Benign Soft Tissue Tumors
There are several benign soft tissue tumors that involve the EAC. These include aural polyps, lipoma, hemangioma, arteriovenous malformation (AVM), lymphangioma, smooth muscle tumors (leiomyomas), tumors of glandular origin, neural origin tumors (schwannomas and neurofi- bromas), and myxomas.105,106 Myxomas of the EAC are extremely rare and occur in association with autosomal dominant familial pigmentation, endocrine tumors, and schwannoma syndrome.107Some of these EAC soft tissue tumors, in particular, the hemangiomas, AVMs, and neurofi- bromas, can bleed extensively at surgery, and a preoperative embolization may be desirable.
Aural Polyps
Aural polyps are a consequence of chronic inflammation within the EAC or middle ear. They are soft tissue masses that elicit no bone erosion or reaction (Fig. 2.18).
Biopsy is usually necessary for diagnosis because they can mimic squamous or basal cell carcinomas and other
Chapter 2 The External Auditory Canal and Pinna
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A B
Fig. 2.16 (A)Coronal computed tomography (CT) scan shows a large external auditory canal (EAC) cholesteatoma filling the EAC and remod- eling its superior and inferior walls. (B)Axial CT in the same patient
shows the mass expanding the EAC and pushing the tympanic mem- brane into the middle ear cavity.
malignancies. Aural polyps have a high rate (52%) of under- lying CH. Due to this high rate, imaging is useful to deter- mine the extent of disease and surgical planning.108In children, COM (43%) and retained tympanostomy tubes (23%) are a predisposing factor, as are mycobacterial infection and Langerhans cell histiocytosis.109Treatment of an aural polyp depends on the underlying cause. Often, the underlying process becomes evident only after topi- cal antimicrobial/corticosteroid therapy.
Lipoma
The diagnosis of lipoma is easily made with imaging due to the presence of fat on CT and very low signal on fat- suppressed MRI (Fig. 2.19). Clinically, a lipoma is covered by epithelium, and the diagnosis may not be obvious on
physical examination. Differential diagnosis includes an angiomyolipoma, of which there are 13 reported cases without von Hippel-Lindau disease, angiofibrolipoma, liposarcoma, and dermoid.110–113Dermoids are more com- mon in the region of the middle ear and eustachian tube than in the EAC, and liposarcomas may show bone erosion.
Arteriovenous Malformations
The external ear is the second most common location for AVMs of the extracranial head and neck. A study of 44 such lesions demonstrated that enlargement of the lesion can occur during childhood, adolescence, pregnancy, or adult- hood. MRI demonstrates enlarged feeding and draining blood vessels with flow voids if the lesions are Schobinger stages II or III. Stage I and II lesions often remain stable A
C
B
D Fig. 2.17 (A)Coronal computed tomography (CT) scan shows a soft
tissue mass (proven keratosis obturans) in the fundus of the external auditory canal (EAC) and resulting in some scalloping of the floor of the
canal. (B)Axial CT in the same patient shows that the mass results in minimal, benign appearing scalloping of the anterior wall of the EAC.
without treatment. Patients who experience lesion expansion can be treated with embolization alone or as a last resort with auricular amputation and prosthesis placement. Proximal vascular ligation does not result in lesion obliteration.114
Hemangioma
Typically, hemangiomas have a bluish appearance on physical examination and enhance intensely on CT and MRI. Cavernous hemangiomas of the EAC with or without TM involvement are rare and need to be treated surgi- cally.115Preoperative digital subtraction angiography and embolization may be useful.
Smooth Muscle Tumors and Leiomyoma
Smooth muscle tumors are very rare EAC tumors and may arise after trauma and result in conductive hearing loss.116 There are two types: one arises de novo from ectopic muscle called arrectores pilorum, and the other arises from smooth muscle at blood vessel walls.105On CT, these lesions demonstrate no bone erosion and are well circumscribed and confined to the EAC.
Tumors of Glandular Origin
The two most common benign glandular tumors of the EAC are ceruminoma (arising from glandular elements and hyperplastic myoepithelial elements) and adenoma/
pleomorphic adenoma (arising from only glandular ele- ments).117The latter type is more common. These benign lesions cannot be differentiated from one another, or even from malignancy, by imaging. These tumors arise from the cerumen glands or from ectopic salivary tissues. Usu- ally, they present from age 30 to 60 years and result in otorrhea and hearing loss without pain. On physical examination, there is a soft tissue mass in the EAC with- out bone erosion. There have been 25 reported cases of pleomorphic adenoma in the EAC; most commonly, the tumor arises at the posterior and posterosuperior walls.118 Adenoid cystic carcinomas and adenocarcinoma are discussed in the section on malignant tumors.
Neurofibroma and Schwannoma
Ten to 60% of neural origin tumors involving the EAC and pinna are found in individuals who have neurofibromato- sis type I (NF1),106and have been reported to have an inci- dence of 6% in a study of pediatric NF1 patients.119Usually other neurofibromas will be visible in other regions on the scan, helping the radiologist to make the diagnosis.
The more virulent form of neurofibromas, the plexiform type, often presents with conductive hearing loss. Even more rarely, a neurofibroma can degenerate into a sar- coma. Origination of a schwannoma from the EAC is very rare.120,121However, secondary involvement of the EAC by schwannomas arising from CN VII or IX may occur.
Benign Bony Tumors Meningiomas
Most commonly, meningiomas arise intracranially and spread to the temporal bone and EAC rather than arising from the temporal bone itself. In general, 20% of menin- giomas may have extracranial spread and may occur in the region of the temporal bone. Meningiomas involving the temporal bone have a more infiltrative pattern than other intracranial meningiomas.122Treatment of meningiomas
Chapter 2 The External Auditory Canal and Pinna
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Fig. 2.18 Axial computed tomography scan shows a small, rounded polyp in the opening of the right external auditory canal.
Fig. 2.19 Coronal computed tomography scan shows a mass involving the entire right external auditory canal. Even in this study with bone window setting, the low density of this lipoma can be appreciated.
involving the temporal bone region is complete surgical excision with yearly follow-up imaging with CT or MRI.123
Exostoses
Exostoses are the most common benign tumors of the EAC.
Exostoses are broad-based, bony growths that occur along EAC suture lines, which result in circumferential narrowing of the EAC bilaterally. The majority of exostoses is found in individuals who swim in cold water (surfer’s ear), and al- though usually bilateral, patients have unilateral complaints (80%).124Their cause is reactive hyperplastic bone formation secondary to repeated cold water exposure. The lesion is
composed of dense lamellar bone superficially with an un- derlying layer of vascularized loosely compact bone. Similar findings have been demonstrated experimentally secondary to cold water infusion into the EAC in guinea pigs.125Exos- toses are extremely rare in African Americans. Exostoses can be diagnosed on physical examination, and the lesions are found in the medial bony EAC near the tympanic annulus at the tympanomastoid and tympanosquamous suture lines.
Patients are usually asymptomatic until critical narrowing results in recurrent OE and conductive hearing loss. CT is the study of choice and demonstrates a broad-based bony narrowing of the EAC with normal-appearing, overlying soft tissue that does not enhance (Fig. 2.20). Imaging also allows
A
C
B
Fig. 2.20 (A)Axial computed tomography (CT) scan shows tiny, inciden- tally found, bone exostosis in the deep and anterior aspect of the right external auditory canal (EAC). (B)In a different patient, axial CT shows a larger bone exostosis in the lateral aspect of the left EAC. (C)In a third pa- tient, axial CT shows a circumferential bone exostosis in the deep aspect of the right EAC. (Case courtesy of Dr. Farida Benoudiba, Paris, France)
for assessment of the course of the facial nerve and aids in avoiding its injury126during surgical intervention. On MRI, these lesions have low T1-weighted and T2-weighted signal following that of cortical bone.
The probability of an exostoses recurring depends on age at presentation and is more common in older individu- als. Additionally, refusal to wear earplugs when swimming, or swimming year-round, especially when accompanied by sailing, diving, and surfing increases the risk of recur- rence.127Sixty-six percent of patients who undergo surgical removal, EAC exostoses have relief of symptoms, but in 29%
symptoms remain unchanged; in 4% of patients symptoms become worse and 6% of patients require reoperation.128
Osteoma
Osteomas, unlike exostoses, are usually unilateral, focal, and pedunculated, arising from one wall of the EAC (Fig. 2.21). At pathology, exostoses and osteomas of the EAC cannot be reliably differentiated, but their clinical appearance and CT appearance are usually specific.129CT is the most appropriate imaging modality. CT with bone algorithm can be used to determine the exact location of the lesion for surgical planning. An osteoma appears as a solitary focal, pedunculated, bony outgrowth. Overlying soft tissues are normal in appearance. Osteomas are located within the membranous portion of the EAC just lateral to the isthmus and attached to the tympanosqua- mous or tympanomastoid suture lines. Osteomas are less common than exostoses. As with exostoses, these lesions are more common in surfers (20%) and individuals who
Chapter 2 The External Auditory Canal and Pinna
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Fig. 2.21 Axial computed tomography scan shows dense osteoma involving the lateral aspect of the right external auditory canal and resulting in significant narrowing.
have a significant exposure to cold water for prolonged periods.130There is also a predisposition for osteomas in individuals who have had previous EAC surgery, and they may be associated with CH.131As with exostoses, surgical intervention is indicated when EAC obstruction results in significant symptoms. Because of the peduncu- lated nature of these lesions, surgical excision is rarely difficult.
Osteopetrosis
Malignant (autosomal recessive) osteopetrosis is a rare bone disease secondary to the formation of dense, brit- tle bone that generally presents in the first 7 years of life. More than one half of patients present in the first year of life. The consequences of this bone formation are poor pneumatization of mastoid air cells and the EAC, IAC, and eustachian tube stenoses. Patients show hearing loss (100% conductive and 26% mixed sensorineural/conductive), unilateral facial paralysis (16%), and otitis media.132 Intermediate autosomal recessive and milder autosomal dominant forms of osteopetrosis (Albers–Schönberg disease or marble bone disease) also exist and present later in life.133
Benign Osteonecrosis of the External Auditory Canal
Benign necrosis of the EAC is a focal, well-circumscribed, necrotizing (“bare bone”) lesion that occurs with chronic OE and has symptoms of otorrhea, itching, and/or otal- gia. Various underlying infections may be present, and with curettage, bone spicules are removed. This process is believed to be secondary to an inflammatory reaction and can be self-limiting, respond to steroids, or require hyperbaric oxygen therapy. Imaging with bone scan demonstrates nonspecific uptake in the temporal bone in the abnormal area, but CT shows no definite bone erosion with soft tissue prominence.134
Other Bony Lesions
Giant cell tumors of the mastoid are very rare, with only 13 reported in the literature.135,136Their imaging findings are nonspecific and include a destructive bone lesion accompanied by soft tissue mass (Fig. 2.22). The diagnosis is based on biopsy. Paget disease and fibrous dysplasia (FD) are two benign entities that cause cranial nerve deficits and osseous impingement upon the EAC, middle and inner ear structures, and orbits.137
FD generally presents during the fourth decade of life and is 3 times more common in females than in males.
The monostotic form of FD is 6 times more common than the polyostotic form and in 10% of cases involves the
temporal bone. The polyostotic form involves the cranio- facial regions in 50 to 100% of patients, and 24% of them have involvement of the temporal bone. The McCune–Albright syndrome is characterized by the polyostotic form of FD in association with endocrinopathy and cutaneous hyperpigmentation. FD is linked to mutations in chromo- some 20q 13.2. EAC occlusion occurs in 22 to 42% of patients, resulting in a conductive hearing loss. A compli- cation of entrapment of squamous debris within the canal is the formation of CH.138 This can secondarily erode bone, resulting in further conductive hearing loss, facial paralysis, and even sensorineural hearing loss from labyrinthine fistula. The otic capsule is characteristically spared by the osseous FD process. Thus, sensorineural hearing loss usually occurs from CH, as above, or as a result of FD involvement of the internal auditory canal with narrowing and neural compression. FD results in a ground glass appearance of the bone at CT and radio- graphic imaging. This appearance is secondary to the mixed osseous and fibrous components seen with the disease, and the amount of density or cystic appearance on CT is variable. On MRI, FD shows variable signal intensities on both T1- and T2-weighted images with significant con- trast enhancement. The appearance of FD on MRI may be bizarre and confusing.
Paget disease occurs in the sixth to eighth decades of life and is seen in 2 to 3% of the population over the age of 60 years. Paget disease is due to increased bone turnover. In the lytic stage, there is a preponderance of osteoclastic activity. The mixed stage demonstrates osteoclastic and osteoblastic changes, whereas the sclerotic form is only osteoblastic. Patients with Paget disease involving the temporal bone present with mixed hearing loss. Conductive hearing loss is due to bone changes such as EAC narrowing and relaxation of the TM from the bone growth. Fibrous fixation of the ossicles and oval window changes also contribute to the conductive hearing loss. In contrast to FD, Paget disease can involve the otic capsule primarily resulting in sensorineural hearing loss.139Paget disease causes bone expansion, and its appearance on CT varies from lytic to blastic. On MRI, Paget disease is of low signal on T1- and high signal on T2-weighted images, with heterogeneous enhance- ment reflecting its hypervascular nature. Occasionally, dural enhancement is seen. Paget disease is usually polyostotic. Rarely, sarcomatous degeneration of Paget disease of the skull occurs, and MRI is the most accurate method for diagnosis, determining precise localization of the tumor and intracranial extension.140The differential diagnosis for Paget disease includes otosclerosis (occurring Fig. 2.22 (A) Axial computed tomography (CT) scan shows an aggres-
sive and destructive lesion centered in the right external auditory canal, but extending posteriorly into the mastoid bone and anteriorly into the temporomandibular joint. (B)Coronal postcontrast magnetic resonance T1-weighted image shows that the tumor (T) enhances
and has eroded through the temporal bone superiorly. There is dural enhancement and thickening in the middle cranial fossa. This was a giant cell tumor at biopsy. (Case courtesy of Dr. Farida Benoudiba, Paris, France.)
A B
in younger patients), osteoradionecrosis, fibrous dyspla- sia (also in younger patients), and syphilis (demon- strates labyrinthine enhancement). Although both FD and Paget disease may have to be surgically treated, new drug therapies may become the standard of care in the future.136
Carcinomas
Carcinoma of the temporal bone represents 0.2% of all head and neck carcinomas. The Pittsburgh Staging Criteria are used to stage squamous cell carcinoma of the tempo- ral bone.139The modified criteria are as follows:
T1: EAC only—with no bone erosion or soft tissue in- volvement
T2: EAC only—bone erosion (less than full thickness)/soft tissue mass of 0.5 cm
T3: Full thickness bone erosion/soft tissue 0.5 cm/
middle ear or mastoid involvement
T4: Cochlea, petrous apex, middle ear wall, carotid canal, jugular foramen, dural, TMJ, or styloid involve- ment; facial paresis and/or soft tissue 0.5 cm thick (Fig. 2.23)
All malignant tumors of the EAC and those of the pinna that secondarily involve the EAC, regardless of
Chapter 2 The External Auditory Canal and Pinna
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A B
C D
Fig. 2.23 (A)Axial computed tomography scan with soft tissue window setting shows a nonspecific mass involving the right temporal bone.
(B)Corresponding bone window settings show the aggressive nature of the mass that erodes the mastoid bone and extends into the middle ear cavity (stage 4 squamous cell carcinoma). (C)Axial contrast-enhanced
magnetic resonance (MR) T1-weighted image shows the mass extends medially into the parapharyngeal space and surrounds the mandibular condyle. (D)Coronal postcontrast T1-weighted MR image shows that the tumor has eroded the temporal bone and invaded the undersurface of the temporal lobe. (Case courtesy of Dr. Farida Benoudiba, Paris, France.)
their histological type, need to be imaged with CT and/or MRI. Imaging is performed not only to assess the primary tumor site and extent but also the possibility of metas- tases. The most common sites of lymphatic metastases are the parotid and jugulodigastric nodes, as these areas represent the normal drainage for the pinna and EAC.
Further drainage is to the internal jugular nodes. Therefore, imaging needs to include the temporal bone, adjacent parotid gland, and neck. CT depicts subtle bone erosion, whereas MRI helps to demonstrate involvement of cra- nial nerve VII or along the superficial temporal nerve (a branch of the second division of the trigeminal nerve), involvement of the pterygopalatine fossa, dura, and/or brain (Fig. 2.24). Due to the differences in resistance in the membranous (lateral) and bony (medial) portions of the EAC, tumors can spread into the soft tissues (more common with lateral EAC origin) or medially into the middle ear through the TM (more common in the bony EAC). Extension of tumor can also occur through the fis- sures of Santorini into the parotid gland and TMJ, as well as through the tympanomastoid suture line to the mas- toid bone and via the infratemporal fossa to the face (Fig. 2.25).140 If extension occurs through the tympa- nomastoid suture, tumor will quickly spread to the entire mastoid, and from there it can gain intracranial access into the middle or posterior fossas. Also, extension from the mastoid into the middle ear can track down the eustachian tube to the fossa of Rosenmüller.
Because the pinna and EAC both contain squamous epithelial tissue, squamous cell carcinoma (SCC) can in- volve one or both structures, or less commonly originate in the middle ear and spread to the EAC.141SCC is signifi- cantly more common in the region of the auricle, and 60 to 90% of all auricular carcinomas are squamous in origin.
Approximately 20% of auricular carcinomas are adenoma- tous/glandular carcinomas and less commonly basal cell carcinomas, melanoma, and metastases. The probability of a carcinoma metastasizing to the auricle is extremely low, but it may occur with breast cancer or less commonly with renal, lung, or prostate cancers. If the carcinoma is diagnosed early, no bone erosion is evident by CT, but as the disease progresses, irregular bone erosion and then destruction of the walls of the EAC occur. The thickness of the skin in the EAC varies from 0.1 to 0.2 mm.142EAC SCC is typically found in elderly individuals and originates in the EAC and extends to the pinna. There is usually accom- panying bone erosion on CT, but without biopsy, the lesion may not be distinguishable from a benign process, such as MOE or even CH.143Prognosis is related to tumor stage and presence or absence of clear surgical margins.144 Tumor staging of EAC carcinomas by the Pittsburgh classification145correlates with survival rates. Combination surgery/radiation therapy is the accepted method for most EAC carcinomas, although some T1 tumors may be treated with either radiation or surgery alone.146Surgery for EAC cancer usually involves excision via a lateral temporal bone
A B
Fig. 2.24 (A)Axial computed tomography scan showing a squamous cell carcinoma arising in the right external auditory canal and destroying the mastoid and temporomandibular joint. There is a permeative pat- tern to the bones in the base of the skull medial to the tumor, suggest- ing invasion. (B)Axial postcontrast magnetic resonance T1-weighted
magnetic resonance image shows that the tumor involves the basi- sphenoid portion of the occipital bone and right-sided longus colli mus- cle. The tumor involves the mastoid, extended into the sigmoid sinus and there is thickened and enhancing dura in the lateral aspect of the right posterior fossa.