ASN CNSA common mistakes
ASN CNSA · Understand the traps and how to avoid them.
Reporting a peak systolic velocity from a midstream sample taken without correcting for the angle of insonation, or accepting an angle greater than 60 degrees.
Candidates chase the highest waveform amplitude on the display and forget that velocity scales with the cosine of the Doppler angle; an uncorrected or steep angle inflates or deflates the value and makes the number non-comparable to published thresholds.
What to do instead
Set the cursor parallel to the vessel wall, keep the angle at or below 60 degrees, and state the angle used. If the vessel cannot be aligned within 60 degrees, report the finding qualitatively and say why a velocity is not being given.
Grading a stenosis by eyeballing the colour image instead of measuring the residual lumen on grayscale and pairing it with the Doppler criteria the lab uses.
Colour blooming and wall-filter dropout distort apparent lumen width; candidates who grade from colour alone systematically overestimate narrowing and skip the velocity and ratio data that anchor the category.
What to do instead
Measure residual diameter and area on grayscale in the same plane, obtain pre- and intrastenotic velocities plus the ICA/CCA ratio, and assign the grade only when the anatomic and haemodynamic findings agree. Document any discordance.
Declaring a vessel occluded when colour fill is absent but no spectral or power Doppler interrogation was performed.
Low flow, a poor insonation window, or an inappropriate velocity scale all produce a colour void that mimics occlusion; candidates stop at the colour image because it looks decisive.
What to do instead
Before calling occlusion, lower the PRF, reduce the wall filter, use power Doppler or contrast where available, and sample with spectral Doppler along the expected course. Report occlusion only when flow cannot be demonstrated by any modality.
Using the same velocity thresholds for the vertebral and basilar arteries that were learned for the carotid bifurcation.
Candidates memorise one set of numbers and apply them everywhere, but the vertebrobasilar system has different normal ranges, smaller calibres, and different angle geometry.
What to do instead
Keep a written reference table of normal and abnormal values by vessel and apply the correct one. Note depth, angle, and segment sampled so the reading physician can judge the measurement.
Failing to identify and report the temporal window quality and the specific segment of the MCA insonated during a TCD study.
Candidates record a velocity without the depth, window, and segment, so the value cannot be interpreted or compared on follow-up; a proximal MCA velocity at 40 mm means something different from one at 60 mm.
What to do instead
For every TCD sample record window, depth, vessel, and mean flow velocity. State whether the window was adequate; if not, say so explicitly rather than reporting an unqualified number.
Interpreting elevated TCD velocities as vasospasm without considering systemic factors such as anaemia, hyperventilation, or increased cardiac output.
Candidates pattern-match high velocity to spasm and skip the clinical context, but velocity reflects flow demand as well as calibre.
What to do instead
Before concluding spasm, review haematocrit, PaCO2, blood pressure, and sedation, and look for a focal velocity gradient and a Lindegaard-type ratio rather than a single absolute value.
Presenting a screening or monitoring study without stating the patient's symptoms, timing from symptom onset, and the clinical question being asked.
Candidates treat the report as a pure image description and omit the context that determines whether a finding is significant; a moderate stenosis means something different when it is symptomatic and recent.
What to do instead
Open the report with indication, symptom laterality, and time since onset, then interpret findings against that context. Flag any finding that changes management urgency.
Reporting a single velocity measurement as the conclusion instead of describing the full spectral waveform morphology.
Candidates focus on the number because it is easy to chart, but damping, tardus-parvus shape, spectral broadening, and loss of diastolic flow carry diagnostic information the number alone cannot convey.
What to do instead
Describe waveform shape, spectral broadening, and diastolic component for each sampled vessel alongside the velocity, and state what the morphology implies about upstream or downstream disease.
Omitting a structured comparison with prior studies or the contralateral side.
Candidates report each study in isolation, so a change over time or an asymmetry that is the real finding goes unremarked.
What to do instead
Include a comparison section citing the prior study date and the contralateral values. If no prior exists, say so and establish a baseline explicitly.
Leaving out technical limitations, such as an inadequate window, patient motion, or a vessel not visualised, and letting the reader assume the study was complete.
Candidates fear that documenting limitations weakens the report, so they omit them; the reader then over-trusts a partial study and may act on incomplete data.
What to do instead
Add a limitations paragraph listing vessels not assessed, window quality, and any factor that reduced diagnostic confidence, and recommend an alternative modality when the study is non-diagnostic.