This is a 13 month old male brought to the 
emergency department with wheezing, coughing, and 
rhinorrhea.  He has had these symptoms for the past 
month.  Tonight, he developed fever which prompted 
his parents to bring him to the E.D.  He was seen by his 
primary care physician three weeks ago.  A chest 
radiograph was obtained on that day, revealing a left 
lower lobe consolidation.  He was treated with albuterol 
syrup and a ten day course of clarithromycin with some 
improvement.  He was noted to have a poor appetite 
and lost approximately one kilogram over the course of 
the month.
     Past medical history.  He was born at 39 weeks 
gestation without complications.  In the nursery, he was 
noted to be tachypneic with subcostal retractions.  A 
chest radiograph in the nursery revealed a left lower 
lobe infiltrate.  He was treated with oxygen and 
intravenous antibiotics.  He was then discharged home 
after one week.  Over the first year of his life, he was 
seen by his pediatrician on seven occasions for upper 
respiratory tract infections.
     Exam in the E.D.:  T 37.5 degrees rectally, P 138, 
RR 52, BP 95/40, oxygen saturation in room air 95%.  
General appearance:  Responsive with diminished 
activity in mild respiratory distress.  HEENT:  Normal 
except for white rhinorrhea.  Neck without adenopathy.  
Lungs clear to auscultation bilaterally.  Breath sounds 
were diminished at the left base.  There were no 
wheezes, rhonchi, or rales.  He has mild subcostal 
retractions and a paroxsymal cough.  Heart regular 
without murmurs.  Abdomen benign.  Color and 
perfusion are good
     Labs in the E.D.:  Hgb 9.6, hct 30.0, WBC 30,600 
with a differential of 48% segs, 13% bands, 33% 
lymphs and 6% monos.  Platelet count 518,000.  A 
blood culture is drawn.  A chest radiograph is obtained.

View CXR [PA view]


[Lateral view]

     The PA view demonstrates a left sided triangular 
density of the medial left lung base.
     On the lateral view, the triangular density is seen 
posteriorly over the left lung base.  Usually, the right 
diaphragm is higher than the left diaphragm.  In this 
case, the left diaphragm, which is higher than the right 
diaphragm, can be identified as the diaphragm with the 
underlying gastric bubble.  In this lateral view, the 
density can be determined to be on the left side.

View density.

     The patient is hospitalized and treated with 
intravenous antibiotics.  The history of recurrent 
pulmonary infections suggests the possibility of a 
pulmonary anomaly.  An aortogram is performed.

View aortogram.

     This aortogram shows contrast injected into the 
aortic arch.  There is a large anomalous vessel from the 
infradiaphragmatic portion of the aorta that supplies the 
abnormal density at the left lung base.  The venous 
phase (not shown) revealed drainage into the  
hemiazygous vein (a systemic vein).  This abnormal 
vascular supply is indicative of a pulmonary 
sequestration.

Discussion
     Pulmonary sequestration (PS) as first described by 
Rektorzik in 1861 is a mass of accessory lung tissue 
with an anomalous arterial supply.  The pulmonary 
tissue is dysplastic and nonfunctioning without any 
connection to the tracheobronchial tree (1).  The 
etiology of this defect is thought to be congenital (2).  
There are two types of pulmonary sequestration: 
intralobar and extralobar.
     Intralobar PS is three to six times more common 
than the extralobar type (3).  In intralobar PS, the 
pulmonary tissue is isolated from the normal lung 
tissue; however, the pleural covering remains 
contiguous with that of the lung.  The left lung is 
involved in 65% of the cases (4).  Typically, the mass is 
confined to the posterior basilar segments of the lower 
lobe of the lung.  There are rarely associated anomalies 
or foregut communications.  The symptoms typically 
occur during early childhood with the patient  presenting 
with recurrent pneumonia.  The diagnosis is made after 
the age of 20 years in fifty percent of this type of PS 
(5).  The incidence of intralobar PS is equal in males 
and females (6).  The arterial supply is via a systemic 
artery and the venous drainage is through the 
pulmonary veins.
     The accessory lung tissue of extralobar PS is 
contained within its own pleural sac and is separated 
from the rest of the lung.  It may be located between 
the inferior surface of the lower lobe and diaphragm, 
below the diaphragm, within the diaphragm, or in the 
mediastinum.  It occurs on the left in greater than 90% 
of the cases (5).  There may be an occasional foregut 
communication and associated anomalies are quite 
common.  These may consist of a diaphragmatic 
hernia, cardiovascular malformation, bronchogenic cyst, 
pectus excavatum, or other lung anomalies (4).  In 
contrast to intralobar PS, extralobar PS is usually 
diagnosed in infancy secondary to respiratory distress 
or feeding difficulties.  Since the accessory tissue is 
sequestered within its own pleura, the chances of 
presentation with an infection are less than that of 
intralobar PS, unless there is a foregut communication.  
The arterial supply is from a systemic artery and the 
venous drainage is typically via the systemic veins, 
rather than the pulmonary veins as seen in intralobar 
PS.
     Most radiographically visible sequestrations occur in 
children over one year of age.  The appearance of the 
chest radiograph depends on several factors:  1) 
whether the lesion is a site of infection, 2) if there is a 
communication with the airway or contiguous lung 
tissue, and 3) if there are other associated lung 
anomalies (7).  Intralobar sequestration typically 
appears as a mass, cystic lesion, or infiltrative shadow 
with ill-defined borders.  The majority of extralobar 
sequestrations are small lesions and are not visible on 
chest radiographs.  However, they may present as an 
infiltrate or mass in the region between the lower lobes 
and the diaphragm (but can also be found in the 
superior or anterior mediastinum, pericardium, or 
infradiaphragmatic region).
     In the diagnosis of pulmonary sequestration, a CT, 
MRI, or ultrasound may be diagnostic.  However, a 
normal study does not exclude the diagnosis.  The gold 
standard for identifying a sequestration is angiography 
(7).  Angiography confirms the anatomy, identifies the 
systemic supply, and shows the venous drainage.
     It is now thought that there are many "variants" to 
the pulmonary sequestration spectrum (8,9) which 
include:  scimitar syndrome, horseshoe lung, cystic 
adenomatoid malformation, and pulmonary 
arteriovenous fistula/malformation.
     In the scimitar syndrome, the anomalous vein drains 
into the inferior vena cava or at its junction at the right 
atrium.  This vein has the appearance of a scimitar.   
This may or may not be accompanied by hypoplasia of 
the right lung and dextrocardia, anomalies of the lobes 
of the right lung, hypoplasia of the right pulmonary 
artery, and an anomalous systemic vascular supply to 
the lung (10).
     The horseshoe lung is a rare congenital anomaly.  It 
is associated with some of the findings of the scimitar 
syndrome.  There is an isthmus of pulmonary tissue 
which extends from the right lung base across the 
midline behind the pericardium and then fuses with the 
left lung base.  Likewise, there may be an anomalous 
systemic supply (1).
     The cystic adenomatoid malformation is an 
abnormality of the pulmonary parenchyma due to an 
overgrowth of bronchioles (1). There is usually a normal 
vascular supply, however there may be an aberrant 
systemic artery.
     Lastly, the pulmonary arteriovenous 
fistula/malformation consists of an abnormal pulmonary 
artery and venous connection (1).  In this condition, 
there is normal pulmonary parenchyma (1) .  
Regardless of which variant is present, a diagnosis is 
suggested clinically and confirmed with angiography.  

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