Diagnosis and Management of Graves' Orbitopathy
with Standardized Echography
Karl C. Ossoinig, MD
Both the A-scan and B-scan techniques are employed to screen the
straight and oblique extraocular muscles for lesions.
In this "Basic Examination of the e.o. muscles, the A-scan
is particularly sensitive in indicating thickening or thinning of
muscles and in differentiating the underlying pathologies, while the
B-scan is very helpful in their topographic evaluation.
The evaluation of extraocular muscles is one of the most
important applications of Standardized Echography:
when the entire capacity of Standardized Echography, i.e., axial
eye length measurements as well as diagnostic evaluations of the
posterior and anterior eye segments, and of the orbital and periorbital
regions, is available, more than 50% of all cases seen in an Echography
Clinic are likely to be (peri)orbital in nature.
Among these patients with (peri)orbital
lesions, cases with disorders of the extraocular muscles (with or
without optic nerve problems) are prevalent at a rate of more than 80%
of these patients. Graves'orbitopathy is the underlying pathology in
more than 80% of these.
Properties of Normal
Normal extraocular muscles have a lower internal reflectivity
than the surrounding orbital fat tissues (smaller average interface
size). Their internal structure is more regular (similar sizes and
regular distribution of acoustic interfaces).
The very large outer surface of the extraocular muscles and the
equally very large surfaces of their sheaths reflect very strongly (Fig.
2 ). Only sound beams
that reach these large enveloping surfaces of a muscle perpendicularly,
allow the display of typical acoustic muscle patterns as characterized
by the internal structure and reflectivity of the muscle.
The thickness, internal structure and reflectivity of the normal
extraocular muscles vary greatly from person to person (and also depend
on the race), but are very similar in the two orbits of the same person.
Children and youthful persons tend to have a lower reflectivity,
older individuals tend to display a higher reflectivity of their normal
A-scan beam is strongly refracted toward the extraocular muscle body at
the outer layers of its sheaths when oblique sound beam incidence
occurs. This refraction makes it possible even in the posterior
orbit, to aim the ultrasonic beam across the muscle producing displays
and allowing precise measurements of true muscle cross-sections (the
same situation as in optic nerve measurements).
The focussed B-scan beam is not sufficiently refracted to always
allow the display of true cross-sectional displays of the extraocular
Basic Scanning and Measurements with Standardized A-scan
For the screening of the 4
straight and the 2 superior
oblique muscles, the A-scan probe is placed opposite the muscle on
the bulbar conjunctive between limbus and fornix.
Probe and beam are first directed anteriorly toward the inserting
tendon. Minimal angling and
shifting of the probe serve the purpose to detect the anterior muscle
pattern. While the eye is
in straight gaze (if possible), the probe is angled posteriorly so that
the beam scans the muscle from anterior to posterior.
If, during this basic scanning, the beam remaines aimed at the
muscle body, the pattern stays displayed on the screen widening and
shifting in a typical fashion. If
the examiner "loses" the muscle pattern, corrective probe
movements must be undertaken to find it again and continue the
screening. This is like all
examination techniques, a more time-consuming and difficult undertaking
for the beginner, but becomes an easy, quick and automatic procedure
with growing experience and improved skills.
The echographer develops automatic reflexes to scan and display
optimal muscle patterns very much like anyone develops reflexes that
guide walking and running or other activities of the body which for the
beginner are impossible or difficult to achieve smoothly and promptly
without thinking and analyzing what and how one is doing it.
1A: Crossection of MR in A-scan
1 C: transverse (top) and longitudinal
(bottom) B-scans of MR
The probe location is maintained the same, whether the examiner
needs to display the inserting tendon, the belly or any other portion of
a straight extraocular
muscle. The probe is only
angled to achieve the complete scanning of the muscle from anterior to
posterior and vice versa. The superior
oblique muscle, in contrast, requires different probe positions for
the display of its inserting tendon and anterior and posterior portions:
a) for the display of the anterior
belly portion, the probe is place inferotemporally on the bulbar
conjunctiva and the beam is angled and shifted in search for the
superior oblique muscle and the trochlea ( the normal trochlea is
recognized by the fact that the muscle pattern cannot be followed
anterior to it - it stops existing when the beam reaches the trochlea
during a forward scan along the muscle).
One needs to consider that the location of the trochlea
varies widely from person to person, but is always symmetric in
the two orbits of the same individual.
b) for the display of the posterior
belly portion, the medial rectus muscle which serves as the guiding
structure, is first scanned into the posterior orbit.
There the beam is angled slightly superiorly
2 (above): Scleral Buckle with over-riding muscle
tendon shown in B-scan demonstrating its usefulness for topographic
documentation. The A-scan
is needed to diagnose the myositis (thickening and low reflectivity of
c) for the display of the inserting
tendon of the superior oblique muscle the probe is placed at the
6:00 meridian behind the limbus and the beam is directed toward the
posterior portion of the 12:00 meridian between equator and optic nerve.
Slight angling and shifting of the beam serves the purpose of
detecting the tendon as a lower reflective episcleral tissue layer with
maximally high surface spikes on either side stemming from the large
inferior (anterior) and superior (posterior) surfaces of the tendon.