Thoracic Imaging 2003 - Society of Thoracic Radiology

TUESDAY
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clinically as recurrent skin and pulmonary abscesses and
extremely high levels of serum IgE.8 Severe staphylococcal
infections are common, but these children are also susceptable
to Candida, H. influenza, Strep. pneumoniae, as well as other
organisms. Lung abscesses leading to large, chronic pneumatoceles
are typical9. Non-infectious features of this syndrome
include delay in shedding of primary teeth, fractures, hyperextensible
joints, and scoliosis. A single-locus autosomal dominant
defect on chromosome 4 has been implicated as the cause,
although there is probably variable expressivity of the disease.10
The immunologic deficiency is complicated and
involves a T-cell imbalance which leads to excessive IgE production,
but decreased IgG antibodies.
Combined humoral and cellular immune deficiencies
Severe combined immunodeficiency (SCID) is heterogeneous
group of disorders caused by defects in stem cell maturation
and resulting in serious infections beginning in infancy.7
Mortality is high, and most patients do not survive beyond early
childhood. T-cell and B-cell functions are affected, and patients
usually demonstrate generalized systemic and circulating lymphopenia.
X-linked and autosomal recessive types of SCID have
been discovered, but the X-linked recessive type is slightly more
common, resulting in the higher incidence of SCID in males.
50% of the patients with the autosomal recessive type lack the
enzyme adenosine deaminase (ADA) leading to a build-up of
deoxyadenosine which is toxic to lymphocytes.6 These patients
can be identified by measuring ADA activity in red blood cells.
Infants with SCID usually fail to thrive and become infected
with a variety of pathogens including fungi, viruses, and
Pneumocystis carinii which can cause overwhelming pneumonia.
Bone marrow transplantation offers variable success. Gene
therapy trials are in progress.
Partial combined immunodeficiency disorders
Wiskott-Aldrich syndrome is an inherited x-linked recessive
disease (chromosome Xpl 1.23 locus) of combined cellular and
humoral immunity, thrombocytopenia, and a skin rash similar to
eczema.11 While the thymus is normal, there is T-cell depletion
in the peripheral blood and lymphoid tissues. 1gM levels are
low, but IgA and lgE are elevated.7 Early mortality from pyogenic
infection or bleeding secondary to the thrombocytopenia
is high. Lymphoma has been reported in those who survive
infancy. Bone marrow transplantation appears to be the only
effective treatment to date.12
Ataxia-telangiectasia is an autosomal recessive disease
(chromosome 1 1q22-23 locus) characterized by progressive
cerebellar ataxia, ocular and cutaneous telangiectasia, and combined
immunodeficiency including thymic hypoplasia and
abnormal humoral immunity. 12 Sinusitis, recurrent pneumonia,
and bronchiectasis are common, but death usually results
from the progressive neurologic defect or lymphoid malignancy.
Cartilage - hair hypoplasia is a rare form of short-limbed
dwarfism associated with a partial combined immune defect.
Severe varicella, vaccinia, and vaccine associated poliomyelitis
have been reported as characteristic complications in this inherited
bone dysplasia I immune deficiency syndrome.6
Disorders of phagocvtosis
Chronic granulomatous disease of childhood is an inherited
disorder in which bacteria may be ingested by neutrophils but
are not killed because of the reduced capacity of intracellular
oxidative enzymes (NADPH oxidase).6 X-linked and autosomal
recessive variants have been identified explaining an increased
incidence in males. Recurrent infections due to catalase producing
organisms such as Staph. aureus, Staph. epidermidis, and
some gram-negative bacteria are common. Lymphadenitis, skin
infection, osteomyelitis, liver abscess, and antral gastritis occur
in addition to recurrent bacterial pneumonia and lung abscess.
The nitroblue tetrazolium (NBT) test can measure the activity of
neutrophil NADPH oxidase and thereby diagnose the disease.
Multiple calcified granulomas in the liver, lung and other organs
are radiologic clues.13
Chediak-Higashi syndrome is a rare, autosomal recessive ,
genetic disorder of neutrophil function manifest by recurrent
bacterial infections.12 While there is peripheral neutropenia,
characteristic giant granules are found in those white cells
which remain. A defect in the transfer of Iysosomal enzymes is
postulated leading not only to abnormal phagocytosis, but also
to partial albanism, neurologic, and platelet disorders. An
increased susceptibility to lymphoid malignancy also occurs.
Complement deficiency syndromes
A wide variety of rare inherited defects in the complement
system have been described which can lead to rheumatologic
syndromes as well as recurrent infection. The pattern of infection
is similar to patients with gamma-globulin deficiency, i.e.,
increased susceptibility to bacterial disease.4
Acquired immune defects in children
The radiology of infection secondary to AIDS in children is
similar their adult counterparts, but two thoracic manifestations
are worthy of note: (I) lymphocytic interstitial pneumonitis
(LIP) and (2) cystic enlargement of the thymus. LIP presents
radiographically as a diffuse reticulonodular pattern throughout
the lungs usually in relatively asymptomatic patients. In fact,
these patients often have higher T-cell counts than those who
develop more severe and overwhelming infection.
Pathologically, lymphoid aggregates are found in the lung with
very little evidence of acute inflammation. The presence of
Ebstein-Barr (EB) virus genome fragments in these lymphocytes
has suggested the possibility that LIP represents an exaggerated
response to EB virus infection. Intermittent steroid therapy
usually causes both radiologic and clinical improvement but
does not totally irradicate the abnormality.
Cystic enlargement of the thymus in pediatric and adolescent
AIDS patients has been described but its cause is unknown.
Mediastinal widening on chest radiography simulates lymphoma,
while contrast enhanced CT reveals benign, cystic
replacement of the gland’4. Long term follow-up remains to be
determined.
Sickle cell disease is responsible for an acquired immunologic
defect secondary to progressive splenic dysfunction in
early childhood leading to an acquired deficiency of opsonin
which is necessary for the ingestion of encapsulated bacteria.
Infections with these organisms, especially the pneumococcus,
can lead to sepsis, primary peritonitis, meningitits, and other
serious life-threatening complications. So called “acute chest
syndrome” often results in extensive lobar consolidations associated
with fever and hypoxemia. Small pleural effusions are not
uncommon. It may be impossible to differentiate in situ vascular
thrombosis from consolidative pneumonia, therefore such
patients are usually treated with antibiotics, transfusions, and
oxygen. Repeat episodes are not uncommon and may lead to
areas of scarring within the lungs.