miércoles, 23 de mayo de 2007


Marcos V Goycoolea, Raúl S Poblete

(In De Sousa, Ch., Goycoolea, M., Ruah, C., Textbook of the Ear, Nose and Throat, Orient Longman Ltd, Ed, Madras, India, 1995; 53-4)

Vascular evaluation can be a very useful tool in otology for a number of clinical conditions such as:

- vertiginous syndromes with drop attacks
- pulsatile and objective tinnitus
- tinnitus of recent onset with a negative otological examination, especially when there is exacerbation of symptoms with head movements
- in the evaluation of sudden sensorineural hearing loss
- vertiginous symptoms with a negative otological examination and inconclusive tests.

The purpose of the vascular study is to evaluate the anatomic and functional integrity of the supra-aortic arterial vessels and of the neck vessels. These vessels are commonly involved with arteriosclerotic degenerative changes in the older population and with congenital or inflammatory pathologies that can be present at any age. Otologic symptoms may be the first manifestation of disease.
In atheromatosis, plaques are developed silently and progressively over the intima of the artery, especially at the level of the bifurcation, gradually reducing the lumen of the compromised vessel. Ulcerations develop without a direct relationship to the size of the plaque. A highly thrombogenic exposed middle layer of the artery is located at the base of these ulcerations. These can cause embolisation towards the brain, where the manifestations will depend on the size of the embolus and the áreas where it is distributed.
These micro-or macro-emboli are the most significant risk from the plaques, and represent the main cause of ischemic cardiovascular symptomatology. Restrictions of blood flow are responsible for a minority of transient ischemic attacks, since for a significant reduction of blood flow, an obstruction of over 75 per cent is required. Smaller-sized stenoses do not diminish the blood flow because they are compensated by distal vasodilatation, which is capable of compensating very efficiently.
It must be mentioned that even a moderate stenosis of neck vessels or their peripheral branches can cause the presence of fremitus over the lesión (of variable intensity) that can be transmitted at a distance, and be perceived in the ear as a pulsatile tinnitus which can at times be modified by neck movements. A similar phenomenon (but continuous) can occur in the presence of arteriovenous fístulas.

Echotomography is a method based on the possibility of obtaining anatomical sections based on acoustic immitance. It uses linear waves (for obtaining rectangular images) and sectorial waves (for obtaining semicircular images) with exploratory frequencies that vary between 2000 and 10 000 Hz. Vascular definition with this method is fairly poor. Only a gross approximation of major vessels can be obtained.

The pulsating echodoppler method consists in adding a pulsating doppler to the probe of the echotomograph. This adds the possibility of obtaining hemodynamic information. The axis of the vessel that is being evaluated is identified, and the vessel is followed in its course by the echograph and the doppler. This allows the examiner to obtain information of flow, by means of sound perception (obtained by the doppler) or by the analysis of the spectrum of the flow speed that appears in the screen of the instrument.

The color echodoppler rinstrument is made by coupling a conventional echotomograph (in which the images are represented by shades of grey), with a doppler system of múltiple detection, capable of providing a dynamic cartography of the flow that is to be evaluated. Conventionally, the flow that goes towards the probe is red, and the flow that goes away from the probe is blue. This does not correspond to the arterial or venous flow, since the colour depends on the position of the probe. The image that is obtained is superimposed over the grey echotomographic image.
This test can give an idea of the velocity of the flow, since red and blue colours experience desaturation (clearing) in a magnitude that is proportional to the increase in velocity. It also informs adequately about the direcion of flow, turbulences, localisation and extensión of stenosed áreas, the degree of stenosis, presence of ulcerated plaques, and even whether plaques are homogeneous (hard and less embolising), or non-homogeneous (soft and highly embolising).
This method does not provide information in cases of complete occlusion of the internal carotid artery, nor does it provide information about the integrity of the Willis polygone, or the sufficiency of intracranial circulation.
This is currently the method of choice for non-invasive vascular evaluation.

Nuclear medicine: Intravenous injection of technetium is useful for delineation of angiomas and arteriovenous fístulas. However it does not help to evaluate stenosis or ulcerated plaques. Arteriography: Selective arteriography was for many years the method of choice for vascular evaluation. Many of its uses have been replaced by echodoppler studies. Arteriography is used for non-definite cases (using digital subtraction) and for patients with surgical indication. This procedure is not free of risk.

1 comentario:

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