Exostosis of External Auditory canal
Exostosis of external auditory canal are broad based bony projections involving the tympanic portion of the external auditory canal. These projections are usually multiple and symmetrical. This condition should be differentiated from osteomas involving the external auditory canal. Osteomas are single and pedunculated involving the tympano squamous suture line.
Image of skull bone showing Exostosis of external auditory canal
|Involves tympanosquamous suture line||Tympanic portion of external canal|
|Benign bone growth||Caused due to swimming|
Etiology of this condition is incompletely understood. These lesions commonly occur during the years of active bone growth. These lesions commonly arise from the periosteum of the tympanic portion of the external auditory canal. These lesions are postulated to arise due to exposure to cold water during this period of active bone growth. This accounts for the high incidence of exostosis in surfers.
Most exostosis are asymptomatic because most of them do not develop to a size sufficient to cause symptoms. Most of these patients are referred by physicians when they observe growths in the external auditory canal.
Active proliferation of exostosis can lead to:
1. Recurrent otitis externa because the self cleansing mechanism of external canal has been compromised
2. Conductive hearing loss: When the aperture becomes reduced to 3 mm high frequency hearing loss occurs, further reduction in size could lead to lower frequency losses.
3. Cholesteatoma involving the external auditory canal
This is a surgical condition. Surgery is indicated only when the patient suffers from recurrent episodes of otitis externa / conductive hearing loss..
Majority of surgical procedures for removal of external canal exostosis is through transmeatal route.
Disadvantages of transcanal route removal:
1. Associated with significant loss of canal wall skin due to damage caused by the rotating burr
2. Visibility is rather poor.
3. Removal is very difficult if exostosis is present close to the ear drum
Post auricular approach:
This has a distinct advantage of good access and visibility.
Incision: Post auricular curvilinear incision approximately 1 cm behind the post auricular fold.
Image showing post aural incision
The skin and subcutaneous tissues are elevated anteriorly to expose Henle's spine. A self retaining retractor is used to retract the soft tissues.
Image showing Henle's spine exposed
Removal of posterior exostosis:
A medium sized cutting burr is used to enter the posterior exostosis. The entry is usually made along its lateral sloping edge. The bony removal is done medially. A thin shell of bone is retained anteriorly to protect the canal skin from injury. Drilling is proceeded medially and posteriorly till the whole mass is removed. When the level of annulus is reached care must be taken to preserve the chorda tympani nerve. The thinned shell of bone collapses or is made to collapse using a thin elevator. The posterior canal skin is left intact over the thinned out shell of bone.
Now an incision is made midway along the posterior canal skin from the top of the canal to the bottom. The posterior canal skin medial to this incision is positioned onto the new contour of the posterior canal wall.
Now the transmeatal approach is resorted to. Incisions are made with a sickle knife superiorly and inferiorly in the canal, extending from the ends of the previous incision laterally to the meatus creating a laterally based posterior canal skin flap. This flap is involuted back into the meatal portion of the canal and held there with the help of a retractor.
Figure showing exostosis of external auditory canal
Burr used to drill exostosis
Figure showing incision over posterior canal wall skin
Posterior canal wall skin flap involuted into the meatus
Removal of anterior exostosis:
Using a round knife, an incision is made in the skin overlying the anterior exostosis from superior to inferior over the dome of the exostosis. The incision proceeds as far medially as possible. Using a cutting burr the anterior exostosis is drilled leaving a thin sleave of bone. This thin sleave protects the skin from damage.
The elevated skin flap is repositioned. Gelfoam pledgets are used to retain the skin flap in position.
Anterior exostosis seen being drilled out
1. Injury to chorda tympani nerve
2. Injury to facial nerve
3. Damage to the ear drum