Procedures I: Lung imaging interpretation & clinical correlation

in PE, 75% of patients

have defects in blood flow that correspond to anatomic subdivisions (such as segments/lobes)

In PEs, 25% of patients have

ill-defined, nonsegmental defects

When a patient has a PE but also had previously healthy lungs, ventilation is

usually well maintained to the affected parts of the lung b/c their bronchial tubes are patent

only 10-15% of patients develop what due to a PE

pulmonary infarction

when is interpretation of VQ for PE less reliable?

when patient has COPD (chronic bronchitis, emphysema, asthma)

V/Q match

a perfusion defect that has any ventilatory abnormality of comparable size

VQ mismatch

a perfusion defect that has no corresponding ventilatory abnormality, or a defect that is more severe or larger than the ventilatory abnormality

stripe sign

a thin line (stripe) of perfused lung tissue at the pleural surface of a perfusion defect

PE present (high probability) from VQ

two or more mismatched (VQ) segmental defects

PE absent (normal perfusion or very low probability)

nonsegmental perfusion abnormalities, perfusion defect smaller than radiographic lesion, two or more matched defects with regionally normal CXR, stripe sign, pleural effusion of 1/3 or more of pleural cavity with no other perfusion defect

nonwedge perfusion defects can be seen with

COPD, pneumonia, lung CA, alveolar edema, or intersitial lung disease

nondiagnostic(low/intermediate probability) for PE on VQ scan

all other findings

CTPA

CT pulmonary angiogram

contradictions for CTPA

-allergy to iodinated contrast

-poor renal function

-non-compliance

VQ scans sensitivity vs CTPA

VQ= 77.4%

CTPA= 97.7%

sensitivity

ability of a test to correctly identify patients with a disease (avoids false negatives)

specificity

ability of a test to correctly identify people without the disease (avoids false positives)

COPD

includes emphysema, chronic bronchitis and caused by cigarette smoke, genetic risk, occupational air, air pollution

radioactive ventilation studies are one of the most sensitive ways of detecting

damage to small airways

in copd, both lungs tend to be affected in

a similar but rarely identical way

most damage to lungs is where

in the lower zones (but can be in upper zones or scattered throughout)

one lung can be more severly affected

characteristic findings on vent study for COPD

areas of lungs retain radiotracer during washout

parts in lung that take longer to get it out (air trapping/retaining)

emphysema

abnormal enlargement of airways with destruction of alveolar walls

loss of capillary beds

decreased gas exchange surface area

ventilation - emphysema markers

marked by air trapping, patchy, may show central hot spots

air trapping with xe133

hot spots with tc99m DTPA

perfusion- emphysema markers

decreased or absent perfusion in emphysematous regions due to desctruction of pulmonary capillaries

matched vent/q in severely damaged areas

mild mismatch can occur in early emphysema if airflow is preserved by capillaries are lost

chronic bronchitis (bronchiectasis)

abnormal inflammation and narrowing of bronchi caused by obstruction of an airway

what can bronchiectasis be caused by

mucus, atelectasis, aspiration of foreign body, cycstic fibrosis, TB

bronchiectasis markers on VQ

vent: patchy/uneven with air trapping

—> can show central airway hot spots if using aerosol

perfusion: normal or mildy reduced perfusion

pulmonary htn

high pressure in the pulmonary arteries

SOB, chest pain, fatigue, swelling in the legs

pulmonary htn occurs when

blood vessels that carry blood to the lungs become narrowed, blocked, or destroyed making ti difficult for the heart to pump blood through the lungs (can cause damage to Rt side of heart)

primary pulmonary htn

unknown cause, poor prognosis and rare

secondary pulmonary htn

increased volume/pressure of blood entering pulmonary arteries:

narrows/obstructs arteries

causes dilation of RV and rt heart failure

caused by CAD, mitral disease, increased LV filing pressure, increased pressure by ventricular defect, emphysema

CTEPH

chronic thromboembolic pulmonary htn - abnormally high pressure in your lungs small blood vessels as a result of prior blood clots in the lungs

how many who have had a PE will get CTEPH

1-4%

tx of CTEPH

pulmonary thromboendarterectomy (removes large, old blood clots)

VQ or CTPA scan for CTEPH

VQ: high sensitivity and specificity

sensitivity= 90-100%

specificity= 94-100%

more sensitive in detecting chronic obstructions even when vessels appear open on a CT

ventilation / perfusion marker for CTEPH

normal vent (mismatch)

perfusion - patchy distribution (rather than wedge)

Asthma

chronic inflammatory disorder- during an acute episode, airways narrow leading to delayed clearance of inhaled radiotracer

acute asthma episode

wheezing, breathlessness, chest tightness, coughing

bronchia spasms, edema, thick mucus, thickening airways

if a pt has asthma before a scan,

they may need a breathing tx before coming

what does asthma show on vq

reversible air trapping if treated

markers of cystic fibrosis on vq

(advanced disease) may show patchy air trapping due to thick mucus and airway obstruction

4 types of lung CA

SCC (squamous cell carcinoma)

small cell carcinoma

Large cell carcinoma

Adenocarcinoma

SCC (squamous cell carcinoma)

30%

often associated with pneumonia/atelectasis

small cell carcinoma

20%

central in origin

strongest correlation to smoking

rapid growth, mets early

worst prognosis

large cell carcinoma

10%

commonly in peripheral region but can grow to distort trachea

adenocarcinoma

40%

usually smaller in diameter and in peripheral regions/terminal bronchioles/alveoli

pleural effusion

fluid in the pleural space usually from blood vessels, lymphatic vessels, or abscess draining into pleura

needle aspiration can drain the fluid if necessary

v/q markers for pleural effusion

can show decreased uptake

fluid compressing lung tissue, may show as “cold” area

lung can’t expand well so there is less air movement

results in a matched defect

ARDS

acute respiratory distress syndrome (Wet lung)

condition where fluid collects in lungs air sacs, depriving organs of o2

caused by critical illness or injury to lung (often fatal, unable to breathe on their own- ventilator)

VQs for ARDS?

extremely rare, but sometimes want to check for PE

can’t control any contamination

might just do perfusion part

pneumothorax

presence of air/gas in the pleural spcae

caused by medical procedures, lung disease, chest injry

can require. chest tube

what happens in a pneumothroax

rupture of visceral pleura

-destroys negative pressure

-can cause partial or complete lung collapse

Atelectasis

Collapse of lung tissue - alveoli cannot inflate properly

only a portion of lung

common post op or with prolonged BR

what findings is considered a high-probability V/Q for PE

two or more mismatched segmental perfusion defects

what condition causes reversible air trapping visible on VQ

asthma

what does a matched defect on a VQ scan mean for a PE

it rules it out generally

what type of scan is preferred for a CTEPH

VQ

ma

how can you tell the difference between a perfusion defect caused by a PE and one caused by pleural effusion

pleural effusion causes a stripe sign at pleural surface- so defect at pleural surface and need a CXR or CT

if a patient receievesa standard dose of MAA, what happens

the systemic MAA particles can cause microvascular obstructions in the brain or other critical organs because the deoxygenated blood gets into systemic system