Introduction

Exostoses are classically defined as benign skin-covered osseous out-growth of external auditory canal (EAC). In contrast with osteomas that are solitary benign osseous tumors, exostoses are more often multiple, bilateral, composed of concentric layers of subperiostal bone with abundant osteocytes and far fewer fibrovascular channels and in so differing from osteomas that are

M.V.m.m.

Farrior J.P.

15,0 mm

13,3 mm

12,0 mm

16,0 mm

13,3 mm

11,0 mm

c

Walls of the EAC - AnteriorDimensions

M.V.m.m.

Farrior J.P.

1,0 mm

0,5 mm

0 mm

4,0 mm

2,7 mm

1,0 mm

Convexity ( )

M.V.m.m.

Farrior J.P.

60º

47º

20º

67,0º

45,6º

39,0º

Tympano/meatal angle (Ð)

Walls of the EAC - AnteriorConvexity, tympano/meatal angle

M.V.m.m.

Farrior J.P.

17,0 mm

15,4 mm

13,0 mm

16,0 mm

11,3 mm

6,0 mm

c

Walls of the EAC - PosteriorDimensions

M.V.m.m.

Farrior J.P.

160º

127º

110º

140,0º

129,3º

110,0º

Walls of the EAC - PosteriorConvexity, tympano/meatal angle,

thikness

Objectives

Learn in detail the anatomy of patients EAC proposed for exostoses surgery and be able to minimize related complications (damage of facial nerve, EAC skin, tympanic membrane, ossicular chain).

The pre-operative evaluation of exostoses in our department has increasingly been based around reconstructed sagital planes approximately perpendicular to the external auditory channel long axis. We studied in detail 80 CT cases (160 ears) referred for surgical evaluation.

The reasons why the sagital plane was deemed essential are:

It is the only plane in which the full perimeter of the EAC can be seen;

It allows uniform evaluation of all exostoses, in relation to their implantation base;

Allows study of the relationship among all exostic components, upper and lower, mostly because it is often possible to define all within a single image;

Permits more accurate measurements by decreasing the tangential and partial volume effects

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Methods

Results

This investigation clearly showed that that the distribution of exostosis in relation to the EAC perimeter is not random. There is a clear pattern involving four main elective locations, in differing combinations:

Anterior location: on the anterior circumference of the tympanic bulk.

Posterior location: on the posterior aspect of the tympanic bulk, external because of the tympanic ring angle.

Forward aticum: roughly corresponding to the deeper anterior horn extremity, by the tympano-squamous suture; this covers the aticum wall.

Backward aticum: roughly corresponding to the posterior horn, also by the tympano-squamous suture close to the posterior tympanic spine.

The anterior focus is necessarily deeper and is often the main responsible for lumen narrowing; therefore its characterization demands particular care for the pre-operative planning.

We propose a classification based on the transversal plane in three grades:

Grade I with a very wide gutter towards the anterior tympanic rim and therefore no significant relation to the tympanic membrane, displaying a 90º angle or wider: there is no need to work very close to the tympanum. (Fig. 6)

Grade II in wich there is a clearly marked para-tympanic gutter usually 90º to 45º; working deeply is necessary but there is a fair membrane safety distance, above 1mm. (Fig. 7)

Grade III corresponds to a narrow para-tympanic gutter usually 45º or under, 1mm or less from the tympanum membrane; encompassing two variants: (Fig. 8)

IIIa: no membrane contact; IIIb: with membrane contact.

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(Fig.B)

Type I: wide para-tympanic gutter and no relation to the tympanic groove (arrow).

Type II: well defined para-tympanic gutter and a fair distance towards the membrane, over 1mm

Type IIIb: narrow para-tympanic gutter and membrane contact (arrow)

Conclusions

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The distribution of exostoses foci in the EAC is not random and can be described within a 4 foci pattern. (Fig. 9,10 and 11)

Although clinics may not correlate with the degree of obstruction, direct measurements can be used as an objective indication of the severity of the underlying lesions.

In our department experience, of up to 500 cases of exostoses surgery, a very low complication rate has been achieved following the implementation of the pre-operative detailel imagiology protocol described above. (three grade classification of the EAC in the transversal plane ct scan). (Table 1)

Uni-focal disease (sagital reformatted plane): in this case a forward aticum focus

Tri-focal disease with: anterior (AN); posterior (PO); and forward aticum (FA) foci

Type IIIb: narrow para-tympanic gutter and membrane contact (arrow)

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Brackmann, Shelton, Arriaga. Otologic Surgery. Second edition, Saunders Company; 2001.

Hetzler, DG, MD, FACS.Laryngoscope.January, 2007.Vol.117, nº1, part2.Supplement Nº113:1-18.

House JW, MD, Wilkinson EP,MD.Volume 138, Issue 5, pages 672-678(May 2008). Otolaryngology-Head and Neck Surgery.

Hughes GB, Pensak ML. Clinical Otology. Thieme Editions;2007.

Karegeannes JC.”Incidence of bony outgrowth of the external ear canal in US Navy divers”. Undersea Hyperb Med 1995;22:301-306.

Kroon DF, Lawson ML, Derkay CS, Hoffmann K and Mc Cook J.Otolaryngology- Head and Neck Surgery.126(5):499-504;2002 May.

Paço, J., MD, PhD. “Doenças do Tímpano”. Edições Lidel;2003.

Snow BBJr, Ballenger JJ. Ballenger´s Otorhinolaryngology Head and Neck Surgery. Sixteenth edition, BC Decker Editions;2003.

Umeda Y, Nakoyima H.”Surfer´s ear in Japan”. Laryngoscope 1989;99:639-641.

Van Gilse PHG. "Des observations ultérieures sur la génèse des exostoses du conduit auditif externe par l´irrigation d´eau froide". Acta

Otolaryngol (Stockh)1938; 26:343.

Wong B. “Prevalance of external auditory canal exostoses in surfers”. Arch Otolaryngol Head and Neck Surg 1999;125:969-972.

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AbstractObjectives: Learn in detail the anatomy of patients external auditory canal (EAC) proposed for exostoses surgery and be able to minimize risk of complications during surgery (damage of facial nerve, EAC skin, tympanic membrane or ossicular chain). Methods:The pre-operative evaluation of exostoses has increasingly been based on ct scan reconstructed sagital planes approximately perpendicular to the external auditory channel long axis. The reasons why the sagital plane was deemed essential are: - It is the only plane in which the full perimeter of the EAC can be seen; - It allows uniform evaluation of all exostoses, in relation to their implantation base; - Allows study of the relationship among all exostic components, upper and lower, mostly because it is often possible to define all within a single image; - Permits more accurate measurements by decreasing the tangential and partial volume effects.

Results:In our Department's experience, of up to 500 cases of exostoses surgeries, the single complication cases have been transient tympanic perforations, especially since we started to have detailed pre-operative imagiology.

Conclusion: Although clinics may not correlate with the degree of obstruction, direct measurements can be used as an objective indication of the severity of the underlying lesions. We consider the EAC evaluation in the sagital plane of outmost importance and propose a radiological classification in 3 grades before exostoses surgery, based on all collected data.

pedunculated and often have a vascular core.

Based on clinical information, a widely held belief states that they occur primarly during the growing years, the osseous proliferation is the result or at least is enhanced by contact of the EAC with cold water during that period. This observation is in accordance with the high incidence of exostoses in “heavy surfers”, practicing in cold water.

All published series identify a high male:female ratio. This male preponderance probably results from the fact that male tend more likely to engage in cold water activities than woman during their growing years.

Most exostoses do not develop to such a degree that surgical removal is required. The establishment of a conductive hearing loss and/or pattern of external otitis are generally considered indication for surgery.

The surgical approach can be retroauricular, endomeatal or endaural technic (the preferred in our Center) and may envolve several potencial complications that occur as a direct consequence of the EAC anatomic

relationships.

Anatomical considerations:

The knowledge of EAC anatomic characteristics and relations to neighbouring structures are considered pre-requisites for lowering incidence of complications associated with exostoses surgery.

Anterior - inferior segment: (Fig. 1 and 2)

Bigger walls, relative to the obliquity of the tympanic membrane, slightly convex, acute tympano-meatal angles

Tympanic quadrants adjacent to these walls have their view and access conditioned by surgical regularization

Postero-superior segment: (Fig. 3 and 4)

Smaller walls, relative to the obliquity of the tympanic membrane, rectilinear or concave, and obtuse tympano-meatal angles

Tympanic quadrants adjacent to these walls have a better exposition

The double embryologic origin of the EAC has a considerable importance for its anatomy and in the formation of exostoses. (Fig. 5)

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The anterior tympanal processus is situated at the junction of the anterior and superior walls and protrudes in 70% of cases into the the EAC. Its mean length is 1,4 mm, with a maximum of 4 mm. Since the medium vertical diameter of the EAC is 9,5 mm we consider its removal crucial doing the exostoses surgery.

otorrinolaringologiacentro de

The importance of imagiology before exostoses surgeryinfante santo

Haúla Haider, MD; Gabriel Branco, MD; Maria da Luz Martins, MD; João Paço, MDPhDOtolaryngology Center, Hospital CUF Infante Santo, Lisbon, Portugal

Labyrintization (minor high frequency loss)

Tinnitus

TMJ dysfunction with capsule perforation without capsule perforation (all resolved)

Tympanic membrane perforation (resolved during surgery)

Stenoses

3%

3%

2,2%0,2%

2,0%

1,8%

0%

0%Facial paralysis

15,0 mm

1 2

3 4

5

6

7

8

9

10

11

Table 1

The posterior tympanal processus at the junction of the posterior and superior walls protrudes only in 10%.

Figure A . Virtual Radiologic endoscopy

Figure B . Tridimensional CT reconstruction of EAC - forward aticum exostose.

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