肺部HRCT基础解读

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Secondarylobule
Knowledge of the lung anatomy is essential
forunderstandingHRCT.
The secondary lobule is the basic anatomic
unitofpulmonarystructureandfunction.
Interpretation of interstitial lung diseases is
based on the type of involvement of the
secondarylobule.
Itisthesmallestlungunitthatissurrounded
byconnectivetissuesepta.
Itmeasures about12 cmand ismade upof
515pulmonaryacini,thatcontainthealveoli
forgasexchange.
The secondary lobule is supplied by a small
bronchiole(terminalbronchiole)inthecenter,
thatisparallelledbythecentrilobularartery.
Pulmonary veins and lymphatics run in the
peripheryof thelobulewithintheinterlobular
septa.
Under normal conditions only a few of these
verythinseptawillbeseen.
There are two lymphatic systems: a central
network,thatrunsalongthe bronchovascular
bundletowardsthecentreofthelobuleanda
peripheral network, that is located within the
interlobular septa and along the pleural
linings.
PublicationdateDecember24,2006
Inthisarticleapracticalapproachisgivenfor
theinterpretationofHRCTexaminations
Wewilldiscussthefollowingsubjects:
Anatomyofthesecondarylobule
BasicHRCTpatterns
Distributionofabnormalities
Differentialdiagnosisofinterstitiallung
diseases
by Robin Smithuis, Otto van Delden and
CorneliaSchaeferProkop
LungHRCTBasicInterpretation
RobinSmithuis,OttovanDeldenandCorneliaSchaeferProkop
RadiologyDepartmentoftheRijnlandHospital,LeiderdorpandtheAcademicalMedicalCentre,
Amsterdam,theNetherlands
Secondarylobule
Secundarylobules.Thecentrilobularartery(in
blue:oxygenpoorblood)andtheterminal
bronchioleruninthecenter.Lymphaticsandveins
(inred:oxygenrichblood)runwithinthe
interlobularsepta
Centrilobulararea isthecentral part ofthe
secundarylobule.
Itisusuallythesiteofdiseases,thatenterthe
lung through the airways ( i.e.
hypersensitivity pneumonitis, respiratory
bronchiolitis,centrilobularemphysema).
Perilymphatic areais the peripheral part of
thesecundarylobule.
It is usually the site of diseases, that are
locatedinthelymphaticsofintheinterlobular
septa ( i.e. sarcoid, lymphangitic
carcinomatosis,pulmonaryedema).
Thesediseasesareusuallyalsolocatedinthe
central network of lymphatics that surround
thebronchovascularbundle.
BasicInterpretation
A structured approach to interpretation of
HRCTinvolvesthefollowingquestions:
WhatisthedominantHRpattern:
reticular
nodular
highattenuation(groundglass,
consolidation)
lowattenuation(emphysema,
cystic)
Whereisitlocatedwithinthesecondary
lobule(centrilobular,perilymphaticor
random)
Isthereanupperversuslowerzoneora
centralversusperipheralpredominance
Arethereadditionalfindings(pleural
fluid,lymphadenopathy,traction
bronchiectasis).
These morphologic findings have to be
combined with the history of the patient and
importantclinicalfindings.
When we study patients with HRCT, we have
to realize that we are looking at a selected
groupofpatients.
Common diseases like pneumonias,
pulmonary emboli, cardiogenic edema and
lungcarcinomaarealreadyruledout.
So uncommon diseases like Sarcoidosis,
Hypersensitivity pneumonitis, Langerhans cell
histiocytosis, Lymphangitic carcinomatosis,
UsualInterstitialPneumonitis(UIP)andmany
others become regular HRCT diagnoses and
canberealAuntMinnies.
Centrilobularareainblue(left)andperilymphatic
areainyellow(right)
TypicalUIPwithhoneycombingandtraction
bronchiectasisinapatientwithidiopathic
pulmonaryfibrosis(IPF)
In the reticular pattern there are too many
lines, either as a result of thickening of the
interlobular septa or as a result of fibrosis as
inhoneycombing.
Septalthickening
Thickening of the lung interstitium by fluid,
fibroustissue,orinfiltrationbycellsresultsin
a pattern of reticular opacities due to
thickeningoftheinterlobularsepta.
Although thickening of the interlobular septa
is relatively common in patients with
interstitial lung disease, it is uncommon as a
predominant finding and has a limited
differentialdiagnosis(Table).
Smooth septal thickening is usually seen in
interstitial pulmonary edema (Kerley B lines
on chest film); lymphangitic spread of
carcinoma or lymphoma and alveolar
proteinosis.
Nodular or irregular septal thickening occurs
in lymphangitic spread of carcinoma or
lymphoma;sarcoidosisandsilicosis.
On the left we see focal irregular septal
thickeningintherightupperlobeinapatient
withaknownmalignancy.
This finding is typical for lymphangitic
carcinomatosis.
There are also additional findings, that
support this diagnosis like mediastinal lymph
nodes and a nodular lesion in the left lung,
thatprobablyrepresentsametastasis.
Pulmonary lymphangitic carcinomatosis
(PLC)
In 50% of patients the septal thickening is
focalorunilateral.
This finding is helpful in distinguishing PLC
from other causes of interlobular septal
thickening like Sarcoidosis or cardiogenic
pulmonaryedema.
Hilar lymphadenopathy is visible in 50% and
usuallythereisahistoryof(adeno)carcinoma.
Identicalfindingscanbeseeninpatientswith
LymphomaandinchildrenwithHIVinfection,
who develop Lymphocytic interstitial
pneumonitis (LIP), a rare benign infiltrative
lymphocyticdisease.
Reticularpattern
Focalseptalthickeninginlymphangitic
carcinomatosis
OntheleftapatientwhohadaCTtoruleout
pulmonaryembolism.
There is a combination of smooth septal
thickening and groundglass opacity with a
gravitationaldistribution.
The diagnosis based on this CT was
cardiogenicpulmonaryedema.
Cardiogenic pulmonary edema generally
results in a combination of septal thickening
andgroundglassopacity.
There is a tendency for hydrostatic edema to
showaperihilarandgravitationaldistribution.
Thickening of the peribronchovascular
interstitium, which is called peribronchial
cuffing, and fissural thickening are also
common.
Common additional findings are an enlarged
heartandpleuralfluid.
Usually these patient are not imaged with
HRCT as the diagnosis is readily made based
on clinical and radiographic findings, but
sometimes unsuspected hydrostatic
pulmonaryedemaisfound.
On the left a patient with both septal
thickening and ground glass opacity in a
patchydistribution.
Somelobulesareaffectedandothersarenot.
This combination of findings is called 'crazy
paving'.
Crazy paving was thought to be specific for
alveolarproteinosis,butisalsoseeninmany
other diseases such as pneumocystis carinii
pneumonia, bronchoalveolar carcinoma,
sarcoidosis, nonspecific interstitial pneumonia
(NSIP), organizing pneumonia (COP), adult
respiratory distress syndrome and pulmonary
hemorrhage.
Alveolar proteinosis is a rare diffuse lung
disease of unknown etiology characterized by
alveolar and interstitial accumulation of a
periodic acidSchiff (PAS) stainpositive
phospholipoproteinderivedfromsurfactant.
Septalthickeningandgroundglassopacitywitha
gravitationaldistributioninapatientwith
cardiogenicpulmonaryedema.
Alveolarproteinosis
Honeycombing represents the second
reticularpatternrecognizableonHRCT.
Because of the cystic appearance,
honeycombingisalsodiscussedinthechapter
discussingthelowattenuationpattern.
Pathologically, honeycombing is defined by
the presence of small cystic spaces lined by
bronchiolar epithelium with thickened walls
composedofdensefibroustissue.
Honeycombing is the typical feature of usual
interstitialpneumonia(UIP).
ThedistributionofnodulesshownonHRCTis
the most important factor in making an
accuratediagnosisinthenodularpattern.
In most cases small nodules can be placed
into one of three categories: perilymphatic,
centrilobularorrandomdistribution.
Randomreferstonopreferenceforaspecific
locationinthesecondarylobule.
Perilymphaticdistribution
In patients with a perilymphatic distribution,
nodules are seen in relation to pleural
surfaces, interlobular septa and the
peribronchovascularinterstitium.
Nodules are almost always visible in a
subpleural location, particularly in relation to
thefissures.
Centrilobulardistribution
Incertaindiseases,nodulesarelimitedtothe
centrilobularregion.
Unlike perilymphatic and random nodules,
centrilobular nodules spare the pleural
surfaces.
The most peripheral nodules are centered 5
10mmfromfissuresorthepleuralsurface.
Randomdistribution
Nodularpattern
HoneycombinginapatientwithUIP
Nodules are randomly distributed relative to
structuresofthelungandsecondarylobule.
Nodules can usually be seen to involve the
pleural surfaces and fissures, but lack the
subpleural predominance often seen in
patientswithaperilymphaticdistribution.
Algorithmfornodularpattern
The algorithm to distinguish perilymphatic,
random and centrilobular nodules is the
following:
Lookforthepresenceofpleuralnodules.
Theseareofteneasiesttoseealongthe
fissures.
Ifpleuralnodulesareabsentorfewin
number,thedistributionislikely
centrilobular.
Ifpleuralnodulesarevisible,thepattern
iseitherrandom(miliary)or
perilymphatic.
Iftherearepleuralnodulesandalso
nodulesalongthecentral
bronchovascularinterstitiumandalong
interlobularsepta,youaredealingwitha
periplymphaticdistribution.
Ifthenodulesarediffuseanduniformly
distributed,itislikelyarandom
distribution.
Perilymphaticdistribution
Perilymphatic nodules are most commonly
seeninsarcoidosis.
They also occur in silicosis, coalworker's
pneumoconiosis and lymphangitic spread of
carcinoma.
Notice the overlap in differential diagnosis of
perilymphatic nodules and the nodular septal
thickeninginthereticularpattern.
Sometimesthetermreticulonodularisused.
On the left a typical case of perilymphatic
distribution of nodules in a patient with
sarcoidosis.
Notice the nodules along the fissures
indicating a perilymphatic distribution (red
arrows).
Alwayslookcarefullyforthesenodulesinthe
subpleural region and along the fissures,
because this finding is very specific for
sarcoidosis.
Typically in sarcoidosis is an upper lobe and
perihilar predominance and in this case we
seethe majorityofnoduleslocatedalongthe
bronchovascularbundle(yellowarrow).
Sarcoidosis
Ontheleftanothertypicalcaseofsarcoidosis.
Inadditiontotheperilymphaticnodules,there
are multiple enlarged lymph nodes, which is
alsotypicalforsarcoidosis.
In end stage sarcoidosis we will see fibrosis,
which is also predominantly located in the
upperlobesandperihilar.
Centrilobulardistribution
Centrilobularnodulesareseenin:
Hypersensitivitypneumonitis
Respiratorybronchiolitisinsmokers
infectiousairwaysdiseases
(endobronchialspreadoftuberculosisor
nontuberculousmycobacteria,
bronchopneumonia)
Uncommoninbronchioloalveolar
carcinoma,pulmonaryedema,vasculitis
In many cases centrilobular nodules are of
groundglassdensityandilldefined(figure).
Theyarecalledacinairnodules.
Treeinbud
In centrilobular nodules the recognition of
'treeinbud' is of value for narrowing the
differentialdiagnosis.
Treeinbud describes the appearance of an
irregular and often nodular branching
structure, most easily identified in the lung
periphery.
Itrepresentsdilated andimpacted(mucus or
pusfilled)centrilobularbronchioles.
Treeinbud almost always indicates the
presenceof:
Endobronchialspreadofinfection(TB,
MAC,anybacterialbronchopneumonia)
Airwaydiseaseassociatedwithinfection
(cysticfibrosis,bronchiectasis)
lessoften,anairwaydiseaseassociated
primarilywithmucusretention(allergic
bronchopulmonaryaspergillosis,
asthma).
Sarcoidosis
Illdefinedcentrilobularnodulesofgroundglass
densityinapatientwithhypersensitivity
pneumonitis
Ontheleftatreeinbudisseen.
In the proper clinical setting suspect active
endobronchialspreadofTB.
In most patients with active tuberculosis, the
HRCTshowsevidenceofbronchogenicspread
of disease even before bacteriologic results
areavailable(6).
Langerhanscellhistiocytosisisan uncommon
disease characterised by multiple cysts in
patientswithnicotineabuse.
In a very early stage, these patients show
only nodules, that later on cavitate and
becomecysts(figure).
Asinallsmokingrelateddiseases,thereisan
upperlobepredominance.
Randomdistribution
Ontheleftapatientwithrandomnodulesasa
resultofmiliaryTB.
The random distribution is a result of the
hematogenousspreadoftheinfection.
Smallrandomnodulesareseenin:
Hematogenousmetastases
Miliarytuberculosis
Miliaryfungalinfections
Sarcoidosismaymimickthispattern,
whenveryextensive
Langerhanscellhistiocytosis(early
nodularstage)
Sarcoidosis usually has a perilymphatic
distribution, but when it is very extensive, it
spreads along the bronchovascular bundle to
the periphery of the lung and may reach the
centrilobulararea.
HighAttenuationpattern
TypicalTreeinbudappearanceinapatientwith
activeTB.
Randomdistributionofnodulesinmiliary
tuberculosis
Langerhanscellhistiocytosis:earlynodularstage
beforethetypicalcystsappear.
Increased lung attenuation is called ground
glassopacity(GGO)ifthereisahazyincrease
in lung opacity without obscuration of
underlying vessels and is called consolidation
if the increase in lung opacity obscures the
vessels.
In both ground glass and consolidation the
increase in lung density is the result of
replacementofairinthealveolibyfluid,cells
orfibrosis.
In GGO the density of the intrabronchial air
appears darker as the air in the surrounding
alveoli.
Thisiscalledthe'darkbronchus'sign
In consolidation, there is exclusively air left
intrabronchial.
Thisiscalledthe'airbronchogram'.
Groundglassopacity
Groundglassopacity(GGO)represents:
Fillingofthealveolarspaceswithpus,
edema,hemorrhage,inflammationor
tumorcells.
Thickeningoftheinterstitiumoralveolar
wallsbelowthespatialresolutionofthe
HRCTasseeninfibrosis.
So groundglass opacification may either be
the result of air space disease (filling of the
alveoli) or interstitial lung disease (i.e.
fibrosis).
The location of the abnormalities in ground
glasspatterncanbehelpfull:
Upperzonepredominance:Respiratory
bronchiolitis,PCP.
Lowerzonepredominance:UIP,NSIP,
DIP.
Centrilobulardistribution:
Hypersensitivitypneumonitis,
Respiratorybronchiolitis
Darkbronchussigningroundglassopacity.
Completeobscurationofvesselsinconsolidation.
肺部HRCT基础解读.pdf

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