Q: Explain this to me in a very simplified manner and make me memorise this thoroughly for my pg exam A: Here is a complete, simplified, exam-ready breakdown of Chapter 49: Interventional Techniques Scott's Brown ENT - covering everything from the images you've shared. --- 🧠 INTERVENTIONAL NEURORADIOLOGY INR - HEAD & NECK The "Block Traffic to the Tumour" Concept --- THE BIG IDEA understand this first Embolization = cutting off the blood supply to a tumour or bleeding vessel before surgery or as treatment itself Think of it like this: before demolishing a building, you cut off the electricity and water. Same idea - before removing a tumour, you cut off its blood supply so it shrinks, bleeds less during surgery, and is easier to remove. --- SECTION 1: WHAT IS INR USED FOR? Use Purpose -------------- Pre-op embolization Reduce blood loss during tumour surgery Palliation Shrink inoperable tumours, reduce pain Definitive treatment When surgery is contraindicated Epistaxis control Stop intractable nosebleeds AV fistula/shunt treatment Devascularize abnormal connections Chemotherapy delivery Direct drug to tumour via catheter --- SECTION 2: TOOLS - THE CATHETERS Two types of catheters: 1. Flow-Directed Catheters - Very light and flexible tip - Carried by blood flow to the target - Used for arteriovenous shunts - Work best when blood flow is fast 2. Over-the-Wire Catheters - Pushed over a guide wire - Larger lumen - can deliver particles AND liquids AND coils - Used when blood flow is slow - Used mainly for head and neck tumours Microcatheters = tiny 0.02 inch / 0.5 mm catheters for small vessels - injected through the main catheter. --- SECTION 3: EMBOLIZATION MATERIALS This is the most high-yield part for PG exams. Learn the table below cold: PARTICLES Table 49.2 - HIGH YIELD Agent Permanent or Temporary Target ------------------------------------- Autologous blood clot Temporary Afferent arteries Gelfoam Temporary Afferent arteries Polyvinyl alcohol PVA Permanent Tumour vessels Trisacryl gelatin particles Permanent Tumour vessels Coils Permanent Large arteries/veins Balloons Permanent Large arteries Alcohol ethanol Permanent Malformations / tumour vessels Sodium tetradecyl sulphate Permanent Malformations / tumour vessels Cyanoacrylate NBCA Permanent Malformations / tumour vessels Onyx EVAL Permanent Malformations / tumour vessels Memory trick for TEMPORARY agents: "AGents are Temporary" = Autologous clot + Gelfoam = Temporary Everything else = Permanent --- PARTICLE SIZE MATTERS - KEY CONCEPT - Smaller particles 40-150 microns → penetrate deep into tumour → better devascularization - Larger particles → block proximal arteries → collaterals develop → blood supply returns - For meningioma pre-op: start with small particles 150 microns to block intratumoral vessels, then use larger particles to block afferent arteries - For inoperable tumours: very small particles 50 microns injected slowly - don't want to stimulate collaterals --- COILS AND BALLOONS - Coils = steel, tungsten, or platinum preferred - inert, not magnetized by MRI - Used for large artery occlusion after a successful temporary balloon test - Also used to close dural arteriovenous fistulas DAVF - Modern coils are retrievable - attached to delivery wire, detached mechanically/hydrostatically/thermally - Balloons = latex or silicone - For temporary test occlusions OR detachable for permanent occlusion - Inflated with radiographic contrast so visible on X-ray --- LIQUID EMBOLIC AGENTS Quick-setting glues/plastics Two main ones to remember: Agent Brand names How it works --------------------------------- NBCA N-butyl-2-cyanoacrylate Histoacryl, Glubran Sets on contact with blood; polymerizes Onyx EVAL - Ethylene Vinyl Alcohol copolymer Onyx Dissolves in DMSO solvent; solidifies when DMSO disperses Both are PERMANENT - used for definitive/palliative treatment. Require significant expertise to use safely. Sclerosants ethanol, sodium tetradecyl sulphate: used for facial vascular malformations and low-flow malformations. --- SECTION 4: EMBOLIZATION TECHNIQUES Transarterial most common - Catheter fed through artery → into tumour's feeding vessels → inject embolic agent - Used for: Meningioma, paraganglioma, JNA, haemangiopericytoma Percutaneous direct puncture - Liquid embolic/sclerosant injected directly into the tumour through skin - First used for hypervascular JNA - Useful for recurrent lesions - Can achieve total or near-total devascularization --- SECTION 5: SPECIFIC TUMOURS HIGH YIELD TABLE 49.3 Commonly Embolized must memorise: 1. Meningioma 2. Paraganglioma 3. Juvenile Nasopharyngeal Angiofibroma JNA 4. Haemangiopericytoma Less Frequently: Schwannoma, Carcinoid, Alveolar sarcoma, Thyroid carcinoma, Granular cell myoblastoma, Capillary haemangioma, Esthesioneuroblastoma, Neurinoma --- SECTION 6: TUMOUR-SPECIFIC DETAILS MENINGIOMA - Arises from arachnoid cap cells / arachnoid granulations - Chromosome 22 defect; associated with NF-2 - Affects women 2x more than men; middle age - Usually highly vascular; transitional subtype = most vascular - Blood supply: branches of external carotid artery + internal carotid artery meningeal branches - On DSA: "blush" pattern dilated feeding arteries + delayed venous phase - Pre-op embolization reduces blood loss - particles PVA or liquid agents NBCA/Onyx - Operate within 7 days of embolization to catch the ischaemia/necrosis window before revascularization - Complication: revascularization can occur as soon as 3-4 weeks after embolization - Complication rate: 3-6% mostly haemorrhage Key exam fact: Meningioma embolization complication = intra-tumoural haemorrhage 24-36 hours after embolization. --- PARAGANGLIOMA Glomus tumour - From paraganglionic chemoreceptor cells neural crest origin - 50% in temporal bone from cochlear promontory = tympanicum, or jugular bulb = jugulare - 35% in carotid body, 12% high cervical vagus - 10% multifocal; 5% secrete catecholamines - Autosomal dominant inheritance some familial - Symptoms: tinnitus, cranial nerve palsy jugulare/vagale, pain - Imaging: CT + MRI CT shows bone involvement; MRI shows soft tissue - Very vascular → good targets for embolization - Blood supply: multi-compartment - arterial from multiple feeding arteries - Intra-tumour AV shunts present → consider percutaneous/liquid embolic - Embolization = adjunct to surgery; rarely definitive - Complications from embolization: 3-6% meningioma range is similar --- JUVENILE NASOPHARYNGEAL ANGIOFIBROMA JNA - Benign but locally invasive tumour of nasopharynx - Histology: vascular spaces no muscle layer mixed with conventional arteriocapillary tree with muscle layers - Target cells = nasal mucosa cells → muscularized vascular channels - Driven by testosterone + oestrogen hypersensitivity → presents at puberty - Presents with: epistaxis + nasal obstruction - Blood supply: branches of external carotid artery mainly internal maxillary artery - If intra-cranial spread: branches of internal carotid artery too - DSA: intense inhomogeneous blush showing full tumour extent - Pre-op embolization = well-established adjunct reduces blood loss, shrinks tumour, improves surgical access - Transarterial most common route; direct puncture with Onyx is also used - Risk of ICA involvement = increases embolization risk significantly --- SECTION 7: EMBOLIZATION FOR EPISTAXIS Key points: - Used for intractable idiopathic epistaxis - Target: sphenopalatine artery superselectively catheterized after locating the bleeding site - Particles, coils, or balloons used - Problem: if IMA internal maxillary artery was previously ligated, subsequent embolization is harder ligation limits effectiveness - so always do embolization BEFORE ligation! Special scenarios: - Osler-Weber-Rendu hereditary haemorrhagic telangiectasia: multiple sessions needed, embolization rarely curative - ICA aneurysm/pseudoaneurysm eroding sphenoid bone → emergency INR needed - Vascular malformation or nasal tumour causing epistaxis → particulate embolization to stop acute haemorrhage Embolization vs IMA ligation: - Embolization generally more reliable than IMA ligation - But do embolization FIRST if both are considered - ligation ruins embolization options later --- SECTION 8: FUNCTIONAL TESTING Balloon Occlusion Test Before permanently sacrificing a major artery: 1. Performed under local anaesthesia patient must be awake for neuro assessment 2. Balloon inflated in target artery for 20-30 minutes 3. Neurological exam performed simultaneously 4. Adequacy of collateral flow assessed by: Doppler US, Xenon CT, SPECT, PET scanning 5. Additional provocative testing: lower BP or give vasodilator e.g. acetazolamide 6. Permanent occlusion only done if test is satisfactory 7. Complication rate for skull base tumour ligation: 5-20% vs aneurysm: only 3% --- QUICK MEMORY AIDS FOR PG EXAM "TEMP" agents Temporary: "AG is TEMP" = Autologous clot + Gelfoam → Temporary Tumours most commonly embolized: "My Pretty Juvenile Haem" = Meningioma, Paraganglioma, JNA, Haemangiopericytoma Embolization PARTICLE SIZE rule: - Small 150 microns = intratumoral vessels first - Large = afferent/proximal arteries last - Too proximal = collaterals form = tumour survives Coil material: Platinum not tungsten - corrodes; not steel - MRI issues NBCA vs Onyx: - NBCA: sets on contact with blood like superglue hitting water - Onyx: sets when DMSO solvent disperses needs DMSO to stay liquid; solidifies as DMSO leaves Meningioma timing: - Operate within 7 days of embolization - Revascularization starts 3-4 weeks after embolization JNA blood supply: - External carotid artery branches mainly IMA/internal maxillary - ICA branches only if intracranial spread --- COMPLICATIONS TO REMEMBER Complication Details ---------------------- Cranial nerve palsy Most common serious complication 4% Stroke Unrecognized spread of emboli Blindness Reported rare but permanent Intra-tumour haemorrhage Meningioma: 24-36 hours after embolization Vessel perforation/rupture At sharp bends middle meningeal artery most common for meningioma Facial ache Most common after paraganglioma embolization Revascularization Occurs 3-4 weeks post-embolization --- ONE-MINUTE EXAM RECAP 1. INR = interventional neuroradiology; embolization = its main tool 2. Temporary agents = Autologous clot + Gelfoam only 3. Permanent agents = PVA, trisacryl gelatin, coils, balloons, alcohol, NBCA, Onyx 4. Platinum coils = preferred MRI safe, non-corrosive 5. NBCA = sets on blood contact; Onyx = sets when DMSO disperses 6. Meningioma: operate within 7 days; NF-2 association; chromosome 22 7. Paraganglioma: 50% temporal bone; neural crest; can secrete catecholamines 8. JNA: puberty; testosterone-driven; ECA supply; no muscle layer histologically 9. Epistaxis: target sphenopalatine artery; embolize BEFORE IMA ligation 10. Balloon occlusion test: local anaesthesia; 20-30 minutes; awake neuro exam
