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Pitfalls in CT PulmonaryPitfalls in CT Pulmonary Angiography
Andetta R. Hunsaker, M.D.
Department of RadiologyDepartment of RadiologyBrigham and Women�s Hospital
Harvard Medical SchoolHarvard Medical School
CT Pulmonary AngiographyCT Pulmonary Angiography
� CTPA revolutionized assessment of PECTPA revolutionized assessment of PE with sensitivity up to 94%-96% and specificity 94%-100%specificity 94% 100%
� Treatment decisions made based on diagnostic studiesdiagnostic studies�If positive � anticoagulation or
l f IVC filtplacement of IVC filter�If negative � no treatment for PE;
alternate diagnosis rendered
Inconclusive outcome in CTPAInconclusive outcome in CTPA
� Meta-analysis: 16 studies evaluatingMeta analysis: 16 studies evaluating 327 patients with either inconclusive, indeterminate, non-interpretable, or psuboptimal CTPA
� 74 patients � no anticoagulant p gtherapy but underwent further dx w/u
� VTE diagnosed in 16.4% on follow-up� Underscores need for F/U
Moores, Ann Intern Med. 2004;141:866-874
Objectives
� Review common pitfalls which cause indeterminate studiesindeterminate studies�Technical �Physiologic�Physiologic�Anatomic
� Discuss pitfalls due to error inDiscuss pitfalls due to error in diagnosis
� Show pitfalls due to tunnel visionShow pitfalls due to tunnel vision� Describe pitfalls with Dual Energy CT� Offer solutions to these pitfalls� Offer solutions to these pitfalls
Case: 23 y/o 450 lb woman has this poor quality study; scanned with 75 mL I-370 q y y;140kVp. What would you recommend?
A)Repeat study with increased l fvolume of contrast
B)MRA
C)Repeat study with increased kVp
D)Another study
Pitfalls in CT Pulmonary Angiography forEvaluation of Pulmonary Embolism Andetta R. Hunsaker, MD
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CTPA Scanning protocol
� Exam usually performed in deep i i i h d iinspiration � causes hemodynamic effects which are similar to valsalva
� Scan delay empirically set at 20sec� Bolus triggering � helpful in CHF,PA gg g p ,
HTN� Volume of contrast materialVolume of contrast material� Selection of kVp (80-120 kVp)
T b t d l ti� Tube current modulation� Patient characteristics
Technical pitfallsTechnical pitfalls
� Motion/breathing artifactMotion/breathing artifact� Improper bolus delay
I i i h l i h� Image review in a sharp algorithm� Improper selection of imaging
parameters� Cursor improperly place on triggering p p y p gg g
scan
Respiratory motion artifactRespiratory motion artifact
�Can result in apparent�Can result in apparent termination of vessels
�Variation in pul blood flow between insp and exp causesbetween insp and exp causes heterogeneous arterial opacificationopacification
�Assessment of lung windowsAssessment of lung windows most helpful
Technical pitfall: MDCT Air Bubbles
� Can see swirling air bubbles due to full detector rotationdetector rotation
� Gated cardiac studies use ½ gantry rotation so slower scan speed with better p spatial but lesser temporal resolution
Physiologic pitfalls
� Abnormality of venous inflow �t i t i t ti f t t (TIC)�transient interruption of contrast (TIC) �SVC obstruction
� Extrapulmonary shunts�Right-to-left shunt (PFO)
� Intrapulmonary shunts�Unilateral increased pul vasc resistance p
due to extensive consolidation
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Transient interruption of contrast
N l t ti i t th i�Normal response to negative intrathoracic pressure with deep inspiration which � venous return of unopacified blood from SVC and IVCreturn of unopacified blood from SVC and IVC
�More common in pregnant patients
�Amount of inflow depends on end diastolic filling pressures, and rate of inspiration
Transient Interruption of contrast
�Clues: lack of opacification of multiple vessels at same level bilaterally w/o vasc expansiony / p
�Presence of unopacified blood in right heart on preceding images followed by unopacified blood inpreceding images followed by unopacified blood in LA,LV and aorta on later images
Pearls: Transient interruption of contrast
�Hyperventilating patient prior to study helps reduce venous accumulation in IVC
�Delaying initial image acquisition by at least 5 y g g q ysecs after insp may allow TIC to pass through pul circulation prior to imaging
�Scan from base to apex allowing at least 3 sec delay prior reaching lower lobe vessels
Transient Interruption
� Speed of scanner will not alter presence of artifact becausepresence of artifact because physiologic inflow during deep insp
� Study of 327 patients (50+ 46� Study of 327 patients (50+, 46 indeterm, 33-)1�TIC more common in neg PE than pos PE�TIC more common in neg PE than pos PE�Likely due to � end diastolic filling
pressures of RA and RVpressures of RA and RV�Leads to � RV output�Prevents or attenuates normal influx of�Prevents or attenuates normal influx of
unopacified blood into RA from IVCGosselin et al 2004 J Thorac Imaging;19(1):1-7
Physiologic Pitfall: Right to left Sh (PFO)Shunt (PFO)
25% 30% f ll l h� 25%-30% of all people have an insignificant PFO at restM t d l t� Most develop no symptoms
� Under certain conditions R � L shunt d l if RA d LAdevelops if RA pressures exceed LA pressuresPh i l i ll h t� Physiologically shunt can occur during valsalva, deep inspiration, or coughingcoughing
Imaging Findings of PFO� Significant and early enhancement in
aorta � Attenuation values in ascending aorta
�� than PA�� than PA � Reason: deep inspiration similar to
Valsalva provokes sudden � in RAValsalva provokes sudden � in RA pressure exceeding LA pressureP i j ti l t ib t t� Power injection may also contribute to buildup of higher RA pressures
� Results in short term R�L shunt with contrast crossing to LA
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Scanning in known PFOScanning in known PFO
� Perform exam in silent respiration orPerform exam in silent respiration or near end expiration
� Longer scan delayLonger scan delay� Always use new IV� Remember that PFO has risk of� Remember that PFO has risk of
potential paradoxic embolism which occurs during sudden � in RAoccurs during sudden � in RA pressure
� Beware of free floating RA thrombiBeware of free floating RA thrombi
Paradoxic Pulmonary Embolism Anatomic Pitfalls
� Bronchovascular segmental anatomyg y�Pulmonary veins�Bronchi � mucoid impactionp�Volume averaging of bronchi
� Hilar interlobar and bronchial lymphHilar, interlobar and bronchial lymph nodes�Nodes smooth inner border chronic PE�Nodes smooth inner border, chronic PE
smooth outer border1
� Peri bronchovascular connective� Peri-bronchovascular connective tissue 1 Filipek et al Seminars in Ultrasound,
CT, and MRI 2004 25(2) 83-98
Anatomic Pitfall: low attenuation tubular branching structurestubular branching structures
�Pulmonary embolism
�Mucous filled bronchi
�Pulmonary veins�Pulmonary veins
�Other types of vascular emboli
Mucoid impaction ith RLLwith RLL
pneumonia
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Mucoid Impaction or PE? MIP image same patient: Mucoid impactionimpaction
Anatomic Pitfall: nodes vs vesselsAnatomic Pitfall: nodes vs vessels
Fused PET CT Images
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Bronchogenic Carcinoma mimicking Chronic PE
Pitfall: Errors in Diagnosis and i d i id l fi dimissed incidental findings
� Mimickers of PE �Tumor thrombi/emboli/�Primary pulmonary artery sarcoma
� Missed carcinomaMissed carcinoma� Intracardiac masses or thrombus
Tumor EmboliTumor Emboli
� Intravascular tumor emboli mayIntravascular tumor emboli may present as large, acute PE
� May produce acute PHTN by vessel� May produce acute PHTN by vessel occlusionM l b li� More commonly, tumor emboli are small and occlude subsegmental
t i l di t iarteries, leading to progressive dyspnea and subacute PHTN
PE or not PE
Tumor EmboliTumor Emboli
� Often associated with recentOften associated with recent organizing thrombi
� Prostate and breast carcinoma are the� Prostate and breast carcinoma are the most common causes of microemboli followed by hepatoma carcinoma offollowed by hepatoma, carcinoma of stomach and pancreas1
Kane et al, Cancer 1975;36:1473-1482
Manifestations of Tumor EmboliManifestations of Tumor Emboli
� Large filling defects in main lobarLarge filling defects in main, lobar, and segmental
� Small subsegmental filling defects� Small subsegmental filling defects causing vasc dilatation and beading which increases over timewhich increases over time
� Small tumor emboli may affect d l l b l t i l dsecondary pul lobule arterioles and
have tree-in-bud appearance
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Pleomorphic Rhabdomyosarcoma Bland or Tumor Thrombus?
Same patient a two months later
DX PA A iDX: PA Angiosarcoma
Pulmonary Artery SarcomaPulmonary Artery Sarcoma
� Uncommon cause of intraluminal arterialUncommon cause of intraluminal arterial filling defect
� Typically unilateral, lobulated, yp y , ,heterogeneously enhancing
� Heterogeneous mass expanding PA; shows g p g ;extravascular extension
� May also show subpleural nodules, consolidation and pleural effusions
� Location: main/proximal PA most frequent
Yi et al J Comput Assist Tomogr 2004;28(1):34-39
B l d G di h
Intravascular Mass Characterization
�Filling defect within
Balanced Gradient echo
gthe LPA: pulmonary angiosarcomag
�Intravascular and TIW double Inversion recoveryextravascular tumor
diagnosed without
TIW double Inversion recovery FSE
intravenous contrast material
3D FSPGR T1 GdIntravascular Mass Characterization
�Enhancing tumor & neovascularization in left
3D FSPGR T1 Gd
PA
U f t t i�Use of contrast is helpful in differentiating enhancing tumor 3D FSPGR T1 Gdenhancing tumor thrombus from non-enhancing bland
3D FSPGR T1 Gd
gthrombus which may co-exist
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Chronic Pulmonary Embolism Versus Pulmonary artery SarcomaVersus Pulmonary artery Sarcoma
Chronic PE
PA Sarcoma
27 Year old male transferred from outside hospital for embolectomyoutside hospital for embolectomy
27 Year old male transferred from outside hospital for embolectomy
MIP iMIP images
DX: High grade myxoid spindle cell sarcoma
MIP Images
Intracardiac abnormality Intracardiac abnormality
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Mixing artifact
RA Thrombus
Right Atrial ThrombusRight Atrial Thrombus
Pitfall: Missed Diagnoses Pitfall: Missed Diagnoses�Extensive consolidation: DDx
�Pneumonia�Pneumonia
�atelectasis
Same patient 3 months laterpDiagnosis: Missed sarcoma
Atypical presentation of acute PE
� Reverse Halo sign: Remember infarction is in DDXinfarction is in DDX
� Symptoms of PE include hemoptysis
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Same patient with Acute PE RLL, infarct and Pleural Effusion Reverse Halo: acute PE and infarction
I+ thin section CT 3 i t3 mos prior to lower
Endocarditis with infected embolus
Artifact due to DECT
� Non-embolic perfusion defects in patients without PE (apical and ant p ( pseg RUL, apical portion LUL, medial seg RML)M i if� Motion artifact
� Beam hardening�R l d hi h d i i�Related to high contrast density in
vessels (BCV, SVC) and heart (RA)� Band like or crescent shaped� Band-like or crescent shaped� Minimized by saline chaser and choice
of craniocaudad scan directionof craniocaudad scan direction
Case: 450 lb woman has this poor quality study. 140 kVp; 75 mL I370 contrast y p;medium What would you recommend
A)Repeat study with increased l fvolume of contrast
B)MRA
C)Repeat study with increased kVp
D)Another study
Back to Initial Case presentation: 450 pound woman with non-dx CTPA study
Posterior RPO LPO
ConclusionConclusion
� Identify reason for indeterminateIdentify reason for indeterminate study (technical, physiologic, anatomic)anatomic)
� Always consider other etiologies for filling defects that mimic bland embolifilling defects that mimic bland emboli
� At times given history of PE can be a di t t t th t ti l didistracter to other potential diagnoses
� Always consider alternative studies