🩸 Fenestrated Endograft Planning

Juxtarenal & Pararenal Aneurysm Anatomy — Why the Standard EVAR Rulebook Fails

Roughly 15–20% of abdominal aortic aneurysms extend to within a few millimeters of the renal arteries, leaving no reliable segment of healthy infrarenal aorta to seal a standard endograft. Juxtarenal aneurysms abut the renal origins with a short but present neck; pararenal aneurysms involve the renal origins directly; suprarenal extension reaches the SMA and celiac trunk. Precise 3D reconstruction of every visceral branch origin — its height, circumferential clock position, diameter, and angulation — is the foundation on which the entire custom device is designed.

• 15–20%: AAA with short/no neck (juxtarenal or pararenal morphology)
• ≥10–15 mm: IFU-compliant neck length (required for standard infrarenal EVAR)
• <4 mm: Typical hostile neck (in juxtarenal aneurysm candidates)
• ≤1 mm: CT slice thickness used (for centerline reconstruction)

Defining juxtarenal, pararenal, and suprarenal aneurysm anatomy

The anatomic classification of complex aneurysms is defined entirely by the relationship between the aneurysm sac and the visceral vessel origins:

• Juxtarenal aneurysm: the aneurysmal dilation begins immediately at or just below the lowest renal artery — a seal zone technically exists but is too short (<10 mm) and often too angulated or conical for a standard endograft to achieve durable fixation and seal per instructions-for-use (IFU).

• Pararenal aneurysm: the aneurysm involves the renal artery origins themselves — there is no cylindrical infrarenal neck at all. A standard graft, if deployed here, would cover one or both renal ostia.

• Suprarenal aneurysm: the aneurysm extends further cephalad to involve the SMA and/or celiac trunk origins, requiring the device to preserve or reconstruct three or four visceral branches rather than two.

Each of these morphologies defeats the basic assumption of standard EVAR: a parallel-walled, non-angulated, adequately long segment of normal aorta above the aneurysm sac in which to seal a covered stent-graft.

Why standard infrarenal EVAR fails without an adequate seal zone

On-label EVAR depends on the proximal neck for two mechanical functions: circumferential seal (preventing type Ia endoleak, blood flow around the graft into the sac) and radial/hook fixation (preventing caudal graft migration under pulsatile aortic pressure).

When the available neck falls below roughly 10–15 mm, or when it is conical (>3 mm diameter change over its length), severely angulated (>60°), heavily calcified, or thrombus-lined, standard endografts placed off-label show markedly higher rates of type Ia endoleak, sac growth, and late migration. Deliberately covering a renal or visceral ostium to "buy" extra sealing length is not an option — it produces immediate end-organ ischemia.

The only ways to treat these aneurysms endovascularly are therefore to build the seal zone higher up the aorta, above the visceral vessels, while incorporating openings that let blood continue to flow into the celiac, SMA, and renal arteries — this is the entire rationale for fenestrated and branched endografting.

Fenestrated vs. Branched Graft Design — Matching a Custom Device to Patient-Specific Anatomy

A fenestrated endograft (FEVAR) has small precisely-cut reinforced openings in the fabric that align with each target vessel ostium, through which a short bridging stent is placed nearly flush with the aortic wall. A branched endograft (BEVAR) instead incorporates a fabric side-tube — directional or helical — that projects into the vessel before the bridging stent is placed, tolerating more anatomic mismatch. Device selection and every fenestration coordinate are derived from centerline CT reconstruction and are unique to each patient — this is bespoke, not off-the-shelf, engineering.

• ±1 mm: Fenestration position tolerance (target accuracy from planning CT)
• 6–8 mm: Typical fenestration diameter (reinforced nitinol-ringed opening)
• 10–20 mm: Directional branch length (fabric cuff projecting into vessel)
• 2–4 vessel: Device configurations (celiac / SMA / bilateral renals)

From centerline CT to fenestration coordinates

Design software (e.g., Cook's TeraRecon-based planning, or in-house centerline tools) unwinds the 3D aortic centerline into a flat 2D "map" of the aortic circumference at every axial level:

• Height (Z-axis): craniocaudal distance from a fixed reference (usually the lowest renal artery or top of the fabric) to each vessel ostium, measured along the curved centerline, not a straight line — this matters enormously in angulated or tortuous aortas.

• Clock position (circumferential angle): each vessel's take-off angle is mapped in degrees around the aortic circumference, referenced to a fixed marker (typically the anterior/posterior midline or a gold radiopaque marker band on the fabric).

• Vessel diameter and early angulation: used to select fenestration size and, for branches, the cuff angle and length so the bridging stent does not kink immediately at its origin.

Every coordinate is specific to one patient's scan on one day — aneurysm growth, positional change, or a repeat CT with different table angulation between planning and manufacturing can shift these coordinates enough to compromise fit.

Fenestrations vs. directional branches vs. scallops

Three opening types are combined within a single device depending on each vessel's anatomy:

• Fenestration: a small reinforced hole (usually nitinol-ringed) used when the vessel origin sits close to the fabric and needs only a short bridging stent nearly flush with the aortic wall — most common for renal arteries.

• Directional branch: a fabric side-tube projecting outward before the bridging stent is placed, providing more length to accommodate vessel origins that are more caudally angled or where precise circumferential alignment is harder to guarantee — commonly used for the SMA and in branched (BEVAR) configurations.

• Scallop: a U-shaped notch cut into the top edge of the fabric, used when a vessel (often the celiac trunk) sits at or very near the top sealing edge of the device and does not need a full circumferential fenestration.

The device is manufactured with the fabric pre-marked with radiopaque gold markers at every opening so the operator can visually confirm orientation under fluoroscopy before and during deployment.

Fenestration positioning is governed by one non-negotiable principle: the opening must align within roughly 1 mm and a few degrees of rotation with the true vessel ostium, because the graft fabric itself cannot be trimmed or repositioned once deployed. Rotational orientation is planned using a fixed anatomic or radiopaque reference, verified twice against the CT before manufacturing sign-off, and re-confirmed by fluoroscopic marker alignment at the start of deployment — a rotational error of even 30–45° can render a fenestration uncannulatable.

Custom Device Manufacturing — Balancing Fabrication Lead Time Against Aneurysm Growth Risk

Unlike an off-the-shelf infrarenal endograft that can be implanted the same day it is opened, a company-manufactured fenestrated or branched device is built to order after a formal engineering review of the patient's CT measurements — a process that in the United States has historically taken 6 to 12 weeks. During that wait, the aneurysm continues to enlarge, and every week of delay carries a measurable, if generally low, incremental rupture risk that must be weighed against the safety benefit of a precisely fitted device.

• 6–12 wks: Company-manufactured lead time (design review + fabrication + shipping)
• <24–48 h: Physician-modified graft (PMEG) (same-institution back-table modification)
• ~3 mm/yr: Mean AAA growth rate (accelerates as diameter increases)
• 0 days: Off-the-shelf multibranch device (e.g. Gore TAMBE, Cook p-Branch)

Company-manufactured custom devices vs. physician-modified endografts (PMEG)

Two pathways exist for obtaining a fenestrated/branched device, each with sharply different timelines:

• Company-manufactured custom device: the planning CT and fenestration map are submitted to the manufacturer's engineering team, who verify measurements, build patient-specific tooling, sew the reinforced fenestrations/branches onto the graft fabric, and perform quality testing before shipment. Regulatory-approved lead time is typically 6–8 weeks in centers with streamlined pathways, but can extend to 10–12 weeks, longer for unusual configurations or during periods of high manufacturing demand.

• Physician-modified endograft (PMEG): the implanting surgeon or a designated on-site team cuts fenestrations into an off-the-shelf standard graft on the back table immediately before the case, under an individual physician-sponsored investigational protocol. This eliminates the manufacturing wait almost entirely — the device can be ready within a day — but shifts fenestration precision, reinforcement quality, and regulatory responsibility onto the local team, and is generally reserved for urgent/symptomatic cases where a custom device cannot be obtained in time.

• Off-the-shelf multibranch platforms (e.g., Cook Zenith p-Branch, Gore Excluder TAMBE): pre-configured devices covering the most common anatomic patterns are stocked and available immediately, at the cost of less patient-specific fit than a fully bespoke device.

Planning around the manufacturing window

Because the wait cannot be eliminated for most elective custom devices, planning teams manage the interval actively rather than passively:

• A surveillance CT or ultrasound is often repeated near the time of manufacturing completion to confirm the aneurysm and vessel geometry have not changed enough to compromise the fenestration coordinates already submitted.

• Growth-rate modeling (using the patient's own prior imaging where available) estimates expected sac diameter at the anticipated implant date, informing whether standard elective timelines are acceptable or whether a PMEG/off-the-shelf pathway should be pursued instead.

• Symptomatic status is reassessed at every visit during the wait — new or worsening abdominal/back pain triggers urgent re-imaging and may convert the plan from custom-manufactured to physician-modified to avoid a dangerous delay.

• Blood pressure control and smoking cessation counseling continue throughout the waiting period, since both measurably affect growth rate and rupture risk independent of the device timeline.

Branch Vessel Cannulation and Bridging Stent Placement

Once the main endograft body is deployed with its fenestrations oriented against the correct vessels, each opening must be individually cannulated with a wire and catheter, then bridged into the target vessel with a covered stent that spans from inside the fenestration into healthy vessel lumen. This is the most technically demanding phase of the procedure, typically requiring simultaneous femoral and upper-extremity (brachial or axillary) access.

• ~80–90%: Upper-extremity access used (of FEVAR/BEVAR cases (brachial/axillary))
• Balloon-expandable: Typical bridging stent type (covered, for renal fenestrations)
• 3–5 h: Mean total procedure time (for 3–4 vessel configurations)
• >95%: Technical cannulation success (in experienced high-volume centers)

Access strategy and sequence of cannulation

Because the fenestrations face cranially and the renal/visceral arteries angle downward and laterally from the aorta, cannulating them from below (femoral access) at a favorable angle is often mechanically difficult. Upper-extremity access — brachial or axillary, usually left-sided — allows a wire and catheter to approach each fenestration from above, in a much more coaxial trajectory with the target vessel.

Typical sequence: 1. Main body deployed from femoral access, partially constrained so the fenestrated segment can still be rotated and adjusted. 2. A sheath is advanced from the brachial/axillary access down through the fenestration. 3. A steerable catheter and hydrophilic wire probe through the fenestration and into the target vessel ostium — celiac and SMA are usually cannulated first (larger, more forgiving angles), renal arteries last (smaller, more angle-sensitive). 4. Once wire access into the distal vessel is confirmed, the catheter is exchanged for a stiffer wire to support stent delivery, and the main body is then fully deployed once all planned vessels are wired.

Bridging stent selection and deployment

The bridging stent is the mechanical link between the fenestration/branch and the native vessel — its selection depends on vessel size, angulation, and fenestration type:

• Balloon-expandable covered stents (e.g., cobalt-chromium or stainless-steel platforms with ePTFE covering): preferred for renal arteries and short fenestration-to-ostium distances, offering precise deployment length and strong radial force, but with less flexibility for angulated origins.

• Self-expanding covered stents: preferred for directional branches and the SMA/celiac, where more length and conformability to angled or mobile vessel segments is needed, at some cost of deployment precision.

Deployment technique: the stent is positioned so a short segment (typically 4–6 mm) projects into the aortic lumen through the fenestration, with the remainder extending into healthy vessel beyond any early angulation — then flared/flanged at the aortic end to seat firmly against the fenestration ring, eliminating any gutter for blood to leak around the stent.

Confirming Branch Patency — Completion Angiography and Long-Term Surveillance

Before the procedure ends, completion angiography must demonstrate brisk, unobstructed contrast flow through every bridging stent into its target vessel, with no kinking, dissection flap, or thrombus. Because branch vessel occlusion or stenosis is the dominant long-term failure mode of fenestrated and branched endografts — more common than the type of sac-related endoleak seen after standard EVAR — lifelong imaging surveillance is a mandatory part of the treatment, not an optional add-on.

• 94–97%: Overall branch patency (1 yr) (per-vessel, contemporary series)
• ~10–15%: Renal branch instability (5 yr) (stenosis, occlusion, or endoleak)
• 1 month: First surveillance CT (then 6 & 12 months, then annually)
• ~10–20%: Branch reintervention rate (over 5-year follow-up)

Completion angiography — what "success" looks like on the table

Immediately after all bridging stents are deployed and flared, a formal completion angiogram is performed from a stable catheter position in the aorta above the fenestrated segment:

• Every target vessel must fill promptly and completely with contrast, with a smooth, non-narrowed lumen through the bridging stent and no visible gutter or jet of contrast tracking around a stent into the sac (a type III-equivalent branch endoleak).

• The bridging stent course is inspected for kinking at the fenestration-to-vessel transition — a subtle kink at this location is the most common precursor to early branch thrombosis and often requires an additional stent to correct before the case ends.

• Any renal artery with sluggish flow, spasm, or a filling defect is treated immediately (vasodilator, additional stent, or thrombectomy) rather than accepted and monitored, since renal branch occlusion causes irreversible nephron loss within a short window.

Lifelong surveillance imaging and the reintervention pathway

Because fenestrated and branched grafts have more failure-prone components (each bridging stent is itself a potential stenosis/occlusion/endoleak site) than a standard endograft, surveillance is more frequent and never stops:

• CT angiography at 1 month establishes the post-procedure baseline for every branch and the sac diameter.

• Further CT at 6 and 12 months, then annually thereafter (sometimes alternating with contrast-enhanced ultrasound to limit cumulative radiation/contrast exposure), tracks each bridging stent for early stenosis, sac diameter for growth (a sign of endoleak even without a visible leak source), and the fenestration/branch fabric for structural integrity.

• A branch showing progressive stenosis is typically treated pre-emptively with balloon angioplasty or a relining stent before it occludes — reactive treatment after occlusion is far less successful than pre-emptive treatment of stenosis.

Registry data consistently show that renal branches are the most failure-prone component (smallest caliber, most angle-sensitive), while celiac and SMA branches — larger and more forgiving — have the highest long-term patency.

Numbered planning workflow, start to finish: (1) high-resolution CTA with ≤1 mm slices and full aortoiliac coverage; (2) 3D centerline reconstruction and vessel-by-vessel height/clock-position mapping; (3) device configuration selection — fenestration, scallop, or directional branch per vessel; (4) manufacturing submission and engineering sign-off, or PMEG back-table planning if urgent; (5) staged or single-setting deployment with upper-extremity access for cannulation; (6) sequential wiring, bridging stent placement, and flaring of each branch; (7) completion angiography confirming patency of every vessel; (8) structured lifelong CT/ultrasound surveillance with pre-emptive treatment of any branch stenosis.