Diagnostic ultrasound ( PDFDrive )

598 PART II Abdominal and Pelvic Sonography
native organ or rejection in a transplanted organ. Occasionally,
biopsy is indicated simply to determine the nature of an incidentally
discovered mass.
Relative contraindications to percutaneous needle biopsy
include severe uncorrectable coagulopathy, lack of a safe biopsy
route, and an uncooperative patient. To assess for inherent
coagulopathy, the most valuable information comes from the
patient history, 3 including bleeding tendency or need for transfusion
or a family history of bleeding diathesis. Patient medications
should also be reviewed for recent use of antithrombotic agents.
he second relative contraindication is the lack of a safe biopsy
route. A biopsy path extending through large vessels such as
the splenic or extrahepatic portal vein increases the risk of
hemorrhage. A biopsy path free of overlying stomach or bowel
is also a preferable route, although such biopsies have been safely
performed using smaller (21-gauge) needles. 4 Biopsies performed
through ascites have also proved to be safe, although drainage
of ascites prior to biopsy may increase target accessibility. 5,6
he third relative contraindication to needle biopsy is an
uncooperative patient in whom uncontrolled motion during
needle placement increases the risk of unanticipated injury and
hemorrhage. his is a particularly common problem in pediatric
patients, and deeper sedation may be required.
Periprocedural Antithrombotic
Management
An efective approach to the management of periprocedural
antithrombotics depends on an understanding of the balance
of hemorrhagic and thrombotic complications. hat is, the
potential risk of hemorrhage from biopsy or drainage in a patient
on an antithrombotic agent versus the risk in that same patient
of a thrombotic event if a blood thinner is discontinued. Signiicant
thromboembolic events, including myocardial infarction
and ischemic stroke, have been shown to occur in 1% to 4% of
select patients in whom aspirin or warfarin is withheld without
bridging therapy. 7-11 Although decisions on periprocedural
antithrombotic management are best made in collaboration with
the referring clinician, the performing radiologist typically makes
the ultimate judgment of whether and when to perform a
procedure for a patient on an antithrombotic agent. It is therefore
important for the radiologist to have a general knowledge of
common anticoagulants and antiplatelet agents as well as the
bleeding risks associated with certain procedures. However, any
withdrawal of a therapeutic agent should be deferred to the
ordering clinical provider, oten following a discussion with the
radiologist regarding procedure-speciic bleeding risk.
Although helpful institutional and society guidelines have
been put forth on the topic of periprocedural antithrombotic
management, true consensus and uniformity in practice remain
elusive. his is due to the expanding pharmacy of antiplatelet
agents and anticoagulation as well as to evolving literature
showing lower bleeding risks for some procedures than previously
thought. In general, our own practice has leaned toward liberalizing
guidelines; that is, foregoing preprocedural labs in certain
patients for lower-risk procedures (supericial biopsies such as
thyroid and supericial lymph nodes as well as thoracentesis,
paracentesis, and supericial abscess drainage) and performing
certain lower-risk procedures, especially if urgent, without
discontinuing antithrombotic agents.
he most commonly encountered antithrombotics in both
inpatient and outpatient populations are the antiplatelet agents
aspirin and clopidogrel (Plavix), the vitamin K antagonist warfarin,
and the clotting factor inhibitor heparin (unfractionated or
low-molecular-weight). Anticoagulants using other mechanisms
such as direct thrombin inhibitors (e.g., dabigatran), direct factor
Xa inhibitors (e.g., fondaparinux), and glycoprotein IIb/IIIa
inhibitors (e.g., abciximab) are being increasingly utilized and
may also be encountered in practice. General familiarity with
mechanisms and metabolism of these agents is important for
decision making. For example, the direct thrombin inhibitor
dabigatran has a half-life of 12 to 14 hours but is excreted by
the kidneys; therefore the period of preprocedural discontinuation,
if pursued for a nonurgent deep biopsy, should be extended in
a patient with renal impairment (6-7 days vs. 4-5 days if normal
renal function in our practice).
For low-risk procedures, such as thoracentesis and paracentesis,
we have found little impact on bleeding risk from therapeutic
anticoagulation or aspirin use. Bleeding complication rates in
coagulopathic and thrombocytopenic patients (international
normalized ratio [INR] > 1.6 and/or platelets < 50 × 10 9 /L) ater
thoracentesis or paracentesis are very low (up to 1%). 12-15 Patients
oten beneit greatly from these procedures. Accordingly, we have
eliminated routine complete blood count prior to these procedures
for most patients and request warfarin be held only if patient is
at low risk for thromboembolic event. If patients will be taking
warfarin at the time of the procedure, an INR should be obtained
within 24 hours prior to procedure to ensure they are not
supratherapeutic. Additional labs may be requested by the
radiologist at their discretion, but we have found this is rarely
needed. Aspirin may also be continued in our practice for
thoracentesis or paracentesis. A similar approach is used for
supericial biopsies and supericial drain placement.
Higher-risk procedures include liver and kidney biopsy as
well as mesenteric, retroperitoneal, or deep pelvic lymph node
biopsy, and deep abscess drainage. Although called “higher risk”
this is relative to other procedures, and the true risk of postprocedural
bleeding, even for these procedures, is low.
Native renal parenchymal biopsies have the highest risk of
postbiopsy bleeding with reported rates of signiicant bleeding
of 0.3% to 6.6%. 16-23 Liver and renal transplant biopsy bleeding
rates are generally lower and at our own institution are 0.5%
and 0.2%, respectively. 16 If a higher-risk biopsy is nonurgent or
elective, aspirin can be held for 5 days beforehand if the risk of
thromboembolic event is acceptably low and then restarted at
24 hours ater biopsy. However, our clinical experience has shown
little if any association of recent aspirin use on signiicant
postprocedural bleeding. In a study of 15,181 percutaneous core
biopsies, the incidence of bleeding in patients taking aspirin
within 10 days before biopsy was 0.6% and that of patients not
taking aspirin was 0.4% (p = .34). 24 his study included 585 liver
biopsies performed in patients with recent aspirin use with a
0.3% risk of major hemorrhage (not signiicantly diferent to the
0.5% in those not taking aspirin). Consequently, we continue to