46 Pediatric ENT Anatomy and Embryology With Radiology Correlates Flashcards
What is the foramen of Huschke?
What is the foramen of Huschke?
The foramen tympanicum, also known as the foramen of Huschke, is an anatomic variation in the tympanic portion of the temporal bone. When present, it is located at the anteroinferior aspect of the external auditory canal (EAC), posteromedial to the temporomandibular joint (TMJ). In most children, the foramen tympanicum gradually becomes smaller and completely closes before the age of 5 years, but it occasionally persists. Because no neural or vascular structures pass through this defect, it is not a true foramen. Persistence of the foramen tympanicum may also predispose the person to the spread of infection or tumor from the EAC to the infratemporal fossa, and vice versa.
How does the size and shape of the external auditory canal differ between children and adults?
How does the size and shape of the external auditory canal differ between children and adults?
In adults, the EAC has a near sigmoid shape with the cartilaginous portion angling posteriorly and superiorly and the bony portion angling anterior inferiorly. Pulling the helix posterosuperiorly straightens the EAC and allows for better visualization of the tympanic membrane. In the infant the EAC is nearly straight. It then elongates and changes shape up till about age 9 when it is nearly adult size.
What is a dimeric tympanic membrane?
What is a dimeric tympanic membrane?
The tympanic membrane is made up of three layers: an inner membranous layer, a middle fibrous layer that gives rigidity to the membrane, and an outer squamous layer. If a tympanic membrane perforation does not heal with the fibrous layer incorporated, then that newly healed portion has only the two layers (dimeric) and results in a thin, floppy segment. This thinned segment is more easily retracted into the middle ear and can affect conduction of sound to the ossicles.
Why are the tympanic membrane and ossicles required for normal hearing?
Why are the tympanic membrane and ossicles required for normal hearing?
Sound as it is presented to us travels through air, while our hearing organs within the inner ear are bathed in fluid. If we attempt to transmit sound from air to fluid there is a 99.9% loss in energy, which is known as an impedance mismatch. The impedance mismatch is overcome by a series of mechanical advantages including a tympanic membrane that is 21 times the size of the stapes footplate, and ossicles that create a lever force of 1.3×. Together these overcome the mismatch in impedance and allow for near full transmission of all sound energy into the inner ear.
What are the innervations of the tensor tympani and stapedius muscles?
What are the innervations of the tensor tympani and stapedius muscles?
The tensor tympani is derived from the first pharyngeal arch and thus is innervated by a branch of the fifth cranial nerve. The stapedius muscle is derived from the second arch and thus is innervated by a branch from the seventh cranial nerve. The dampening effects of these two muscles can result in a reduced sound transmission of 15 dB.
Why is the stapes shaped like a stirrup?
Why is the stapes shaped like a stirrup?
The stapedial artery is transiently present in fetal development connecting the future external carotid arterial system with the internal carotid system. This vessel goes through the middle ear and the primordial stapes creating the structure of the stapes known as the obturator foramen. A persistent stapedial artery (Figure 46-1) is very rare and may be associated with pulsatile tinnitus, conductive hearing loss, and an absent ipsilateral foramen spinosum.
Figure text: Persistent stapedial artery. Axial CT images reveal (A) a normal foramen spinosum on the right (arrowhead) and (B) an absent foramen spinosum on the left (arrowhead). Images acquired more cephalad through the left ear illustrate the course of the persistent stapedial artery (C) ascending in a small canal on the surface of the posterior cochlear promontory (arrow), and (D) resulting in an enlarged anterior tympanic segment of the facial nerve canal (arrow).
What are the two most common congenital abnormalities of the ossicles?
What are the two most common congenital abnormalities of the ossicles?
The two most common ossicular abnormalities are a congenitally fixed stapes and incudostapedial discontinuity. Isolated abnormalities of the stapes are more likely to be unilateral while congenital abnormalities of the other ossicles are more likely to be bilateral.
What are the nerves that run through the middle ear?
What are the nerves that run through the middle ear?
Jacobson’s nerve is a branch of CN IX and runs across the tympanic promontory innervating the middle ear mucosa and eustachian tube and providing parasympathetic innervation to the parotid gland. Arnold’s nerve is a branch of the vagus nerve that gives sensory innervation to the external auditory canal. This nerve is sometimes stimulated when cleaning the ear and can make a patient cough. The chorda tympani nerve branches from the descending portion of the facial nerve (Figure 46-2) and runs medial to the malleus before exiting the middle ear through the petrotympanic fissure. Finally, the facial nerve may be dehiscent superior to the oval window or may be positioned within the middle ear in congenitally malformed ears.
Figure text: Facial nerve. Axial CT images demonstrate the course of the facial nerve (black arrowheads), including (A) the labyrinthine segment, (B) the tympanic segment, and (C) the mastoid segment. Coronal reformat CT image (D) illustrates the course of the tympanic segment (white arrowhead) passing under the lateral semicircular canal (arrow). Relevant anatomy includes (A) the vestibule (v) and vestibular aqueduct (white arrow), (B) the interrelationship between the head of the malleus (m) and body of incus (i) in the epitympanum, and (C) the apical and basal turns of the cochlea (a & b), the jugular bulb (j), and the chorda tympani (white arrow).
What are the named segments of the facial nerve that run through the temporal bone and which is the narrowest?
What are the named segments of the facial nerve that run through the temporal bone and which is the narrowest?
The internal auditory canal segment of the facial nerve is 7 to 8 mm in length and runs superior to the cochlear nerve (think of the mnemonic “7up/Coke down”). The labyrinthine segment extends from the internal auditory canal to the geniculate ganglia; this is the narrowest segment and most prone to damage secondary to trauma and/or swelling. The tympanic segment runs from the geniculate ganglion to the second genu, running in the medial wall of the tympanic cavity over the round window and below the bulge of the lateral semicircular canal. The final segment is the mastoid or vertical segment (Figure 46-2).
What is the cochleariform process and what is its relationship to the facial nerve?
What is the cochleariform process and what is its relationship to the facial nerve?
The cochleariform process is a curved ridge of bone that houses the tendon of the tensor tympani muscle. This ridge of bone is also a good landmark denoting the anterior position of the tympanic portion of the facial nerve.
What are the boundaries of the sinus tympani?
What are the boundaries of the sinus tympani?
The borders of the sinus tympani are formed by the ponticulus superiorly and subiculum inferiorly. This space is difficult to visualize during surgery without the use of a mirror or angled endoscope. Clinically this area is important during surgery for cholesteatoma, as the cholesteatoma may have grown into the sinus and can be difficult to extract.
What is the promontory of the middle ear?
What is the promontory of the middle ear?
This bulge on the medial surface of the middle ear represents the prominence of the basal turn of the cochlea.
What are some commonly described developmental abnormalities of the cochlea and when does developmental arrest occur?
What are some commonly described developmental abnormalities of the cochlea and when does developmental arrest occur?
- Cochleovestibular Aplasia, formerly known as a Michel deformity (arrest third week): Complete absence of cochlear and vestibular structures (Figure 46-3)
- Cochlear Aplasia (arrest late third week): Absent cochlea; normal, dilated or hypoplastic vestibule and semicircular canals
- Common Cavity (arrest fourth week): Cochlea and vestibule form a common space (Figure 46-4)
- Incomplete Partition Type I (arrest fifth week): Cystically enlarged cochlea without internal architecture; dilated vestibule, mostly enlarged internal auditory canal
- Cochlear hypoplasia (arrest sixth week): Distinctly recognizable separation of cochlear and vestibular structures; small cochlear bud
- Incomplete Partition Type II, formerly known as a Mondini deformity (arrest seventh week): Cochlea with 1 1/2 turns, cystically dilated middle and apical turn (cystic apex), slightly dilated vestibule (Figure 46-5)
Figure text 4: Common cavity malformation. (A) Axial and (B) coronal reformat CT images demonstrate a featureless common cavity representing a rudimentary cochlea, vestibule, and semicircular canals (arrows). In this anomaly, otic placode development is arrested in the fourth gestational week, following differentiation into the otocyst.
Figure text 5: Cochlear incomplete partition type II. (A) Axial CT image reveals deficiency of the interscalar septum between the middle and apical turns (arrowhead) in this patient with a (B) large vestibular aqueduct (arrow).
Of the above developmental deformities which are the most common?
Of the above developmental deformities which are the most common?
Incomplete partition type II followed by a common cavity
What is the most common finding on a CT scan of a profoundly deaf child?
What is the most common finding on a CT scan of a profoundly deaf child?
The most common finding is a radiographically normal inner ear. It is presumed that the malformation is limited to the membranous labyrinth, which cannot be seen by our imaging modalities and represents 90% of children with profound hearing loss.
Why are neonates considered obligate nasal breathers?
Why are neonates considered obligate nasal breathers?
In neonates the larynx is elevated with the epiglottis in apposition to the soft palate. This allows the infant to drink and breathe simultaneously, but this also means that infants have difficulty breathing through their mouths (Figure 46-6).
Figure text: Normal airway. Lateral radiographs in (A) a 13-day-old and (B) a 14-year-old illustrate normal airway anatomy. a: adenoids; sp: soft palate; e: epiglottis; ae: aryepiglottic folds; h: hyoid; C2: odontoid process.
Why does the recurrent laryngeal nerve wrap around the aortic arch on the left and subclavian artery on the right?
Why does the recurrent laryngeal nerve wrap around the aortic arch on the left and subclavian artery on the right?
The sixth arch, which is important in laryngeal development, is also important in the development of the aortic arch and subclavian artery. As portions of the sixth arch descend to form these great vessels it carries the recurrent laryngeal nerve with it. A nonrecurrent laryngeal nerve on the right is a rare entity associated with an aberrant right subclavian artery (abnormal development of the sixth arch) (Figure 46-7).
Figure text: Aberrant subclavian artery. A, Oblique image from an esophagram shows an extrinsic posterior indentation on the esophagus (black arrow). B, Sagittal T2-weighted image of the cervical spine, in a different patient, reveals an aberrant right subclavian artery (white arrow) coursing posterior to the trachea (t) and esophagus (e). (pa: pulmonary artery, ao: aorta).
What is CHAOS?
What is CHAOS?
CHAOS stands for congenital high airway obstruction syndrome. It is a failure of the airway to recannulate during embryological development of the larynx (laryngeal atresia) (Figure 46-8) or upper trachea. If this is not identified prenatally the survival rate is very low because the patient is unable to be ventilated unless there is a corresponding tracheoesophageal fistula.
Figure text: Laryngeal atresia. Sagittal HASTE image from a fetal MRI reveals a high airway obstruction, at the level of the larynx (arrowhead), with distension of the distal trachea (asterisk) secondary to failure of the airway to recannulate during embryogenesis.
