Page 93 - Libro 2

5 — Uncommon Pathology of the Carotid System
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in the artery wall, whereby blood can extravasate out the arterial wall into the surrounding tissue.4 Pseu- doaneurysms may also form at an endarterectomy site or the anastomosis of a carotid bypass graft. The blood flow outside of the artery wall forms a spherical or ovoid mass bordered by the surround- ing tissues. There may or may not be a thrombus formed within the mass or sac. The channel con- necting the pseudoaneurysm mass to the artery is called the pseudoaneurysm “neck,” and may be short or long, wide or thin. Characteristically, blood flow within the neck has a to-and-fro appearance as blood flows out of the artery, to the mass, and back into the artery again.
SIGNS AND SYMPTOMS
Patients will usually present with a palpable, pulsa- tile mass in the neck associated with a history of trauma, whether iatrogenic or otherwise. The pres- ence of a carotid bypass graft with a pulsatile mass is also an appropriate indication for a duplex ultra- sound examination. A TIA or stroke is also possible, but rupture rarely occurs.
SONOGRAPHIC EXAMINATION TECHNIQUES
A transverse overview of the carotid arteries in col- or will typically be the easiest and fastest way to determine the area of interest for further examina- tion. A mass, either partially or completely filled with color, will be noted adjacent to the artery. Typ- ically, the color flow within the pseudoaneurysm in transverse view will demonstrate a “yin-yang” appearance, with a red color on half of the mass and a blue color on the other half, demonstrat- ing flow into and out of the mass. Upon further investigation with careful color control of gain and scale, a point will be noted in the artery wall as a defect, which allows blood flow extending beyond the arterial wall into the color-filled “neck” of the pseudoaneurysm. The neck may be short with flow going directly into the mass, or long and winding. The diameter of the disruption in the wall and the neck of the pseudoaneurysm are variable. However, the key feature of the neck is a to-and-fro Doppler flow pattern, usually with high velocities. Veloci- ties in the pseudoaneurysm mass itself are typically much lower due to the larger diameter. Pseudoan- eurysms may thrombose spontaneously, so a vari- able amount of thrombus may be present. The color scale may be decreased to obtain adequate color filling. Steering angles and planes of view may need to be varied to estimate the percentage of mass that is thrombosed.
A sonographer must be careful not to confuse a pseudoaneurysm with an enlarged lymph node or a tumor. A lymph node or tumor may also appear to be a mass with color flow within it, but the flow pat- terns in a lymph node or a branch feeding the node will have either a typical arterial waveform, not to- and-fro, or demonstrate a venous waveform pattern. A tumor will also be missing the pendulum flow pat- tern in the branches feeding it, which are character- istic of a true pseudoaneurysm.
TECHNICAL CONSIDERATIONS
A transverse overview of carotid artery from clavicle to mandible is performed first to identify a mass adja- cent to the artery. Color is very helpful in identifying a pseudoaneurysm, especially if it is not completely filled with a thrombus. Document the PA in color demonstrating the red and blue color pattern associ- ated with these structures. The largest diameter of the PA should be measured in both longitudinal and transverse views. Some laboratories choose to esti- mate the amount of thrombus in the PA (i.e., 30%, 50%, nearly completely thrombosed) as this will help the clinician to decide on a treatment. Many PAs thrombose spontaneously, and those with long necks that are nearly thrombosed are most likely to completely thrombose without intervention. B-mode images may document this estimate in multiple planes of view.
To identify the location of the source of the PA, color is used to follow the neck from the PA to the artery. In addition, there will be a color change along the wall of the native artery at the perfo- ration (i.e., color aliasing) and possibly a color bruit. Spectral Doppler is used to identify the to- and-fro flow pattern associated with the neck of a true PA. If possible, try to measure the perfora- tion in the artery wall using B-mode. This is not always possible and the measurement should be taken very carefully. It can be used as an estimate of the size of the wall injury. Lastly, demonstrate Doppler flow patterns pre-PA and post-PA in the native artery.
DIAGNOSIS
Pulsatile color flow in the mass with a yin-yang, red and blue appearance is the classic presentation of a PA. The most important characteristic to dem- onstrate for the diagnosis of PA is the to-and-fro Doppler flow pattern in the neck of the PA. As men- tioned in the preceding section, a thrombus may or may not be noted in the mass and an estimate of the percentage of the thrombus may be helpful to the physician.