leg dvt normal
anatomy
deep veins of the thigh
the blue line shows the cfv scan plane.
ultrasound of the cfv, pre and post compression.
the blue line shows the distal fv scan plane.
ultrasound of (superficial) femoral vein
popliteal vein
the blue arrow shows the popv scan direction.
ultrasound of popv
deep veins of the calf
transverse mid calf.
hover mouse over to see the scan plane.
transverse ultrasound view of the posterior tibial and peroneal veins.
pre & post compression.
longitudinal ultrasound image of calf veins. split screen, color doppler and b-mode.
a sagittal scan plane for the calf veins.
scan protocol
role of ultrasound
to exclude deep vein thrombosis as a cause for pain and swelling in the lower limb. also as a screening tool in post operative lower limb surgery or patients with a known pulmonary embolus, looking for a source of their embolus.
limitations
obese patients, or those with severe oedema will limit the scan quality resulting in only being able to exclude occlusive thrombus acoustic windows and detail may be limited in patients with open wounds/sutures.
patient preparation
the patient can be scanned supine,erect or seated in a reclined position to allow access to the groin.
the calf veins are easier to view when the legs are lower than the torso allowing some venous distension. (eg erect or seated on the side of the bed)
equipment setup
use a mid frequency probe (5-8mhz). often using a curvi-linear probe is easier than a linear probe, particularly when doing compression views.
low prf (velocity) colour / power / doppler settings with low wall filter when assessing veins with low velocity flow. be prepared to change frequency output of probe (or probes) to adequately assess both superficial and deeper structures.
common pathology
non compressibility or filling defects with colour doppler.
acute thrombus will be hypoechoic and difficult to see on b-mode without increasing your gain settings. it will generally slightly distend the vein and be focally tender. the thrombus propogates proximally with a ‘tongue’ projecting into the lumen at its moost proximal end. as the thrombus ages, it becomes more echogenic. old, chronic thrombus will be echogenic, retracted from the vein walls with recanalised flow through and around it.
scanning technique
examine the deep veins from the groin to the ankle.
this technique will examine the common femoral vein (cfv), (superficial) femoral vein (sfv) and popliteal vein (popv). in the calf, the posterior tibial and peroneal veins (both usually paired) are assessed. the anterior tibial veins are so rarely subject to thrombosis that they are not examined as a matter of routine. if there has been direct trauma to the antero-lateral shin, this area should be examined.
common femoral & (superficial) femoral veins
begin with the patient supine. if possible slightly externally rotate the affected leg. in transverse, high in the groin crease, locate the cfa & cfv at the sapheno-femoral junction. compress the vein. you should see complete apposition of the vein walls (ie they should touch and the vein compress completely). be cautious of suggesting thrombus incorrectly due to poor compressibility at valves. continue to follow the vein sequentially compressing down to the distal thigh. document the normal anatomy and any pathology found, including doppler images demonstrating flow.
popliteal vein
seat the patient on the side of the bed to help dilate the veins for easier visualisation.
place the probe transversely at the knee crease in the popliteal fossa. locate the popliteal artery and vein. check the compressibility of the popliteal vein throughout the popliteal fossa. be cautious not to mistake the often prominant muscular veins (gastrocnemius veins) for the popliteal vein. whislt not truely deep veins they are generally large and still pose a lesser risk of embolisation. as such, you should also examine these as possible causes of the patient’s symptoms.
calf veins
patient still seated as above.
transversely, with the toe of the probe on the medial edge of the mid tibia, locate the paired posterior tibial and peroneal veins.
a common variant is for there to be a single vein instead of a pair. generally the single vein will be slightly larger than if paired. if you have adequate detail, assess their compressibility along their length. alternatively, in longitudinal, use colour doppler to confirm their patency.
common pathology/ differential diagnoses
common differential diagnoses identifiable on ultrasound are:
- bakers cyst (semi-membranosis-gastrocnemial bursa) in the medial popliteal fossa.
- superficial venous thrombosis of varices and the long/short saphenous veins.
- calf muscle tears
basic hardcopy imaging
a leg dvt series should include the following minimum images:
- cfv: pre/post compression
- proffunda femoris
- sfv proximal ts: pre/post compression
- sfv proximal ls: with colour doppler
- sfv distalts: pre/post compression
- sfv distal ls: with colour doppler
- popv ts: pre/post compression
- popv ls: with colour doppler
- posterior tibial veins ls colour doppler
- peroneal veins ls colour doppler
- sapheno-femoral-junction
document the normal anatomy. any pathology found in 2 planes, including measurements and any vascularity.