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Computed tomography of the orbit is used to diagnose various diseases of the ophthalmological profile. Usually, doctors resort to this diagnostic method if they suspect a bone defect or oncological formations.
Against the background of statistics on the annual growth of metastatic tumors of orbital localization, CT of the orbit is one of the most commonly used examination options for detecting neoplasms. Due to the high sensitivity and accuracy of the results, it is possible to detect even small neoplasms, which guarantees the start of treatment at an early stage of the development of the disease.
Features of CT of the orbit
The principle of diagnostics is based on the use of X-ray capabilities. The rays are directed strictly to the upper part of the head, pass through the area under study. Due to this, visualization is gradually formed, which includes layered images of the eye sockets themselves.
Such an approach guarantees a high-quality image of not only the structure of the optic nerve, but also the vessels of the retina, as well as the immediate eyeball, the muscles that hold it, and even the state of the lacrimal glands. And far from always the cause of a sharp deterioration in well-being in a given part is the growth of the tumor.
Sometimes the result of the analysis provides information about an extensive inflammatory process of a completely different etiology, or even degeneration, the consequences of a recent severe injury.
Computed tomography is a more advanced method of studying the health of the orbit than the classic X-ray.
Experts highly appreciate this method of medical progress for a reduced percentage of harmful radiation during manipulation and high information content compared to a simple X-ray image.
Another undoubted advantage is non-invasiveness. Since the human eye is one of the most sensitive organs, any interference with its normal functioning is fraught with serious complications and prolonged pain.
Classical examination options involve the involvement of various instruments, which in fact, at the slightest contact with the shell of the eye, guarantee, if not injury, then discomfort. Here, there will be no unpleasant sensations.
Another significant victory of the authors of the procedure was the period of its implementation. Unlike the same MRI, which takes about half an hour, computed tomography lasts many times less.
This is suitable for patients suffering along the way from claustrophobia, or complaining of regular pain in the area of the organs of vision.
Indications and contraindications
Usually, an examination of the orbit is prescribed not only with direct suspicion of eye dysfunction, but also if you want to exclude the risks of orbital disease.
This means that the main indications for the appointment of diagnostics include the following aspects:
- destruction of bone tissue of various origins;
- suspicion of foreign bodies;
- injuries of both the orbit itself and the entire face;
- protrusion of the eyeball;
- inflammatory process in the retina and orbit.
The last point also affects ailments in terms of destabilization of the optic nerve. Thanks to visualization, it is possible to determine the morphological state of the eyeball, as well as to identify the possible involvement of surrounding tissues in the inflammatory process.
But most often, patients of an oncological dispensary are sent to do such a specific diagnosis, who need to confirm or refute the defeat of metastases in the presence of a primary tumor. If the patient’s vision worsens during the treatment itself, then the oncologist can send him for an additional examination to exclude retinal damage.
In addition, it is possible to prescribe a diagnosis in the presence of a pain syndrome of unknown origin. This also includes a sharp decrease in the quality of vision for no apparent reason and constant headaches against the background of any volumetric process.
Despite the fact that the technique is a truly expanded information picture of the current state of health of the organs of vision, it has a number of significant contraindications. In particular, it is strictly contraindicated for pregnant women at all stages of pregnancy, since even minimal exposure to x-rays can provoke inhibition in the development of the fetus, or its pathology. For the same reason, the procedure is not performed on children under the age of 14.
Separately, situations are considered when the doctor prescribes to the patient not just a standard CT scan, but with the use of a contrast agent, as a more accurate informative method.
It should be borne in mind that if the patient has an allergic reaction to the components of the contrast agent, then its use is contraindicated. Also, the list of contraindications was supplemented:
- chronic liver and kidney failure;
- intolerance to iodine in any form;
- severe diabetes mellitus.
The problem lies in the fact that all of the above slows down the rate of excretion of contrast products, which automatically means that the toxins of the substance are deposited in the body instead of being removed naturally.
Women should be careful during lactation. They need to give up breastfeeding after the end of the diagnosis for at least two days.
Preparation rules
Since the study involves taking a series of images at once, the patient must be prepared to be patient and listen carefully to the commands of the X-ray technician, which are given through two-way communication, which involves the presence of a microphone near the couch with the patient. A microphone is necessary for emergency situations, if a person suddenly becomes ill, or he cannot continue to be in a certain position motionless.
If it is not necessary to use a contrast agent to assess the anatomical features of the eye and the structures that surround it, then there are no significant restrictions for the patient. But if contrasting is necessary, a person should stop eating approximately four hours before the appointed time.
To do this, the doctor first informs not only the place of the procedure, but also the time. But a specific diet a few days before CT is not provided for by the rules.
A separate conversation with a specialist deserves people suffering from claustrophobia, elderly patients and adolescents. All of them can be frightened by the closed space in which the head end of the table turns out. We are talking about the scanner tunnel, which is designed to rotate around the head, periodically emitting loud beeps that do not look like clicks.
Also, do not panic if immediately after the introduction of a contrast solution, the patient’s health worsens. There are a number of characteristic symptoms of side effects from the administered agent, which are a medical norm. These include:
- sensation of tide;
- fever attack;
- headache;
- salty metallic taste;
- nausea, up to vomiting.
Since an allergic test is performed on the patient before diagnosis, no other significant deviations should be recorded in him. But, just in case, the specialist is still obliged to clarify whether the ward has an individual intolerance to iodine in its pure form, or as part of seafood. This can also serve as the basis for an allergic reaction of the body.
The final preparatory stage is the removal of absolutely all metal objects. This applies to jewelry and even clothing with metal buttons. It is not for nothing that in private clinics people are given cotton hospital suits, which do not include metal parts.
How is the procedure?
First, the patient is comfortably laid on his back on a special x-ray table. It is usually sufficient to warn the person not to move, but this does not always work, especially with older patients. Therefore, in some cases, the laboratory assistant additionally fixes the head with the help of special straps.
Next, the head end of the table is moved under the scanner, which begins to rotate around the head in order to project the eye sockets from different angles for a clear picture.
The incoming information is stored on a magnetic tape, and the slices themselves are projected onto a computer screen. Usually this is enough, but in case of unforeseen situations, the selected sections are also photographed. If further contrast is planned, then the substance is administered after the first series of imaging, and then the procedure is repeated again.
The norm and deviations from it
The conclusion of the radiologist usually comes in the form of an encrypted document involving medical terms. The attending physician himself should explain what was written after the conclusion is brought to him by the patient, or the research center hands over the document.
To conclude about a possible deviation, the doctor will take into account not only the shape, structure of the orbit, but also its size, as well as localization. The normal result is the mention of dense bone tissue of the orbit, which contrasts sharply with fatty tissues. The latter should also be dense, but not so much as to approach the texture of the bone counterpart.
Also normal is a distinct outline of the optic nerve and well-visible medial, lateral rectus muscles, which are responsible for the muscular activity of the eye.
Moreover, straight muscle fibers should be thin dense bundles that fit the eyeball and are located behind it.
But usually computed tomography indicates some deviations from generally accepted requirements due to intraorbital or extraorbital volumetric formations. They are the primary sources of problems that promise:
- enlargement of the eyeballs;
- contour deformation;
- destruction of bone tissue.
The displacement of normal structures by pathological formations threatens with a sharp loss of vision, which leads to a general deterioration in the quality of life. Thanks to the study, the doctor will be able to find out not only the location of the lesion, but also its exact nature.
In conclusion, additional structures that have a heterogeneous density may be mentioned, which most often indicates tumors of a metastatic nature. Well-demarcated masses of uniform density may also be mentioned, which is more likely to indicate encapsulated tumors. They can be both benign and malignant, and therefore require histological verification. Benign neoplasms such as hemangiomas are successfully treated in the early stages. Also in the conclusion, characteristic signs of intracranial tumors can be recorded. They involve sprouting into the orbit, which is expressed in squeezing the optic nerve. Vivid examples of this are meningiomas and gliomas, as well as tumors of the secondary type. The latter additionally provoke an expansion of the optic nerve canal, which can also be detected when studying the results of computed tomography.
A three-dimensional image helps to establish the degree of damage in case of fractures of the bones of the orbit, as well as to identify the causes of unilateral exophthalmos. Only due to numerous angles will it be possible to consider the emerging erosion of the medial wall of the orbit. The disease is considered a direct consequence of the damage to the ethmoid bone, but since it will not be possible to determine the volume of education in the orbit with alternative diagnostic methods, CT has to be used.
Additionally, testing can reveal damage to the paranasal sinuses, some of which are also provocateurs for the development of exophthalmos.
Even establishing problems with a change in the size of the medial, lateral, or both muscles at once is a task that modern diagnostics can handle. And if you additionally use a contrast agent, you will be able to collect data on the stability of the blood flow circulating in the alleged affected tissues.