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
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).
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.
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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