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Table 1. Dimensions of OEAC at Annulus and Isthmus/Mid-Canal Section (COM Group).
Axial View
Annulus Section, mm

Mean (SD)
Range
P valuea

Isthmus/Mid-Canal Section, mm

Lesion Side

Normal Side

Lesion Side

Normal Side

8.85 (0.52)
7.4-9.8

8.88 (0.46)
8.0-9.9

5.76 (0.74)
4.5-7.4

5.75 (0.10)
4.2-7.4

.508

.834
Coronal View

Mean (SD)
Range
P valuea

Lesion Side

Normal Side

Lesion Side

Normal Side

9.03 (0.78)
7.6-11.3

9.06 (0.69)
7.7-10.5

6.39 (1.08)
4.4-9.2

6.34 (1.10)
4.4-9.2

.567

.139

Abbreviation: COM, chronic otitis media; OEAC, osseous external auditory canal.
a
Calculated by paired t test.

Table 2. Dimensions of OEAC at Annulus and Isthmus/Mid-Canal Section (Normal Group).
Axial View
Annulus Section, mm

Mean (SD)
Range
P valuea

Isthmus/Mid-Canal Section, mm

Right Side

Left Side

Right Side

Left Side

8.76 (0.56)
7.4-10.2

8.83 (0.47)
7.6-9.8

5.43 (0.77)
3.8-7.5

5.38 (0.70)
4.0-7.2

.06

.29
Coronal View

Mean (SD)
Range
P valuea

Right Side

Left Side

Right Side

Left Side

8.98 (0.65)
7.4-10.3

8.90 (0.67)
7.4-10.1

5.99 (0.80)
3.8-8.0

5.93 (0.86)
3.8-7.8

.12

.36

Abbreviation: OEAC, osseous external auditory canal.
a
Calculated by paired t test.

reliable details of temporal bone anatomy.15 Therefore, we
conducted this study to evaluate the EAC by HRCT. We
focused on the osseous portion of the EAC because it consisted
of approximately the medial two-third of EAC and could be
evaluated clearly on HRCT. In addition, the osseous portion of
EAC was not as elastic as the cartilaginous portion and was the
main portion to enlarge while performing canaloplasty.
In the literature and based on clinical observations, the
shape of the OEAC has been suggested to be an etiologic factor
in chronic otitis externa (COE).14 But, does the shape of OEAC
also play a role in the pathogenesis of COM? There were studies that attempted to classify the shape of OEAC. In 1980,
Eckerdal and Ahlqvist reported 3 different shapes of the
OEAC: cone-shaped (64.1% of the normal patients),
hourglass-shaped (32.1%), and ovoid (3.8%).16 Another study7
used axial CT images with slice thicknesses of 1.5 and 2 mm to
distinguish 8 different shapes with the uniform shape (same as
the cylindrical shape), which was most prevalent among

normal people. In a more recent study by Mahboubi in 2012,
the shape of OEAC was divided into 5 groups, with the most
common type to be conical (64%). In this study, we followed
the most comprehensive classification developed by Mahboubi. Similarly, we found the most prevalent shape of OEAC
in both the COM and the control group were cylindrical and
conical shape, followed by hourglass shape. Regarding the
prevalence of OEAC shape, there was no difference between
the lesion ears in the COM group and normal ears in the control
group. In other words, the shape of OEAC does not seem to
play as important a role as COE in the pathogenesis of COM.
As we mentioned earlier, those patients with COM appeared
to have smaller EAC dimensions, and routine canalplasty was
suggested while performing tympanoplasty.4 However, in this
study, we found that there was no difference in the OEAC
measurements between lesion ears and normal ears in the COM
group (Table 1). In addition, there was no difference between
lesion ears in the COM group and normal ears in the control
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