CT scan of the head is normal.

A CT scan of the head usually starts at the base of the skull and works its way up. The resulting images on the film are oriented so that the slices are seen from the caudal side (from below). Therefore, all the anatomical structures are inverted from left to right. The topogram shows the location of each slice.

First, evaluate the soft tissues of the head. The presence of swelling may indicate head trauma. Then, in the skull base scans, analyze the basilar artery at the brainstem level. Image quality is often reduced by artifact bands extending radially from the pyramids of the temporal bones.

When performing CT examinations in trauma patients, it is essential to use a bone window to search for fractures of the sphenoid bone, zygomatic bones, and cranial vault.

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

The structures of the orbit are usually examined in special scanning planes.

The pons/medulla oblongata is often unclear due to artifacts. The pituitary gland and the hypothalamic infundibulum are visualized between the superior wall of the sphenoid sinus and the sella turcica. Of the sinuses of the dura mater, the sigmoid sinuses are easily found. The basilar and superior cerebellar arteries are located anterior to the pons. The tentorium cerebelli is posterior to the middle cerebral artery. It should not be confused with the posterior cerebral artery, which appears at the next scan level. The inferior (temporal) horns of the lateral ventricles and the 4th ventricle are clearly defined. The air cells of the mammillary process and frontal sinus are also well visualized. The presence of fluid in their lumen indicates a fracture (blood) or infection (exudate).

The superior wall of the orbit and the petrous pyramid may appear as an acute hemorrhage in the frontal or temporal lobe due to the partial volume effect.

The density of the cerebral cortex behind the frontal bone is often higher than that of adjacent areas of brain tissue. This is an artifact caused by the effect of the distribution of the rigidity of X-rays passing through bone tissue. Note that the vascular plexuses in the lateral ventricles are enhanced after intravenous administration of contrast. On scans without contrast, they may also be hyperdense due to calcification.

The branches of the middle cerebral artery are defined in the Sylvian fissure. Even the artery of the corpus callosum, which is a continuation of the anterior cerebral artery, is clearly visualized. Due to similar density, it is often difficult to distinguish the optic chiasm and the hypothalamic infundibulum.

In addition to the above-mentioned cerebral arteries, the falx cerebri is a structure of increased density.

Mixing of the median structures is an indirect sign of cerebral edema. Calcification of the pineal gland and vascular plexuses is often determined in adults and is not a pathology. Due to the effect of private volume, the upper part of the tentorium cerebelli often has an unclear, blurred outline. Therefore, it is difficult to differentiate the vermis of the cerebellar hemispheres from the occipital lobe.

It is especially important to examine carefully the thalamus, internal capsule, and subcortical ganglia: the caudate nucleus, putamen, and globus pallidus. The names of the remaining anatomical structures, designated by numbers on these pages, can be found on the front cover.

The patient's head is not always positioned evenly during the examination. The slightest turn of the head leads to asymmetry of the ventricular system. If the upper pole of the lateral ventricles does not occupy the entire width of the slice, the image loses clarity (partial volume effect).

This phenomenon should not be confused with cerebral edema. If the cerebral sulci are not smoothed out (in the external sap) and their configuration is preserved, edema is unlikely.

When assessing the width of the SAP, it is important to consider the patient's age. When looking for poorly delineated hypodense areas of edema due to stroke, the paraventricular and supraventricular white matter of the brain should be examined. Cysts may be a residual phenomenon after a stroke. In the late stage, they are well visualized and have the density of CSF.

Calcifications in the falx cerebri are often detected in the upper sections. Such areas of calcification have no clinical significance and should be differentiated from calcified meningioma. The presence of CSF in the sulci of the cerebral hemispheres in adult patients is an important sign that excludes cerebral edema. After analyzing the sections in the soft tissue window, we move on to the bone window. It is important to carefully examine all images, exclude fractures and metastatic lesions of the skull bones. Only then can the CT examination of the head be considered completely complete.

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Normal orbital anatomy (axial)

The facial skeleton and orbits are usually examined with thin sections (2 mm) using a 2 mm step. The scanning plan is the same as for head CT. On the lateral topogram, section lines are marked parallel to the initial scanning line running along the lower wall of the orbit, at an angle of about 15° to the horizontal (axial) plane.

The images produced by the scan are viewed from below, so the structures seen on the right in the image are actually located on 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 bone by a tumor.

The lower sections of the orbit clearly show structures containing air: parts of the maxillary sinuses, the nasal cavity with the turbinates, the sphenoid sinus and the cells of the mammillary processes. If they are filled with fluid or soft tissue, this is a sign of pathology - a fracture, an inflammatory or tumor process.

On the left side of the image, two structures related to the mandible are identified. These are the coronoid process and the head, which participates in the formation of the temporomandibular joint. The internal carotid artery in the carotid canal of the temporal bone is difficult to distinguish using either a soft tissue or bone window.

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

It is not always possible to precisely align the patient's head with the sagittal plane. Therefore, even a small lateral shift results in the temporal lobe being visualized on the section only on one side, while the air cells of the mastoid process are determined on the other side.

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

The inferior oblique muscle of the eye is determined at the base of the orbit, which, due to its uniform density, is often poorly delimited from the lower eyelid. In the hypophyseal fossa on the anterior surface of the inclined processes/back of the sella turcica, the pituitary gland is located, on the lateral sides of which the siphons of the internal carotid arteries are visualized.

A slight turn of the head leads to asymmetry of the eyeballs and their muscles. The inner wall of the nasolacrimal canal is often so thin that it is not clearly differentiated on sections. The appearance on the image of the inclined process of the sella turcica between the infundibulum of the hypothalamus and the siphon of the internal carotid artery only on the left side can puzzle the doctor.

After intravenous administration of contrast agent, the branches of the middle cerebral artery, originating from the internal carotid artery, are accurately visualized. The optic nerve, passing through the intersection of the optic tract, merges with the surrounding cerebrospinal fluid. Attention should be paid to the symmetrical arrangement of the muscles of the eyeball, located in the retrobulbar tissue.

The eyeball contains a lens that is distinguished by its increased density.

Axial studies of the eye sockets and facial skull end with the appearance of the frontal sinus on the section.

The gantry tilting capabilities of CT are limited. To obtain coronal images, patients were previously positioned as shown on the topogram - lying on their stomach with their head tilted back. Currently, coronal reconstructions are recreated computer-aided by processing three-dimensional data obtained on multi-slice CT scanners with a narrow collimation beam. This avoids difficulties in examining patients with trauma and possible damage to the bones or ligaments of the cervical spine. Typically, the images obtained are a frontal view, so anatomical structures defined on the patient's right will be on the left in the image and vice versa: as if you were sitting opposite the person and looking at his face.

When it is necessary to exclude bone fractures, a bone window and sections with a width and scanning step of 2 mm are usually used. In this case, even the thinnest fracture lines become clearly visible. If a fracture of the zygomatic arch is suspected, an additional section is made in the axial projection.

The anterior images clearly show the eyeball and the adjacent extraocular muscles. The inferior oblique muscle of the eye is often only visible in coronal sections because, unlike other extraocular muscles, it does not pass through the retrobulbar tissue.

If chronic sinusitis is suspected, it is very important to evaluate the lumen of the semilunar cleft, which opens into the middle nasal meatus. This is the main route for the evacuation of paranasal sinus secretions.

Sometimes congenital hypoplasia of the frontal sinus or asymmetry of other sinuses is found 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 obtained enlarged. This leads to clear visualization of even such small structures as the auditory ossicles, cochlea, 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 slice thickness and a scanning step of 2 mm. The patient is placed on his back, and the markings are made according to the topogram. Visualization is performed in the bone window, so the soft tissues of the head, the cerebellar hemispheres and the temporal lobes are poorly displayed. The internal carotid artery, cochlea, internal and external (auditory canal) are determined slightly to the side of the auditory ossicles and semicircular canals. The funnel-shaped depression along the posterior contour of the pyramid is the endolymphatic duct opening into the SAP.

Variations of normal anatomy of the head CT

After examining the soft tissues of the head, it is necessary to examine the internal and external cerebrospinal fluid-containing spaces. The width of the ventricles and superficial cerebrospinal fluid gradually increases with age.

Since the child's brain fills the entire cranial cavity, the external CSF is barely visible. With age, the sulci widen and the CSF becomes more visible between the cerebral cortex and the cranial vault. In some patients, this physiological decrease in cortex volume is especially noticeable in the frontal lobes. The space between them and the frontal bone becomes quite large. This so-called frontal "involution of the brain" should not be mistaken for pathological brain atrophy or congenital microcephaly. If a CT scan is performed on an elderly patient, the examiner should interpret the pathological smoothing of the convolutions as diffuse cerebral edema. Before making a diagnosis of edema or cerebral atrophy, you should always pay attention to the patient's age.

Incomplete fusion of the septum pellucidum, as a developmental feature, can lead to the formation of a so-called cyst of the septum pellucidum. Usually, only the part of the septum located between the anterior horns of the lateral ventricles is involved in the process. Less often, the cyst spreads to the entire space up to the posterior horns.

The radiologist rarely encounters an ocular prosthesis in patients who have undergone enucleation of the eye. In patients with a history of orbital tumor, continued tumor growth in the retrobulbar space must be excluded during the review of CT scans.

Partial volume effects

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

Since the upper pole of the ventricle does not occupy the entire thickness of the slice, its image becomes unclear, the density decreases, and it can be mistaken for the area of the stroke. When comparing this slice with the one located below, the situation becomes clearer, since the asymmetry of the contour of the lateral ventricles is clearly determined.

This example demonstrates the importance of correctly positioning the patient's head during the examination. The accuracy of positioning is checked by the nose in the anteroposterior projection, using the positioning beam on the gantry. By fixing the head with soft pads, its involuntary movements can be reduced to a minimum. If the patient is on a ventilator or unconscious, additional fixation of the head with a special tape may be necessary.

One of the first steps in interpreting a head CT scan is to examine the soft tissues. A contusion site with a subcutaneous hematoma is a direct sign of cranial trauma and requires careful examination of the tomograms to search for an intracranial hematoma. Many patients with trauma cannot fix their heads during a CT scan, which leads to significant head displacements. In this case, the asymmetry of the contours of the upper wall of the orbit, sphenoid bone, or pyramid (in this example, symmetry is preserved) leads to an erroneous diagnosis of acute intracranial hematoma due to the hyperdense bone area.

In order to clearly determine whether the area found is actually a hematoma or a consequence of the asymmetrical position of the skull base, adjacent sections should be compared. In this example, the high density is due to the partial volume effect. Despite the obvious contusion of the soft tissues of the frontal region on the right, no intracranial hemorrhage was detected. Note the significant artifacts due to the effect of the distribution of X-ray hardness, superimposed on the brainstem. Such artifacts do not occur with MRI at this level.