Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

HEAD AND NECK RADIOLOGY
Year
: 2011  |  Volume : 21  |  Issue : 4  |  Page : 274--278

Lesions in the external auditory canal


Priyank S Chatra 
 Department of Radiology, Yenepoya Medical College, Deralakatte, Mangalore - 575 018, Karnataka, India

Correspondence Address:
Priyank S Chatra
Department of Radiology, Yenepoya Medical College, Deralakatte, Mangalore - 575 018, Karnataka
India

Abstract

The external auditory canal is an S- shaped osseo-cartilaginous structure that extends from the auricle to the tympanic membrane. Congenital, inflammatory, neoplastic, and traumatic lesions can affect the EAC. High-resolution CT is well suited for the evaluation of the temporal bone, which has a complex anatomy with multiple small structures. In this study, we describe the various lesions affecting the EAC.



How to cite this article:
Chatra PS. Lesions in the external auditory canal.Indian J Radiol Imaging 2011;21:274-278


How to cite this URL:
Chatra PS. Lesions in the external auditory canal. Indian J Radiol Imaging [serial online] 2011 [cited 2019 Nov 17 ];21:274-278
Available from: http://www.ijri.org/text.asp?2011/21/4/274/90687


Full Text

 Introduction



The external ear consists of the auricle and the external auditory canal (EAC). The EAC is divided into two parts. The lateral one-third is cartilaginous and the medial two-third is bony [Figure 1]. [1] The main function of the EAC is to conduct sound waves in the form of vibrations to the tympanic membrane. The most common congenital lesion affecting the EAC is atresia. Inflammatory lesions include malignant otitis externa and osteomyelitis. Bone tumors are the most common neoplastic lesions encountered. Trauma can cause injury to the EAC. Miscellaneous conditions like accumulated ear wax and cholesteatoma also affect the EAC. Most of these lesions can be diagnosed clinically; however imaging is often required to evaluate the extent of the lesion, feasibility for surgery, differential diagnosis and to rule out complications. High resolution CT scan (HRCT) is a good tool to assess EAC abnormalities.{Figure 1}

 EAC Atresia



Atresia of the EAC can occur in isolation or it may be associated with middle ear and inner ear dysplasia. Isolated EAC atresias are amendable to surgery. [2] The outcome of surgeries performed in the presence of middle and inner ear dysplasia are not encouraging. [3] HRCT of the temporal bone [Figure 2] is indicated for preoperative planning. Preoperatively, the radiologist should look for contraindications for surgery such as atretic oval and or round window and unfavorable course of the facial nerve. [2] In addition, we also need to look for structures that may cause problems during surgery such as reduced volume of the middle ear cavity and poor pneumatization of the temporal bone. [4] Additional anomalies need to be looked for as well, such as the presence of severe incudomallear dysplasia, which when present has to be resected, as well as dysplastic stapes, which may need to be replaced by a prosthesis. [5] 3D reconstructed images should demonstrate the volume of the middle ear cavity [4] and also the distance from the middle ear structures to the atretic EAC [Figure 2]A-D and reveal any other anomalies of the external ear.{Figure 2}

 Malignant Otitis Externa



Malignant otitis externa is a misnomer as it is not a malignant condition; it is termed "malignant" because of the aggressive clinical behavior and high mortality associated with it. [6] Mortality has currently decreased to 20% from 30-40% due to good improved antibiotics. [7] Malignant otitis externa is a result of infection of the EAC with Pseudomonas aeruginosa. It is commonly seen in the elderly and in diabetic patients. [8] The infection soon spreads into the adjacent structures such as the temporomandibular (TM) joint, middle ear, mastoid air cells, and skull base. CT scan demonstrates the presence of an asymmetric soft tissue density in the EAC, with or without extension into the surrounding structures [Figure 3]A. Involvement of the temporalis muscle leads to formation of a temporalis abscess, which is seen as diffuse muscle thickening with hypodensity [Figure 3]B. Involvement of the TM joint is seen as widening of the joint space, with irregularity of the articular margins. Temporal bone osteomyelitis is seen as increased density of the bone, with linear periosteal reaction [Figure 3]C, and accompanied by a soft tissue density around the EAC and mastoid. Differential diagnosis includes cholestatoma and squamous cell carcinoma of the EAC. Early diagnosis of this condition is important as aggressive management is necessary to avoid morbidiy and mortality.{Figure 3}

 Bone Tumors



Osteochondroma (exostosis) is the most common benign tumor found in the EAC. [9] Other tumors include osteoma, bone island, and osteoid osteoma. [10] Malignant tumors include Ewing sarcoma, osteosarcoma, and squamous cell carcinoma. [11] Osteomas can be single or multiple. Multiple osteomas are associated with Gardner syndrome, which is a constellation of polyps of the colon, multiple osteomas, and multiple impacted or unerupted teeth, in association with skin and soft tissue tumors. [12] Osteomas are asymptomatic and present as slowly growing pedunculated masses in the EAC. [13] HRCT [Figure 4]A demonstrates a bony outgrowth projecting into the EAC. Imaging of the cranium [Figure 4]B and C is indicated in these cases to look for additional osteomas.{Figure 4}

 External Auditory Canal Injuries



EAC injuries can be due to blunt trauma or penetrating injuries. Road traffic accidents are the most common cause of blunt trauma. Trauma is usually associated with injury to the pinna, with or without TM joint dislocation. [14] EAC injuries may or may not be associated with temporal bone fractures. HRCT shows the presence of high-density fluid (hematoma) in the EAC, with fracture fragments [Figure 5]A and E and associated TM joint dislocation [Figure 5]B-D. Three-dimensional CT volume-rendered images demonstrate laceration of the pinna.{Figure 5}

 Ear Wax (Cerumen)



Accumulation of wax in the EAC is a physiological process. Cerumen impaction is considered pathological only when it produces symptoms or prevents assessment of the ear canal, the audiovestibular system, or both. Diagnosis is mainly clinical and CT scan is only indicated when impaction removal has been unsuccessful. HRCT demonstrates a hypodense lesion filling the EAC [Figure 6]. Fat attenuation within the lesion and the presence of a rim of air around the lesion confirm the diagnosis. [15]{Figure 6}

 Cholesteatoma



Cholesteatomas arise as a result of ingrowth of the stratified squamous epithelium of the EAC into the middle ear. [16] The EAC is a rare site for cholesteatoma. Cholesteatomas can be primary (idiopathic) or secondary. Secondary cases are due to trauma or inflammatory disease and are much more common than the primary form. [17] Seung-Ho Shin et al. [18] classified EAC cholestetomas (EACC) into four groups based on the CT scan and clinical findings. Stage I cholesteatoma is limited to the EAC. Stage II cholesteatoma involves the tympanic membrane and the middle ear. An EAC cholesteatoma is considered stage III if in addition to the EAC it involves the mastoid air cells [Figure 7]. In stage IV cholestetomas the lesion extends beyond the temporal bone.{Figure 7}

EACC must be differentiated from malignant otitis externa. EACC is a slowly progressing chronic disease and is well localized, with a soft tissue density eroding one of the walls of the EAC. [19] On the other hand, malignant otitis externa is a rapidly progressive disease and a diffuse process involving most of the EAC. [20] Malignant otitis externa shows enhancement of the soft tissue on contrast-enhanced studies, whereas there is no enhancement in the case of cholesteatomas. Diffusion MRI imaging is of particular help in tricky situations. EACC show prompt diffusion restriction [Figure 8]A-D, whereas malignant otitis externa does not show restriction on diffusion. [21]{Figure 8}

 Conclusion



The EAC is an important part of the temporal bone and is involved in sound conduction. HRCT has an integral role in the diagnosis and management of lesions in the EAC. MDCT coupled with 3D reconstruction helps in better visual representation of these lesions and thus facilitates appropriate management.

References

1Fatterpekar GM, Doshi AH, Dugar M, Delman BN, Naidich TP, Som PM. Role of 3D CT in the Evaluation of the Temporal Bone. Radiographics 2006;26:S117-32.
2Gassner EM, Mallouhi A, Jaschke WR. Preoperative Evaluation of External Auditory Canal Atresia on High-Resolution CT. AJR Am J Roentgenol 2004;182:1305-12.
3Lambert PR, Dodson EE. Congenital malformations of the external auditory canal. Otolaryngol Clin North Am 1996;29:741-60.
4Yeakley JW, Jahrsdoerfer RA. CT evaluation of congenital aural atresia: What the radiologist and the surgeon need to know. J Comput Assist Tomogr 1996;5:724-31.
5Klingebiel R, Bauknecht HC, Freigang B, Kaschke O, Linke R, Meuschel-Wehner S, et al. Multislice Computed Tomographic Imaging in Temporal Bone Dysplasia. Otol Neurotol 2002;23:715-22.
6Chandler JR. Malignant external otitis. Laryngoscope 1968;78:1257-94.
7Pérez P, Ferrer MJ, Bermell A, Ramírez R, Saiz V, Gisbert J. Malignant otitis externa. Our experience. Acta Otorrinolaringol Esp 2010;61:437-40.
8Ludwig BJ, Foster BR, Saito N, Nadgir RN, Castro-Aragon I, Sakai O. Diagnostic Imaging in Nontraumatic Pediatric Head and Neck Emergencies. Radiographics 2010;30:781-99.
9Filippkin MA, Kurilenkov GV, Zelikovich EI. Temporal bone CT in the diagnosis of acquired diseases of the external auditory canal. Vestn Rentgenol Radiol 2004;1:10-4.
10Das AK, Capt GP, Kashyap RC. Osteoma of the Mastoid Bone - A Case Report. Med J Armed Forces India 2005;61:86-7.
11De Foer B, Kenis C, Vercruysse JP, Somers T, Pouillon M, Offeciers E, et al. Imaging of Temporal Bone Tumors. Neuroimaging Clin N Am 2009;19:339-66.
12Madani M, Madani F. Gardner's Syndrome Presenting with Dental Complaints. Arch Iran Med 2007;10:535-9.
13Hsiao SH, Liu TC. Osteoma of the External Ear Canal. Otol Neurotol 2003;24:960.
14Thangarajah T, McCulloch N, Thangarajah S, Stocker J. Bilateral temporomandibular joint dislocation in a 29-year-old man: A case report. J Med Case Reports 2010;4:263.
15Beatrice F, Bucolo S, Cavallo R. Earwax, clinical practice ACTA Otorhinolaryngologica Italica 2009;29(Suppl 1):1-20.
16Semaan MT, Megerian CA. The Pathophysiology of Cholesteatoma. Otolaryngol Clin North Am 2006;39:1143-59.
17Ghazi B, Salima K, Trabelsi S, Ouertatani L, Tababi S, Beltaief N, et al. Spontaneous external auditory canal cholesteatoma: Report of 3 cases. Oto-Rhino-Laryngologie France 2008;94:383-6.
18Shin SH, Shim JH, Lee HK. Classification of External Auditory Canal Cholesteatoma by Computed Tomography. Clini Experimental Otorhinolaryngol 2010;3:24-6.
19Heilbrun ME, Salzman KL, Glastonbury CM, Harnsberger HR, Kennedy RJ, Shelton C. External Auditory Canal Cholesteatoma: Clinical and Imaging Spectrum. AJNR Am J Neuroradiol 2003;24:751-6.
20Applebaum EL, Duff BE. Ear and temporal bone, I: Clinical considerations for non-neoplastic lesions of the ear and temporal bone. In: Fu YS, Wenig BM, Abemayor E, Wenig BL, editors. Head and Neck Pathology with Clinical Correlations. Philadelphia: Churchill Livingstone; 2001. p. 668-78.
21Kavanagh EC, Fenton DM, Griesdale D, Graeb DA. MRI of Acquired Cholesteatoma Presenting as a Temporal Lobe Mass. AJR Am J Roentgenol 2005;185:788-9.