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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