Deb Coghlan AMS (Vascular and General ) Brisbane, Australia

Transcription

1 Deb Coghlan AMS (Vascular and General ) Brisbane, Australia ANEURYSMAL DIISEASE The infrarenal aorta enlarges with age, and is the commonest site for arterial aneurysms. An aneurysm is a permanent focal dilatation and elongation of an artery. An aneurysm may be defined as a 50% increase in diameter compared to the expected normal diameter of the aorta, more practically, when the aortic diameter exceeds 3cm. Abdominal aortic aneurysms (AAAs) primarily affect elderly males (sex ratio 4:1), with a prevalence of up to 5%. Ruptured AAAs are responsible for approximately 1.5% of the total mortality in males over 55 years of age, and the thirteenth commonest cause of death in the Western world. Natural History. A 5cm AAA has a 5-6% per year rupture rate, increasing with the size of the aneurysm up to 25% for a 7cm aneurysm. The rupture rate has been reported to be >50% for aneurysms >7cm. The expansion rate of AAAs is 2-3mm per year, and increases as the aneurysm enlarges. In our practice patients with asymptomatic AAAs <5cm are followed with ultrasound. CT scans are not normally ordered until the aneurysm reaches 5-5.5cm, or if there has been rapid growth of the aneurysm (more than 6mm in 6 months or 10mm in one year). Another rule of thumb is if the aneurysm growth is more than 10% in a year. Although abdominal aneurysms may cause symptoms due to pressure on surrounding structures, approximately 75% remain asymptomatic at initial diagnosis. In recent years the options for repair have changed dramatically with the development of endovascular techniques. Endovascular Aneurysm Repair (EVAR) was introduced by Parodi in the early 1990s and is now the operative approach for over half of AAAs treated in Australia. This is due to the lower post operative mortality rate of EVAR (1-2%) compared to open repair (3-5%) The best results continue to follow carefully planned elective treatment before complications of rupture, thrombosis, or embolism occur. The contrast in mortality between elective surgery (2-5%) and ruptured abdominal aortic aneurysm repair (50-70%) remains one of the most striking examples of the importance of early recognition and proper treatment of aneurysms

2 Types of Aneurysms. A true aneurysm forms as a result of a weakness of the arterial wall structure and it involves all of the layers of the arterial wall. A false or "pseudoaneurysm" is actually a pulsatile contained haematoma formed by the extravasation of blood outside the vessel as a result of a penetrating injury or rupture of a native vessel. The term "ectatic" is used to describe a dilated vessel whose diameter is enlarged but not sufficiently enough to classify it as an aneurysm. Aortic aneurysms may be caused by disorders such as atherosclerosis, mycosis, syphilis, trauma, Takayasu's disease scleroderma, or other idiopathic aortitis Aneurysms are usually described as being either fusiform (cylindrical) or saccular (out pouching involving predominantly a portion of the wall). Aortic dissection most often occurs because of a tear or damage to the inner wall of the aorta. This usually occurs in the thoracic portion of the artery, but may also occur in the abdominal portion.

3 A. OBJECTIVES To determine the location of the aneurysm (infrarenal or suprarenal) To determine the longitudinal, anteroposterior and transverse dimensions of the aneurysm To determine channel patency To determine iliac artery involvement To determine renal artery involvement To evaluate the periaortic region for masses, haemorrhage or adenopathy To identify presence of other lesions, including but not limited to, aortic dissection and pseudoaneurysm. B. INDICATIONS Pulsatile abdominal mass Abdominal bruit Bilateral leg pain or weakness Distal emboli Abdominal, flank or back pain Evaluation of interventional treatments, such as endoluminal stent placements. Follow up of know aortic aneurysms C. CONTRAINDICATIONS AND LIMITATIONS Excessive bowel gas Dressings, sutures, tubes etc Extreme abdominal girth Uncooperative patient D. EQUIPMENT AND SUPPLIES High-resolution real-time imager and integrated, pulsed, range-gated Doppler with colour flow imaging MHz transducer, depending on size of patient. Printer or DICOM for hard copy prints of spectral waveforms and images of vessels. Acoustic gel. Transept cleaning agent or other agent that is acceptable for use with ultrasound equipment. E. PATIENT PREPARATION Patients should be fasted after midnight. However elderly and diabetic patients may have a cup of tea an one piece of toast approximately 3 hrs prior to the examination. Patients may take routine medications. Lab personnel should greet the patient by name and introduce themselves. An interview of the patient should include indications for study as listed above as well as any other relevant history or symptomatology.

4 GENERAL CONSIDERATIONS Positioning of patient: The patient is generally examined in a supine position. In some patients, especially those with extreme abdominal girth, it may be necessary to turn the patient onto the left side and to use the liver as an acoustic window. To image the proximal aorta turn the patient onto the right side and use the kidney as an acoustic window to image the mid-aorta. Despite the large girth a good window can be obtained with the patient lying onto their left side. This is also an excellent view when imaging a tortuous aorta. Abdominal gas may also be a problem. Imaging from the side will often ovoid the stomach and duodenal gas. TEST PROTOCOL Evaluate the entire length of the abdominal aorta in the transverse plane. Begin at xiphoid process and scan distal to the bifurcation. NOTE: When scanning in the transverse plane, always keep the transducer perpendicular to the vessel. An oblique view will produce erroneous diameter measurements. When scanning the tortuous aorta be sure to remain in the true orthogonal 90 angle to the aorta.

5 Identify the renal arteries and take a measurement and picture at this level. Locate the renal arteries with colour. If there is turbulence take a Duplex recording. At this point turn the colour off and measure the aorta at this level. At the site of maximal dilatation, measure and record the maximum diameter. These measurements are taken from outer wall to outer wall, and if thrombus is present measure the residual lumen. Measure the aorta at the bifurcation. Evaluate entire length of the abdominal aorta in the longitudinal plane. The proximal aortic images should include the celiac axis and superior mesenteric artery, to ensure there is no supra renal artery aneurysm. Measure any dilatations in both AP and transverse.

6 In the longitudinal position locate the renal arteries and measure the distance from the renal artery to the aneurysm. In the longitudinal view turn the colour on, this will enable you to view either the right or left renal artery, you can then measure the length from the renal artery to the aneurysmal dilatation. Measure the longitudinal distal aorta measuring the cranial/caudal extent of the aneurysm. Document the distal neck from the distal extent of the aneurysm to the bifurcation. Document the shape of the aneurysm, characterizing it as either fusiform or as saccular, or dumbbell shaped Typical fusiform aneurysm Saccular aneurysms may be difficult to image particularly posterior protrusions (dotted line outlines saccular protrusion) Dumbbell or bi-lobed aneurysms are also quite common.

7 DUPLEX EXAMINATION Spectral tracing should be taken in the following locations, maintaining a 60 degree angle or less. Peak systolic velocity (PSV) should be recorded. Evaluate the supra renal segment and if a stenosis of the celiac axis or SMA is suspected these should be evaluated At the level of the renal arteries Mid aorta Distal aorta If an area of stenosis is noted, a PSV should be taken before the stenosis, thru the stenosis (being careful to evaluate the highest possible velocity), and post stenosis noting any post stenotic disturbance. If a colour bruit is seen at the renal artery origin examine take a Doppler trace at the origin and record the peak systolic velocity. In our practice we also routinely evaluate the renal artery origins and the initial examination. Normal spectral Doppler trace of the supra renal aorta. Spectral trace of the renal artery origins. Any stenotic areas should be noted and compared to the aortic velocity and a RAR (renal artery ratio) recorded. Note the increased velocities in the right renal artery, and normal velocities on the left. The aortic velocity at the level of the renal arteries was 107 cm/sec giving an RAR of 3.2 = <60% stenosis. Mid aortic waveforms may be bi or tri-phasic however within the aneurysm you usually notice a decrease in velocity with waveforms dampened usually bi-phasic and often turbulent.

8 The aortic walls should be carefully examined for signs of irregularity Colour Doppler is also of value when examining the internal lumen of the aneurysm as irregular thrombus and soft anechoic areas can be a sign of unstable plaque that may embolise distally. Irregular mixed thrombus which was embolising to the lower extremities. ILIAC ARTERY ANEURYSMS Although isolated iliac aneurysms are quite rare (<1%) iliac aneurysms associated with Aortic aneurysms are found in up to 20% of patients. The iliac arteries should be evaluated in both the transverse and longitudinal planes from the bifurcation to the inguinal ligaments. If an aneurysm is present measure the greatest diameter in both the transverse and longitudinal planes, the same as described in the aortic section. If possible measure the distance from either the bifurcation of the aorta or from the internal iliac artery. A spectral trace should be taken in the CIA, IIA, EIA. Any plaque or stenosis should be documented. Transverse image of a iliac aneurysm measuring the AP and transverse measurement as well as the residual lumen. Colour Doppler image of a CIA aneurysm with measurement from the aortic bifurcation to the proximal portion of the aneurysm. A normal spectral trace demonstrating the high resistant tri-phasic flow of the CIA.

9 REPORTIING If a patient is found to have an aneurysm greater than 6 cm at the maximum diameter measurement, or there is a concern that the aneurysm is unstable, the referring physician or his designee is contacted before the patient leaves the Laboratory. Data is assembled on appropriate worksheet and sent to a vascular surgeon for reporting. Detailed pathology, velocity information and measurements are documented onto a detailed worksheet allowing the referring doctor to quickly assess the information. Representative images are placed into the worksheet and all other images are kept on file electronically and available for or printing. An interim report is faxed to the referring physician the same day and a copy of the final report is sent to the referring physician. CLEANIING AND CARE OF EQUIIPMENT Acoustic gel is wiped from transducer, which is then cleaned with Transept disinfectant. Infectious disease policy is followed with all patients regardless of known infectious disease status.