Color Doppler Imaging of the Orbital
Disorders
Author: Dr.
Jayanta Kumar Das, DO, DNB
Associate Consultant, Sri Sankardeva Nethralaya
Guwahati – 28
A number of methods have been utilized for the
investigation of blood flow in the orbit. Many however, are restricted to the
investigation of animal models because of their invasive and destructive
nature. Color Doppler ultrasound imaging [commonly referred to as Color Doppler
Imaging (CDI)] overcomes some of these shortfalls. It has proven to be a useful
method for examining the hemodynamics of the blood flow of the orbit.
The
visualization of the vasculature adds a new dimension to establishing the
diagnosis and proper management. This principle was applied to human diseases
in 1957. In the orbital region, its use was first described by Erickson2.
Chistian Andreas Doppler (1803-1853) first described the principle of using the
change in the frequency of waves to measure the velocity of an object.
It has successfully demonstrated changes in orbital
hemodynamics associated with a variety of pathological conditions, central
arthritis, Non Ischemic Optic Neuropathy etc. it has been used to detect the
visualization of orbital tumors. It has demonstrated arterialized superior
ophthalmic veins in cortic- cavernous fistulae. It may be useful as an adjunct
to C.T. for evaluation of suspected vascular lesion of the orbit.14,15
The initial experience with color Doppler imaging
in the evaluation of the normal orbits has shown that Color Doppler Flow
Imaging is consistently possible through a para-ocular approach2,6.
Erickson (1989) also displayed normal vena-verticosae, central retinal veins
and superior ophthalmic vein.
Color Doppler spectral analysis in normal
individuals allowed quantitative assessment of blood flow velocities Lieb W E
et al in 1992, using color image as a guide which included 400 normal
individuals found that the ophthalmic artery might allow insight into ocular
and orbital haemodynamic. Wolfgang et al used the technique of CDI in 210
normal individuals to determined the maximum systolic, end diastolic, and mean
flow velocities in the Ophthalmic and other major arteries of orbit.15
Examination technique
The scans are usually performed with the patient
supine, eye closed and directing gaze towards the ceiling. Usually 7.5 to 10
MHZ ultrasound scanner have been used and applied with contact jelly through
the closed upper lid while examiner’s hand rests upon the orbital margin to
minimize the pressure on the globe. Blood flow in the retro bulbar orbit is
detected by the production of color pixels on the visual display unit. [(EDV)
Two index, the Pulsatility Index and Resistive Index are important. Former one
for arterial and later one special for venous system. In general, it is useful
to first obtain a B-scan image of the optic nerve, which provides the
ultrasonographer with the most useful landmark for the detection of the various
orbital blood vessels. The ophthalmic artery is situated either above or below
the optic nerve into the posterior orbit before passing forward in the nasal
orbit in a horizontal plane slightly superior to that of the optic nerve.
The superior ophthalmic
vein is usually a larger sized vessel than the other veins. For superior
ophthalmic vein, takes an oblique course superior to the optic nerve in the
center of the retro bulbar orbit. To locate the superior ophthalmic vein is
difficult. Hence flow pattern of the ophthalmic vein studied only with
suspected venous abnormality (orbital Varix, CCF).
Orbital Disorders
Color Doppler imaging with the correlation of CT,
MRI and with good clinical evaluation in the recent years have provided
exquisite detail of the orbital disease.9,8 The role of plain
radiography, venography and orbital angiography now has a limited role in
orbital imaging. The aim of orbital color Doppler imaging is to detect an
orbital lesion and to determine its position within the orbit. Though
venography or angiography is steel gold standard to detect in some small A-V
malformation, with good clinical evaluation and by the help of CDI, were able
to limit the differential diagnosis.
Neoplastic Disorders : The orbital masses may be
successfully evaluated, for its vascularity with its characteristic by Color
Doppler Imaging.7 It is useful not only in determining the possible
tumor type but also in assessing the effect of vascular flow in orbital or
ocular vessels. Intra conal neoplastic lesion i.e. Optic nerve glioma is
typically avascular, and hence does not reveal any vascularity in CDI.
Meningiomas, on the other hand, may be extremely vascular and demonstrate
dramatic vascularity.7
Intra-conal orbital mass demonstrated a reduction
in the central retinal artery peak systolic velocity, during abduction of the
corresponding to the onset of amaurosis fugax. However, gaze induced changes in
the velocities can be seen in some normal individuals, perhaps for technical
reasons.
In cavernous haemangiomas, the speed of flowing
blood is usually so low and stagnant that the flow velocities are below the
detection lever, and the compression of the central retinal or ophthalmic
artery can be easily detected but in malignant tumors, significant vascularity
can be seen within the tumor.16 In orbital varices, CDI shows the
dynamic changes throughout inspiration and of the orbital varix during
inspiration, the stagnant flow during maximum filling, and the flow directed
into the depth of the orbit during expiration.
Intra-lesional flow detection and its
characterization in orbital tumor hold promise not only in limiting the
differential diagnosis but also in defining the histopathology. The vessels
within the lesion, a dilated superior ophthalmic vein, pulsation and secondary
hypertrophy of intra ocular muscles were useful indicators regarding the
vascular nature of the lesion.
The intra-conal lesion, especially the intra-conal
neoplasm and orbital haematoma produce increased pressure in the optic nerve
sheath and optic nerve tissue, as a result the time velocity waveform
demonstrated abnormally high vascular resistance in the orbital vessels.
Inflammatory : In pseudo tumor cerebri,
reduced velocities compared to controls were found in the central retinal and
posterior ciliary arteries with increased pulsatility index in the central
retinal artery. Forty-eight hours after optic nerve sheath decompression an
increase in the blood velocities was detected in those patients whose vision
improved but not in those, whose vision deteriorated.41,0 In case of
inflammatory lesion, the individual vascular pattern were need to be studied in
order to characterize these lesions.
Vascular disorders : A variety of occlusive
diseases of the orbit have been examined by CDI.
In cranial arteritis, serial CDI has demonstrated
that blood flow in the ophthalmic artery may be come undetectable when
deterioration occurs in the patient’s condition despite apparent control of the
disease process by corticosteroid therapy. Color Doppler imaging has also been
used to detect decreased velocities in the central retinal artery in patients
with progressive nonarteritic ischemic optic neuropathy compared with
unaffected contra lateral eyes.1,8,17
Dilated orbital veins, particularly the superior
ophthalmic vein, are demonstrable in patients with caroticocavernous fistula.
The blood flow in the veins shows a pulsatile arterial pattern. The direction
of flow may be variable, and in the vortex veins this may be bi-directional. In
one patient the velocities in the superior ophthalmic vein returned to a venous
pattern after embolization of the fistula. Reversal of flow in the superior
ophthalmic vein has also been described in a case of thrombophlebitis of the
cavernous sinus and in two cases of orbital apex tumor. However, it may also be
seen in normal individuals. The relevance of these findings is therefore
uncertain.1,5
Orbital arteriovenous malformation has shown low
resistance. The filling and emptying of the blood flow in orbital varices can
be imaged during the Valsalva maneuver.16 Although intermittent
pulsating exophthalmos is rather characteristics and in many cases diagnostic
of an orbital varix, imaging of the varix is mandatory for confirming the
diagnosis and to demonstrate the extent of the lesion. The non-invasive
technique CT/MRI is very expensive as compared to the CDI. Hence there is a
need for alternative of orbital varix and color Doppler is the only non-expensive,
no-invasive technique which is able to detect orbital varix. Wolfgang opines
that CDI appears to be a simple procedure for definitive diagnosis of an
orbital varix.
Summary
Color Doppler Imaging (CDI) can detect most of the orbital
diseases and orbital vascular disorders. The exact topography of the lesion can
be altered by gray scale. There is an increased blood flow velocity in
inflammatory diseases. There is however no specific pattern of Color Doppler
blood flow. Intra-conal mass lesions produced impaired retinal and optic nerve
blood flow which can be detected in CDI. Color Doppler Imaging is a useful and
valuable imaging modality needed for evaluation and follow up of orbital
diseases and orbital vascular disorders. Because it is a no-invasive, it has
very negligible radiation hazards. It is useful for tissue differentiation and
characterization. The method is most applicable in the clinical environment. It
provides us with perhaps the most practical means yet of investigating the
haemodynamics of the orbital conditions.
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