CT and MR imaging findings of tumors and tumor-like
conditions of the external auditory canal
Poster No.:
C-1784
Congress:
ECR 2010
Type:
Educational Exhibit
Topic:
Head and Neck
Authors:
K. D. Song, H.-J. Kim, E. Kim, S. T. Kim; Seoul/KR
Keywords:
external auditory canal, tumor or tumor-like conditions, CT and MR
DOI:
10.1594/ecr2010/C-1784
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Page 1 of 15
Learning objectives
In this poster we will review the basic anatomy and spatial relationship of the external
auditory canal(EAC). And then, we will categorize various tumors and tumor-like
conditions of the EAC. Finally, we will review the CT and MR imaging findings of them.
The aim is to improve the understanding of wide spectrum of tumors and tumor-like
conditions of the EAC
Background
EAC itself is very simple tubular structure. However, surrounding structures are very
complex. Therefore, to know tumors and tumor-like conditions more exactly, it is
needed to understand the anatomy of the EAC and spatial relationship of the EAC with
surrounding structures.
Anatomy
EAC is an S-shaped tubular structure extending from the bottom of the concha to the
tympanic membrane. It is directed medially, forward, and slightly upward at first. Then,
it courses medially and backward, and lastly passes medially, forward, and slightly
downward.
EAC is composed of the cartilaginous portion and the osseous portion.
The cartilaginous portion: It is a lateral one third portion of the EAC, and continuous
with auricular cartilage. Its skin is thick, and contains hairs, sebaceous, and ceruminous
glands. The cartilage is deficient at the upper and back part of the canal.
Page 2 of 15
The osseous portion: It is a medial two third portion of the EAC, and continuous with
bony walls of the middle ear. It is narrower than the cartilaginous portion. Its skin is much
thinner and contains no hairs or glands.
Spatial relationship with surrounding structures
Anterior: In front of the osseous part is the condyle of the mandible. It is frequently
separated from the cartilaginous part by a portion of the parotid gland. The movements
of the jaw influence to some extent the lumen of this latter portion.
Posterior: Behind the osseous part are the mastoid air cells, separated from the canal
by a thin layer of bone. The deepest portion of the canal is related to the mastoid antrum
posteriorly.
Superior: Immediately superior to the osseous is middle cranial fossa. Variable
tegemental air cells may be interposed. The deepest portion of the canal is related to the
epitympanum superiorly.
Inferior: The jugular bulb is located inferiorly. The inferior wall of the canal is composed
of dense bone, but in some instances, it may be thin, exposing an enlarged or dehiscent
jugular bulb.
Page 3 of 15
Fig.: Fig. 1. Anatomy of the EAC A. Horizontal section through left ear; upper half of
section. B. External and middle ear, opened from the front. Right side
References: From Gray's Anatomy of the Human Body. Fig. 907 and 908
Page 4 of 15
Fig.: Fig. 1. Anatomy of the EAC A. Horizontal section through left ear; upper half of
section. B. External and middle ear, opened from the front. Right side
References: From Gray's Anatomy of the Human Body. Fig. 907 and 908
Imaging findings OR Procedure details
Imaging Findings
Various diseases involve the EAC. However, there was not a systematic classification
of them. At first, tumors and tumor-like conditions of the EAC are defined as masses
that involve the EAC primarily or secondarily. They are classified into five categories:
congenital lesions, infectious and inflammatory diseases, benign tumors, malignant
tumors, and miscellaneous conditions according to the etiologies of the diseases (Tab. 1).
Page 5 of 15
Table 1. Classification of tumors and tumor-like conditions of the EAC
Classification
Congenital lesions
Diseases
•
•
•
Infectious and Inflammatory diseases
•
•
•
•
•
The first branchial cleft
anomaly
Venolymphatic malformation
Diseases related to the
enlarged foramen of Huschke
cholesteatoma
Chronic external otitis (Medial
canal fibrosis)
Malignant external otitis
Tuberculosis
Fungal infection (Otomycosis)
Benign tumors
•
•
•
•
•
•
•
•
•
Exostosis
Osteoma
Nevus
Hemangioma
Pilar sheath acanthoma
Meningioma
Polyp
Papilloma
Grandular tumors
(ceruminous adenoma,
pleomorphic adenoma,
syringocystadenoma
papilliferum)
Malignant tumors
•
•
•
•
•
•
•
Squamous cell carcinoma
Basal cell carcinoma
Glandular tumors (adenoid
cystic, mucoepidermoid,
adenocarcinoma)
Sarcomas (granulocytic
sarcoma, Ewings sarcoma,
rhabdomyosarcoma)
Melanoma
Sebaceous cell carcinoma
Metastatic lesions
Lymphoma
•
•
•
Impacted cerumen
Keratosis obturans
Granulomatous diseases
•
Miscellaneous conditions
Page 6 of 15
Congenital lesions
The first branchial cleft anomalies
Anomalies of the first branchial cleft arise from incomplete closure of the ectodermal
portion of the first branchial cleft. Whether the defect is a fistula, sinus, or cyst depends
on the degree of closure.(1) Of the first branchial cleft anomalies, which account for up
to 8% of all branchial amomalies. 68% are cysts, 16% are sinuses, and 16% are fistulas.
(2) The anomaly begins on the floor of the external auditory canal either at the level of
the bony-cartilaginous junction or in the cartilaginous portion, follows the seam between
the mandibular and hyoid arches, and ends in the submandibular region more or less
distally, depending on the extent of the disturbance of the fusion.(1) Contrast-enhanced
CT scan reveals a well-defined, nonenhancing mass of fluid attenuation(Fig. 2).If the
lesion is resected limitedly, recurrence is inevitable. Therefore, only complete surgical
excision with wide exposure of the lesion can cure it.
Diseases related to the enlarged foramen of Huschke
The foramen of Huschke, also known as the foramen tympanicum, is an anatomic
variation in the tympanic portion of the temporal (tympanic) bone. Tympanic bone
develops from fusion of membranous ossification points. If they are not fused and there is
a osseus defect, we call it persistant foramen of Huschke. When present, it is located at
the anteroinferior aspect of the EAC, posteromedial to the temporomandibular joint (TMJ).
(3) The reported prevalece rate of persistent foramen of Huschke ranges from 4.6%
to 9.1%.(3, 4) Diseases related to the enlarged foramen of Huschke are occasionally
reported. Herniation of soft tissue from TMJ to EAC through the persistant of foramen
of Huschke can cause TMJ pain, and it can be mistakenly considered as a EAC tumor.
Infectious or tumoral condition can spread from the EAC into the infratemporal fossa,
and vice versa. On CT images, osseus defect at the anteroinferior aspect of EAC with or
without herniation of soft tissue is seen (Figs.3).
Infectious and Inflammatory disease
Cholesteatoma / Keratosis obturans
Acquired cholesteatoma is an inflammatory mass which is a cystic structure lined by
keratinizing stratified squamous epithelium. . It is most commonly involves middle ear
cavity, and rarely occurs in the EAC. An incidence of 0.15 for primary cases, while
0.30 for all cases per year per 100,000 inhabitants was reported.(5) It is quite lower
than the incidence rate of the middle ear cholesteatoma, 9.2 per year per 100,000.
EAC cholesteatoma occurs in individuals over 40 years of age.(2) The most common
presenting symptoms are otalgia and otorrhea. EAC cholesteatoma is seen as an
EAC soft-tissue mass with associated bone erosion and intramural bone fragments on
Page 7 of 15
CT images (Fig. 4). Compelete surgical resection of the cholesteatoma sac and the
surrounding necrotic bone is needed for successful treatment. On otoscopic examination,
EAC cholesteatoma can be difficult to distinguish from other diseases especially keratosis
obturans. Because EAC cholesteatoma may require surgical intervention, whereas
keratosis obturans is managed medically, distinguishing these entities is important.
Keratosis obturans occurs in patients under the age of 40 years who have a history of
sinusitis or bronchiectasis. Severe pain and conductive deficit may occur, but otorrhea
is rare. Keratin plug fills the canal rather than extending into and destroying the bony
wall (Fig. 5).(2)
Chronic external otitis (Medial canal fibrosis)
Medial canal fibrosis is uncommon disease entity characterized by formation of mature
fibrous tissue in the medial aspect of the bont EAC lateral to the tympanic membrane. The
pathogenesis is unclear. However, it is speculated that an insult to the EAC and tympanic
membrane epithelium initiates the process. This may be infectious or traumatic or arise de
novo in patients with associated dermatitis. This initial insult produces granulation tissue.
The granulation tissues become infected and form fibrous plugs occluding the EAC, and
lined by skin.(6) It usually occurs in the fifth decade of life. A typical imaging finding is
the soft tissue filling the EAC adjacent to a normal, air-containing middle ear space (Fig.
6). The treatment consists primarily of topical applications and regular suction toilet in
an early stage. Despite the best efforts in this regard relentless progression to the dry,
stenotic stage is often inevitable. In the fibrous stenotic stage surgery is the only effective
intervention.(7)
Malignant external otitis
Malignant external otitis is a severe infectious disease typically seen in elderly patients
with diabetes mellitus. It is also seen in individuals who are immune-suppressed such as
those who have leukemia or lymphoma, or those who have undergone chemotherapeutic
regimens. The most common cause is Pseudomonas aeruginosa. Patients typically
present with severe otalgia, otorrhea. Malignant external otitis likely begins at the
junction of the cartilagious portion and the osseus portion of the EAC. An uncontrolled
infection may spread by numerous pathways and can cause chondritis and osteomyelitis
extending posteriorly into mastoid, anteriorly into the temporomandibular joint, or medially
toward petrous apex. Most commonly it spreads inferiorly via the fissues of Santorini,
those tiny anterior clefts in cartilaginous portion of the canal to involve the soft tissues
inferior to the temporal bone. Initially it can be seen as nonspecific findings such as areas
of soft-tissue density in the external canal and fluid in the mastoid or middle ear. More
advanced and omnious findings include bone erosion, obliteration of fat planes inferior
to the temporal bone, parapharyngeal space involvement, masticator space disease,
mass effect in the nasopharynx, clivus erosion, and intracranial extension (Fig. 7).
(8) Treatment includes meticulous glucose control, aural toilet, systemic and ototopic
Page 8 of 15
antimicrobial therapy, and hyperbaric oxygen therapt. Surgical removal of the lesion
requires resection of large portions of the temporal bone. Surgery is now reserved for
local debridement, removal of bony sequestrum, or abscess drainage.
Fungal infection (Otomycosis)
Otomycosis is a common fungal infection of the ear that is seen in the tropical and
subtropical regions of the world. Its prevalence as high as 9% among patients who
present with signs and symptoms of otitis externa has been reported.(9) Its prevalence
is greatest in hot, humid, and dusty areas of the tropics and subtropics. Aspergillus
and Candida species are the most commonly identified fungal pathogens. The most
common symtoms include otalgia, otorrhea, and pruritus. In addition, hearing loss and
aural fullness can occur as a result of accumulation of fungal debris in the canal.(10) It can
be usually diagnosed by clinical exam. Appropriate topical antifungal agents and frequent
debridements usually results in prompt resolution of symptoms. However, recurrence or
residual disease can be common.
Benign tumors
Exostosis / Osteoma
Exostoses are a condition in which the external auditory canal becomes stenotic
secondary to hyperplastic bone formation. On the other hand, osteomata are considered
as true bone tumors. Although these can produce similar clinical picture in sex and
age incidence, exostoses and osteomata usually are considered separate clinical
entities. Exostoses are multiple, bilateral and broad based and are found medial to the
sutures on the tympanosquamous or tympanomastoid bone, whereas osteomata are
single, unilateral, and pedunculated and rise from the tympanic suture line laterally.
(11) Exostoses are thought to be a reactive condition secondary to multiple cold water
immersions, or recurrent otitis externa. Ears with exostoses have been called surfer's ear
or Australian ears. These are usually asymptomatic unless it is enough large to trap water
and debris or to cause impingement on the motion of the ossicular chain. Most common
symptom of exostoses is conductive hearing loss. Water and debris trapped medial to it
can cause otitis externa, otorrhea and otalgia. On CT scan findings of exostoses appear
as broad based lesion with no deep extension (Fig. 8), while an osteoma is seen as a
well-demarcated, hyper-dense attenuating outgrowth tumor (Fig. 9). The treatments of
both of two disease entities are essentially the same. Frequent cleaning of debris from
the EAC can be sufficient for small non-complicating lesions, while large lesions causing
EAC obstruction and hearing impairment require surgical removal.
Nevus
Page 9 of 15
Nevus is generally considered to be a benign neoplastic proliferation of melanocytes.
Nevus is subdivided into junctional, compound and intradermal nevus. However, These
are transitional stages in the life cycle of nevi, which start out as junctional nevi and,having
become intradermal nevi.(12) Intradermal nevus arising within the EAC was reported
firstly by Youngs et al.in English literature.(13) If its size is small, it does not cause any
symptom and is detected incidentally (Fig. 10). However, as its size becomes larger,
it can present with aural obstruction and conductive deafness or cause the trapping of
water within the canal and a predisposition to recurrent attacks of acute otitis externa.(14)
Glandular tumors (benign and malignant tumors)
Ceruminous glands are modified apocrine glands found in the deep dermis of skin
lining the cartilaginous portion of the external auditory canal. (15) Ceruminous glandular
tumors include benign tumors such as ceruminous adenoma, pleomorphic adenoma,
and syringocystadenoma papilliferum, and malignant tumors such as ceruminous
adenocarcinoma, adenoid cystic carcinoma, and mucoepidermoid carcinoma.(16) The
typical presenting feature is an intra-dermal lump or cyst with or without impaired
hearing. It occurs more frequently in female than male. Benign tumors present with an
average age of 57 years, whereas malignant tumors present with an average age of
44 years.(17) Ceruminous adenomas are composed of glands in which epithelial and
outer myo-epithelial cells are present (Fig. 11). Ceruminous adenocarcinomas may be
cytologically bland with an infiltrating margin as above, or may have more obviously
malignant cytological features such as significant nuclear pleomorphism or a brisk mitotic
rate. They may have a partly papillary architecture. Adenoid cystic carcinomas have
the same appearance as those found in other sites, such as salivary gland, breast,
vulva or skin. There are characteristic cribriform islands of cells with punched out 'holes'
giving rise to the so-called 'Swiss cheese' appearance (Fig. 12). Pleomorphic adenoma,
syringocystadenoma papilliferum and muco-epidermoid carcinoma are similar to their
counterparts in other areas of the skin.(15) Benign tumors are best treated by wide
local excision, while malignant tumors require an initial aggressive wide en bloc surgical
resection with possible postoperative radiation and long-term follow-up.(18)
Malignant tumors
Malignant tumors of the external auditory canal is infrequent, with an incidence of
approximately 1 per million population per year.(19) Carcinomas of the EAC constitute
less than 1% of all head and neck malignant neoplasms.(20) Although squamous
cell carcinoma(SCC) of the EAC is very uncommon malignant tumor, it represents
approximately 90% of all malignant tumors of the EAC.(21) Other malignant tumors
that can involve the EAC basal cell carcinoma, adenocarcinoma, adenoid cystic
carcinoma, ceruminous carcinoma, malignant fibrous histiocytoma, chondrosarcoma and
osteosarcoma.
Page 10 of 15
Squamous cell carcinoma(SCC)
The prevalence of this tumor is between 1 and 6 people per 1 million population.(22)
Although its pathogenesis is incompletely understood, there are possible risk factors
such as chronic inflammation, chronic external otitis, chronic suppurative otitis media,
cholesteatoma, radiation/radiotherapy, chlorinated disinfectants, some toxic agents (e.g.,
4,4#-Thiodianiline) and Thio-TEPA.(23) It occurs more often in women. It presents with an
ulcerative EAC mucosal lesion that may mimic otitis externa or EAC cholesteatoma (Fig.
13) (Fig. 14). Early symptoms include otorrhea, otalgia and conductive hearing loss. The
tumor destroys the adjacent bone in the EAC and middle ear and invades the surrounding
soft tissue. Extension into middle cranial fossa, matoid, and soft tissue beneath the
temporal bone is common. The temporomandibular joint, the parotid gland, and the
carotid canal can be involved.(2) Combination therapy with surgery and radiotherapy
provided a higher 5-year survival rate than surgery or radiotherapy alone.(24) However,
the proper management is still under debate because this tumor is rare and a staging
system is not established.
Melanoma
Malignant melanoma can arise within the epithelium over the temporal bone as a primary
lesion or as a result of a local or distant metastasis. This tumor may arise from the
temporal bone's squamous epithelium or from its associated mucosal portions.(25)
The external ear constitutes 7% to 16%of all head and neck cutaneous melanomas.
Approximately 60% of external ear malignant melanomas occur on the helix and antihelix
of the pimma. Primary involvement of the EAC has been only rarely reported.(26)
The CT finding is a soft tissue mass within the external auditory canal without bony
erosion or tympanic invasion in early stage, but this is nonspecific. On MRI, melanin
classically shows a characteristic signal intensity as hypersignal on T1-weighed image,
and relatively low-signal intensity on T2-weighed image (Fig. 15). But these findings do
not seem to be constant. Surgical resection, lymph node dissection and radiotherapy
are the usual treatment for most cutaneous melanomas associated with lymphnode
metastases.
Metastases
Metastatic tumors to the external auditory canal are rare. According to the report that
included the temporal bone, middle ear and external ear, metastatic breast carcinoma is
the commonest primary cancer, followed by lung, prostate and renal carcinoma.(27)
Page 11 of 15
Conclusion
The EAC is a more complex structure than is often initially appreciated because
surrounding structures should be considered together when we evaluate the diseases
involving the EAC. A wide variety of disease entities such as congenital lesions, infectious
and inflammatory diseases, benign tumors and malignant tumors may involve the EAC.
Some disease entities are very rare and radiologic findings of some diseases overlap with
those of another diseases. However, A understanding of the anatomy of the EAC and the
spatial relationship with surrounding structures, and a familiarity with the wide spectrum
of radiologic findings of these disease entities may lead to improved diagnostic accuracy.
Personal Information
References
Page 12 of 15
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Page 15 of 15