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A Novel Functional Imaging Method of the

Eustachian Tube Cuneyt M. Alper1,2, Tanya J. Rath3,4, J. Douglas Swarts2, Miriam S. Teixeira2, William J. Doyle2

1) Division of Pediatric Otolaryngology, Children's Hospital of Pittsburgh of UPMC, 2) Department of Otolaryngology, University of Pittsburgh School of Medicine

3) Department of Radiology, University of Pittsburgh School of Medicine, 4) Division of Neuroradiology, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania

INTRODUCTION

DISCUSSION

RESULTS

A. 1.25 mm in soft tissue

algorithm, soft tissue window

(Window 145, Level - 55).

The paratubal fat (black

arrows) is seen similar in

density to subcutaneous fat

(white arrow) displayed as

dark grey. No definite air

density could be visually seen

in the eustachian tube when

using air (white asterisk) in the

nasopharynx as a reference.

B. Displayed in thinner 0.625

mm bone algorithm with a

lower level (Window 432,

Level -200), small foci of air

(black arrows) were

suspected in the eustachian

tube using air (white asterisk)

in the nasopharynx as a

reference.

C. When the window was

narrowed and dichotomized

(Window 1, Level -200) to

show only air displayed as

black, versus all other

densities displayed as white,

only 2 small foci of possible

air(black arrow) could be

seen, suggesting that air

passing through the

eustachian tube during the

forced response test is not

clearly detected by CT due to

inadequate special resolution

and partial volume averaging

with adjacent paratubal fat.

Figure 2. Figure 2 A, B. Axial 0.625 mm low dose eustachian tube CT

(kVp 100 mA 200 ; Window 974/Level 271) after instilling water soluble

iodinated contrast in to the middle ear cavity and eustachian tube. A.

Iodinated contrast which is displayed as white is easily seen within the

eustachian tube (white arrows) and in the nasopharynx (black asterisk)

B. An oblique reformat along the long axis of the eustachian tube

following the instillation of water soluble contrast into the eustachian

tube. The entirety of the cartilaginous portion of the eustachian tube

(black arrows) is easily visualized with dense contrast from the bony

eustachian tube to the nasopharynx. Contrast is seen pooling in the

nasopharynx (black asterisk)

ABSTRACT

Outcome Objectives: 1) Image the

Eustachian tube (ET) lumen by CT

scanning during ET function (ETF)

testing; 2) Characterize the differences

in image quality for different scanning

protocols, and 3) Establish a novel

research methodology for studying ET

anatomy and physiology.

Methods: In a cadaver head without

craniofacial or otologic abnormalities,

the tympanic membrane was

perforated and ETF test was done

using the forced response test (FRT)

in a CT scanner. Opening (OP), steady

(PS) and closing (CP) pressures were

measured during forced air flow from

the middle ear (ME) to the

nasopharynx across the open ET.

Temporal bone CT scans with 0.625

mm thickness were done at a low and

standard radiation doses before and

during the steady flow (SF) phase of

the FRT, after instilling iodinated

contrast into the ME and ET, and after

the FRT cleared the contrast from the

ET. Multiplanar reformats of the ET

were created using post-processing

software.

Results: The average OP, PS and CP

values were 488±249, 376±101 and

211±62 daPa. While a distinct ET

lumen could not be demonstrated

during the FRT done with air at any

radiation dose, CT with intra-luminal

contrast clearly demonstrated the

entire ET lumen. Post-contrast FRT

demonstrated residual contrast

outlining the lumen.

Conclusion: Standard temporal bone

CT dose provided a slightly better

signal-to-noise than low dose CT but

neither provided adequate spatial

resolution to demonstrate an air filled

ET during FRT. ET lumen was easily

visualized with iodinated water soluble

contrast at all radiation doses.

Combining ETF testing and CT

imaging has potential research

applications.

This is the first report of combining a reliable ET

function test (FRT) with CT scan for visualizing the

ET lumen. While ET lumen is closed at rest (unless

patulous), and current standard imaging techniques

fail to capture the tube during this short opening

time. FRT maintains a steady opening through the

lumen while constantly running air with a pump.

However, even though the lumen is kept open, the

CT scan was unable to demonstrate a distinct air

column. Instilling water soluble contrast facilitated

the visualization of the ET lumen , however, running

FRT after contrast still showed contrast but no air

column. Running FRT pump at high speed or using

standard temporal bone and high dose CT scan

protocols did not change the outcome. In conclusion,

there was no difference in the ability to detect air

with any of the techniques though the radiologists

found the standard T bone CT and high dose to be

visually more pleasing with less noise.

Scanning of a cadaveric head was performed helically

on a 64-channel multidetector CT scanner (GE

LightSpeed VCT; GE Healthcare, Milwaukee, WI).

Forced Response Test (FRT) was performed by running

air with a pump from the external ear canal, through

middle ear and the ET into the nasopharynx. FRT

standard speed was 23 cc/min., and high speed was 60

cc/min. This was repeated after injection of water

soluble iodinated contrast (IC) through the middle ear.

The sequence of CT protocols performed were as

follows with example images provided in Figure 1:

1. A (localizer) -Low dose (100kVp, 180mA, pitch

0.969)

2. B (helical) -Low dose (100kVp, 200mA, pitch 0.531)

with standard speed FRT

3. B CT technique with IC

4. B CT technique with IC and standard speed FRT

5. Standard dose Temporal bone CT (120kVp, 195 mA)

with standard speed FRT

6. B CT technique with IC and high speed FRT

7. High dose CT (120fVp 320 MA) with IC and high

speed FRT

Axial 0. 625 mm bone and 1.25 mm soft tissue

reconstructions were performed for all scans. An edge

enhancing reconstruction kernel was used (Bone Plus;

GE Healthcare, Milwaukee, WI). All reformats were

performed by a CAQ certified neuroradiologist (T.J.R)

using dedicated post-processing software (Vitrea®

Core; Vital Images, Minnetonka, MN). Axial oblique

and coronal oblique 1 mm thick reconstructions with 1

mm increment parallel and perpendicular to the long

axis of the ET were obtained.

We would like to acknowledge Barton F. Branstetter IV,

MD, Professor of Radiology, University of Pittsburgh, for

his review of images and input with respect to this

project.

The Eustachian tube (ET) is a natural tube that

connects the middle ear (ME) to the back of the

nose (nasopharynx). The posterior 1/3 of the ET is

a bony extension of the ME with a patent lumen

while the anterior 2/3 is a membrano-cartilaginous

structure that opens into the nasopharynx. The

physiologic functions attributed to the ET are middle

ear pressure regulation, clearance of secretions and

protection from reflux of nasal secretions. The ET is

usually closed due to the natural pressure of the

surrounding tissue and is opened intermittently by

the active contraction of the tensor veli palatini

(mTVP) and levator veli palatini (mLVP) muscles,

allowing equilibrium between the ambient and

middle ear pressures.

Inefficient ET openings are associated with the

progressive development of ME under pressure and

set the basis for several middle ear diseases such

as acute and chronic otitis media, otitis media with

effusion (OME), retraction pockets, cholesteatoma,

barotrauma and hearing loss.

The ET is located at the base of the skull and its

complexity and difficult access resulted in frustrated

attempts of imaging studies previously. Another

challenge comes from the fact that the ET has a

virtual lumen that only opens for a few hundred

milliseconds during middle-ear and ambient

pressure equalization (0.2 – 0.4 sec on average).

An example of ET imaging is nasopharyngoscopy, a

routine outpatient procedure in which a flexible or

rigid endoscope is introduced through the nostrils

allowing examination of the nasal cavity and the

back of the nose. It requires expensive equipment,

the use of topical anesthesia and decongestants, is

uncomfortable and cannot be tolerated by many

patients, especially young children. Although it is

very useful for assessment of peritubal diseases

and nasal and pharyngeal infectious or

inflammatory processes, it only allows the

visualization of the opening of the tube and

sometimes a few millimeters of the lumen.

Magnetic Resonance Imaging (MRI) and

Computerized Tomography (CT) are imaging

techniques largely used by the medical community

to study biological tissues from all regions of the

body. The development of high resolution three-

dimensional (3-D) reconstruction software has

broadened their use to explore the anatomy of small

structures such as the ET. Initially, MRI seemed

ideal as it does not involve ionizing radiation

exposure, but unfortunately it is limited by very long

scan time, significant imaging artifacts and large

asymmetric voxel sizes. When those variables are

applied to small areas, the 3-D reconstructions yield

a poorly defined image. On the other hand, recent

publications have shown that the faster helical CT

scans can provide clear reconstructions of the

lumen and surrounding tissues along all ET

segments. Although promising, this is only possible

in patients with a patulous ET, a situation in which

the tube remains abnormally open. This limits the

usefulness of the technique to only a subset of

patients, as the great majority of ET problems come

from failure to dilate the cartilaginous segment due

to strictures or poor muscular efficiency.

A study was conducted in order to develop a novel

functional imaging model for visualization of the ET.

METHODS AND MATERIALS

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paratubal muscles and eustachian tube opening assessed by sonotubometry and videoendoscopy. Arch Otolaryngol

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Inc, 2005.

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Accessed on 10/17/2012.

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14. Takasaki K, Sando I, Balaban CD, Haginomori S, Ishijima K, Kitagawa M. Histopathological changes of the

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918-923, 2004.

ACKNOWLEDGEMENT

REFERENCES

Cuneyt M. Alper, M.D. Professor of Otolaryngology

Director, Pediatric Otolaryngology

Fellowship Program

Children’s Hospital of Pittsburgh of UPMC

Department of Otolaryngology

University of Pittsburgh School of Medicine

Email: Cuneyt.Alper@chp.edu

Phone: 412-692-8577

Website: http://www.chp.edu/CHP/ent

CONTACT

University of Pittsburgh

Supported in Part by:

National Institute of Health

P-50 Grant DC007667

R21 Grant DC013167

Figure 1. Figure 1 A, B & C. Axial CT, low dose eustachian tube all

obtained during the same forced response test displayed in different

techniques.

A B

A

C

B