Echoencephaloscopy

Echoencephaloscopy (Echo, synonym - M method) is a method for detecting intracranial pathology based on the echolocation of the so-called sagittal structures of the brain, normally occupying a middle position with respect to the temporal bones of the skull. When a graphic recording of the reflected signals is made, the study is called echoencephalography.

[1], [2], [3], [4], [5], [6], [7], [8], [9], [10]

Indications for echoencephaloscopy

The main goal of echoencephaloscopy is the rapid diagnostics of volumetric hemispheric processes. The method makes it possible to obtain indirect diagnostic signs of the presence / absence of a one-sided bulk supratentorial hemispheric process, to estimate the approximate size and location of volumetric education within the affected hemisphere, as well as the condition of the ventricular system and the circulation of the CSF.

The accuracy of the listed diagnostic criteria is 90-96%. In some observations, in addition to indirect criteria, it is possible to obtain direct signs of hemispheric pathological processes, that is, signals directly reflected from a tumor, intracerebral hemorrhage, traumatic hematoma, small aneurysm or cyst. The probability of their detection is very small - 6-10%. Echoencephaloscopy is most informative for lateralized volume supratentorial lesions (primary or metastatic tumors, intracerebral haemorrhage, sheath traumatic hematoma, abscess, tuberculoma). The resulting M-echo displacement makes it possible to determine the presence, side-by-side, approximate localization and volume, and in some cases the most probable character of pathological formation.

Echoencephaloscopy is absolutely safe for both the patient and the operator. The permissible power of ultrasonic vibrations, which is on the verge of damaging action on biological tissues, is 13.25 W / cm ², and the intensity of ultrasonic radiation with echoencephaloscopy does not exceed hundredths of a watt per 1 cm ². There are practically no contraindications to echoencephaloscopy; described the successful conduct of the study directly at the scene of an accident even with an open craniocerebral trauma, when the position of the M-echo could be determined from the side of the "unaffected" hemisphere through the intact bones of the skull.

Physical on-line echoencephaloscopy

The method of echoencephaloscopy was introduced into clinical practice in 1956 thanks to the innovative research of the Swedish neurosurgeon L. Lexell who used a modified apparatus for industrial flaw detection known in the art as a method of "nondestructive testing" and based on the ability of ultrasound to reflect from the boundaries of media having different acoustic resistance. From an ultrasonic sensor in a pulsed mode, an echo through the bone penetrates the brain. In this case, three most typical and repeating reflected signals are recorded. The first signal is from the skull bone plate, on which an ultrasound transducer is installed, the so-called initial complex (NK). The second signal is formed by reflecting the ultrasound beam from the median structures of the brain. They include an interhemispheric cleft, a transparent septum, a third ventricle and an epiphysis. It is generally accepted to designate all these formations as a middle echo (M-echo). The third recorded signal is due to the reflection of ultrasound from the inner surface of the temporal bone, which is opposite to the location of the radiator, the final complex (CC). In addition to these most powerful, permanent and typical signals for the healthy brain, in most cases it is possible to record small amplitude signals located on either side of the M-echo. They are due to the reflection of ultrasound from the temporal horns of the lateral ventricles of the brain and are called lateral signals. Normally, the lateral signals have a lower power compared to the M-echo and are symmetric with respect to the median structures.

I.A. Skorunsky (1969), under the conditions of an experiment and clinic, carefully studied echoencephalotography, proposed a conditional separation of signals from the median structures to the anterior (from the transparent septum) and middle-posterior (III ventricle and epiphysis) sections of the M-echo. Currently, the following symbols for the description of echograms are generally accepted: NK - the initial complex; M - M-echo; Sp D is the position of the transparent partition on the right; Sp S - the position of the transparent partition on the left; MD is the distance to the M-echo on the right; MS is the distance to the M-echo from the left; CC is the final complex; Dbt (tr) - inter-temporal diameter in the transmission mode; P is the amplitude of the M-echo pulsation in percent. The main parameters of echoencephaloscopy (echoencephalographs) are as follows.

• The depth of sounding is the greatest distance in the tissues, on which it is still possible to obtain information. This indicator is determined by the amount of absorption of ultrasonic oscillations in the tissues under study, their frequency, the size of the radiator, the gain level of the receiving part of the apparatus. In domestic devices, sensors with a diameter of 20 mm with a radiation frequency of 0.88 MHz are used. These parameters allow to obtain the depth of sounding with a length of up to 220 mm. Since the average cross-sectional size of the adult skull, as a rule, does not exceed 15-16 cm, the depth of sounding up to 220 mm seems to be absolutely sufficient.
• The resolving power of the device is the minimum distance between two objects at which the signals reflected from them can still be perceived as two separate pulses. The optimal pulse repetition rate (at an ultrasound frequency of 0.5-5 MHz) is established empirically and is 200-250 per second. Under these conditions of location, a good signal recording quality and a high resolution are achieved.

Methods of conducting and deciphering the results of echoencephaloscopy

Echoencephaloscopy is carried out practically in any conditions: in a hospital, a polyclinic, in an ambulance, at a patient's bedside, in the field (with an autonomous power unit). No special preparation of the patient is required. An important methodical aspect, especially for beginning researchers, is to consider the optimal position of the patient and the doctor. In the overwhelming majority of cases, the study is more convenient to carry out in the patient's position lying on the back, preferably without a pillow; the doctor on the moving armchair is on the left and slightly behind the patient's head, right in front of him are the screen and the instrument panel. With the right hand, the doctor freely and at the same time with some support on the parieto-temporal region of the patient makes echolocation, if necessary turning the patient's head to the left or to the right, while the free left hand carries out the necessary movements of the meter of the site.

After lubrication of the fronto-temporal parts of the head with contact gel, echolocation is performed in a pulsed mode (a series of waves of duration 5x10 ⁶ s, 5-20 waves in each pulse). A standard sensor with a diameter of 20 mm with a frequency of 0.88 MHz is first installed in the lateral part of the brow or on the frontal hill, orienting it towards the mastoid process of the opposite temporal bone. With a certain experience of the operator next to the NK approximately in 50-60% of observations it is possible to fix the signal reflected from the transparent partition. An auxiliary guideline is a much more powerful and constant signal from the temporal horn of the lateral ventricle, which is usually determined 3-5 mm beyond the signal from the transparent septum. After determining the signal from the transparent septum, the sensor is gradually moved from the border of the scalp towards the "ear vertical". In this case, the mid-posterior sections of the M-echo, reflected by the third ventricle and the epiphysis, are located. This part of the study is much simpler. It is easiest to detect the M-echo when the sensor is placed 3-4 cm up and 1-2 cm anterior to the external auditory meatus - in the projection zone of the third ventricle and the epiphysis on the temporal bones. The location in this area allows to register the maximum median echo, which also has the highest pulsation amplitude.

Thus, the main features of the M-echo include dominance, a significant linear extension, and a more pronounced pulsation in comparison with lateral signals. Another sign of the M-echo is an increase in the distance of the M-echo from front to back by 2-4 mm (approximately 88% of patients). This is due to the fact that in the overwhelming majority of people the skull has an ovoid shape, that is, the diameter of the pole shares (forehead and occiput) is less than the central (parietal and temporal zones). Consequently, in a healthy person with an inter-temporal size (or, in other words, a terminal complex) of 14 cm, a transparent septum on the left and right is 6.6 cm apart, and the third ventricle and epiphysis at a distance of 7 cm.

The main goal of the Echo-UPS is to determine the M-echo distance as accurately as possible. The identification of the M-echo and the measurement of the distance to the median structures should be carried out repeatedly and very carefully, especially in difficult and doubtful cases. On the other hand, in typical situations in the absence of pathology, the M-echo pattern is so simple and stereotyped that its interpretation does not present any complexity. For an accurate measurement of distances, it is necessary to clearly combine the base of the leading edge of the M-echo with the reference mark with alternate locations on the right and left. It should be remembered that in the norm there are several variants of echograms.

After detecting the M-echo, measure its width, for which the mark is first applied to the front, then to the trailing edge. It should be noted that the data on the relationship between the interventricular diameter and the width of the third ventricle, obtained by N. Pia in 1968 when comparing echoencephaloscopy with the results of pneumoencephalography and pathomorphological studies, correlate well with CT data.

The ratio between the width of the third ventricle and the inter-temporal size

Width of the third ventricle, mm	Intervisual size, cm
3.0	12.3
4.0	13.0-13.9
4.6	14.0-14.9
5.3	15.0-15.9
6.0	16.0-16.4

Then, the presence, quantity, symmetry and amplitude of the lateral signals are noted. The echo pulsation amplitude is calculated as follows. Having received on the screen the image of the signal of interest, for example, III ventricle, with the help of a change in the pressing force and the angle of inclination, such an arrangement of the sensor is found on the head covers, at which the amplitude of this signal will be maximum. Further, the pulsating complex is mentally divided into percentages such that the top of the pulse corresponds to 0%, and the base to 100%. The position of the vertex of the pulse at its minimum amplitude value will indicate the amplitude of the pulsation of the signal, expressed in percent. The pulse amplitude is assumed to be 10-30%. In some domestic echoencephalographs, a function is provided that graphically records the amplitude of the pulsation of the reflected signals. To do this, when locating the third ventricle, the reference mark is accurately brought under the leading edge of the M-echo, thereby isolating the so-called probe pulse, and then transferring the device to the recording mode of the pulsating complex.

It should be noted that the registration of echolarsis of the brain is a unique but clearly underestimated possibility of echoencephaloscopy. It is known that in the inextensible cavity of the skull in the period of systole and diastole, there occur successive volumetric vibrations of the media, associated with a rhythmic fluctuation of blood that is intracranial. This leads to a change in the boundaries of the ventricular system of the brain relative to the fixed beam of the transducer, which is recorded in the form of echolapulsation. A number of researchers noted the effect of the venous component of cerebral hemodynamics on echolapse. In particular, it was pointed out that the villous plexus acts as a pump, sucking the cerebrospinal fluid from the ventricles towards the spinal canal and creating a pressure gradient at the level of the intracranial system-the spinal canal. In 1981, an experimental study was carried out on dogs with the modeling of progressive brain edema with continuous measurement of arterial, venous, liquor pressure, echolocation monitoring and ultrasonic dopplerography (UZDG) of the main vessels of the head. The results of the experiment convincingly demonstrated the interdependence between the magnitude of intracranial pressure, the nature and amplitude of M-echo pulsation, and also the parameters of extra- and intracerebral arterial and venous circulation. With a moderate increase in cerebrospinal fluid pressure, the ventricle, normally a small slit-like cavity with almost parallel walls, becomes moderately stretched. The possibility of obtaining reflected signals with a moderate increase in amplitude becomes very likely, which is reflected in the echo- pulsogram in the form of an increase in pulsation to 50-70%. With an even greater increase in intracranial pressure, a completely unusual echolocation character is recorded, which is not synchronous with the rhythm of cardiac contractions (as in the norm), but "fluttering" (undulating). With a pronounced increase in intracranial pressure, the venous plexus subsides. Thus, with a significantly hampered outflow of cerebrospinal fluid, the ventricles of the brain become excessively expanded and take on a rounded shape. Moreover, in cases of asymmetric hydrocephalus, which is often observed in unilateral volumetric processes in the hemispheres, the compression of the homolateral interventricular Monroe orifice by the dislocated lateral ventricle results in a sharp increase in the impact of the CSF jet into the opposite wall of the III ventricle, causing its trembling. Thus, the phenomenon of fluttering pulsation of the M-echo, registered with a simple and accessible method, against the background of a sharp expansion of III and lateral ventricles in combination with intracranial venous circulation according to USDG and transcranial Dopplerography (TCD) is an extremely characteristic symptom of occlusive hydrocephalus.

After the end of work in the pulse mode, the sensors switch to a transmission study in which one sensor emits and the other receives the emitted signal after it passes through the sagittal structures. This is a kind of test of the "theoretical" midline of the skull, in which the absence of displacement of the median structures the signal from the "middle" of the skull exactly coincides with the M-echo of the distance measurement left during the last scoring of the leading edge.

When the M-echo is shifted, its value is determined as follows: from a greater distance to the M-echo (a), subtract a smaller (b) and divide the resulting difference in half. The division into 2 is made in connection with the fact that when measuring the distance to the median structures the same bias is taken into account twice: once added to the distance to the theoretical sagittal plane (from the greater distance) and another time subtracted from it (from the smaller distance ).

CM = (a-b) / 2

For the correct interpretation of echoencephaloscopy data, the question of physiologically permissible within the limits of the M-echo dislocation is of cardinal importance. Much credit for solving this problem belongs to L.R. Zenkov (1969), convincingly proved that the deviation of the M-echo should not be more than 0.57 mm. In his opinion, if the displacement exceeds 0.6 mm, the probability of a volumetric process is 4%; the M-echo shift by 1 mm raises this figure to 73%, and the shift by 2 mm - up to 99%. Although some authors consider such correlations to be somewhat exaggerated, nevertheless, it is clear from this carefully verified by angiography and surgical interventions that the researchers who believe physiologically tolerable values of displacement of 2-3 mm are at risk of being mistaken. These authors significantly reduce the diagnostic capabilities of echoencephaloscopy, artificially excluding small displacements, which should have been identified when the cerebral hemisphere begins to damage.

Echoencephaloscopy in tumors of the cerebral hemispheres

The size of the displacement in determining the M-echo in the area above the external auditory meatus depends on the location of the tumor along the hemisphere's length. The greatest displacement is recorded with temporal (11 mm in average) and parietal (7 mm) tumors. Naturally, smaller dislocations are fixed in tumors of the pole lobes - occipital (5 mm) and frontal (4 mm). With tumors of the medial localization, the displacement may not be present or it does not exceed 2 mm. There is no clear correlation between the magnitude of the displacement and the nature of the tumor, but in general, with benign tumors, the displacement is on the average less (7 mm) than in malignant (11 mm).

[11], [12], [13], [14], [15], [16], [17], [18]

Echoencephaloscopy with hemispheric stroke

The goals of Echoencephaloscopy in hemispheric stroke are as follows.

• Tentatively determine the nature of acute disturbance of cerebral circulation.
• To assess how effectively the edema of the brain is eliminated.
• To predict the course of a stroke (especially hemorrhage).
• Determine the indications for neurosurgical intervention.
• Evaluate the effectiveness of surgical treatment.

Initially, there was an opinion that hemispheric hemorrhage was accompanied by a shift in M-echo in 93% of cases, whereas in ischemic stroke the dislocation frequency did not exceed 6%. Subsequently, carefully verified observations showed that this approach is inaccurate, since hemispheric cerebral infarction causes displacement of the midline structures much more often - up to 20% of cases. The reason for such significant discrepancies in the evaluation of the possibilities of echoencephaloscopy was the methodological mistakes made by a number of researchers. First, it is a lack of account of the relationship between the rate of appearance, the nature of the clinical picture and the time of echoencephaloscopy. Authors who conducted echoencephaloscopy. In the first hours of acute cerebrovascular accident, but did not observe in dynamics, did note the displacement of the median structures in the majority of patients with hemispheric hemorrhages and the absence of such with cerebral infarction. However, in the case of daily monitoring it was found that if intracerebral hemorrhage is characterized by the occurrence of a dislocation (an average of 5 mm) immediately after the development of a stroke, then with a cerebral infarction, the M-echo displacement (on average by 1.5-2.5 mm) occurs in 20 % of patients after 24-42 hours. In addition, some authors considered a bias greater than 3 mm to be diagnostic. It is clear that, at the same time, the diagnostic capabilities of echoencephaloscopy were artificially lowered, since it is with ischemic insults that the dislocation often does not exceed 2-3 mm. Thus, in the diagnosis of hemispheric stroke, the criterion for the presence or absence of M-echo displacement can not be considered absolutely reliable, nevertheless it can generally be assumed that hemispheric hemorrhages usually cause an M-echo displacement (on average by 5 mm), while an infarction the brain is either not accompanied by a dislocation, or it does not exceed 2.5 mm. It was found that the most pronounced dislocation of the median structures with a cerebral infarction is observed in the case of prolonged thrombosis of the internal carotid artery with the separation of the Willis circle.

With regard to predicting the course of intracerebral hematomas, we found a pronounced correlation between localization, magnitude, rate of hemorrhage development, and size and dynamics of M-echo displacement. Thus, with an M-echo dislocation of less than 4 mm, the disease, in the absence of complications, usually ends safely with respect to both life and recovery of lost functions. On the contrary, when the median structures were displaced by 5-6 mm, the lethality increased by 45-50% or the gross focal symptomatology remained. The prognosis became almost completely unfavorable with a M-echo shift of more than 7 mm (lethality 98%). It is important to note that modern comparisons of CT and echoencephaloscopy data with respect to the prognosis of hemorrhage have confirmed these long-established findings. Thus, repeated echoencephaloscopy in a patient with acute cerebrovascular accident, especially in combination with UZDG / TKDG, is of great importance for non-invasive assessment of the dynamics of disorders of hemo- and liquor circulation. In particular, some studies on clinical and instrumental monitoring of stroke have shown that for patients with severe craniocerebral trauma and patients with a progressive course of acute cerebrovascular accident, so-called ictus - sudden repeated ischemic-liquorodynamic crises - is characteristic. They are especially frequent in the early hours, and in a number of cases, an increase in edema (M-echo displacement), along with the appearance of "fluttering" echolocation of the third ventricle, preceded the clinical picture of a breakthrough of blood into the ventricular system of the brain in cases of severe venous discirculation and sometimes reverberation elements in intracranial vessels. Consequently, this easy and affordable comprehensive ultrasound monitoring of the patient's condition can be a good reason for repeated CT / MRI and an angioneurosurgeon consultant to determine the feasibility of decompression craniotomy.

[19], [20], [21], [22], [23], [24], [25], [26]

Echoencephaloscopy with traumatic brain injuries

Accidents are now identified as one of the main sources of death of the population (primarily from craniocerebral trauma). The experience of examination of more than 1500 patients with severe craniocerebral trauma with the help of echoencephaloscopy and USDG (the results of which were compared with CT / MRI data, surgical intervention and and / or autopsy) testifies to the high information content of these methods in recognizing complicated brain trauma. A triad of ultrasound phenomena of traumatic subdural hematoma was described:

• M-echo displacement by 3-11 mm contralateral to hematoma;
• Presence in front of the final complex of a signal directly reflected from the adrenal hematoma when viewed from the uninfected hemisphere;
• Registration at UZDG of a powerful retrograde flow from the orbital vein on the side of the lesion.

Registration of these ultrasound phenomena allows in 96% of cases to establish the presence, side-effect and approximate dimensions of the subshell blood accumulation. Therefore, some authors consider it necessary to carry out echoencephaloscopy to all patients who have even had an even slight head injury, since there can never be complete certainty that there is no subclinical traumatic hematoma. In the overwhelming majority of cases of uncomplicated TBI this simple procedure reveals either an absolutely normal picture or minor indirect signs of an increase in intracranial pressure (amplification of the amplitude of pulsation of the M-echo in the absence of its displacement). At the same time, an important question is being resolved about the expediency of carrying out expensive CT / MRI. Thus, it is in the diagnosis of complicated TBI, when the growing signs of compression of the brain sometimes leave no time or opportunity for CT, and trepanation decompression can save the patient, echoencephaloscopy is essentially a method of choice. It was this application of a one-dimensional ultrasound study of the brain that earned such glory L. Leksell, whose studies were called by contemporaries "a revolution in the diagnosis of intracranial lesions." Our personal experience in the use of echoencephaloscopy in the neurosurgical department of the emergency hospital (prior to the introduction into clinical practice of CT) confirmed the high information content of ultrasound location in this pathology. The accuracy of echoencephaloscopy (when compared with the clinical picture and routine radiography) in the recognition of shell hematomas exceeded 92%. Moreover, in some observations there were discrepancies in the results of clinical and instrumental determination of the localization of traumatic hematoma. In the presence of a clear dislocation of the M-echo in the direction of the unaffected hemisphere, focal neurological symptoms were determined not by a counter-infection, but by a homolaterally detected hematoma. This was so contrary to the classical canons of topical diagnostics that an expert in echoencephaloscopy sometimes required a lot of effort to prevent neurosurgeons planned trepanation of the skull on the side opposite to pyramidal hemiparesis. Thus, in addition to identifying hematomas, echoencephaloscopy can clearly determine the side of the lesion and thereby avoid a serious error in surgical treatment. The presence of pyramidal symptoms on the homolateral hematoma side is probably due to the fact that with pronounced lateral displacements of the brain there is a dislocation of the pedicle, which is pressed against the sharp edge of the tentorial tenderloin.

[27], [28], [29]

Echoencephaloscopy with hydrocephalus

The hydrocephalus syndrome can accompany intracranial processes of any etiology. The algorithm for detecting hydrocephalus with the help of echoencephaloscopy is based on the evaluation of the relative position of the signal from the M-echo measured by the transmission method, with reflections from lateral signals (mean-average index). The magnitude of this index is inversely proportional to the degree of expansion of the lateral ventricles and is calculated by the following formula.

SI = 2ДТ / ДV ₂ -ДV ₁

Where: SI - average-average index; DT is the distance to the theoretical midline of the head with the transmission method of the study; DV ₁ and DV ₂ - distances to the lateral ventricles.

Based on the comparison of echoencephaloscopy with the results of pneumoencephalography, E. Kazner (1978) showed that the SR in adults is normally> 4, the values bordered on the norm should be 4.1 to 3.9; pathological - less than 3.8. In recent years, a high correlation of such indicators with CT results has been shown.

Typical ultrasound signs of hypertension-hydrocephalic syndrome:

• expansion and cleavage to the base of the signal from the third ventricle;
• an increase in the amplitude and length of lateral signals;
• amplification and / or undulating character of the M-echo pulsation;
• an increase in the index of circulatory resistance by UZDG and TKD;
• registration of venous dyscirculation along extra- and intracranial vessels (especially in the ophthalmic and jugular veins).

[30], [31], [32], [33], [34], [35], [36], [37], [38], [39], [40]

Possible sources of errors in echoencephaloscopy

According to the data of the majority of authors who have considerable experience in the use of echoencephaloscopy in routine and urgent neurology, the accuracy of the study in determining the presence and side-effect of voluminous supratentorial lesions is 92-97%. It should be noted that even among the most sophisticated researchers, the incidence of false positive or false negative results is highest when examining patients with acute brain damage (acute cerebrovascular accident, TBI). A significant, especially asymmetric, edema of the brain leads to the greatest difficulties in interpreting the echogram: because of the presence of multiple additional reflected signals with a particularly sharp hypertrophy of the temporal horns, it is difficult to clearly define the leading front of the M-echo.

In rare cases of bilateral hemispheric foci (most often tumor metastasis), the absence of M-echo displacement (due to the "equilibrium" of the formations in both hemispheres) leads to a false-negative conclusion about the absence of a volumetric process.

With subtentorial tumors with occlusal symmetrical hydrocephalus, a situation may arise where one of the walls of the third ventricle occupies an optimal position for the reflection of ultrasound, which creates the illusion of displacement of the median structures. The correct recognition of stem lesions can be helped by recording the undulating pulsations of the M-echo.