10.3 Saphenous Vein Mapping Protocol & Criteria

10.3 Saphenous Vein Mapping Protocol & Criteria

Autogenous vein bypass grafting remains the gold standard revascularization strategy for critical limb ischemia, infrainguinal peripheral arterial disease (femoral-to-popliteal and femoral-to-tibial bypass), and multivessel Coronary Artery Bypass Grafting (CABG). Compared to prosthetic conduits such as expanded polytetrafluoroethylene (ePTFE) or Dacron, autologous saphenous veins deliver significantly superior long-term patency rates, superior compliance matching, and robust natural resistance to bacterial infection. Preoperative duplex vein mapping provides the vascular surgeon with a detailed anatomical and functional blueprint of available autogenous conduits, preventing unnecessary surgical incisions and reducing operative time.

Anatomical Compartments & Saphenous Architecture

A comprehensive understanding of lower extremity fascial planes is essential to distinguish true conduit trunks from superficial tributaries and embryologic variants.

The "Saphenous Eye" in Transverse B-Mode Cross-Section

            Skin Surface / Epidermis
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
           Subcutaneous Adipose Tissue
                 [Tributary Vein] (Outside Compartment!)
      -------------------------------------- Superficial Fascia (Saphenous Fascia)
          \                              /
           \     ( * GSV * )            /   Saphenous Compartment ("Saphenous Eye")
            \   [True Conduit]         / 
      ====================================== Deep Muscular Fascia
                Muscular Compartment
             (e.g., Vastus Medialis / Tibia)

1. The Great Saphenous Vein (GSV) & The "Saphenous Eye"

• The True Saphenous Compartment: The trunk of the GSV does not wander randomly through the subcutaneous fat. Instead, it travels within a discrete anatomical canal termed the saphenous compartment. In transverse cross-section, this compartment is bounded superficially by the hyperechoic superficial fascia (saphenous fascia) and deeply by the hyperechoic deep muscular fascia.
• The "Saphenous Eye" Landmark: The two fascial leaflets envelope the circular, anechoic GSV to form a characteristic biconvex shape resembling an Egyptian eye, with the vein serving as the "pupil". Identifying the vein strictly within this fascial eye confirms that the vessel is the true GSV trunk rather than an accessory tributary.

2. Accessory Saphenous Veins

• Anterior Accessory Saphenous Vein (AASV): Courses along the anterior and anterolateral thigh. Crucially, at the proximal thigh, the AASV travels within its own distinct fascial compartment located directly anterior to the companion femoral artery and vein (the "alignment sign"). It unites with the GSV within $1\text{ cm}$ of the saphenofemoral junction. If the main GSV is hypoplastic or absent, the AASV may serve as an alternative bypass conduit.
• Posterior Accessory Saphenous Vein (PASV): Courses along the posteromedial thigh and calf. In the lower leg, the posterior accessory vein (formerly the posterior arch vein) connects with the Cockett perforators.

3. Anatomical Variants: Duplication vs Segmental Hypoplasia

• True Duplication: True complete duplication of the GSV is exceptionally rare ($< 1-2\%\text{ of limbs}$). To be classified as a true duplication, both venous channels must reside side-by-side within the exact same saphenous fascial compartment over an extended distance. Most clinical reports of "duplication" are pseudo-duplications, where one vessel is the true GSV in the compartment and the other is a large accessory tributary in the subcutaneous fat.
• Segmental Aplasia / Hypoplasia: Occurs in up to 10% to 30% of limbs. The GSV trunk within the fascial compartment becomes markedly diminutive or absent over a segment (typically in the mid-calf or distal thigh), while a subcutaneous tributary leaves the compartment, bridges the gap, and re-enters the compartment distally.

Preparation and measurement conditions

Use a comfortable warm setting, appropriate dependency or tourniquet augmentation, and light probe pressure to reduce false small measurements. Record position and whether the vein was augmented. Cold, recent compression, hydration, and technique can alter caliber. Use a probe that resolves the superficial wall without excessive pressure and maintain contact with adequate gel.

A fixed room temperature, tilt angle, or tourniquet pressure is not universal for every patient or system. Follow the validated mapping protocol and clinical precautions. Check unexpected small segments in multiple planes and trace continuity rather than measuring only the best-looking isolated segment.

Quantitative and qualitative conduit assessment

Measure inner diameter at named sites under documented distension and with minimal compression. Record usable continuous length, depth, branches, wall thickening, thrombus, webs, prior treatment, and caliber changes. Suitability depends on the operation and surgeon's criteria. Diameters around 2.5–3 mm are often favorable planning examples, but there is no universal minimum shared by every bypass and patient.

A 1.8 mm segment remains a small potentially limiting finding after technique is verified. Map alternative GSV, SSV, or arm veins as requested. Do not assign an unsupported 50–70% 30-day failure rate or reject the vessel independently. A large segment with diseased walls or an unusable intervening segment may also be unsuitable.

Describe fascial compartments and follow the actual course. The GSV has a characteristic compartment, but accessory saphenous trunks may have their own compartments; “outside the GSV eye” is not synonymous with an ordinary tributary in every case.

Step-by-Step Mapping Protocol & Surgical Skin Marking

Mapping requires real-time transverse and longitudinal duplex interrogation, caliper measurement, and indelible skin marking to guide the surgical incision:

Surgical Skin Marking Technique at 5-10 cm Intervals

        Proximal Thigh (SFJ)           Mid Thigh               Distal Thigh            Knee Joint
             [ O ] --------------------- [ O ] ------------------ [ O ] ---------------- [ O ]
             4.2 mm                      3.6 mm                   3.2 mm                 3.0 mm
                                           | (Branch)
                                           v
                                      [Tributary Marked: X]

1. Stepwise Mapping Protocol

1. Saphenofemoral Junction (SFJ): Locate the CFV in the groin crease. Identify the SFJ and measure the ostial diameter. Note the entrance of the superficial epigastric vein.
2. Thigh Interrogation: Track the GSV down the medial thigh within its saphenous eye. Acquire inner-to-inner transverse caliper measurements at:
   • Proximal thigh ($5\text{ cm}$ below SFJ)
   • Mid-thigh
   • Distal thigh ($5-10\text{ cm}$ above knee)
3. Knee & Calf Interrogation: Track the GSV across the medial knee joint line and down the medial calf immediately anterior to the tibia down to the medial malleolus. Acquire measurements at:
   • Knee joint line
   • Proximal calf
   • Mid-calf
   • Distal calf ($5\text{ cm}$ above medial malleolus)
4. Branch Identification & Documentation: As the transducer moves along the vein, identify all major exit branches and tributaries. Document their location and clock-face orientation (anterior vs posterior). In an in situ vein bypass (where the vein remains in place, valves are lysed with a valvulotome, and the ends are anastomosed to the artery), unligated branches will siphon arterial blood directly into the venous system, creating high-flow arteriovenous (AV) fistulas that cause graft steal and early failure.

2. Surgical Skin Marking Protocol

• Technique: Center the vein perfectly in the transverse B-mode image. Using a non-toxic surgical skin marker, place a dot directly adjacent to the center of the probe on the patient's skin. Move the probe $5\text{ to }10\text{ cm}$ distally, re-center the vein, and place another mark. Connect the dots with a solid line to trace the exact projection of the vein onto the skin surface.
• Marking Branches: Identify all major branching points and draw a short perpendicular "tick mark" or "X" to notify the surgeon to dissect and ligate the branch.

3. Alternative Autogenous Conduits: Small Saphenous & Arm Veins

• If the bilateral GSVs are absent, $< 2.0\text{ mm}$, or heavily diseased:
  • Small Saphenous Vein (SSV): Map the SSV from the lateral malleolus up the posterior calf within the "eye of the SSV" to the popliteal crease. Caliber $\ge 2.5-3.0\text{ mm}$ is acceptable.
  • Cephalic & Basilic Veins (Upper Extremity): Map the cephalic vein (lateral arm/forearm) and basilic vein (medial arm/forearm) from wrist to axilla. A minimum distended caliber of $\ge 2.5\text{ mm}$ is required. The basilic vein is typically larger, softer, and less prone to prior venipuncture phlebitis than the cephalic vein.