Suspected superior vena cava obstruction

ACR AC Thoracic Venous Occlusions; MDCT SVC literature

Two things must come out of one acquisition: the level and length of the venous obstruction, and the cause. That makes it a venous-phase study with a deliberately chosen injection strategy — the arm you inject is part of the protocol, not a nursing detail.

Facial and upper limb swelling, plethora, distended neck and chest wall veins, often with a known or suspected mediastinal malignancy or a long-term central venous catheter.

Referenced decision support — confirm against your local protocol.

Decision support, not a directive. Protocols and timings shown are typical published ones — your local protocol takes precedence, and the vetting radiologist decides.

The request in front of you

Everything is optional. Leave a field alone and the answer assumes nothing — the verdict updates as you go.

Study requested

What the referrer actually asked for. It is evidence of intent, not a constraint on the right answer.

Contrast as written

What the request form says, not what it should say.

Age

Pick a band, or type an exact age if it matters.

years

Pregnancy status

Renal risk factors

The question a vetter can actually answer from the request. An explicit “none known” is a real answer, and it removes checks rather than deferring them.

Previous contrast reaction

The pathway — tap anything already done

Marking a study complete moves the answer on. A patient arrives partway through a pathway far more often than at the start of one.

Accept as requested

CT Chest — Contrast-Enhanced (Venous Phase)

CT Chest

What we'd amend, and why

A venous-phase delay lets contrast fill the whole thoracic venous system and the collateral pathways that have opened around the obstruction, which is what defines its level and completeness — an arterial-timed scan shows a dense unopacified segment that is indistinguishable from a thrombosed one. The injection strategy matters as much as the delay: dense undiluted contrast arriving from one arm produces streak artefact that can create or conceal a filling defect at the confluence, so diluted or simultaneous bilateral upper limb injection is used when the veins themselves are the question. The same acquisition shows the mediastinal mass or nodal disease causing the compression, which is what most of these patients actually need staged.

Nothing needs resolving before this goes ahead. Routine checks below are owned downstream.

How was this decided?

pathwayadult — Adults
rulerule-contrast-reaction-premed — Prior contrast reaction and elective premedication; checked by Nurse before the scan
rulerule-metformin — Metformin and iodinated contrast; checked by Radiographer at the scanner
rulerule-paeds-dose — Child-sized technique and contrast dose; checked by Radiographer at the scanner
rulerule-pregnancy-ionising — Pregnancy status before an ionising exposure; checked by Radiographer at the scanner
rulerule-renal-iodinated — Kidney function and intravenous iodinated contrast; checked by Radiographer at the scanner
rulerule-iv-access — Intravenous access adequate for the planned injection; checked by Radiographer at the scanner

Decision support only. Local protocol takes precedence.

Handled at the scanner(4)nothing for you to do

Settled and owned downstream. Each returns to a radiologist only on the stated trigger.

Metformin and iodinated contrast
Confirm whether the patient takes metformin or a metformin-containing combination, and if so whether ACR Category II applies (eGFR below 30, known or suspected AKI, or an arterial catheter study likely to cause renal embolisation). If Category I — that is, no AKI and eGFR at or above 30 — no action of any kind is needed.
Radiographer at the scannerAt the scanner
Flags back if: The patient takes metformin AND meets ACR Category II — eGFR below 30 mL/min/1.73 m2, known or suspected acute kidney injury, or an arterial catheter procedure with likely renal arterial embolisation. Metformin plus a normal or mildly reduced eGFR is explicitly NOT a flag-back: there is no need to stop metformin before or after intravenous iodinated contrast in Category I patients, and no need to re-check creatinine afterwards.
Child-sized technique and contrast dose
Confirm that a size- or weight-based protocol is selected — child-sized kV and mAs against size-based diagnostic reference ranges — and that contrast volume is calculated by weight rather than taken from an adult default. Weight-based iodinated contrast volumes of roughly 1.5–2.0 mL/kg are widely used in paediatric CT.
Radiographer at the scannerAt the scanner
Flags back if: No paediatric or size-based protocol exists on the scanner for the requested examination, or the requested coverage or number of phases exceeds what the clinical question needs — for example a multiphase study where a single phase answers it, or whole-body coverage for a focal question.
Pregnancy status before an ionising exposure
Make the pregnancy enquiry immediately before the exposure and record the answer. In the UK this is a statutory operator duty discharged at the time of exposure under the employer’s written procedures required by IR(ME)R 2017 — it is not something the vetting radiologist can perform or pre-empt, and a request is complete without it.
Radiographer at the scannerAt the scanner
Flags back if: The patient states that she is, or may be, pregnant AND the uterus is in or near the primary beam. The exposure is then paused for re-justification by the IR(ME)R practitioner before it proceeds.
Intravenous access adequate for the planned injection
Site and test a cannula that supports the protocol flow rate, preferring an antecubital or large forearm vein, and observe the injection for extravasation. A 20-gauge or larger cannula is preferred for flow rates of 3 mL/s or more.
Radiographer at the scannerAt the scanner
Flags back if: No cannula can be sited that supports the protocol flow rate — for example only a 22-gauge hand or foot cannula for a CT angiogram needing 4–5 mL/s; or the only available access is a central line or port that is not labelled power-injectable; or an extravasation occurs.

Pathways

Big forks are separate pathways; the first whose conditions match is the one used.

Adults

Matches your inputsDefault

Role	Study & protocol	Why this answers the question
First line	CT Chest CT Chest — Contrast-Enhanced (Venous Phase) usually appropriate	A venous-phase delay lets contrast fill the whole thoracic venous system and the collateral pathways that have opened around the obstruction, which is what defines its level and completeness — an arterial-timed scan shows a dense unopacified segment that is indistinguishable from a thrombosed one. The injection strategy matters as much as the delay: dense undiluted contrast arriving from one arm produces streak artefact that can create or conceal a filling defect at the confluence, so diluted or simultaneous bilateral upper limb injection is used when the veins themselves are the question. The same acquisition shows the mediastinal mass or nodal disease causing the compression, which is what most of these patients actually need staged.
Problem solving	Ultrasound venous Doppler (limb) Venous duplex ultrasound for deep vein thrombosis	Duplex of the internal jugular, subclavian and axillary veins answers a narrower question quickly and without contrast: is there thrombus in the accessible upper limb and neck veins, and are the waveforms pulsatile and respirophasic as they should be. Loss of that variation in an accessible vein is indirect evidence of a central obstruction the probe cannot see. It is the right test when the concern is catheter-related limb thrombosis rather than central compression.

Pitfalls

Reading the mixing artefact where opacified and unopacified blood meet in the brachiocephalic vein or SVC as thrombus. It is a timing phenomenon, not a clot, and repeating at a longer delay resolves it.
Accepting an arterial-phase or CTPA-timed acquisition to answer a venous question — the veins are not yet opacified.
Reporting the obstruction without describing the collateral pathways. Extensive collaterals indicate chronicity and predict how the patient will tolerate a delay; their absence in a symptomatic patient suggests acute occlusion.
Missing that the request needs staging as well as venous mapping. One correctly timed acquisition can do both if the coverage is right.
Injecting into the symptomatic arm alone, which is often the one with the obstructed drainage — the bolus goes into collaterals and never opacifies the segment in question.
Treating this as a purely radiological question. Stridor, laryngeal or lingual oedema, a patient who cannot lie flat, or reduced consciousness from cerebral oedema is an airway and oncological emergency, and the imaging is arranged around the patient rather than the patient around the imaging — scanned semi-erect if that is what it takes, with an anaesthetist informed and the study accepted as technically limited rather than deferred to a better slot.
Repeating a failed technique. Where severe obstruction has diverted the bolus into collaterals so the central veins never fill, the answer is a changed strategy — diluted contrast, simultaneous bilateral upper limb injection, a longer delay, or in the extreme a femoral injection — not the same arm, the same rate and the same timing a second time.
Reporting the obstruction without saying what kind it is. Extrinsic compression by tumour or nodes, intraluminal thrombus on a catheter or pacing lead, and post-radiotherapy or post-instrumentation fibrosis lead to completely different treatments — stent, anticoagulation and line removal, or oncological therapy — and the distinction is available on the same acquisition if it is looked for.

Priors — what to pull first

Look for previous central line or pacing lead insertions and their dwell times — device-related stenosis is now a common cause and changes the intervention.
If there is a known malignancy, retrieve the last staging study: rapid growth of a previously small mediastinal mass changes the treatment intent as well as the venous plan.

What makes a good request

A good request states which arm has usable venous access, whether a central catheter or pacing lead is in place and for how long, and whether stenting is being considered — the last of these changes what the report has to measure.
Where a stent is planned, the report needs the length of the occluded segment, the calibre of the normal vein above and below it, the state of the brachiocephalic confluence and the azygos, and the presence of thrombus as distinct from extrinsic compression.
Symptom severity and airway compromise, not the imaging appearance alone, drive the urgency.

Scoring this once it is done

The classification and risk tools this question ends in.

eGFR (CKD-EPI 2021 Creatinine)Lung Cancer TNM Staging (9th Edition)Lung-RADS v2022 (Screening LDCT)RECIST 1.1 Tumor Response PERCIST 1.0 PET Response

How these studies are acquired

Contrast, phases and timing for every study on the pathways above.

CT Chest — Contrast-Enhanced (Venous Phase)Venous duplex ultrasound for deep vein thrombosis

Confirm locally

CT Chest — Contrast-Enhanced (Venous Phase): timings are typical — confirm against local protocol.
Timings, contrast volumes and rates above are typical published values. Your department's protocol, scanner and patient population decide the actual numbers.
Safety thresholds and premedication policy follow local policy where it differs from the cited guidance.

References

Implemented from the cited published sources. Educational and workflow support only; confirm against current guidelines and local policy before clinical use.