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Paper text:
iliac vein compression syndrome ( ivcs ) is most commonly due to may  thurner variant , an anatomic variant wherein the right common iliac artery overlies the left common iliac vein and compresses it against the lumbar spine .
one study estimates that 24% of the us population has this variant , which is defined as 50% luminal constriction of the left common iliac vein , and all patients were asymptomatic .
the incidence of a may  thurner variant developing symptomatic ivcs from a perforated pedicle screw is not known , but presumably very low .
herein , we present a patient with probable may  thurner variant anatomy who developed near complete occlusion of the left common iliac vein due to the compression by a perforated pedicle screw .
she had a long history of superficial varicosities and painful venous hypertension , previously treated with sclerotherapy and bilateral great saphenous vein ablations .
these therapies provided her with partial relief , but she was still experiencing daily symptoms .
six years prior , she also had l2s1 spinal fusion for degenerative joint disease . in the emergency department
, she reported that she had woken up with severe pain and heaviness in her left leg from the knee down with her right leg being at baseline .
initial workup was negative for deep venous thrombosis , and after obtaining a magnetic resonance imaging ( mri ) of the lumbar spine , her neurosurgeon did not think that the pain was related to her back .
vascular ultrasound of her left leg showed venous insufficiency in the small saphenous and giacomini veins .
those findings were not severe enough to cause the level of discomfort that she was experiencing , so magnetic resonance angiography ( mra ) of the pelvis was ordered .
this study showed narrowing of the left common iliac vein to 0.2 cm ( fig .  1 ) , with a tortuous right common iliac artery crossing over the constriction .
the findings were consistent with non - thrombotic may  thurner syndrome , which was thought to be the cause of her new symptoms . 

figure  1:narrowing of the left common iliac vein to 0.2 cm ( mri ) .
, there was perforation of a pedicle screw through the anterior cortex of her l5 vertebral body , from prior spinal fusion .
this interaction was well visualized during intraluminal inflation of a 12 mm  40 mm high - pressure balloon ( fig .  2 ) and
because the screw tip was completely unyielding , a 14 mm  60 mm wallstent was used instead of the 16 mm stent we typically use , so as to avoid undue compression of her overlapping right common iliac artery . after the procedure , the patient 's symptoms were greatly improved .
follow - up venography performed 4 months postoperatively showed a patent stent with slight eccentric compression at the protruding screw and no evidence of in - stent stenosis . 

figure  2:perforation of a pedicle screw through the anterior cortex of l5 vertebral body visualized during intraluminal inflation of a 12 mm  40 mm high - pressure balloon . 

figure  3:intraoperative radiograph showing posterior compression of a wall stent within the left common iliac vein .
perforation of a pedicle screw through the anterior cortex of l5 vertebral body visualized during intraluminal inflation of a 12 mm  40 mm high - pressure balloon .
intraoperative radiograph showing posterior compression of a wall stent within the left common iliac vein .
perforation of the anterior vertebral cortex is a known complication of instrumented posterior spinal fusion with one study of 4790 pedicle screw insertions showing an incidence of 2.8% .
however , the level of risk caused by these perforations is thought to be very low . a literature review of 35 630 pedicle screw placements identified no patients with vascular compromise of any kind and only two visceral complications that were of clinical significance . however , there are several documented reports of serious complications caused by anterior vertebral body perforation .
outline a case of esophageal impingement caused by protruding pedicle screws at the t3 level .
penetrations into the lung and ureter have also been documented [ 4 , 7 ] . however , to our knowledge , this is the first reported case of iliac vein compression caused by pedicle screw perforation that has been reported . in this patient ,
the tortuous left common iliac artery probably did play a role by restricting the anterior movement of her left common iliac vein and causing the compression exerted by the screw to be more significant than anticipated . as in classic
may  thurner syndrome , we speculate that pressure from the screw produced chronic irritation of the vascular endothelium with resultant proliferation , thickening and stenosis explaining why her symptoms did not arise until 6 years after the hardware was placed .
stent placement was chosen in this case because it was felt to be the most effective modality for restoring patency of the vessel .
pedicle screw impingement of the aorta has also been successfully corrected with endovascular stent placement .
however , in that case , they did elect to retract the screw as well .
none of the patients studied went on to develop any sequelae as a result of vessel contact ; thus , the authors of that article do not recommend repositioning of screws found to be in contact with a major vessel .
this case demonstrates the level of scrutiny that must be applied when dealing with pathology in close proximity to any implanted object . in our patient ,
neither lumbar mri nor pelvic mra was able to correctly identify a perforated pedicle screw as the cause of iliac vein compression .
this is likely an exceedingly rare event , but the fact remains that standard imaging techniques are not always able to detect the interference of orthopedic hardware with essential internal structures .
pedicle screw perforations are not uncommon , but they typically do not have any clinical ramifications . however , their proximity to major vessels and other vital structures makes them a potential cause of serious morbidity .
this is more likely to occur in a patient who has a predisposition to pathology , such as may  thurner syndrome
. these susceptibilities may not be clinically obvious , so a high level of suspicion should be used whenever unexplained signs or symptoms arise in areas of prior orthopedic instrumentation .
may  thurner syndrome is an anatomic variant where the right common iliac artery compresses the left common iliac vein . 
 the variant exists in a significant portion of the population , but is usually asymptomatic ; however , clinically significant stenosis can occur by iatrogenic means . in this report 
 , we describe a patient who presents with left lower extremity pain and swelling . 
 initial workup for deep vein thrombosis was negative . 
 after being referred to our venous clinic , a magnetic resonance angiography revealed narrowing of the left common iliac vein with a tortuous right common iliac artery crossing over the constriction . during left iliac vein stent placement , a pedicle screw from a prior l2s1 spinal fusion 
 was noted to be perforated through l5 vertebral body impinging the posterior aspect of the vein . 
 this case demonstrates that increased scrutiny must be applied when dealing with pathology in close proximity to any implanted medical device .