75635

CTA Abdominal Aorta and Bilateral Iliofemoral Lower Extremity Runoff

CPT code 75635 describes a comprehensive computed tomographic angiography (CTA) study focused on the abdominal aorta and the arterial system extending through the lower extremities. This procedure is a non-invasive diagnostic tool used to visualize the vascular anatomy from the level of the diaphragm down to the feet. The process begins with the administration of iodinated contrast material, typically via a power injector into a peripheral vein. This allows for high-resolution imaging during the arterial phase of contrast enhancement. The imaging protocol often involves bolus tracking, where the CT scanner monitors the arrival of contrast in the proximal aorta to trigger the scan sequence automatically at the moment of peak opacification. The scan encompasses the abdominal aorta, the celiac trunk, superior and inferior mesenteric arteries, renal arteries, and the primary focus: the iliac, femoral, popliteal, and trifurcation vessels including the tibial and peroneal arteries. One of the defining characteristics of CPT 75635 is that it inherently includes image post-processing, such as multiplanar reformats (MPR), maximum intensity projections (MIP), and 3D volume rendering. These techniques are essential for surgeons and interventionalists to evaluate the degree of stenosis, the length of occlusions, the presence of aneurysmal dilation, and the quality of runoff, which is the distal arterial flow necessary for successful surgical or endovascular intervention. The procedure is critical in the management of peripheral arterial disease (PAD), as it provides a detailed map of atherosclerotic plaque distribution and calcification, which guides the choice between balloon angioplasty, stenting, or bypass grafting. By including both the abdominal and lower extremity segments in a single acquisition protocol, 75635 offers a holistic view of the systemic nature of atherosclerosis and ensures that inflow disease is not overlooked when treating distal symptoms.

Clinical Indications

  • Evaluation of symptomatic peripheral arterial disease (PAD) with intermittent claudication.
  • Assessment of critical limb ischemia (CLI) including rest pain, non-healing ulcers, or gangrene.
  • Preoperative planning for lower extremity revascularization (bypass surgery or endovascular intervention).
  • Evaluation of suspected abdominal aortic aneurysm (AAA) with extension into the iliac arteries.
  • Follow-up of previous vascular bypass grafts or endovascular stents.
  • Evaluation of acute limb ischemia or arterial trauma to the lower extremities.
  • Assessment of suspected arterial emboli or thrombosis.
  • Screening for vascular abnormalities such as popliteal entrapment syndrome or cystic adventitial disease.

Procedure Steps

  1. Patient positioning in the CT gantry, typically supine with feet first.
  2. Establishment of high-flow intravenous access, usually 18-20 gauge in the antecubital vein.
  3. Performance of a non-contrast topogram or scout view to define the scan range (diaphragm to toes).
  4. Optional acquisition of non-contrast images of the abdomen/pelvis if needed for calcification baseline.
  5. Administration of non-ionic iodinated contrast via power injector at a rate of 4-5 mL/sec.
  6. Implementation of bolus tracking software with a ROI (region of interest) placed in the suprarenal abdominal aorta.
  7. Automated initiation of the CT scan once the Hounsfield Unit threshold (e.g., 150 HU) is reached.
  8. Rapid acquisition of thin-slice (0.5mm to 1.5mm) axial images from the diaphragm to the distal lower extremities.
  9. Image reconstruction and transfer to a 3D workstation.
  10. Generation of post-processed images including MIP, MPR, and 3D volume-rendered reconstructions to evaluate vessel patency and stenosis.

Coding Guidelines

  • CPT 75635 is a comprehensive code and includes non-contrast images if performed during the same session.
  • Do not report 75635 in conjunction with 74175 (CTA Abdomen), 73706 (CTA Lower Extremity), or 75625-75630 (Aortography).
  • Image post-processing (3D rendering) is included in 75635; do not report 76376 or 76377 separately.
  • If only the abdominal aorta is imaged without lower extremity runoff, use 74175.
  • If only the lower extremities are imaged without the abdominal aorta, use 73706.
  • If performed in a facility setting, use modifier 26 for the professional component; if in an office setting, report the global code without modifiers.
  • For bilateral procedures, 75635 is defined as bilateral in the code descriptor, so modifier 50 is not applicable.

Associated ICD-10 Codes