Computer tomography of the head is normal

Computer tomography of the head usually starts from the base of the skull and continues upwards. The resulting images on the film are oriented so that the slices are visible from the caudal side (bottom). Therefore, all the anatomical structures turn upside down from left to right. The topogram shows the location of each section.

First, evaluate the soft tissues of the head. The presence of swelling may indicate a trauma to the head. Then, in the skull base scans, analyze the state of the main artery at the level of the brainstem. The image quality is often reduced due to bands of artifacts going radially from the pyramids of the temporal bones.

When conducting a CT scan, patients with trauma should use a bone window to look for fracture of the sphenoid bone. Bilge bones and the cranial vault.

In the caudal sections, the basal parts of the temporal lobes and the cerebellum are visualized.

Structures of the orbit are usually examined in special scanning planes.

The bridge / oblong brain is often seen indistinctly due to artifacts. Between the top wall of the wedge-shaped sinus and the Turkish saddle, hypophysia of the hypothalamus funnel is visualized. From the sinuses of the dura mater, it is easy to find sigmoid sinuses. The main and upper cerebellar arteries are located in front of the bridge. The cerebellum is situated posteriorly from the middle cerebral artery. It should not be confused with the posterior cerebral artery, which appears at the next level of scanning. The lower (temporal) horns of the lateral ventricles and the 4th ventricle are clearly defined. Air cells of the mastoid process and frontal sinus are also well visualized. The presence of fluid in their lumen indicates a fracture (blood) or infection (exudate).

The upper wall of the orbit and the pyramid of the temporal bone due to the effect of a partial volume may look like an acute hemorrhage in the frontal or temporal lobe.

The density of the cerebral cortex located behind the frontal bone is often higher than in neighboring areas of the brain tissue. This is an artifact caused by the effect of the distribution of the rigidity of X-rays passing through the bone tissue. Note that the vascular plexus in the lateral ventricles is strengthened after intravenous administration of contrast medium. On scans without contrast, they can also be hyper-densal due to calcification.

In the sylvian furrow, the branches of the middle cerebral artery are determined. Clearly visualized, even the artery of the corpus callosum, which is a continuation of the anterior cerebral artery. Because of the similar density, it is often difficult to distinguish between the visual crossover and the hypothalamus funnel.

In addition to the above-mentioned cerebral arteries, the structure of increased density is the brain sickle.

Mixing median structures is an indirect sign of brain edema. Calcification of the pineal gland and vascular plexuses is often determined in adults and is not a pathology. Due to the effect of a particular volume, the upper part of the nasal lobe of the cerebellum often has an indistinct, diffuse contour. Therefore, it is difficult to distinguish worms and hemispheres from the occipital lobe.

It is especially important to carefully examine the thalamus, inner capsule and subcortical ganglia: caudate nucleus, shell and pale ball. The names of the remaining anatomical structures, indicated by the numbers on these pages, you can find on the front page cover.

The head of the patient is not always located exactly when it is examined. The slightest turn of the head leads to asymmetry of the ventricular system. If the upper pole of the lateral ventricle does not occupy the entire width of the cut - the image loses clarity (the effect of a particular volume).

This phenomenon should not be confused with brain edema. If the grooves of the brain are not smoothed (in the outer SAP) and their configuration is preserved, edema is unlikely.

When assessing the width of the SAP, it is important to take into account the age of the patient. When searching for poorly demarcated hypotense areas of edema due to stroke, the paraventricular and supraventricular white substance of the brain should be examined. Cysts can be a residual phenomenon after a stroke. In the late stage, they are well visualized and have a CSF density.

The upper sections often define calcifications in the brain crescent. Such areas of calcification have no clinical significance and should be differentiated from calcified meningioma. The presence of CSF in the furrows of the cerebral hemispheres in adult patients is an important feature that excludes cerebral edema. After analyzing the sections in the soft-tissue window, go to the bone window. It is important to carefully examine all images, exclude fractures and metastatic damage to the bones of the skull. Only after this, CT scan of the head can be considered complete.

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Normal anatomy of the orbit (axial)

The facial skeleton and orbitals are usually examined in thin sections (2 mm) using a 2 mm pitch. The scan plan is the same as for a computer tomography of the head. On the lateral topogram, the cut lines are marked parallel to the line of the initial scan, which runs along the bottom wall of the orbit, at an angle of about 15 ° to the horizontal (axial) plane.

The images obtained by scanning are a bottom view, so the structures visible in the picture on the right are actually located in the patient's left and vice versa.

Pathological changes in the soft tissue structures of the orbits and paranasal sinuses are easily detected when viewing images in the soft tissue window. The bone window is used to diagnose fractures and contact destruction of the bone with a tumor.

On the lower sections of the orbit, the structures containing air are clearly visible: parts of the maxillary sinuses, the nasal cavity with shells, the sphenoid sinus and the cells of the mastoid processes. If they are filled with liquid or soft tissue content, this is a sign of pathology - a fracture, an inflammatory or tumor process.

On the left side of the image, two structures that are related to the lower jaw are defined. This is the coronoid process and the head that participates in the formation of the temporomandibular joint. The internal carotid artery in the sleep canal of the temporal bone is difficult to distinguish when using a soft-tissue or bone window.

In the pyramid of the temporal bone, the drum cavity and the vestibule of the bone labyrinth are determined.

It is not always possible to accurately align the patient's head with respect to the sagittal plane. Therefore, as a result of even a slight lateral displacement, the temporal lobe is visualized on the cutoff only on one side, and on the other hand the air cells of the mastoid process are determined.

On the slices of the base of the skull it is difficult to trace the course of the internal carotid artery and to determine the boundaries of the pterygoid fossa, through which, among other structures, pass the large palatine nerve and nasal branches of the pterygoid plexus (from V and VII pairs of cranial nerves).

On the basis of the orbit, the lower oblique muscle of the eye is determined, which, due to the same density, is often poorly delimited from the lower eyelid. In the hypophyseal fossa on the anterior surface of the inclined processes / back of the Turkish saddle there is a pituitary gland, on the sides of which the internal carotid arteries are visualized.

A small turn of the head leads to asymmetry of the eyeballs and their muscles. The inner wall of the nasolacrimal canal is so thin that it is not clearly differentiated on the slices. The appearance on the image of the inclined process of the Turkish saddleback between the hypothalamus funnel and the siphon of the internal carotid artery only on the left side may puzzle the doctor.

After intravenous administration of the contrast medium, branches of the middle cerebral artery, beginning from the internal carotid artery, are accurately visualized. The optic nerve, passing through the intersection of the visual tract, merges with the surrounding cerebrospinal fluid. You should pay attention to the symmetrical arrangement of the muscles of the eyeball located in the retrobulbar fiber.

In the eyeball is determined the lens, which is distinguished by an increased density.

Axial studies of the orbit and facial skull end with the appearance of a frontal sinus on the cut.

The possibility of tilting gantry on CT is limited. To obtain images in the coronal plane, patients were previously laid out as shown on the topogram - lying on the abdomen with the head thrown back. Currently, coronal reconstructions are recreated by a computer method by processing three-dimensional data obtained on multi-slice computer tomographs with a narrow beam of collimation. Thus, it is possible to avoid difficulties in examining patients with trauma and possible damage to the bones or ligamentous apparatus of the cervical spine. Usually the images obtained are a front view, so the anatomical structures that the patient identifies on the right, on the image will be on the left and vice versa: as if you were sitting opposite the person and looking in his face.

When bone fractures are required, a bone window and sections with a width and a scanning step of 2 mm are usually used. In this case, even the finest fracture lines become clearly visible. If you suspect a fracture of the zygomatic arch, make an additional cut in the axial projection.

On the front images clearly visible eyeball and adjacent to the eye muscles. The lower oblique muscle of the eye is often visualized only on coronal sections, because unlike other eye muscles it does not pass in the retrobulbar fiber.

If suspected of chronic sinusitis, it is very important to evaluate the lumen of a half-moon crevice opening into the middle nasal passage. This is the main way to evacuate the secretion of the paranasal sinuses.

Sometimes congenital hypoplasia of the frontal sinus or asymmetry of other sinuses is detected without any pathological consequences.

Normal anatomy of the temporal bone (coronal)

To assess the organ of hearing and balance, the pyramids of the temporal bone are scanned in thin sections without overlapping (2/2). To ensure optimal resolution, not the entire skull is examined, but only the required part of the pyramid. Moreover, both pyramids are examined separately, and their images are enlarged. This leads to a clear visualization of even such small structures as auditory ossicles, snails and semicircular canals.

Normal anatomy of the temporal bone (axial)

Scanning in the axial plane is performed with the same parameters as in the coronal plane, i.e. Without overlapping, with a cut thickness and a scanning step of 2 mm. The patient is put on his back, and the markup is done according to the topogram. Visualization is carried out in the bone window, so the soft tissues of the head, hemisphere of the cerebellum and temporal lobes are displayed poorly. Somewhat apart from the auditory ossicles and semicircular canals, the internal carotid artery, the snail, is determined. Inner and outer (auditory passage.) The funnel-shaped depression along the posterior contour of the pyramid is the endolymphatic duct opening in the SAP.

Variants of normal anatomy of the CT of the head

After studying the soft tissues of the head, it is necessary to examine the internal and external liquor-containing spaces. The width of the ventricles and surface EPS gradually increases with age.

Since the brain of the child fills the entire skull cavity, the outer EPS is barely visualized. With age, the furrows widen, and CSF becomes more prominent between the cerebral cortex and the cranial vault. In some patients, this physiological decrease in the volume of the cortex is particularly noticeable in the frontal lobes. The space between them and the frontal bone is quite large. This so-called frontal "brain involution" should not be mistaken for pathological brain atrophy or congenital microcephaly. If a CT scan is performed on an elderly patient, the investigator should consider the pathological smoothness of the gyri as a diffuse cerebral edema. Before you diagnose cerebral edema or atrophy, you should always pay attention to the patient's age.

The incomplete fusion of a transparent septum, as a developmental feature, can lead to the formation of a so-called transparent septal cyst. Usually only part of the septum, located between the anterior horns of the lateral ventricles, is involved in the process. Less often the cyst extends to the entire space to the hindbusts.

The radiologist rarely encounters an eye prosthesis in patients who have undergone enucleation of the eye. In patients who have a history of ocular tumor, in the process of viewing CT scans it is necessary to exclude the continued growth of the tumor in the retrobulbar space.

Partial volume effects

One of the most important rules for interpreting CT images is always to compare several neighboring slices. If the patient's head is even slightly inclined during scanning, then, for example, one lateral ventricle can be determined on the cut (d _S ). And the opposite does not fall into it. In this case, only the upper pole is visible on the image.

Due to the fact that the upper pole of the ventricle does not occupy the entire thickness of the cut, its image becomes indistinct, the density decreases, and it can be mistaken for the region of the stroke. When this slice is compared with the lower location, the situation becomes clear, since the asymmetry of the contour of the lateral ventricles is clearly determined.

This example demonstrates how important it is to properly position the patient's head during the study. Accuracy of laying is checked on the nose in an anteroposterior projection using a positioning beam on the gantry. When fixing the head with soft pads, her involuntary movements can be reduced to a minimum. If the patient is on or is unconscious, it may be necessary to fix the head with a special tape.

One of the first steps in the interpretation of computer tomography of the head is the examination of soft tissues. The site of the injury with the presence of subcutaneous hematoma is a direct sign of a trauma to the skull and requires a thorough examination of the tomograms in order to search for intracranial hematoma. Many patients with trauma during the CT scan can not fix the head, which leads to significant displacements. In this case, the asymmetry of the contours of the upper wall of the orbit, the sphenoid bone or the pyramid (in this example, the symmetry is preserved) leads to an erroneous diagnosis of acute intracranial hematoma due to the hyperdense portion of the bone.

In order to clearly determine whether the found area is in fact a hematoma or a consequence of the asymmetric position of the base of the skull, it is necessary to compare the adjacent sections. In this example, a high density is due to the effect of a particular volume. Despite the obvious bruise of soft tissues of the frontal region to the right, intracranial hemorrhage was not revealed. Pay attention to significant artifacts due to the effect of X-ray stiffness distribution, layered on the brain stem. With MRI at this level, such artifacts do not arise.