Clinical Radiology (1998) 53, 155-157
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EARLY STRUCTURAL FAILURE OF AN ANTHEOR INFERIOR VENA CAVA FILTER
THE RAD1OLOGICAL INVESTIGATION OF SUSPECTED L O W E R LIMB DEEP VEIN THROMBOSIS
S m - We read with interest the early StlUctural failure of a modified Antheor filter  and report a similar experience. A 38-year-old woman presented to another hospital with a 12-h history of chest pain. In her medical history she had been diagnosed with systemic lupus erythematosus at the age of 25, and had an iliofemoral thrombosis and pulmonary emboius in September 1996 despite adequate anticoa~lation. A modified Antheor filter was inserted at that time and her anticoagulation continued. On this admission a CXR was normal but an AXR showed the filter to he fractured. She was referred to our institution for removal of the filter and insertion of a new one. An initial cavagram clearly demonstrated that two fractured struts had penetrated the caval wall; the filter had also migrated 3 cm cephalad (Fig. 1). We attempted to remove it using a 25ram gooseneck snare (Amplatz, Whithear Lake, MN) and then with a vascular retrieval forceps (Cook UK, Letchworth, Hertfordshire, UK). This proved impossible as the filter was clearly adherent to the wall and therefore unlikely to migrate further. A pulmonary angiogram was performed and was normal and so a new filter was not required. Further clinical investigation revealed the patient's pain to be musculoskeletal in origin. We concur with King et al. that the clinical significance of a fractured filter is not clear, however it is important that further problems with Antheor filters are reported so that radiologists and clinicians are aware of these complications. The Antheor filter is no longer available and is the subject of a voluntary recall.
Sm - Burn et al.  conclude that colour Duplex ultrasound (CDUS) is the most appropriate first line imaging technique for suspected deep vein thrombosis (DVT), with venography 'reversed for occasional technical failures'. The authors who are obviously Doppler enthusiasts, have biased their discussion to support their preconceived notions, avoiding any mention of possible advantages of venography, and drawn conclusions that are not warranted by their methodology. A postal survey cannot determine which is the better technique, only the frequency with which it is employed~ It is far from clear that CDUS is the most appropriate first line technique for the following reasons: (1) Accuracy - CDUS does not image the lower calf veins and iUiac vein as reliably as venography, and even the femoropopliteal segments are sometimes difficult when the patient is very obese/ oedematous or postoperative patients with scars or dressings on the legs. Chronic DVT is often not detectable by CDUS due to collateral formation. The authors state that the significance of isolated calf vein DVT is doubtful as it is often not treated. This may be true but it does not follow that correct diagnosis of isolated calf DVT is unimportant - a normal venogram effectively excludes DVT whereas a negative CDUS does not in the calf, which can be a problem for future management if symptoms recur. (2) Speed - A venogram takes 15 rain to perform, about the same time as CDUS, but venography is a definitive examination and no follow up scans are required, an important consideration for the over-stretched radiologist! (3) Safety - I am not aware of any significant complications of venography in the last 5 years at my hospital other than minor contrast reactions such as vomiting and rashes, spanning several hundred venograms. It is minimally invasive. Improved accuracy of venography probably outweighs any small gain in safety with CDUS. (4) Permanent record - The entire examination is captured on film and any observer error is open to later review/correction unlike CDUS. (5) Skill mix/machine usage - The number of radiologists capable of performing venography at most hospitals (including my own) greatly exceeds those experienced at CDUS. In addition, there is terrific pressure
G. J. O'SULLIVAN T. M. BUCKENHAM A. M. BELLI
Department of Vascular Radiology St. George's Hospital London, UK
Reference 1 King LJ, Dacie JE. Case report: early structural failure of an Antheor inferior vena caval filter. Clinical Radiology 1997;52:632-633.
Fig. 1 - Subtracted and unsubtracted images of the inferior vena cavagram which demonstrate the fractured struts. On two views (b and d). They clearly lie outside the lumen and are embedded in the wall. 9 1998 The Royal College of Radiologists.