DVT and lower limb ultrasound

My DDU point form notes on DVT and lower limb ultrasound…

The rest of my DDU notes are here.

Important problem

DVT common

~ 12% of PE cases dead in 1 month

DVT/PE

mechanism

Virchow’s triad

↑ coagulability

vessel injury

stasis

DVT commonly begin in calf veins

significance of calf vein thrombosis controversial

~10-20% propagate to proximal veins

initially common for large part of clot to be nonadherent to wall

= free-floating thrombus

cf by 7-10 days more organized, adherent

up to 95% of PE due to clots from lower extremity DVT

because lower limb much more common in general population

cf in high risk trauma patients ~33% are in sites other than legs

risk of upper limb DVT embolization unclear: 0-36% in various papers

risk factors

age

vessel injury

CVC / pacemakers

previous DVT

varicose veins

↑ coagulability

malignancy

sepsis

IBD

nephrotic syndrome

thrombophilia

OCP

pregnancy

trauma / surgery

stasis

immobilisation

obesity

stroke / paresis

heart failure

~30% of ICU patients

~50% of multisystem trauma patients

~80% of acute spinal patients

Dx

clinical Dx unreliable

DVT: tumor, rubor, calor, dolor • rarely phlegmasia cerulea dolens

PE: SOB, CP, haemoptysis, RHF, CV collapse, death

other Ix

venograms

contrast required

invasive

less repeatable

require transport

can cause DVT

USS

often as part of a protocol for reliability and to ensure cost-effective approach

depending on study, up to 97% sensitive, 96% specific

Lower limb

Deep venous anatomy of the lower limbs

3 compartments

—skin—

superficial

—saphenous fascia— also hyperechoic, visible on ultrasound

contains main trunks of GSV, SSV and accompanying nerves

saphenous

—muscular fascia— visible on ultrasound, perforated by … perforators

deep

—bone—

deep venous system

IVC → common iliacs: no valves • left common iliac runs under right CIA

internal iliac vein: deep and medial to external iliac vein

external iliac vein: usually no valves • crosses inguinal ligament to become…

common femoral vein: usually no valves

confluence is below the saphenofemoral junction and CFA bifurcation

profunda femoris = deep femoral vein currently

femoral vein: commonly duplicated – suspect if small vein seen • previously superficial femoral vein

runs through adductor canal

popliteal vein: commonly duplicated

—saphenopopliteal junction is here—

gastrocnemius veins

soleal veins and sinuses

—these next veins are generally paired and run with the artery—

anterior tibial veins

posterior tibial veins

peroneal veins

superficial veins of interest

great saphenous vein = long saphenous vein

from anterior of medial malleolus to saphenofemoral junction ~2.5 cm below inguinal ligament

many named branches especially near SFJ / perforators important in venous mapping for varicose veins

short saphenous vein = lesser saphenous vein

from posterior of lateral malleolus to saphenopopliteal junction above gastroc and soleal junction with popliteal vein

Scanning approach

environment

Comfortable temperature to avoid vasoconstriction

Legs dependent where possible (reverse Trendelenburg ≥ 30°)

Knee flexed slightly, external rotation

if patient able, “Where is it sore?” → look carefully there

calf veins, popliteal veins → leg over side of bed on stool ideal

venous preset

low PRF ~1000Hz for low velocity flow

low colour wall filter

orientation

Marker cephalad or right side of patient

Probe marker on right of screen (operator’s left)

transducer

10 MHz for superficial ideal – not the focus of this scan

7-11 MHz linear “ideal” due to ↑ axial resolution per McLean et al

5 MHz linear for deep and junctions

3.5 MHz curved for iliacs

Doppler approach

sample volume size ↑ to cover the vessel

compression USS vs Duplex

Limited compression USS looks for compressibility at 2 or 3 points

CFV and PV ± FV ± compression along FV

literature on compression vs Duplex

emergency medicine

many studies

sensitivity ranges from ~90-100% vs vascular technologist performed proximal Duplex ultrasound and/or venography (X-ray or CT)

specificity 75-99%

training variable – as little as 10 mins in some studies

rapid (e.g. 3.5 mins)

intensive care

few studies

86% sensitivity and 96% specificity vs vascular tech Duplex in best study

important to image FV – study that failed to do this had 63% sensitivity, mainly due to FV DVTs

practical pointers

vein wall coapt with little / no distortion of adjacent artery

in transverse to avoid slipping off vein

avoid excessive pressure initially when locating veins!

fresh thrombus can partially deform

partial collapse of vein, partial collapse of artery with ↑ pressure → non-occluding thrombus

if too deep for compression → CFD

if can’t find vein → look for artery ± CFD

vein vs artery

Duplex sequence

summarized from McLean / Thrush and Hartshorne 

CFV

CFV at groin in transverse → compress

will also distend with Valsalva if iliacs patent

rotate into longitudinal →

CFD, spectral Doppler, looking for spontaneous phasic flow

back to transverse, follow distal to SFJ → compress

follow GSV a few cm → compressions

follow CFV to confluence, and follow profunda a few cm → compressions

FV

remember commonly duplicated

transverse, compressions each 1-2 cm along medial thigh

~1/2 way down will need hand under thigh

when no longer able to compress move to…

popliteal V

transverse, compressions back to overlap with FV scan

follow distally, including gastrocnemius ± soleal branches

calf veins

start distally

medially

PT (shallower) and peroneal (deeper)

use CFD and augmentation to identify

both transverse and longitudinal useful

laterally

for peroneal if unable to compress / see medially

anterior

anterior tibial v rare site of isolated thrombosis

if desired, image longitudinally in notch immediately lateral to sharp anterior border of tibia

iliac veins

if desired

incompressible

image with 3.5 MHz curved probe, with CFD / spectral Doppler with flow augmentation manoeuvres

medial and deep to arteries

may be easiest to image from groin with tilt

bowel gas main limitation

vena cava

similar to iliac veins, transverse and longitudinal with CFD and spectral Doppler

Rapid LEDVT sequence

summarized from McLean > Thrush and Hartshorne 

anterior

start just below inguinal ligament

CFV compression (to distinguish artery vs vein, and to exclude DVT)

move down to SFJ compression

GSV compression 2 cm inferior to SFJ

now compress every 2 cm to upper border of patella

posterior

start mid popliteal fossa

PV compression (to distinguish artery vs vein, and exclude DVT)

follow proximally as far as possible

then follow distally, compressing every 1-2 cm until PV branches into calf veins

Normal appearances

static or slow moving blood can produce echoes

CFD should show spontaneous, phasic flow in proximal veins and complete colour filling in transverse and longitudinal plane with augmentation (calf squeeze / plantar and dorsiflexion)

gastroc and soleal veins may have poor colour flow imaging

similarly, spectral Doppler should augment with distal squeeze (based on Thrush & Hartshorne, by at least 100%) and demonstrate respiratory variation confirming lack of proximal obstruction

neither rules out non-occlusive thrombus / thrombus with good collaterals

do not use as sole assessment

Abnormal appearances

clots

distended veins at site and distally

unable to fully compress

hyperacute: small ↑ echogenicity

(subacute vs chronic difficult to distinguish)

CFD

occlusive: absence of colour fill

nonocclusive

colour flow voids, with flow between thrombus and wall in longitudinal and transverse

full colour fill just proximal to tip

 spectral Doppler

↓ flow, ↓ augmentation

pitfall: good collateralisation

occlusive iliac thrombosis

low volume continuous cf phasic flow in CFV

little / no response to Valsalva

evolution of clots

lysis

may be rapid with small thrombi → normalisation of appearance ± valve function

large thrombus takes weeks

retracts, ↑ echogenicity

recanalization → tortuous flow channel(s)

may be partial → old residual thrombus, fibrosed valve cusps

fibrosis

if remains permanently occluded

may appear as small cord next to artery

± collateralisation

dilated superficial veins with CFV / CIV occlusion

GSV as collateral with FV / PV occlusion

common problems

duplicated systems not noted

veins misidentified

especially in popliteal fossa / upper calf

e.g. gastroc vs PV / SSV

unable to visualise iliacs

detecting fresh thrombus in vein damaged by previous DVT difficult

Mimics of DVT

thrombophlebitis

= inflammation + thrombosis of superficial veins

hard cord, calor, dolor

scan cautiously – significant if thrombus tip extends to SFJ / SPJ, with risk of proximal embolization

haematoma

well defined anechoic area in soft tissues ± tracking in fascial planes

veins in area often compressed / too painful to image

lymphoedema

commonly unilateral calf

thickened subcutaneous layer with fine B-mode speckle (“grainy” image)

degraded image → hard to see veins

cellulitis

tumor, rubor, calor, dolor

USS: oedema + hyperaemic flow in veins and arteries

oedema

tissue splaying by multiple interstitial channels

if CCF, see pulsatile flow pattern in proximal veins

potential to mistake for arterial flow

check direction on CFD

Baker’s cysts

bursa arising between medial head of gastrocnemius and semimembranosus tendons

if extends into upper calf → swelling, pain, discomfort

if ruptures → acute severe pain (d/dx acute DVT)

if compresses PV, other deep veins → can cause DVT … so always look for DVT

appearance

easiest to see in transverse

anechoic (occasionally echogenic debris)

oval or crescent

tail trails away to joint space

lymph node enlargements

↓ drainage → limb swelling

rubor, calor, dolor locally

± compress adjacent vein

on USS mainly hypoechoic with ↑ echogenicity centrally

potential to confuse with thrombosed vein

heterogeneous colour flow Doppler signal

other d/dx

abscesses, muscle tears, AVF

Cover image: Red blood cells illustration by the National Cancer Institute