Abdominal Vascular Ultrasound PDF

MUHAMMAD YOUSAF SENIOR LECTURER MS MIT (UOL)  B.Sc (Hons) MIT (UHS) ARDMS (USA) ABDOMINAL VASCULAR ULTRASOUND  AORTA Trunk artery  Ascending aorta arises from left ventricle; first branches of the aorta are the coronaries  Aortic arch starts at the level of the innomi...

MUHAMMAD YOUSAF SENIOR LECTURER MS MIT (UOL)  B.Sc (Hons) MIT (UHS) ARDMS (USA) ABDOMINAL VASCULAR ULTRASOUND  AORTA Trunk artery  Ascending aorta arises from left ventricle; first branches of the aorta are the coronaries  Aortic arch starts at the level of the innominate artery and extends to distal to the left subclavian artery  Three branches of the arch in order of origin: innominate artery, left common artery, left subclavian artery    Descending aorta extends through the chest and abdomen until it bifurcates at the level of the umbilicus  Descending thoracic aorta - above the diaphragm  Descending abdominal aorta - below the diaphragm  Courses anterior to the spine and to the left of the IVC Posterior to the IVC until the level of the umbilicus  Distributes blood to organs and limbs   Lower resistance in the upper abdominal aorta due to low resistance branches; higher resistance in the distal aorta due to high resistance branches  In most cases the branch is named after the organ it is feeding Paired Branches: Suprarenal arteries  Renal arteries    Gonadal arteries  Lumbar arteries  Common Iliac arteries  Unpaired Branches:  Celiac Axis  SMA   IMA Anterior Branches:  Celiac Axis  SMA  IMA  Gonadal arteries  Lateral Branches: Renal arteries    Common Iliac arteries  COMMON ILIAC ARTERIES: (CIA)  Originate at the aortic bifurcation at L3 or L4, umbilicus level  Supply legs and pelvis  Bifurcate into the internal and external iliac arteries  High resistance flow  Above the umbilicus, arteries course posterior to veins   Below the umbilicus, the arteries course anterior to the veins; common iliac arteries are anterior to the common iliac veins  INTERNAL ILIAC ARTERY: (IIA)  AKA hypogastric artery  Travels medially and supplies the pelvic organs, NOT GONADS Triphasic or biphasic, lower resistance than the common iliac  EXTERNAL ILIAC ARTERY: (EIA)  Travels laterally to pass under the inguinal ligament to become the common femoral artery  Courses along the medial side of the psoas muscle  Supplies the extremities with blood  Triphasic, higher resistance than the common iliac  Indications:  Abdominal pain  Pulsatile mass  AAA on plain film  F/U AAA  Trauma  Decreased pedal pulses Exam Technique:  2.5MHz to 6.5MHz curvilinear array - adult  4MHz to 8MHz curvilinear array - pediatric  Phased array may be used for larger patients  Patient must be NPO to best visualize the abdominal vasculature  Supine, oblique and decub positions may be necessary  2D, Color and Doppler evaluation of proximal, mid and distal segments with iliac arteries at bifurcation  US of the Aorta:  Best anatomic landmark for abdominal structures  Longitudinal - anechoic, hollow tube anterior to spine  Transverse - anechoic, circular structure to the left of the IVC  AP and transverse measurements should be obtained  Gradual distal tapering should be identified in the normal aorta  Becomes more anterior distally  Average Normal Measurements:  Proximal-2.0-2.6 cm; portion between diaphragm and celiac axis/SMA  Mid-1.6-2.4 cm; portion from celiac axis/SMA to just below renal artery origins  Distal-1.1-2.0 cm; portion from below renal arteries to iliac bifurcation Iliacs-0.6-1.4 cm  Doppler of the Aorta:  High resistance  Average velocity 70 to 100 cm/sec  Clean spectral window  Biphasic above renal arteries due to numerous low resistance branches (organ arteries)  Triphasic below renal arteries due to high resistance branches (iliacs)  When evaluated as part of a mesenteric, iliac or renal artery exam the aorta is usually assessed with Doppler just proximal to the branch of interest to compare flow patterns AORTIC PATHOLOGY  Coarctation:  Congenital narrowing of the aorta  Most commonly occurs distal to the origin of the left subclavian  Decreased flow distal to the obstruction  Monophasic flow with continuous flow in diastole identified in the abdominal aorta  Causes lower extremity ischemia  Decreased bilateral pedal pulses  Decreased bilateral ankle pressures; brachial pressures may be elevated if renal flow affected  Because the arch is proximal to the obstruction, flow to the head and neck is usually normal  Systemic HTN is usually present because the coarct causes renal ischemia and the renin-angiotensin system is activated causing increased systemic pressure  Aortic Ectasia:  Lack of tapering of the aorta as it travels distally, size remains constant from proximal to distal portions  Can be a precursor to aneurysm formation  Abdominal Aortic Aneurysm: (AAA)  True aneurysm  Symptoms include pulsatile abdominal mass, low back pain, abdominal bruit  Ruptured AAA can cause hypotension, severe abdominal pain, shock, death  Most commonly forms in the infrarenal aortic segment  Types:  1. Fusiform - vessel wall stretches in a circumferential manner; all three wall layers intact  2. Saccular - formed with a stalk connecting dilated wall portion to main vessel; usually associated with wall dissection  3. Berry - tiny out pouching, usually found in cerebrum/circle of willis; usually congenital  4. Mycotic - due to infection in the artery and the arterial wall; syphilis most common  5. Vasculitis - due to inflammatory process of vasa vasorum and tunica adventitia  Focal dilatation of the aorta >3cm; AP diameter is the most reliable measurement for assessing AAA  Another method used to identify an aneurysm is if there is a 50% increase in the diameter of an aortic segment compared to the adjacent unaffected segment  Above the Renal Arteries - Surgical intervention asap  Below the Renal Arteries - Most common; surgical intervention at a diameter >5.5cm  Serial exams will be scheduled more frequently as the aneurysm size increases; one exam per year 3-4cm size, exam every 3 months 5cm in size  Aneurysm diameter change of >4 mm on a yearly follow up exam, the next follow-up should be at 3 months  Arteriography normally performed prior to surgery; CTA also commonly performed to obtain most accurate diameters of the aorta Stent or graft placement usual treatment  Complications:  Rupture most common and most critical complication  Decreased flow to extremities  Blue Toe Syndrome with thrombus accumulation and embolization to the toes; acute ischemia causes color changes in the toes  Affects renal circulation and systemic BP if proximal to renal artery origins, if kidneys are ischemic they raise BP to increase flow  Sonographic Appearance:  Measure outer wall to outer wall  Aneurysmal >3cm diameter  Possible thrombus accumulation causes increased echogenicity in the lumen  Turbulence seen with color and PW Doppler evaluation, Yin Yang sign on color shows swirling flow  Aortic rupture can demonstrate free fluid in the perirenal space between the kidney and psoas muscle; may see debris due to blood content  Graft Placement:  Used to improve and streamline flow through a stenosis or AAA  Endovascular graft easier and better for patient than external graft or surgical resection of a AAA  Intravascular Ultrasound (IVUS):  Can be used to guide the graft during placement   Physician uses an ultrasound catheter to visualize the lumen prior to the procedure and evaluate the best location for the endoluminal graft placement Advantages of IVUS over Angiography during Angioplasty:  No need to cut the aorta to insert the graft  No radiation  No contrast required   Can provide reconstructed 2D and 3D images of the vessel and lumen  Limitations of IVUS:  Catheter size limits the vessels that can be evaluated  Introduction of the catheter can lead to arterial spasm  Significant atherosclerosis can blur the image  Images suffer from ringdown artifact caused by dead space   Cost of the disposable ultrasound catheter; cannot be heated/sterilized because the piezoelectric elements will lose their US properties Intraoperative Duplex Ultrasound:  Can be used to assess the flow changes during and after the procedure   Surgeon places transducer directly on the open wound or exposed vessel; requires sterile technique  Sonographer may be asked to assess distal flow at the ankles during and after the procedure (outside of sterile field)  Recovery room monitoring includes pressure cuffs, PVR, PPG, PW Doppler or CW Doppler evaluation of the ankle/feet/toes  Complications:  Stenosis  Thrombosis  Endoleak - blood leakage outside the graft but inside the aneurysm being treated by the graft