap the oval window and descend into the atretic plate. This form of CAA is associated with anomalies of the bony labyrinth and abnormal course of the facial nerve.
Treatment
6 EXTERNAL HEALTH CANAL ATRESIA AND STENOSIS 27 ing of the malleus and incus and a medial compartment containing a normal stapes.
Imaging Findings
Coronal CT obtained in a patient with external auditory canal atresia shows an abnormal course of the tympanic membrane and descending segments of the facial nerve (arrows. Although bacterial infections of the skin of the external ear canal are the most common cause, fungal infection can also occur (otomycosis).
Pathology
Bone destruction and invasion of the temporal bone and mastoid are characteristic of malignant otitis externa. Figure 7-1 Computed tomography (CT) of malignant otitis externa. A) Axial and (B) coronal CT of the right temporal bone reveals an abnormal soft tissue mass (large arrow) with destruction of the cortical margins of the external auditory canal (small arrows).
Chol Cana
Soft tissue mass in the EAC with adjacent bony erosion, most often along the posteroinferior wall of the canal. Assess for extension to the middle ear or erosion of the mastoid air cells, facial nerve canal, and tegmen tympani.
Suggested Readings
- CHAPTER 9 Exostoses Hemant Parmar
- CHAPTER 10 External Auditory Canal Osteoma Ashok Srinivasan
- CHAPTER 11 Squamous Cell Carcinoma Dheeraj Gandhi
- CHAPTER 12 Basal Cell Carcinoma Vaishali Phalke
- CHAPTER 13 Melanoma Vaishali Phalke
Figure 9–1 (A,B) Axial CT of the left temporal bone shows a broad, pedunculated bony lesion (arrows) arising from the bony portion of the external auditory canal. Figure 12–2 (A,B) Axial contrast-enhanced studies performed through the external auditory canal region reveal a more advanced and ulcerated basal cell carcinoma.
Mela
Ossi
A small cholesteatoma of the middle ear presents as a well-circumscribed nodular mass, most often in the upper anterior quadrant of the middle ear. CT is also useful in the evaluation of more extensive lesions, mastoid involvement, and ossification and bone erosions.
Aber as ed
This leads to prominence of the tympanic portion of the facial nerve, an indirect imaging sign of PSA. Internal carotid angiography demonstrates the presence of a persistent stapedial artery arising from the intrapetrosal portion of the internal carotid artery or from the anomalous internal carotid artery.
A bony dehiscence cannot be detected or excluded on MRI, but a lateral lobulation of the jugular bulb on coronal MRI images may indicate the presence of a dehiscence. A high carotid artery is diagnosed when the top of the jugular foramen is seen at the level of the basal turn of the cochlea.
Acut
Chro
Figure 20–1 Axial computed tomography (CT) of the temporal bones was obtained in a patient with long-standing chronic otitis media. Note the adjacent sclerosis of the surrounding bone (large arrows), which is due to the long-standing chronic process.
Acqu
Less common pars tensa cholesteatomas typically involve the facial recess and sinus tympani of the posterior tympanum. An independent middle ear mass with bony destruction or ossicular erosion on CT is a cholestere atom 90% of the time.
Chol
Destruction of the middle ear ossicles, isolated petrous apex involvement, or labyrinthine involvement are rare. The mass extends medially and invades the posterior aspect of the middle ear cavity (curved arrow.
Para
Within the temporal bone region, they occur in the middle ear cleft of the cochlear promontory (20%) or hypotympanum (25%) as glomus tympanicum tumors, the jugular foramen region (50%) as glomus jugulare tumors, or just below the skull base (5%) as glomus vagal tumors. On CT scans, a small middle ear paraganglioma is best localized and delineated because of the superior spatial resolution.
Differential Diagnosis
CHAPTER 26 Hemangioma
High-resolution (1 to 2 mm) non-contrast CT performed in the axial and coronal planes and reconstructed with a "detail" (bone) algorithm best delineates the facial nerve canal. Thin-section multiplanar pre- and postcontrast T1- and T2-weighted scanning is best for delineating the overall extent of lesions, especially when it does not enlarge the facial nerve canal.
Differential Diagnosis (Geniculate Hemangiomas)
Aggressive surgery to remove the temporal bone portion of the lesion is the treatment of choice, especially when middle ear symptoms are present. Primary extracranial meningioma in the vicinity of the temporal bone: a benign lesion rarely recognized clinically.
Squa
Treatment for squamous cell carcinoma of the middle ear (and all temporal bones) includes surgery, chemotherapy, and post-surgical radiation. Bilateral squamous cell carcinoma of the middle ear and clinical review of an additional 5 cases of middle ear carcinoma.
Aden
In patients with these lesions, middle ear masses and temporal bone destruction are best delineated on CT scans. Only multiplanar, non-contrast CT scans are needed to determine the extent of these middle ear lesions.
Angiography
Primary adenoidal cystic carcinoma of the middle ear is so rare that no specific clinical features can be described. Other middle ear neoplasms (eg, schwannoma, hemangioma) and infectious processes are much more common than adenoid cystic carcinomas of the temporal bone.
Rhab
Extensive involvement of the temporal bone from the petrous apex to the apex of the mastoid is also described. Associated middle ear abnormalities and cerebrospinal fluid/peri-lymph leak are common in these patients (24%).
This term is overused to describe many anomalies of the inner ear. Anomalies of the semicircular canals (SCC) may coincide with the presence of a morphologically normal cochlea.
Anatomy and Embryology
Larg
Figure 36–1 Axial computed tomography (CT) of the right ear shows a stenotic internal auditory canal ( arrows. Congenital absence (atresia, aplasia) of the oval window is a known cause of congenital hearing loss.
Oval
The appearance of the tumor on magnetic resonance imaging (MRI) varies depending on the size of the tumor. Tumors may involve the base of the skull only when they are large and in the region of the jugular foramen when they are large.
Tran
Malfunction may be due to recurrent middle ear disease (otitis media or cholesteatoma), granulation tissue, or adhesions or displacement (subluxation, dislocation, or extrusion) of the prosthesis. The peduncle projects medially and extends to the head of the stapes (PORP) or the base/oval window of the stapes (TORP).
