DR. RAJESH REDDY SANNAREDDY
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Flow Diversion Treatment for Brain Aneurysms

Advanced endovascular treatment for large, giant, fusiform, and wide-neck brain aneurysms in Hyderabad by Dr. Rajesh Reddy Sannareddy.

Flow Diversion Treatment for Brain Aneurysms

Introduction

For most brain aneurysms — small, saccular, with a well-defined neck — endovascular coiling or surgical clipping provides effective, durable treatment. But a significant subset of aneurysms do not fit neatly into either category. Large and giant aneurysms whose sheer volume makes complete coil packing impractical. Fusiform aneurysms with no defined neck that cannot be coiled or clipped conventionally. Wide-neck aneurysms where coils herniate into the parent artery. Giant partially thrombosed aneurysms causing TIAs, seizures, or progressive weakness by pressing on adjacent brain. For these complex cases, flow diversion has transformed what is achievable.

Flow diversion is a fundamentally different concept from conventional coiling. Rather than filling the aneurysm sac with coils from the inside, a flow diverter is deployed in the parent artery — across the aneurysm neck — and works from the outside in. The dense mesh of the device redirects blood flow away from the aneurysm, causes progressive thrombosis within the sac over weeks to months, and simultaneously scaffolds the parent artery to form a new, smooth arterial wall that permanently excludes the aneurysm. The result is a biological cure, not a mechanical plug.

Dr. Rajesh Reddy Sannareddy, Senior Consultant Endovascular Neurosurgeon in Hyderabad, is trained in the full range of flow diversion devices — including the Pipeline Embolisation Device, FRED, Surpass, SILK, p64, and Derivo — with hands-on experience from his Fellowship in Interventional Neuroradiology (FINR) at the University Hospital, Zurich and visiting scholar exposure at Barrow Neurological Institute, Phoenix. He is one of the few neurosurgeons in Hyderabad with dedicated training in these advanced endovascular techniques.

What Is Flow Diversion and How Does It Work?

A flow diverter is a high-porosity braided mesh stent deployed within the parent artery — the artery from which the aneurysm arises — across the aneurysm neck. Unlike conventional stents, flow diverters have very high metal surface coverage — typically 30–35% of the luminal wall — achieved by braiding dozens of fine metal wires into a mesh tube.

The Two Mechanisms of Flow Diversion

  1. Haemodynamic flow redirection: The high metal coverage acts as a flow barrier at the aneurysm neck. Inflow into the aneurysm sac is reduced by approximately 60–80% immediately after deployment. Blood that previously entered the sac with each heartbeat is redirected along the stent into the distal artery, no longer pushing against the aneurysm wall.
  2. Progressive aneurysm thrombosis and neointimal healing: With reduced flow in the sac, blood stagnates and progressively clots. Over weeks to months, the thrombus organises and is replaced by connective tissue. Simultaneously, endothelial cells migrate across the stent struts at the aneurysm neck, forming a new arterial wall that permanently seals the aneurysm from the circulation — a healing process, not just a mechanical blockage.
Key Principle: The key insight of flow diversion is that it treats the parent artery, not the aneurysm, with preservation of flow through the side branches in majority of cases. By remodelling the diseased arterial segment where the aneurysm arose, flow diversion achieves durable occlusion through biological healing — which is why its results for large and complex aneurysms are superior to those of conventional coiling.
How Flow Diversion Works for Brain Aneurysms

Flow Diversion Devices: The Full Spectrum

Several flow diversion devices are available. Dr. Rajesh Reddy's training includes experience with the following extrasaccular flow diverters:

Device Mechanism Best Suited For Key Feature
Pipeline Embolisation Device (PED) High-porosity braided cobalt-chromium mesh across aneurysm neck Large/giant ICA aneurysms; paraclinoid ICA; fusiform; recurrent wide-neck Most studied; occlusion rates 85–93% at 12 months; FDA and CE approved
FRED (Flow Re-Direction Endoluminal Device) Dual-layer braided nitinol; inner high-mesh layer over neck Similar to Pipeline; also wide-neck MCA and basilar aneurysms Visible inner/outer layers on fluoroscopy; easier deployment confirmation
Surpass Streamline Braided cobalt-chromium; higher metal coverage than Pipeline Large aneurysms; complex neck geometry High mesh density; single device covers wider neck widths
SILK Flow Diverter Low-profile braided nitinol; high mesh coverage Wide-neck fusiform and saccular aneurysms Very flexible; useful for tortuous anatomy
p64 Flow Modulation Device Braided nitinol; retrievable and repositionable Wide-neck aneurysms; need for precise placement Fully retrievable before detachment — high safety margin
Derivo Embolisation Device Braided nitinol with anti-thrombogenic surface Wide-neck saccular and fusiform aneurysms Surface modification may reduce thromboembolism risk
Pipeline Flex with Shield Technology PED with phosphorylcholine anti-thrombogenic coating Patients who may not tolerate standard dual antiplatelet therapy Coating reduces platelet adhesion; potential for modified antiplatelet regimen

The Pipeline Embolisation Device — The Most Studied Flow Diverter

The Pipeline consists of 48 cobalt-chromium and platinum-tungsten wires braided into a self-expanding cylindrical mesh. The Pipeline Flex — the current generation — incorporates a resheathing capability: the partially deployed device can be recaptured and repositioned if initial placement is suboptimal, significantly improving deployment safety and accuracy. The Pipeline Flex with Shield Technology adds a phosphorylcholine surface coating that reduces platelet adhesion and may allow modified antiplatelet regimens in selected patients.

When Is Flow Diversion the Right Treatment?

Flow diversion is not a first-line treatment for all aneurysms — it is a specialised tool for cases where conventional approaches are inadequate or associated with unacceptably high recurrence rates:

Aneurysm Type Why Flow Diversion Is Preferred Occlusion Rate
Large aneurysm (10–24 mm) Coiling alone has high recanalisation; sac volume makes complete coil packing impractical; flow diverter treats entire neck in one device 85–90% at 12 months
Giant aneurysm (≥ 25 mm) Surgery carries very high morbidity; coiling alone invariably recanalises; flow diversion achieves progressive occlusion without entering the sac 73–86% at 6 months; continues improving to 90%+ at 24 months
Fusiform aneurysm No defined neck — cannot be coiled or clipped conventionally; flow diverter lines the parent artery, excluding the fusiform segment Variable; depends on length of fusiform segment
Wide-neck saccular aneurysm Dome:neck ratio < 1.5; coils herniate into parent artery; stent-assisted coiling has higher recurrence; flow diverter treats neck without entering sac 80–90% at 12 months
Paraclinoid ICA aneurysm Optimal anatomical fit for Pipeline; alternative is complex skull base surgery 85–93% at 12 months (best results in class)
Recurrent aneurysm after coiling Coil mass compacted; re-coiling has high re-recurrence; flow diverter treats residual neck and prevents further recanalisation 75–85% at 12 months
Blister / Pseudoaneurysm Thin fragile wall — clipping risks tearing; coiling has poor geometry; flow diverter supports the parent artery wall and promotes healing Moderate; often requires supplemental coiling
Giant partially thrombosed aneurysm Embolic TIAs, seizures, or progressive hemiparesis from mass effect; flow diversion causes progressive thrombosis and sac shrinkage, reducing mass effect and eliminating embolic source Variable; sac shrinkage continues over 12–24 months
Note on Acute SAH: Flow diversion is generally not recommended for acutely ruptured aneurysms in the acute SAH setting. The dual antiplatelet therapy required to prevent stent thrombosis significantly increases the risk of haemorrhagic complications in a patient who has just experienced a subarachnoid haemorrhage. In exceptional circumstances — such as a ruptured blister aneurysm or giant aneurysm anatomically unsuitable for coiling — flow diversion may be considered, but this requires expert case-by-case judgement.
When Is Flow Diversion Used for Brain Aneurysms

The Flow Diversion Procedure: What Happens

Pre-Procedure: Dual Antiplatelet Preparation

Flow diversion requires mandatory dual antiplatelet therapy before the procedure. Aspirin 150 mg and clopidogrel 75 mg or Ticagrelor 180 mg/day are started 5–7 days before planned deployment. Platelet function testing (VerifyNow P2Y12 assay) is performed on the day of procedure in selected cases to confirm adequate clopidogrel effect — poor responders may require prasugrel or ticagrelor. Inadequate antiplatelet effect at deployment significantly increases the risk of in-stent thrombosis.

DSA and 3D Angiography — Sizing the Device

A high-quality 3D rotational DSA is essential for flow diverter sizing. The diameter and length of the device must precisely match the parent artery — too large and it will not fully appose the vessel wall; too small and it will be undersized at the neck. Device sizing software provides measurements of the parent artery diameter proximal and distal to the aneurysm, neck width, and the length of artery requiring coverage.

Device Deployment

Under general anaesthesia, a guide catheter is positioned in the internal carotid or vertebral artery. A microcatheter is navigated past the aneurysm neck into the distal parent artery. The flow diverter is deployed by slowly retracting the microcatheter — allowing the mesh to expand and conform to the arterial wall across the aneurysm neck. Correct apposition is confirmed with contrast injections and DSA. An immediately post-deployment DSA confirms neck coverage and visible flow reduction in the sac. Intraprocedural Dyna CT or Vaso CT softwares help in assessing apposition of stent to the vessel wall.

Adjunctive Coiling

For aneurysms more than 1.5 cm where spontaneous thrombosis after flow diversion alone would be slow, adjunctive coiling within the sac may be performed at the same sitting. The coils partially fill the sac and accelerate thrombosis, reducing the risk of delayed aneurysm rupture during the progressive occlusion phase and also helping to decompress the mass effect more rapidly.

Inside Flow Diversion Procedure

Outcomes and Evidence for Flow Diversion

Occlusion Rates

  • PUFS trial (Pipeline for Uncoilable or Failed Aneurysms): 73% complete occlusion at 6 months and 86.8% at 180 days for large/giant uncoilable ICA aneurysms — the landmark study that led to FDA approval
  • IntrePED registry: 5.6% major stroke or death rate in 793 patients across 21 centres — establishing real-world safety data
  • PREMIER trial (Pipeline for ICA aneurysms 7–12 mm): 76.9% complete occlusion at 12 months — expanding Pipeline indication beyond large/giant aneurysms
  • Multiple single-centre series: 85–93% complete occlusion at 12 months for paraclinoid ICA aneurysms — the best flow diversion results reported for any anatomical location

Sac Shrinkage After Flow Diversion

One of the most clinically rewarding outcomes of successful flow diversion — particularly for large and giant aneurysms causing mass effect — is progressive shrinkage of the aneurysm sac over months to years. As the organised thrombus reabsorbs and the sac collapses, symptoms from compression — visual loss, cranial nerve palsies, headache, hemiparesis — gradually improve. For giant partially thrombosed aneurysms, sac shrinkage also eliminates the embolic source responsible for TIAs and reduces seizure frequency. This shrinkage is a unique advantage of flow diversion over coiling, where the sac volume is maintained by the coil mass.

Transient Worsening After Flow Diversion

A distinctive phenomenon after flow diversion of large and giant aneurysms is transient worsening of mass effect symptoms in the weeks after treatment. As the aneurysm sac thromboses, the clot may initially swell — temporarily increasing volume and worsening compression on adjacent structures (optic nerve, cranial nerves, brainstem, or adjacent cortex). This perianeurysmal oedema is managed with short courses of oral corticosteroids and typically resolves as the thrombus organises and shrinks. Patients should be counselled that symptoms may transiently worsen before improving — this is expected and does not indicate treatment failure.

Risks of Flow Diversion: An Honest Assessment

Flow diversion is a more complex procedure than standard coiling and carries specific risks that patients must understand:

  • Thromboembolic stroke: The most significant complication — approximately 3–6% across major series. Pre-procedural dual antiplatelet therapy and platelet function testing are the primary preventive measures.
  • Delayed aneurysm rupture: A paradoxical but rare complication (approximately 1–2%) — particularly in large and giant aneurysms — during the progressive thrombosis phase. Adjunctive coiling may reduce this risk.
  • Perforator artery occlusion: Small perforating arteries covered by the device mesh may rarely be affected — approximately 1–3% in published series. Modern flow diverters are designed to preserve perforator flow.
  • In-stent stenosis or thrombosis: Occurs in approximately 3–5% of cases. Stenosis is usually asymptomatic; acute thrombosis requires emergency endovascular management.
  • Incomplete occlusion: Approximately 10–15% of aneurysms do not achieve complete occlusion at 24 months — requiring assessment for supplemental coiling or a second flow diverter.
Once complete aneurysm occlusion is confirmed on follow-up angiography, the long-term outcome is excellent — with very low rates of rebleeding and durable aneurysm exclusion. This contrasts with large aneurysms managed with coiling alone, where recanalisation and retreatment rates remain high indefinitely.

Antiplatelet Therapy and Follow-Up After Flow Diversion

Antiplatelet Protocol

Dual antiplatelet therapy — aspirin (75–150 mg) and clopidogrel (75 mg) or Ticagrelor 180 mg/day — is required for 6 months after flow diverter deployment. After 6 months, clopidogrel is stopped and aspirin continued for at least 3–5 years or indefinitely (duration at the discretion of the treating doctor). Stopping either medication without consulting Dr. Rajesh Reddy risks in-stent thrombosis. Any planned surgical procedure during the dual antiplatelet period — including dental surgery — must be discussed in advance.

Follow-Up Angiography Schedule

  • 6 months: DSA — primary assessment of aneurysm occlusion; confirms device apposition and absence of in-stent stenosis
  • 12 months: DSA or MRA or CTA — second assessment; most aneurysms that will achieve complete occlusion have done so by this point
  • 24 months: MRA or CTA — confirms sustained occlusion; identifies late incomplete occlusion requiring retreatment
  • Annual MRA, CTA or Selective DSA thereafter: for select cases of large/giant aneurysms — long-term surveillance to confirm ongoing sac shrinkage and absence of recanalisation
Follow-up angiography after flow diversion is not optional — it is an integral part of the treatment. Unlike a surgical clip that provides an immediately verifiable mechanical seal, flow diversion relies on progressive biological occlusion that must be confirmed on imaging. Skipping follow-up creates unacceptable uncertainty.

Why Choose Dr. Rajesh Reddy for Flow Diversion in Hyderabad?

Flow diversion requires a level of endovascular expertise and judgement that goes beyond standard coiling. Correct device sizing, precise deployment, management of deployment challenges, and recognition of complications are skills built through dedicated training and case volume.

Flow Diversion Expertise — Dr. Rajesh Reddy

  • FINR — Fellowship in Interventional Neuroradiology, University Hospital, Zurich, a high-volume European cerebrovascular centre
  • Visiting Scholar — Barrow Neurological Institute, Phoenix (one of the highest-volume cerebrovascular centres in North America); Okayama University, Japan; Klinikum Stuttgart, Germany
  • Double board certified neurosurgeon (MCh + DNB) — surgical understanding of cerebrovascular anatomy underpins every endovascular decision
  • Trained in the full spectrum: simple coiling, balloon-assisted coiling, stent-assisted coiling, Flow Diversion — treatment recommendation based on aneurysm anatomy, not available technique
  • Several complex neurosurgical and endovascular procedures across a 15+ year career
  • Clinical acumen and judgement gained through years of training with leading global experts

Frequently Asked Questions

Q1: How long does it take for the aneurysm to close after flow diversion?
Flow diversion does not close the aneurysm immediately — it initiates a progressive biological process. Most patients show significant reduction in aneurysm filling on the 6-month DSA, with complete or near-complete occlusion in the majority by 12 months. For large and giant aneurysms, the occlusion process may continue for 18–24 months or beyond. For giant partially thrombosed aneurysms, progressive sac shrinkage reduces the mass effect and eliminates the embolic source over the same period — symptoms such as hemiparesis, seizures, or TIAs typically improve as the sac shrinks.
Q2: Will I need blood thinners after flow diversion? For how long?
Yes. Dual antiplatelet therapy — aspirin and clopidogrel or Ticagrelor — is required for 6 months after flow diverter deployment. After 6 months, aspirin continued for at least 3–5 years (in select cases indefinitely) at the treating doctor's discretion. It is essential not to stop either medication without medical advice. Before any surgical procedure — including dental extraction — during the dual antiplatelet period, Dr. Rajesh Reddy must be consulted.
Q3: Can flow diversion be used for a ruptured (bleeding) aneurysm?
Flow diversion is generally not the first-line treatment for acutely ruptured aneurysms in the SAH setting. The dual antiplatelet therapy required to prevent stent thrombosis significantly increases the risk of further bleeding. For most ruptured aneurysms, coiling or clipping is preferred. Flow diversion may be considered in exceptional circumstances — such as a ruptured blister aneurysm or giant aneurysm anatomically unsuitable for coiling — requiring careful expert judgement.
Q4: I have a giant (3 cm) aneurysm — will flow diversion cure it?
For giant aneurysms, flow diversion offers the best available outcomes of any modality — complete occlusion rates of 73–90% at 12–24 months. A proportion will require supplemental coiling or additional treatment. Importantly, even partial occlusion continues to improve over subsequent years as thrombosis and healing progresses. For giant partially thrombosed aneurysms causing mass effect symptoms, the progressive sac shrinkage after flow diversion also relieves compression on adjacent brain structures over months. Dr. Rajesh Reddy will discuss what outcome is realistic for your specific aneurysm.
Q5: My vision has been affected by a large aneurysm pressing on my optic nerve — will flow diversion help?
This is one of the most rewarding outcomes of flow diversion for large paraclinoid or ophthalmic artery aneurysms. As the aneurysm thromboses and progressively shrinks, the compression on the optic nerve is gradually relieved — most patients with vision loss from aneurysm mass effect experience meaningful visual improvement. However, results vary from person to person. Patients treated earlier in the course of visual deterioration achieve better outcomes than those with longstanding severe compression.
Q6: Are there aneurysms for which flow diversion does not work?
Flow diversion is not effective for all aneurysm types. Very distal aneurysms beyond accessible arterial segments may not be reachable. Posterior circulation aneurysms — particularly at the basilar tip and PICA — have less evidence for flow diversion and carry higher periprocedural risk due to the density of perforating arteries. Wide-neck bifurcation aneurysms at the MCA or basilar tip are generally better treated with intrasaccular devices (WEB, Contour, Artisse) than with a flow diverter that would need to be placed across a branch vessel.