01Core principlesThe concepts and mechanisms needed to understand the subject.
Interventional radiology is a clinical specialty built around precise access under imaging. Diagnostic procedures obtain tissue, fluid, pressure or angiographic information; therapeutic procedures open, close, drain, ablate or support a structure. The image is part of the treatment, not merely a picture taken beforehand. Real-time visualisation shortens the path from skin to target, helps avoid bowel, pleura, nerves and major vessels, and permits immediate checks such as contrast flow, device position or cessation of extravasation. A small incision does not make the procedure trivial: many patients are acutely ill, and a minimally invasive route can still cause major haemorrhage or organ injury.
The operator first translates the referral into a defined clinical objective. Examples include draining an infected collection, relieving an obstructed kidney, stopping arterial bleeding, restoring blood flow, sampling a lesion or delivering treatment to a tumour. The safest useful technique depends on anatomy, urgency, physiological reserve, prior surgery, imaging visibility and what will happen if the intended route fails. Interventional radiologists therefore work with surgeons, physicians, anaesthetists, radiographers, nurses, pathologists and other specialists before, during and after treatment.
Most procedures share a cycle: confirm that intervention is indicated; review imaging and hazards; prepare the patient and team; gain controlled access; perform the diagnostic or therapeutic manoeuvre; verify the immediate endpoint; secure the access site; and monitor for early and delayed complications. Each stage can change the plan. A collection with no safe percutaneous window may need surgery; an angiogram may show that vasospasm rather than fixed occlusion explains poor flow; a drain that is well positioned but not functioning may be blocked, loculated or too small for its contents. Good practice treats the imaging, physiology and clinical course as one data set.
Key points
- Interventional radiology uses ultrasound, fluoroscopy, CT or MRI to place a needle, wire, catheter or device accurately for diagnosis or treatment through a small access route.
- The clinical question determines both the target and modality: ultrasound gives real-time soft-tissue and vascular guidance without ionising radiation, fluoroscopy follows wires and contrast dynamically, and CT maps deep structures and gas well.
- The Seldinger sequence is needle entry, guidewire passage, needle removal, tract dilation and catheter or sheath placement; wire position must remain controlled throughout every exchange.
- Planning integrates indication, alternatives, consent, recent imaging, coagulation and antithrombotic status, renal function when iodinated contrast is likely, infection risk, allergy history and a safe route to the target.
- A technically successful procedure is not automatically a clinical success: haemostasis, source control, drainage, tissue diagnosis or symptom relief must be demonstrated and followed over time.
- Complications are anticipated from the route and target: bleeding, infection, non-target injury, thrombosis, embolisation, contrast reaction, kidney injury, sedation-related compromise and radiation effects.
- Radiation exposure must be individually justified and optimised; collimation, appropriate pulse rate, last-image hold, efficient geometry and avoiding unnecessary runs reduce dose without sacrificing the clinical objective.
- A peri-procedural checklist supports correct patient, procedure, site, imaging, equipment, medicines, specimens, post-procedure instructions and escalation planning.
02Mechanisms and patternsImportant relationships and how to distinguish them.
Most interventions can be analysed as safe entry, maintained wire or needle control, delivery of a catheter or device, completion of a targeted manoeuvre and imaging or physiological confirmation of the intended endpoint.
Ultrasound is portable and shows vessels, fluid and soft tissue in real time; fluoroscopy excels at devices and contrast flow; CT provides cross-sectional localisation for deep or poorly sonographically visible targets; combined guidance is common.
Biopsy, aspiration, venography, angiography and pressure measurement answer a defined question, but sample adequacy, correct labelling and prompt transport are as important as needle placement.
Drainage, embolisation, angioplasty, stenting, thrombectomy, ablation and access-device placement alter anatomy or physiology; the endpoint must relate to the clinical aim rather than device deployment alone.
A transpleural route risks pneumothorax, a transhepatic route risks bleeding or bile leak, vascular access risks haematoma and distal ischaemia, and contaminated systems may seed infection; route planning predicts surveillance needs.
Team briefing, equipment readiness, explicit wire and device counts, closed-loop communication, a pause before irreversible deployment and a documented handover reduce preventable technical and communication failures.
03Interpreting evidenceInformation, measurements and their limitations.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Review of current cross-sectional and ultrasound imaging - Why
- Confirm the target, define anatomy and select a route with an acceptable risk-benefit balance.
- Interpretation and limitations
- Assess target size and visibility, intervening bowel or pleura, vessels, collateral supply, access options and signs that the referral question has changed since the scan.
- 02
Pre-procedure clinical and laboratory assessment - Why
- Identify physiological, haemostatic, renal, infective and anaesthetic hazards that could alter timing or technique.
- Interpretation and limitations
- Interpret blood count, coagulation, renal function and other tests in the context of procedural bleeding risk, planned contrast, sepsis, comorbidity and antithrombotic medicines; one universal threshold does not fit every procedure.
- 03
Intra-procedural imaging - Why
- Maintain safe trajectory and document anatomy, flow or device position while treatment is delivered.
- Interpretation and limitations
- Use the modality that answers the immediate question, minimise unnecessary exposure and recognise artefact, respiratory motion, vessel overlap or contrast reflux that can mimic satisfactory placement.
- 04
Endpoint assessment - Why
- Establish whether the immediate technical goal has been reached and whether a complication has occurred.
- Interpretation and limitations
- Examples include stopped extravasation, restored flow, free drain aspiration, contrast passage through a stent, adequate ablation coverage or an intact distal circulation; each is interpreted against the clinical objective.
- 05
Post-procedure observation and targeted imaging - Why
- Detect early haemorrhage, infection, thrombosis, organ injury, device migration or treatment failure.
- Interpretation and limitations
- Vitals, pain, wound or access-site findings, drain output and distal perfusion often lead; ultrasound, radiography, CT or angiography is added when the expected recovery pattern is not seen.
04Applied reasoningWorked examples connecting principles to decisions.
01Worked case: obstructed infected kidneyPlan image-guided decompressionA septic patient has hydronephrosis from an obstructing ureteric stone, thrombocytopenia, a distended collecting system on CT and no immediate endoscopic access.+
- 1Identify urgent source control as the objective, resuscitate and give cause-appropriate antimicrobials while urology, radiology and anaesthesia agree that percutaneous nephrostomy is the practical decompression route.
- 2Review CT and bedside ultrasound for laterality, calyceal dilatation, retrorenal bowel and a feasible posterior calyx; assess platelets, coagulation, antithrombotics and cardiorespiratory tolerance without delaying life-saving drainage unnecessarily.
- 3Use aseptic technique, local anaesthesia and ultrasound-guided puncture, confirm collecting-system entry with urine and minimal contrast when appropriate, then maintain guidewire control while dilating and placing a locking drain.
- 4Aspirate a specimen for microbiology, secure and connect the catheter, document urine appearance and output, and give clear flushing, bag, escalation and replacement instructions.
- 5Verify decompression by clinical improvement and drain function; failure of urine output, worsening sepsis, bleeding or displacement prompts immediate tube and collecting-system assessment rather than assuming technical placement equals source control.
02Elective planningConvert a referral into a procedure planA stable patient is referred for an image-guided diagnostic or therapeutic intervention.+
- 1Define the intended clinical benefit, alternative treatments and the consequence of delay or non-treatment with the referring team and patient.
- 2Choose target, modality, route, patient position, device range, analgesia or anaesthesia plan and rescue options from recent imaging and comorbidity.
- 3Reconcile antithrombotics and other medicines, obtain relevant laboratory tests, address infection and contrast risks, and record consent including common and material patient-specific harms.
- 4Brief the team and verify patient, site, procedure, equipment, specimens and post-procedure destination before starting.
03Unexpected deteriorationLink physiology to the procedural hazardA patient becomes hypotensive, hypoxic, confused or severely painful during or soon after an intervention.+
- 1Pause the intervention, call for help and stabilise airway, breathing and circulation while checking monitoring, sedation timing and access sites.
- 2Use procedure anatomy to prioritise bleeding, contrast reaction, embolic ischaemia, pneumothorax, sepsis or target-organ injury and perform immediate bedside checks.
- 3Reverse or treat the likely mechanism and obtain urgent imaging or angiography when needed, keeping surgical, anaesthetic and critical-care escalation active.
- 4Document the event, treatment and exposure, communicate it at handover and arrange follow-up for delayed consequences.
05Checking understandingVerify the reasoning, revisit uncertainties and apply feedback.
- Record baseline and serial heart rate, blood pressure, oxygen saturation, respiratory rate, consciousness and pain at a frequency matched to sedation, illness severity and procedural risk.
- Inspect arterial or venous access sites for bleeding and swelling and document distal colour, temperature, capillary refill and pulses before and after vascular intervention.
- Track drain or catheter position, output, patency, character and securement; sudden cessation, blood, leakage or unexpected pain requires assessment rather than blind flushing.
- Review haemoglobin, renal function, inflammatory markers or coagulation selectively when blood loss, contrast exposure, infection or organ dysfunction makes the result actionable.
- Record radiation dose indicators and contrast volume, compare practice with local diagnostic reference levels and review unexpectedly high exposure or extravasation.
- Define who will review results, exchange or remove devices, assess clinical success and act on histology or microbiology so that technical care is connected to the treatment pathway.
06Special situationsVariants, exceptions and circumstances that change the usual approach.
Wire control preserves access
Loss of guidewire position can turn a routine exchange into a fresh puncture or an emergency; the operator should know where both wire ends are throughout manipulation.
Contrast is a diagnostic test
A small injection can confirm cavity, vessel or lumen position, but forceful or excessive injection may rupture, dissect, reflux or obscure the anatomy being assessed.
Endpoint depends on intent
Complete vessel occlusion may be desired in haemorrhage but harmful in flow-preserving embolisation; the correct endpoint is defined before the irreversible step.
Clinical failure can follow technical success
A correctly positioned drain cannot resolve undrained locules, and a patent stent cannot reverse established infarction; response must be measured beyond the image.
Small incision, full perioperative thinking
Consent, asepsis, anaesthesia, haemostasis, recovery, rescue capability and follow-up remain necessary even when the access wound is only millimetres long.
07Common pitfallsFrequent interpretation and management errors.
- 01
Accepting a referral label without defining the question, target and intended change in management.
- 02
Choosing a familiar modality when another gives a safer path or more reliable endpoint.
- 03
Treating coagulation results as isolated pass-or-fail numbers without procedural risk, urgency and antithrombotic context.
- 04
Advancing a needle, wire or catheter against resistance instead of stopping to confirm position and cause.
- 05
Calling device deployment a success without confirming flow, haemostasis, drainage, sample adequacy or distal perfusion.
- 06
Providing vague handover after placing a drain or access device, leaving no owner for output review, flushing, exchange, removal or abnormal results.
- 07
Forgetting that pain, agitation or oxygen desaturation may be the earliest sign of bleeding, pneumothorax, embolic injury or oversedation.