Download Exostoses and Osteomas of the EAC

The journey is as important as the destination.
Review of an important conduit; external auditory
canal and its pathologies.
Umar S. Chaudhry MD*, Michelle Naidich MD*, Erin N. McComb MD*
* Section of Neuroradiology,
Northwestern Memorial Hospital, Chicago, IL.
The external auditory canal (EAC) has a variety of pathologies and variations. In our
experience radiologists can overlook this important passageway or underestimate its
significance. Our aim is to make the radiologist, either in-training or in practice, familiar
with the anatomy and imaging of the EAC.
Patient A
Axial non contrast CT
PRE TEST:
- Name the pathology in each patient
- Which one is related to cold water
exposure?
Patient B
-
What is the pathology in Patient A and B?
-
Are there any histological differences?
Axial non contrast CT
-
What are the possible factors predisposing to Patient A pathology?
-
Which is more symptomatic?
Coronal non contrast CT
Coronal non contrast CT
Axial non contrast CT
PRETEST
Name the pathology and any associated findings.
Do you expect to see inner ear abnormalities?
Functions of the EAC
- Conduction of sound
- Contribution to directional and frequency selection
- Mechanical protection from temperature and humidity
- Production of cerumen
5th Week
1st
pharyngeal
arch
1st pharyngeal
pouch
10th Week
Embryology
18th Week
Canalization of
the meatal plug
Meatal plug
An in-pouching of the first pharyngeal
cleft forms the primitive EAC
Ectoderm
Endoderm
The in-pouching makes contact with
the first pharyngeal pouch and the
medial aspect proliferates to form the
meatal plug
Canalization of the meatal plug
produces the EAC, including the
outer ectodermal layer of the
tympanic membrane
Development of EAC through eary life
Axial Non contrast CT
Normal EAC in a newborn
At birth, the EAC is 2 cm in
length and is straight.
The tympanic membrane
horizontal.
Normal EAC in three year old
At three years, the EAC
shows close to mature
angulation of the canal, and
the bone in the inner ⅔
nearly complete.
Normal EAC in an 18 year old
Elongation of the EAC
continues until 9 years. At
puberty, the dormant
apocrine glands and hair
start functioning.
Histology
Desquamation occurs radially and centrifugally from the TM.
Additionally, the desquamation moves laterally from the
Keratinized
epithelium
inner ⅔ of the EAC
to clear thesquamous
skin and debris.
Outer ⅓ contains glands and hair follicles, similar to the skin
everywhere else in the body ( i.e. keratinized squamous
epithelium that measures approximately 0.5 - 1.0 mm)
Inner ⅔ is devoid of glands and is contiguous with the
tympanic membrane, at which point the average
thickness is 0.2 mm
Tympanic membrane
Thickness
The exact mechanism of this migration is not clear, but may be
due to reduced intercellular adhesion and differentiation of
keratinocytes.
Anatomy
The external ear is comprised of the pinna and the EAC. The EAC extends from the external meatus to the lateral margin of the
tympanic membrane. The average adult length of the EAC is 2-3 cm. The outer ⅓ is cartilaginous and the inner ⅔ is osseous. The
outer cartilaginous portion is variable in dimension with jaw movement. The narrowest portion is the isthmus, a point just medial to
the osseous and cartilaginous junction.
Figure: Axial depiction of the EAC
Normal axial CT of the EAC
Anatomy
Normal axial CT of the EAC
Normal Coronal CT of the EAC
Normal axial CT of the EAC
Conhco-meatal angle
Osseous-cartilaginous junction
Isthmus
Cartilaginous bony angle
The EAC is “S” shaped. On an axial plane, it bends first anteriorly, then posteriorly, and finally anteriorly again.
Two angles are seen on the axial plan; the concho-meatal angle and the cartilaginous bony angle. On the
coronal view, the EAC is bowed superiorly and then the inner ⅔ downslopes.
Sensory innervation and drainage of the EAC
Generally, innervation of the ear is one of the most
complex in the body, with overlapping innervation. A
simplified version is as follows:
•
Auriculotemporal from V3 - anterior auricle, anterior wall of EAC
•
Auricular branch of VII - posterior/superior bony EAC
•
Auricular branch of X - inferior bony EAC and posterior/superior
cartilaginous EAC
•
Lesser occipital nerve and Greater auricular nerve from C2 and C3
spinal nerves - posterior and inferior auricle, adj skin
Fissures of Santorini, described by an Italian anatomist
are present in the anterior and inferior aspect of the
cartilaginous EAC. Normally, these allow flexibility of the
auricle; however, these can also act as pathways for
spread of disease from the EAC to the parotid gland or
vice versa.
Figure: Axial depiction of the EAC
Imaging Recommendations
- CT is the main “work horse” for imaging of the EAC, which is understandable as this is mainly an air
containing structure. Osseous integrity and anatomy play a key role in differentiating various
pathologies.
- Multi planar, high resolution CT (< 1 mm collimation) is the preferred protocol
- Contrast may be added if infection or a mass is suspected
- MRI is useful to assess for skull base and cranial nerve involvement as well as intracranial extension
- Nuclear medicine has limited utility, but can be considered when other modalities are not conclusive
-
Bone scan: Sensitive but not specific for infection, tumor, and other bone diseases
-
Gallium Scan: Optimal for imaging infection, but is expensive
Congenital pathologies
- Congenital EAC pathologies comprise 1-5 % of all branchial cleft abnormalities
- EAC atresia is a rare entity, with an incidence that varies from 1 in 10 to 20,000
- EAC atresia can be:
- Bilateral in one-third of patients
- Osseous, membranous, or both
- Syndromes/findings that are associated with EAC atresia:
- Craniofacial anomalies, such as Goldenhaar syndrome or Treacher Collins syndrome
- Microtia or hypoplastic pinna
EAC atresia
- A radiologist should assess:
- EAC, TM, size of middle ear cavity, ossicles, mastoid air cells, oval window, round window,
course of the facial nerve, and for the possible presence of a congenital cholesteatoma
- EAC atresia can occur with ossicular and middle ear cavity dysplasias
- In EAC atresia, the tympanic segment of the facial nerve canal shortens
- The inner ear structures (cochlea, vestibule, and semicircular canals) are not usually affected
because they arise from a different embryologic anlage
EAC atresia
Complete atresia of the EAC
Complete atresia of the EAC
Inner ear is normal
Abnormality of the pinna
Non contrast axial temporal bone CT
Non contrast axial temporal bone CT
Non contrast Coronal temporal bone CT
Acute Otitis Externa (AOE)
- Defined as “Diffuse inflammation of the external ear canal, which may also involve the pinna or tympanic
membrane”
- A hallmark of AOE is intense tenderness of the tragus and/or pinna that is disproportionate to the findings
on visual inspection
- The majority (98%) of AOE cases in North America are bacterial
- The most common pathogens are Pseudomonas aeruginosa (20%-60% prevalence) and
Staphylococcus aureus (10%-70% prevalence), often occurring as a polymicrobial infection
- AOE is more common in regions with warmer climates, increased humidity, or increased water exposure
from swimming
AOE – role of radiology
- Usually imaging is not required
- Imaging may be considered in the following situations:
-
Clinical concern for malignant otitis externa
Non responsive to treatment
Exclude pathologies that mimic AOE, such as TMJ dysfunction
Atypical presentation
- Risk factors for complications include:
- Tympanostomy tube, diabetes, immunocompromised state, prior radiotherapy
AOE
Contrast axial temporal bone CT
Patient with uncomplicated AOE. There is soft tissue thickening and enhancement
along the EAC. No underlying bony erosions are seen. Additionally, there is a
prominent, enhancing pre auricular lymph node.
AOE
Figure 1
Patient with uncomplicated
AOE. There is soft tissue
thickening and
enhancement along the left
EAC, as compared to the
normal right side (figure 1).
The inflammation and
enhancement also involve
the left pinna
Contrast axial temporal bone CT
Contrast Coronal temporal bone CT
Malignant otitis externa (MOE)
- The term malignant otitis externa was first used in 1968 by Chandler (also known as necrotizing external
otitis)
- MOE is an aggressive infection that predominantly affects elderly, diabetic, or immunocompromised
patients
- P aeruginosa is isolated from exudate in the ear canal in more than 90% of cases
- MOE can have a high morbidity and mortality, although with aggressive, timely treatment, mortality rates
have been reduced from 50% to 10–20%
- MOE usually begins insidiously at the osseous-cartilaginous junction.
- The tympanic membrane is usually resistant to the infectious process
- The fissures of Santorini allow access to the adjacent structures, with infection spreading rapidly through
soft tissue, cartilage and bone and causing necrosis
Malignant otitis externa: Role of imaging
- Radiology is very important for the initial diagnosis as well as identifying complications and extent of
disease
- CT is sensitive to bone erosion and is of particular value in assessing the middle ear, mastoid, bony facial
nerve canal, petrous apex and carotid canal
- MRI provides added benefit in assessment of the parotid region, meninges, cranial nerves and medullary
bone spaces
- Retro condylar fat infiltration has been proposed as one of the most frequent diagnostic findings in
patients with necrotizing external otitis
- Bone erosion is an important imaging ; however, in early stages of osteomyelitis, before bone
demineralization has occurred, bony changes may not be evident on CT
Imaging findings and spectrum of MOE
Anterior extension can involve
the TMJ and parotid gland
Medial extension can involve the facial nerve,
with erosion of the facial nerve canal or
stylomastoid foramen as well as asymmetrical
enhancement of the nerve
Epicenter of
the infection
Medial extension can also involve the jugular
foramen; affecting the cranial nerves IX, X, and XI.
The CN X is usually the first of these cranial
nerves to be affected.
Intracranial involvement can cause meningitis,
abscess formation and sinus thrombosis
Posterior extension to the mastoid
process can lead to bony destruction or
erosion on CT
MOE in a patient with ear pain and a history of diabetes mellitus
Contrast enhanced axial, soft
tissue windows
*
Axial bone windows
- Soft tissue inflammation, thickening and
enhancement
- Effacement of retro condylar fat pad
Bony erosion of the mastoid air cells
Patient with uncontrolled diabetes and findings of malignant otitis externa with complications
Contrast enhanced axial, soft tissue windows
Contrast enhanced Coronal soft tissue windows
*
Absence of contrast in the left sigmoid
sinus, indicating venous thrombosis
Rim enhancing collection subjacent to
the mastoid tip, compatible with an
abscess
Sarcoidosis affecting the EAC
- Sarcoidosis is a multi-system disorder of unknown origin that is characterized by non-caseating
granulomas
- Approximately 20–30% of patients with systemic sarcoidosis have cutaneous involvement, with
10–35% having specific lesions
- Given that the EAC contains skin similar to the rest of the body, sarcoidosis has been reported to
occur in the EAC. This involvement, however, is very rare
- Sarcoidosis usually presents with inflammation, although imaging findings are non specific
- Other skin conditions that can affect the EAC included psoriasis and Lichen planus
Patient with histological confirmed Sarcoidosis of the EAC
Contrast enhanced Coronal soft tissue windows
Contrast enhanced axial bone and soft tissue windows
Extensive soft tissue thickening
and enhancement of the left EAC
Axial bone windows demonstrate no bone erosion in the
region of the soft tissue thickening
EAC cholesteatoma (EACC)
- Cholesteatoma is a cystic mass that is lined by keratinizing stratified squamous epithelium and is
associated periostitis and bone erosion
- EACC is rare with an incidence of 0.15 cases per 100,000 (compared with 9.2 cases per 100,000
for middle-ear cholesteatoma)
- The etiology of external auditory canal cholesteatoma remains unclear
- Many authorities believe that idiopathic external auditory canal cholesteatoma results from a reduced migratory
capacity of the canal epithelium, which leads to ‘keratinisation in situ’
- Epidemiologically-linked risk factors for the development of external auditory canal
cholesteatoma include smoking, diabetes mellitus and repeated microtrauma (e.g. from cotton
buds or hearing aids)
EAC cholesteatoma
- Most cases are spontaneous/idiopathic or occur after surgery and/or trauma to the EAC,
although ear canal stenosis or obstruction have also been described as a causative factors
- The majority of idiopathic external auditory canal cholesteatomas occur along the inferior canal
wall. This is thought to be due to the relatively poor blood supply to the skin at this site
- The most common presenting symptoms of an idiopathic external auditory canal cholesteatoma
are unilateral otorrhea and mild to moderate otalgia
- If the cholesteatoma invades into the mastoid, it may also erode the facial nerve canal, sigmoid
sinus and semicircular canals. Erosion through the anterior wall of the canal may affect the
temporomandibular joint
- Rarely, in advanced cases, extension into the posterior fossa has been reported and can result in
an intracranial abscess
EAC cholesteatoma
- Bone erosion is thought to be related to proteolytic enzymes within the cyst lining. Another contributing
factor is formation of granulation tissue
- High-resolution temporal bone CT examination is the gold standard for imaging
- EACC is most commonly seen as an EAC soft-tissue mass with associated bone erosion and intramural
bone fragments
- The bone erosion adjacent to the soft-tissue mass can vary from being smooth (similar to a middle ear cholesteatoma) to
irregular, secondary to the necrotic bone and periostitis
- It is important to evaluate for extension into the middle ear cavity as well as for integrity of the facial
nerve canal, tegmen tympani, and mastoid air cells, because these features may change the surgical
management
- Naim et al. developed a (I–IV) staging system for external auditory canal cholesteatoma, based on the
extent of erosion into nearby structures
EAC cholesteatoma
**
Non contrast axial temporal bone CT
Soft tissue mass within the EAC is posterior
in location
Non contrast Coronal temporal bone CT
Smooth bony erosion of the inferior wall
of the EAC is present adjacent to the
soft tissue mass
Keratosis Obturans (KO)
- The original description of KO was published by Toynbee in 1850, and the term keratosis obturans
was coined by Wreden in 1874. KO and EACC have been considered variants of the same disease
until Piepergerdes et al. classified these diseases as separate entities in 1980.
- There are clinical and radiographic differences between these entities, and often radiology is
integral to the diagnosis
- KO is the accumulation of large plugs of desquamated keratin in the EAC. The distinguishing
feature between KO and EACC is the absence of bone erosion and bony spicules in KO
- Patients with KO usually present with acute conductive hearing loss and accompanying severe
pain. In contrast, EACC is characterized by otorrhea and chronic, unilateral, dull pain secondary to
invasion of the canal wall.
Keratosis Obturans (KO)
- KO generally occurs in younger patients, and it is often bilateral.
- Development of KO is attributed to eczema, seborrheic dermatitis, and bronchiectasis
- It is thought that the sympathetic stimulation of the ceruminous glands causes subsequent
formation of an epidermal plug
- Imaging with CT of KO demonstrates a soft-tissue plug in the auditory canal, often with
generalized canal widening
- Because KO produces a pattern of bony expansion rather than erosion, invasive complications are
unlikely
Keratosis Obturans (KO)
Non contrast Coronal temporal bone
Soft tissue fills the bilateral osseous EACs without evidence of bony erosion
Exostoses and Osteomas of the EAC
- Exostoses are more common than osteomas, occurring in 6.36 of 1,000 patients
- Exostoses occur usually at the tympanomastoid or tympanosquamous suture lines, adjacent to
the bone-cartilage junction
- Histologically, there is debate regarding the differences between exostoses and osteomas;
however, most authorities believe that osteomas are true neoplasms whereas exostoses are a
reaction of the bone
- Osteomas are usually less symptomatic, but can lead to canal obstruction
Exostoses and Osteomas of the EAC
- Exostoses are usually bilateral, sessile, and have a strong association with chronic cold water
exposure, hence the use of the name ”surfers ear” for this pathology
- Osteomas appear as a single, unilateral, pedunculated mass that is not associated with a specific
etiology
- T1-weighted MRI may show hyperintense signal that is representative of bone marrow within the
medullary continuity in the osteoma
Osteoma of the EAC
Non contrast axial bone CT
Non contrast Coronal bone CT
Non contrast axial bone CT
Unilateral, pedunculated osseous
mass in the right EAC. The left EAC is
normal.
Bone density, pedunculated mass within the
EAC, compatible with an osteoma.
Exostoses of the EAC
Non contrast Coronal temporal bone CT
Non contrast axial temporal bone CT
Non contrast Coronal temporal bone
Bilateral circumferential, sessile osseous lesions in the EACs
Malignancies of external auditory canal
- Primary malignancies of EAC very rare, with an incidence that is <1 per million per year
- Squamous cell carcinoma (SCC) is the most common primary malignant tumor of the EAC,
accounting for 80% of all tumors of EAC
- Adenoid cystic carcinoma is the second most common tumor, which accounts for only 5%
- The symptoms of EAC tumors are often insidious and can be clinically misdiagnosed
- Imaging plays an important role in delineating factors which play a role in determining survival:
- Tumor extent
- Erosion of bone
- Brain involvement
SCC of the external auditory canal
- Lymph node metastases are much more commonly seen with SCC than other malignancies of
the EAC. Additionally, there is a tendency for SCC to undergo necrosis
- In comparison to SCC of EAC, adenoid cystic carcinoma has a higher risk of recurrence and
distant metastases
- SCC is more likely to grow along the entire length of the EAC, whereas adenoid cystic carcinoma
tends to grow along the superficial portion of the EAC
- CT can demonstrate destruction of the temporal bone
- On MRI, axial and coronal T1WI can show involvement of subcutaneous tissues, parotid gland,
and parapharyngeal space
- MRI post contrast T1 images are useful for identifying dural or brain invasion
SCC of the external auditory canal
Non contrast axial temporal bone CT
Non contrast Coronal temporal bone CT
Soft tissue mass growing along the entire length of the EAC
Adenoid cystic carcinoma of the external auditory canal
Coronal fat saturated T2 weighted images
Non contrast axial temporal bone CT
Axial Post contrast T 1 weighted images
Soft tissue mass growing along the superficial aspect of the EAC
Staging of malignancies in the external auditory canal
- There is no recognized American Joint Committee on Cancer or International Union against
Cancer staging system
- The T staging that is currently available, and is still in the process of evolution, was adopted from
a series of articles that were published by the Pittsburgh University for SCC of the EAC
From: Cancer of the External Auditory Canal,
Arch Otolaryngol Head Neck Surg.2002;128(7):834-837
Metastasis to the EAC
- The majority of metastases to the temporal bone are from a breast primary (21%), followed by
the lungs (12%), kidneys, prostate, and liver
- Temporal bone metastases are most commonly found in the petrous portion, the internal auditory
canal, or the mastoid process, but are extremely rare in the EAC
- There is currently no accepted staging system for non-SCC tumors of the EAC. Most authors
apply the Pittsburgh SCC staging system for patients with non-SCC
- Radiographically, it may be difficult to differentiate primary malignancy from metastatic tumor.
Therefore, clinical history becomes important to suggest metastases.
Cerumen in the EAC
Cerumen can masquerade as a mass of the EAC. However, if air can be visualized circumferentially around
the soft tissue, then a diagnosis of cerumen can be made. If the findings are equivocal, visual inspection
should be performed.
EAC density with have air all around it
Post Test
• Slide 1: A: Exostoses and B: Osteoma. Exostoses are associated with cold water exposure
Patient A
Patient B
• Slide 2: EAC atresia. Pinna abnormality. Usually are not associated with inner ear abnormalities
EAC Lesion
Diffuse soft tissue thickening
Osseous, but otherwise non aggressive
Focal soft tissue
Surrounding inflammation and fat stranding?
Unilateral
Summary and Algorithm
Yes
No
Consider AOE or
malignant otitis externa
Exostoses
(especially if symmetric)
Air around it
Yes
No
Yes
Osteoma
Underlying bone
destruction or local
lymph nodes?
Cerumen
No
Underlying osseous erosion?
No
KO should be considered
Yes
Suspect Malignancy
No
Yes
Check for internal calcifications
KO, inflammation (including
Sarcoidosis), or malignancy
Yes
EACC is favored
No
EACC or malignancy
is a possibility
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