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Paediatric Cardiothoracic Surgery: Answers
309
esophageal atresia with upper pouch tracheoesophagel fistula. J Pediatr Surg.
2008;43:E33-5.
Bagolan P, Iacobelli Bd Bd, De Angelis P, et al. Long gap esophageal atresia and esophageal
replacement: moving toward a separation? J Pediatr Surg. 2004;39:1084-90.
Al-Qahtani AR, Yazbeck S, Rosen NG, et al. Lengthening technique for long gap esophageal
atresia and early anastomosis. J Pediatr Surg. 2003;38:737-9.
Boyle EM Jr, Irwin ED, Foker JE. Primary repair of ultra-long-gap esophageal atresia: results
without a lengthening procedure. Ann Thorac Surg. 1994;57:576-9.
4.9 Answer: D
Cystic fibrosis is the commonest genetically inherited disease in white populations
with a
frequency of 1 in 2500 newborns. It is being increasingly recognised
as important in non-
white populations. It is an autosomal recessive disease caused
by mutations in the CFTR
(cystic fibrosis transmembrane conductance
regulator) gene. Over 1600 mutations of the
CFTR gene have been described with the commonest mutation being the deletion of
phenylalanine at codon 508 (phe508del, until recently known
as ∆F508). This occurs in about
70% of patients with cystic fibrosis. Different
mutations in this gene have varying effects on
CFTR function
and can result in different phenotypes of the disease. Some
mutations will
result in milder forms of the disease, although
there is not enough evidence about these rarer
mutations to
counsel patients about their prognosis. Although the CFTR protein is
expressed
in many cells and has several functions yet not all of
these have been linked with disease. The
primary function of
the CFTR protein is as an ion channel that regulates liquid
volume on
epithelial surfaces through chloride secretion and
inhibition of sodium absorption.
The "low volume" hypothesis commonly provides an explanation for airway disease in
cystic
fibrosis. Mucociliary clearance,
the lungs‘ innate defence mechanism, fails due to
reduced volume of
airway surface liquid. A patient with cystic fibrosis cannot
effectively clear
inhaled bacteria due to the mucociliary
dysfunction. In addition, there is an
excessive
inflammatory response to pathogens. For a given bacterial
load, a person with cystic fibrosis
will have up to 10 times
more inflammation than a person with a lower respiratory tract
infection but without the disease. Similarly
for other insults such as viruses or even for
airborne particulate
matter and pollutants there is excessive inflammatory response. The
reasons for the excessive inflammatory
response to pathogens are not fully elucidated. The
abnormal
composition and secretion of mucus may also be significant. At
birth, the airway is
uninfected and probably uninflamed, although
some controversy exists in this area, but the
end result of
the abnormalities described above is irreversible airway damage
with
bronchiectasis and respiratory failure in most patients. Ion and water abnormalities may also
cause disease
in other epithelia-lined organs.
References
Davies JC, Alton EW, Bush A. Cystic fibrosis. BMJ. 2007;335:1255-9.
Riordan JR, Rommens JM, Kerem B, et al. Identification of the cystic fibrosis gene: cloning
and characterization of complementary DNA. Science. 1989;245:1066-73.
Matsui H, Grubb BR, Tarran R, et al. Evidence for periciliary liquid layer depletion, not
abnormal ion composition, in the pathogenesis of cystic fibrosis airways disease. Cell.
1998;95:1005-15.
Shahzad G. Raja
310
Gibson RL, Burns JL, Ramsey BW. Pathophysiology and management of pulmonary
infections in cystic fibrosis. Am J Respir Crit Care Med. 2003;168:918-51.
4.10 Answer: C
The gold standard for the confirmation of cystic fibrosis (CF) diagnosis is the sweat test
with quantitative iontophoresis with pilocarpine. The collection methods are the Gibson-
Cooke procedure and the Macroduct sweat collection system (Wescor, Logan, UT, USA). In
both, the sweat is stimulated by iontophoresis with pilocarpine, after which it is collected with
paper filter or gauze (Gibson-Cooke) or in a microbore tube (Wescor). The sample is then
analyzed to determine the concentration of sodium chloride. The minimal acceptable sweat
volume is 75 mg in the Gibson-Cooke procedure and 15 mL for the Macroduct system.
Patients with the disease have
raised concentrations of sodium and chloride (>60 mmol/l,
diagnostic; 40-60 mmol/l, intermediate (but more likely to be
diagnostic in infants); <40
mmol/l, normal). However, undoubted
cases of cystic fibrosis with normal sweat electrolytes
have
been described. Newer techniques have reduced the amount of
sweat needed. The test
needs to be done by someone trained
and experienced. For this reason the diagnosis will
usually
be made in secondary and tertiary centres, although primary
care professionals play a
vital role in identifying the patients
who need investigation. In the rare cases where the
diagnosis
remains in doubt, other diagnostic tests are available—for
example, measurement of
the nasal potential difference to assess
altered salt transport is available in a few specialist
centres
in the UK.
References
Davies JC, Alton EW, Bush A. Cystic fibrosis. BMJ. 2007;335:1255-9.
Rosenstein BJ, Cutting GR, for the Cystic Fibrosis Foundation Consensus Panel. The
diagnosis of cystic fibrosis: a consensus statement. J Pediatr. 1998;132:589-95.
Middleton PG, Geddes DM, Alton EW. Protocols for in vivo measurement of the ion
transport defects in cystic fibrosis nasal epithelium. Eur Respir J. 1994;7:2050-6.
4.11 Answer: A
The lung begins evolution in the third week of gestation when it develops as a ventral
diverticulum on the floor of the primitive foregut. The ensuing development of the lung is
then generally divided down into 5 phases including the embryonic, pseudoglandular, acinar
(or canalicular), saccular, and alveolar phases. During the embryonic phase (26 days to 6
weeks gestation), 2 lung buds eventually give rise to 5 lobar bronchi that come to be
associated with the developing pulmonary arteries and veins. The pseudoglandular phase (6 to
16 weeks gestation) involves development of the conducting airways and also includes the
first appearance of cartilaginous tracheal rings, pseudostratified columnar epithelium, and
cilia. The basic structure of the gas exchange units of the lung appear in the acinar phase (16
to 28 weeks gestation) including the initial differentiation of the Type I and Type II
pneumocytes. The distal airspaces continue to multiply and evolve into more complex gas
exchange units during the saccular phase (28 to 34 weeks gestation), while the alveolar phase
continues from 34 weeks of gestation to beyond birth and truly represents the time during
which the majority of alveolar development occurs. Approximately 20 million thick walled
air sacs exist at birth and these proliferate into 300 to 600 million alveoli by about 2 years of
age after which lung growth occurs more in terms of volume and alveolar size. In this way,
Paediatric Cardiothoracic Surgery: Answers
311
the surface area for gas exchange in the lung increases from 3 to 4 m
2
in the neonate to 75 m
2
in the adult.
References
Mendeloff EN. Sequestrations, congenital cystic adenomatoid malformations, and congenital
lobar emphysema. Semin Thorac Cardiovasc Surg. 2004;16:209-14.
Kimura J, Deutsch GH. Key mechanisms of early lung development. Pediatr Dev Pathol.
2007;10:335-47.
4.12 Answer: A
Sequestration may be defined as a segment of the lung separated from the remainder of
the lung such that it is not in continuity with the upper tracheo-bronchial tree and it receives
arterial blood supply from an aberrant branch of the aorta rather than the pulmonary artery.
This lesion is further divided into 2 variants, extralobar sequestration (ELS) and intralobar
sequestration (ILS).
ELS is a discrete mass of pulmonary parenchyma existing outside the pleural covering of
the lung; i.e., the sequestered lung is enclosed entirely by a separate pleural investment. It is
suggested that this develops when independent conglomerations of cells with respiratory
potential arise from the primitive foregut (oesophagus) distal to the normal lung bud. There is
evidence to suggest that homeobox gene Hoxb-5 is necessary for normal airway branching
and development and abnormal expression of the homeobox genes is associated with the
developmental abnormalities seen with bronchopulmonary sequestration. ELS are most
commonly found on the left side (66%) adjoining the oesophagus and between the lower lobe
and diaphragm. These independent clusters of cells may arise so caudally that as often as 15%
of the various types of sequestrations may be found in subdiaphragmatic and retroperitoneal
locations and frequently misdiagnosed. An intraabdominal, extralobar pulmonary
sequestration may present as a suprarenal mass electively resected using laparoscopic
techniques. While 80% of the time the ELS derives its blood supply from the descending
thoracic or abdominal aorta, arterial supply of extralobar sequestrations may also be derived
from the great vessels or branches thereof. Venous drainage is to the azygous or hemiazygous
system 80% of the time, with the remainder either partially or completely draining by the
pulmonary venous system.
References
Mendeloff EN. Sequestrations, congenital cystic adenomatoid malformations, and congenital
lobar emphysema. Semin Thorac Cardiovasc Surg. 2004;16:209-14.
Liejala M, Louhino I. Extralobar sequestration of the lung in children. Prog Ped Surg.
1987;21:98-106.
Volpe MV, Archavachotikul K, Bhan I, et al. Association of bronchopulmonary sequestration
with expression of the homeobox protein Hoxb-5. J Pediatr Surg. 2000;35:1817-1819.
Danielson PD, Sherman NJ. Laparoscopic removal of an abdominal extralobar pulmonary
sequestration. J Pediatr Surg. 2001;36:1653-1655.
Stocker JT. Sequestrations of the lung. Sem Diag Path. 1986;3:106-121.
Shahzad G. Raja
312
4.13 Answer: B
Congenital lobar emphysema (CLE) is characterized by progressive hyperexpansion of an
upper lobe or the right middle lobe after birth. The basic pathologic abnormality in CLE is
overdistention of otherwise normal alveoli without destruction of alveolar walls. Suggested
causes include a focal deficiency of bronchial wall cartilage, deficient connective tissue
stroma that results in abnormal support of alveolar walls, and intrinsic or extrinsic obstruction
of an affected bronchus. These abnormalities are believed to result in a check-valve
mechanism, with progressive hyperinflation of the involved lobe after birth. Rarely, CLE is
caused by extrinsic compression from a vascular abnormality such as an avalvular pulmonary
artery or patent ductus arteriosus.
CLE accounts for 10–15% of congenital masses of the lung in most large series, but is
rarely diagnosed by prenatal sonography, with the first case not reported until 1992. CLE on
prenatal sonograms appears as a uniformly echogenic lesion with associated mass effect. The
apparent failure of foetal sonography to detect CLE is poorly understood, but one plausible
explanation is that foetal lung fluid maintains patency of the affected airway during foetal
life, with the check-valve mechanism not occurring until expulsion of this fluid after birth.
Also, similar cellular and fluid composition and thus echogenity of the affected lobe to
normal lung may contribute to this inability of prenatal scans to detect CLE.
Progressive respiratory distress early in life is the presenting feature in more than 90% of
cases. In the first few days of life, bronchial obstruction may result in delayed clearance of
foetal lung fluid, with an opaque mass shown in the affected lobe on initial radiographs of the
chest. Two-thirds of patients with respiratory symptoms at the time of birth have this pattern.
Chest x-rays obtained after the first few days of life show a hyperlucent, expanded upper or
middle lobe with associated shift of the mediastinum, as well as atelectasis of the ipsilateral
lower lobe. Radiography remains the primary imaging modality for evaluation of infants with
CLE. Computed tomography (CT) is not indicated in most cases. CT is beneficial in selected
cases to distinguish between CLE, a large Type I congenital cystic adenomatoid malformation
and contralateral pulmonary hypoplasia. CT demonstrates overexpansion and decreased CT
attenuation of the affected lobe with no evidence of cystic change in CLE.
References
Winters WD, Effmann EL. Congenital masses of the lung: prenatal and postnatal imaging
evaluation. J Thorac Imaging. 2001;16:196-206.
Stigers KB, Woodring JH, Kanga JF. The clinical and imaging spectrum of findings in
patients with congenital lobar emphysema. Pediatr Pulmon. 1992;14:160-170.
4.14 Answer: A
Bronchogenic cysts are congenital lesions believed to arise
from the primitive ventral
foregut. They may be mediastinal, intrapulmonary,
or, less frequently, in the lower neck.
Approximately two-thirds
are within the mediastinum, and one-third are intraparenchymal.
They account for 40%–50% of all congenital
mediastinal (intrathoracic) cysts, and there is a
slight male
predominance. The frequency of bronchogenic cysts is unknown
most likely
because most patients are asymptomatic. An average incidence of 20 cases over a 20-year
period has been reported in published literature.
The cysts are lined by ciliated
columnar or
cuboidal epithelium and contain mucoid material. Their walls contain smooth
muscle and
often cartilage. They are sometimes intrapulmonary,
typically in the medial third of the lung.
Paediatric Cardiothoracic Surgery: Answers
313
Mediastinal
cysts may be paratracheal (usually right-sided), carinal,
or hilar. The carinal
location is most frequent. They can also
be located in the posterior as well as anterior
mediastinum where they may need to be differentiated from other
more frequent anterior
mediastinal cysts such as cystic teratoma,
thymic cysts, or cysts derived from ectopic thyroid
glands.
Bronchogenic cysts do not initially communicate with the tracheobronchial
tree. Infection
or instrumentation of the cyst may lead to air-filled
cyst or an air-fluid level. Symptoms due to
the size and position of the cyst are experienced by two-thirds of the patients. Symptoms
are
most frequently caused by compression of the trachea or
bronchi, which leads to cough,
wheezing, stridor, dyspnoea, cyanotic
spells, and pneumonia. 20% of patients with
intraparenchymal cysts develop infection, usually secondary to communication with
the
tracheobronchial tree. However, most bronchogenic cysts
in children are found incidentally
when imaging is performed
for other reasons.
Bronchogenic cysts are rarely detected with foetal sonography.
Avni and associates in
1986 reported the first case in the medical literature. They are usually seen as a unilocular,
fluid-filled cyst in the middle or posterior mediastinum. Differential
diagnoses include
oesophageal duplication cyst, neuroenteric
cyst and congenital cystic adenomatoid
malformation. Intrapulmonary
bronchogenic cysts are usually located in the lower lobes.
In
infants and children, the chest radiograph is diagnostic
for bronchogenic cysts in 75% of
cases. The
cysts appear
as water-density mass lesions in chest radiographs because of the
serous or mucous fluid content. Intrapulmonary cysts may show air or an air-fluid level due to
communication with the tracheobronchial
tree.
CT has the capability of locating an intrathoracic cyst, defining
its extent and relation to
key structures, and characterizing
the intrinsic density. The cyst has variable attenuation
values. The density of mucus-containing cyst is often higher
than that of water; this also may
be due to the presence of
calcium in the cyst fluid. The cysts show no contrast
enhancement,
but when they become infected they may show wall
enhancement.
T1-weighted magnetic resonance (MR) images show that the intrinsic signal intensity
ranges from low to high depending on cyst contents. On T2-weighted
MR images, the cysts
are typically high in signal intensity. The possibility of malignancy should be considered
when a solid component is seen in a cyst wall at CT or MR imaging.
References
Berrocal T, Madrid C, Novo S, et al. Congenital anomalies of the tracheobronchial tree, lung,
and mediastinum: embryology, radiology, and pathology. Radiographics. 2004;24:e17.
Winters WD, Effmann EL. Congenital masses of the lung: prenatal and postnatal imaging
evaluation. J Thorac Imaging. 2001;16:196-206.
Kim KW, Kim WS, Cheon JE, et al. Complex bronchopulmonary foregut malformation:
extralobar pulmonary sequestration associated with a duplication cyst of mixed
bronchogenic and esophageal type. Pediatr Radiol. 2001;3:265-268.
Avni EF, Vanderelst A, Van Gansbeke D, et al. Antenatal diagnosis of pulmonary tumors:
report of two cases. Pediatr Radiol. 1986;16:190-192.
Shahzad G. Raja
314
4.15 Answer: C
Most tumours within the anterior mediastinum are of the thymic, lymphatic, or germ cell
origin. Occasionally, especially in children, tumours of vascular origin are found in the
anterior superior compartment of the mediastinum.
Lymphoma is the third most common malignancy in children, but is the most common
malignancy of the mediastinum in children, representing approximately one- half of all
mediastinal malignancies. Approximately two-thirds of lymphomas are non-Hodgkin‘s and
one-third Hodgkin‘s lymphoma. Lymphomas may involve all compartments in the
mediastinum. In children, lymphoma occurs most frequently in the anterior and middle
compartments. There is very little role for surgical resection of lymphomas. Most children
with mediastinal lymphoma have coexistent cervical or supraclavicular lymphadenopathy that
is readily accessible to biopsy. Video-assisted thoracoscopic biopsy or a Chamberlain
procedure are reserved for those rare situations in which tissue cannot be obtained by other
means.
Airway compression and symptoms are usually seen in many children with larger
lymphomas. If these patients require a surgical procedure, preoperative radiation and
chemotherapy may be indicated to decrease this tumour bulk. Surgical debulking may be
indicated in very rare situations in which a child presents with so bulky a tumour that airway
compression is life-threatening.
Non-Hodgkin‘s lymphoma represents approximately two-thirds of mediastinal
lymphomas and Hodgkin‘s lymphoma represents about one-third of the cases in children.
Non-Hodgkin‘s lymphoma is usually synonymous with lymphoblastic lymphoma in children,
although non-lymphoblastic (large cell) may occur rarely. Children with non-Hodgkin‘s
lymphoma often present with symptoms related to local compression such as cough, stridor,
respiratory distress, superior vena cava obstruction. Generalized symptoms are often present
and include fever, night sweats and weight loss. Pleural effusions and cervical adenopathy are
commonly present and provide a convenient opportunity for diagnosis. Bone marrow
involvement occurs in over one-third of patients.
Hodgkin‘s lymphoma presents in adolescents and young adults. Children with Hodgkin‘s
lymphoma are more likely to experience systemic symptoms of weight loss, night sweats, and
malaise and less likely to have pleural effusions. In most children, the diagnosis can be made
by lymph node biopsy. Rarely tissue must be obtained by direct biopsy of the mediastinal
mass or bone marrow aspirate. Nodular sclerosing is the most common cell type, representing
approximately 75% of cases.
References
Jaggers J, Balsara K. Mediastinal masses in children. Semin Thorac Cardiovasc Surg.
2004;16:201-208.
4.16 Answer: D
Primary mediastinal tumours and cysts are relatively rare in the pediatric population.
They represent an interesting and heterogeneous group of congenital and neoplastic lesions
more than half of which are malignant (Table). Most children with mediastinal masses are
symptomatic with some being life-threatening. Lymphoma is reported to be the most common
lesion. Neurogenic tumours are the most common benign lesion and the second most
common malignancy. Most mediastinal masses, irrespective of whether they are malignant or
Paediatric Cardiothoracic Surgery: Answers
315
benign, require surgical intervention either for diagnosis or for definitive treatment. The
surgical management is often curative and depends on accurate preoperative imaging.
Neurogenic tumours are usually located in the posterior mediastinum and originate from
the sympathetic ganglia (ganglioma, ganglioneuroblastoma, and neuroblastoma), the
intercostal nerves (neurofibroma, neurilemoma, and neurosarcoma), and the paraganglia cells
(paraganglioma). Rarely, these tumours are located in the anterosuperior mediastinum.
Whereas the majority of neurogenic tumors are benign in adults, a larger percentage is
malignant in children.
Germ cell tumours are supposed to originate from primordial germ cells that fail to
complete the migration from the urogenital ridge and come to rest in the mediastinum. These
can be either benign or malignant neoplasms. These tumours are classified as teratomas and
teratocarcinomas, seminomas, embryonal cell carcinomas, choriocarcinomas, and endodermal
cell tumors. While these tumours are identical cell types to those that occur in the gonads,
they are not regarded as metastases from the gonadal origin. In children, the mediastinum is
the fourth most common site for teratomas, after the ovary, sacro-coccygeal region and testis.
Mature teratomas are those with mature tissue components. Immature teratomas are those
with embryonic mesenchyme, immature neuro-ectoderm and/or blastema. Occasionally,
malignant germ cell elements may occur within mature teratomas, but this is very uncommon.
The majority of benign mediastinal teratomas occur in the anterior mediastinum, however
some occur in the posterior mediastinum. Most mature teratomas are large well-circumscribed
masses that contain tissue derived from three germinal cell layers. Most contain mature
ectodermal elements such as skin, pilo-sebaceous units, and mature neuroglial tissue. Cystic
elements are often lined by various epithelia including respiratory and mucinous. Other
tissues that may be present include bone, cartilage, smooth muscle, fat, and endocrine tissue,
including pancreatic and thyroid tissue.
Table. Mediastinal Tumors and Cysts by Location
Anterior
Middle
Posterior
Lymphoma
Enterogenous cyst
Neurogenic tumors
Germ cell tumor
Mesothelial cyst
Neurenteric cyst
Thymoma
Lymphoma
Lymphoma
Hemangioma
Thoracic duct cyst
Parathyroid adenoma
Granuloma
Thymic cyst
Hamartoma
Lipoma
Aberrant thyroid
Lymphangioma
References
Jaggers J, Balsara K. Mediastinal masses in children. Semin Thorac Cardiovasc Surg.
2004;16:201-208.
Shahzad G. Raja
316
4.17 Answer: E
Ganglioneuroma, ganglioneuroblastoma, and neuroblastoma represent a continuum of
maturation and differentiation (Table). Ganglioneuromas, composed of ganglion cells and
nerve fibers, are benign tumours originating from the sympathetic chain. These are the most
common neurogenic tumours in children. Traditionally, they present at an early age and as an
incidental finding on routine chest radiography. Rarely, they cause symptoms by pressure on
the nerve root or spinal cord. Magnetic resonance imaging is useful in delineating the
relationship of the neurogenic tumours to adjacent structures like the spinal cord, aorta and
oesophagus. These tumours are fully differentiated and are composed of mature ganglion and
Schwann cells. They are well encapsulated and on cross-sectional imaging, they often show
areas of cystic degeneration. Surgical resection provides definitive cure.
Table. Cells of Origin for Common Neurogenic Tumors
Intercostal Nerve
Sympathetic Ganglia
Paraganglia Cells
Neurofibroma
Ganglioma
Paraganglioma (pheochromocytoma)
Neurilemoma
Ganglioneuroblastoma
Neurofibrosarcoma
Neuroblastoma
Ganglioneuroblastomas exhibit an intermediate degree of differentiation between
ganglioneuromas and neuroblastoma. The ganglioneuroblastoma is malignant, possesses a
recognizable capsule and usually produces symptoms. They are composed of both mature and
immature ganglion cells. They can be divided into two categories: composite
ganglioneuroblastoma and diffuse ganglioneuroblastoma. Composite ganglioneuroblastoma is
composed primarily of mature neuroblasts with focal areas of primitive neuroblasts.
Approximately 65 to 70% of patients have evidence of metastatic disease at the time of
presentation. Diffuse ganglioneuroblastoma, as the name suggests, is composed of a diffuse
mixture of well-differentiated primitive neuroblasts. Compared to composite
ganglioneuroblastoma, less than 5% of patients with diffuse variety develop metastases.
Neuroblastoma is a highly malignant tumour that occurs in young children and infants.
Most are found in children younger than 3 years of age. These tumours constitute over 50%
of the neurogenic tumours in the mediastinum, and the intrathoracic lesions account for
approximately 20% of all neuroblastomas in children. Grossly, the mass may be smooth, but
often it is irregular in outline and involves adjacent structures. Histologically, these tumours
consist of small, round, immature cells organized in a rosette pattern. Areas of degeneration
and calcification are common. These are highly malignant neoplasms that frequently have
metastasized before diagnosis. Common sites of metastatic disease are regional lymph nodes,
bone, brain, liver, and lung. Presenting symptoms are variable and include cough, dyspnoea,
chest pain, Horner‘s syndrome, paraplegia, fever, and lassitude. In some infants, spontaneous
abnormal eye movements thought to be caused by an immune response may be observed.
Various paraneoplastic syndromes have been reported, including profuse watery diarrhoea
related to vasoactive intestinal polypeptide production and a pheochromocytoma-like
syndrome owing to catecholamine secretion.
Ganglioneuroblastomas and neuroblastomas are staged from Stage I, a well-
circumscribed noninvasive tumor, to Stage IV-S, with evidence of distant metastatic disease.
Stage I and II disease are appropriately treated with complete surgical excision. Stage III and
Paediatric Cardiothoracic Surgery: Answers
317
greater demand multimodal therapy: surgical debulking, systemic chemotherapy and radiation
treatment. Prognosis is variable and highly dependent on stage of disease. For all patients
with ganglioneuroblastomas, 5-year survival is 88%. An overall 5-year survival rate of 22% is
reported for neuroblastomas.
Neurolemomas are benign tumours arising from perineural Schwann cells. These tumours
are well circumscribed and have a defined capsule. In contrast to neurilemomas,
neurofibromas are poorly encapsulated and consist of randomly arranged spindle-shaped
cells. These tumours originate as a proliferation of the peripheral nerve. Both are associated
with neurofibromatosis. Surgical excision results in cure.
References
Jaggers J, Balsara K. Mediastinal masses in children. Semin Thorac Cardiovasc Surg.
2004;16:201-208.
Saenz NC. Posterior mediastinal neurogenic tumors in infants and children. Seminars in
Pediatric Surgery. 1999;8:78-84.
4.18 Answer: A
Tracheomalacia (TM) is the most common congenital abnormality of the trachea. It is
more commonly seen in premature infants but can be an isolated finding in healthy infants. It
is thought to be a consequence of the inadequate maturity of tracheobronchial cartilage, either
from premature delivery or from an innate immaturity despite normal gestation. Some authors
have reported no gender predominance in the primary form of the disease, whereas others
have reported a definite male predominance.
Disease processes that lead to the formation of an abnormal cartilaginous matrix of the
trachea are included as primary forms of TM. These associated diseases, which include
polychondritis and chondromalacia, result in dysmaturity of the collagen fibers and weakness
in the tracheobronchial tissue. TM is also clearly associated with the mucopolysaccharidoses,
such as Hunter syndrome and Hurler syndrome, as well as with many other genetic
syndromes.
The most common associated disease is tracheoesophageal fistula, which has been
classified by some as an acquired form rather than a congenital form of the disease. In the
majority of healthy and even premature infants, primary TM is a self-limiting disease. Most
infants outgrow the condition by the age of 2 years. In the patients with connective tissue
disorders and congenital syndromes, the effects of TM often persist and may even be fatal.
Acquired or secondary TM is caused by the degeneration of normal cartilaginous support
from a variety of causes. Acquired TM is more common than the congenital form. There is a
male predominance of the acquired form, but the reason for that is unknown. It commonly
results from protracted endotracheal intubation, with the associated insults of increased
airway pressure, oxygen toxicity, and recurrent infections. Premature infants with respiratory
distress syndrome seem to be the most predisposed to this condition, as their supporting
structures are not yet mature. As more and more premature infants are treated for respiratory
distress syndrome, the incidence of TM may very well increase.
Shahzad G. Raja
318
References
Masters IB, Chang AB, Patterson L, et al. Series of laryngomalacia, tracheomalacia, and
bronchomalacia disorders and their associations with other conditions in children. Pediatr
Pulmonol. 2002;34:189-195.
Carden KA, Boiselle PM, Waltz DA, Ernst A. Tracheomalacia and tracheobronchomalacia in
children and adults: an in-depth review. Chest. 2005;127:984-1005.
4.19 Answer: C
Congenital diaphragmatic hernia (CDH) is defined as a protrusion of abdominal viscera
into the thorax through an abnormal opening or defect that is present at birth. In some cases,
this protrusion is covered by a membranous sac. On the contrary, diaphragmatic eventrations
are extreme elevations, rather than protrusions, of part of the diaphragm that is often atrophic
and abnormally thin. CDH, with an incidence of ∼1 in every 3,000 live births, is a relatively
common birth defect. CDH is often associated with potentially lethal lung hypoplasia and
pulmonary hypertension. Despite advances in therapy, mortality remains high, especially
among severely affected infants, and long-term morbidity among survivors is common.
The most common type of CDH is the posterolateral, or Bochdalek-type, hernia, which
accounts for 90%–95% of CDH cases. Other types of CDH include anterior retrosternal or
peristernal Morgagni hernias, central (septum transversum) hernias, and pars sternalis hernias,
which are found in the pentalogy of Cantrell—a rare association involving abnormalities of
the anterior diaphragm, sternum, heart, and abdominal wall.
The recurrence risk for isolated cases of CDH is often reported to be <2% on the basis of
a mathematical model of multifactorial inheritance risk. Empiric data also suggest a relatively
low recurrence risk for CDH. However, there are multiple examples of familial cases of CDH
in the literature. Trisomy 13, 18, and 21 and 45,X are the most common aneuploidies
associated with CDH. Structural abnormalities—including deletions, duplications, inversions,
and translocations—of nearly all chromosomes have also been described in association with
CDH.
Vitamin A (retinol) and its derivatives (retinoids) are essential for embryonic
development. Abnormalities in the retinoid signaling pathway and its downstream targets
have long been postulated to lead to the development of CDH. The first connection between
retinoids and CDH resulted from the observation that 25%–40% of the offspring of rat dams
that were fed a diet deficient in vitamin A developed CDH and that the proportion of affected
pups diminished when vitamin A was reintroduced into the diet in midgestation.
References
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Holder AM, Klaassens M, Tibboel D, et al. Genetic factors in congenital diaphragmatic
hernia. Am J Hum Genet. 2007;80:825-45.
Lin AE, Pober BR, Adatia I. Congenital diaphragmatic hernia and associated cardiovascular
malformations: type, frequency, and impact on management. Am J Med Genet C Semin
Med Genet. 2007;145C(2):201-16.