DISEASES OF THE AIRWAYS IN CHILDHOOD
Introduction
Imaging modalities are fundamental and irreplaceable tools in the evaluation of obstruction of the airways in infants and children. The causes of such an obstruction differ by age. This is why each case should be studied carefully and "children should not be treated as little adults" (1).
The imaging methods used in the investigation of obstruction of the airways are: radiographs, fluoroscopy, barium meal examination of esophagus, C.T and M.R.I.
In every day’s medical practice, radiorgraphs are to be used firstly, since in many cases these examinations give us important information on the diagnosis and the right therapeutic treatment of various diseases. Nevertheless, the technological development and the use of new diagnostic methods as Helical Computed Tomography, High Resolution CT, Ultrafast CT (image 1) changed the imaging algorithm of the obstructive diseases of the airways in children (1). Nowdays, the study of the anatomic unit of the lung parenchyma (pulmonary lobule) is possible through the use of HRCT. The correlation of radiological images and histological findings becomes more precise. A referrence in the mainer causes of obstruction of the airways will follow, starting from the trachea, up to the small peripheral airways.
· Laryngeo-tracheo-bronchitis or CROUP
Laryngeo-tracheo-bronchitis or CROUP is the most frequent reason of obstruction of the central airways in children. It is due to a virus infection, most frequently by the parainfluenza virus, and individuals below the age of 4 are those affected. Clinically the patients suffer of paroxysmal cough and respiratory wheeze. The diagnosis of CROUP is mainly clinical, however it may be radiologically confirmed by neck radiographs (face and profile), that should exclude other reasons of obstruction such as, a foreign body. The pathognomonic finding in CROUP is the conoid thinning of the subglottic part of the trachea (pencil- like sign), due to local edema in the region (1).
Recommended radiological examination:Neck radiograph(F+P)
· Tracheal and paratracheal masses
The frequency of
tracheal and paratracheal masses that influence the central airways is related
to the age of patients and the location of the lesion
(image 2).
Subglottic hemangiomas are the most frequent reason of obstruction of the
central airways due to soft tissue masses, in infants,[2].
Clinically, infants present respiratory wheeze and cough. Fifty per cent (50%)
of all cases with tracheal hemangiomas present dermal hemangiomas as well.
Subglottic hemangiomas are usually of round shape and eccentric location. The
radiological findings are not specific. Usually on CT, an eccentric pressure on
the trachea is illustrated which can help the differential diagnosis from
CROUP,
in which central stenosis of the trachea is seen.
Other uncommon tracheal and paratracheal masses are neuroblastomas, abscesses,
fibromas, mucocelles, chondromas, adenomas, neurinomas, histiocytosis,
rabdomyosarcomas and lymphomas.
In elder children, laryngeal papillomas are the usual reason of obstruction of the central airways. (2).
Recommended radiological examinations are: Chest radiograph and Computed Tomography of the neck and chest.
· Tracheomalacia
Tracheomalacia is a condition in which the walls of the trachea coincide due to absence, hypoplasia or malacia of the cartilaginous tracheal rings [3].
The trachea remains open during the respiratory circle despite the applied pressure, because of the presence of the cartilaginous rings. When these cartilaginous rings do not have the required rigidity, the walls of the inferior (mediastinal) part of the trachea coincide during the exhalation, meanwhile during the inhalation, the walls of the superior part of the trachea are the ones to coincide [ 4 ]. The best method for the diagnosis of tracheomalacia is fluoroscopy, with which changes in dimension of the trachea during inhalation and expiration are possible to be observed. Computed Tomography (with axial and coronal images), gives useful information as well, on the anatomy of the trachea and on it’s possible abnormalities. Finally, the technological evolution of Computed Tomographers (capability of 32 slices per second , multislice CT) [ 5 ], makes them offer brilliant diagnostic images of the trachea during the whole of the respiratory circle.
Tracheomalacia has been categorized by Benjamin[ 6 ] in primary and secondary type.
The primary type is infrequent. Connective tissue damages, as in hondromalacia and Larsen’s syndrome [ 3 ], are included among the reasons. The most common reasons of the secondary type of tracheomalacia are : wounding of the cartilaginous rings of the trachea by the endotracheal tube in intubated patients, exterior pressure of the trachea by vessels (mainly the anonymous artery), complications of other diseases like the tracheo-esophageal fistula and finally bronchopulmonary malformation.
Recommended radiological examination: Computed Tomography (multislice CT)
Obstruction of bronchi
· Cystic adenomatous dysplasia
Cystic adenomatous dysplasia is a rare, congenital cystic abnormality of the lungs. In most cases one lung or a lobe, is affected. The affected part of the lung presents multiple cysts and in some cases, lack of the normal bronchial tree may be seen. The imaging findings are characteristic on Computed Tomography, where multiple cysts are found along with puncuated opacities due to mucus retention (6). Moreover, compression of the adjacent normal lung is observed and the mediastinum is displaced to the opposite hemithorax.
Recommended radiological examination: Thorax CT.
· Lobar emphysema
Lobar emphysema is a congenital disease, which is characterized by hyperinflation of one or more lobes. The most oftenly affected lobes are: the left upper lobe (42 – 43%), the right medial (32 – 35%) and the right upper lobe (20%) (7). In 50% of all cases there is no obvious explanation, while in the rest, stenosis of the ipsilateral bronchus coexists, which results in growing “valve-like” emphysema.
It is very common that these patients, during the infancy present respiratory insufficiency (90%) (7). Radiologicaly the suffering lobe is found distended and of high radiolucency and the mediastinum is deviated to the opposite side (image 3).
Recommended radiological examinations: Chest radiograph, CT, thorax H.R.C.T.
· Endobronchial lesions
The most frequent causes of endobronchial obstruction during childhood are the aspiration of foreign bodies and the impaction of mucus. Other reasons, like granulomas due to tuderculosis or bronchial tumors, are infrequent.
Foreign bodies or mucus are usually impacted in main or lobar bronchi and obstructive or "valve-like" emphysema is the outcome. The foreign body acts like a valve, in a way that the air amount that enters the lung during the inhalation will not be released during the exhalation (2). Clinically, the patient presents an acute feeling of choking, dyspnea or cough and reduction of the respiratory whisper. In acute obstructive emphysema, the plain chest radiograph that is obtained during the phase of inhalation, is usually negative. On the contrary, if the chest x-ray is obtained during the phase of expiration, distention and high radiolucency of the suffering lung are observed. The mediastinum is displaced to the healthy lung (6).
Recommended radiological examinations: Chest radiograph and broncography.
· Ectogenic pressure of bronchi
The main causes of ectogenic pressure of bronchi in children, are vascular formations, enlarged lymphnodes and other mediastinal masses (image 4,5,6). The most frequent reason of vascular formation in infants is the double aortic arch. The diagnosis is easy, when the barium meal examination of the esophagus is performed. However for the precise appointment of vascular abnormalities, C.T and M.R.I of the mediastinum are of high diagnostic sensitivity and speciality [ 8 ].
Recommended radiological examination: Thorax CT
· Bronchiolitis
Bronchiolitis is an inflammation of small peripheral airways, the bronchioli. It is usually an acute ectogenic infection more often from syncytial virus or adenovirus [9]. The peripheral airways in infants and in young children are of smaller diameter in comparison to the airways of elder children and adults. When inflammation of the bronchioli takes place, edema and exudation will follow. This condition will provoke stenosis of the bronchioli lumen, which results in entrapment of air, mainly during expiration [10]. Clinically, bronchiolitis will provoke serious respiratory difficulty and intense cough.
On plain chest X-rays, the “ valve-like ” emphysema, which is developed due to the partial obstruction of the bronchioli by thick excretions, will be illustrated as lung hyper-inflation, widening of the intercostal spaces and depression of the diaphragm. Peribroncial thickening and perihilar opacities, due to inflammation of the bronchioli walls and the interstitial tissue, may also be illustrated [9]. The above findings are seen much better on C.T, particularly on H.R.C.T (image 7).
Recommended radiological examination: Thorax H.R.C.T.
· Asthma
Asthma is a chronic inflammatory disorder of the peripheral airways, that is characterized by reversible obstruction of them and hyper-reactivity to a variety of stimuli. This condition is characterized by bronchiospasm, that causes paroxysmal cough and dyspnea. The radiological findings depend on the stenosis of the bronchioli lumen [5].
On the chest radiograph, the consequences of the entrapment of the air at the expiration are: high lucency of the lungs, increasement of the anteroposterior diameter of the thorax, depression of the diaphragms and peripheral pulmonary attenuation. Chest X-rays will also exclude other possible causes of dyspnea as tumors, foreign bodies and complications of asthma, like pneumothorax, pneumomediastinum, arterial pulmonary hypertension and infections [8].
Recommended radiological examination: Chest radiograph.
· Bronchiectasis
Bronchiectasis are permanent dilatation of the bronchi or the bronchioli, due to destruction of elastic muscular fibres of the bronchi wall, due to chronic inflammation [11]. Depending on their form, bronchiectasis are distinguished in cylindric, sac-like and cystic. Moreover they are subdivided in congenital and in acquired.
Congenital bronchiectasis are found in the cystic fibrosis of lungs (image 8), which is the most frequent reason [12], and in various syndromes, like the Kartagener’s syndrome. Acquired bronchiectasis are usually complications of inflammation of the bronchi and the lungs. Other reasons of congenital bronchiectasis are the chronic obstruction of a bronchus by a foreign body or a benign tumor e.t.c
Most of the times, the findings on a radiograph are not specific. Cystic bronchiectasis might be seen as multiple cystic shapings containing fluid levels, because of the presence of air and excretions. Parallel linear opacities are also possible to be observed (tram-lines sign). Tubular opacities might be seen as well, due to peribronchial fibrosis and thickening of the bronchi walls (image 9,10,11). With the C.T, particularly the HRCT of the thorax, the various types of bronchiectasis are illustrated. HRCT is a method of high diagnostic sensitivity and constitutes the method of choice for the diagnosis of bronchiectasis [9].
Recommended radiological examination: Thorax H.R.C.T.
· Obstructive bronchiolitis
Obstruction of the peripheral airways from fibrous tissue is the reason of obstructive bronchiolitis. Obstructive bronchiolitis can be complete or partial. Fibrosis is developed as a result of inflammation and destruction of the bronchioli epithelium. Usual causes are inhalation of toxic substances, diseases of connective tissue, reactions to medicines e.t.c. The chest X-ray can be normal or highly radiolucent lungs can be revealed, peripheral pulmonary desolation and nodular or reticulo-nodular opacities.
The Swyer – James – McCloud syndrome is a unilateral obstructive bronchiolitis as a result of serious bronchiolitis in infants. On chest radiographs the affected lung is small in size and of high lucency or normal in size but with a small ipsilateral pulmonary artery [9].
Recommended radiological examination: Radiograph of thorax.
· Obstructive bronchiolitis in combination with organised pneumonia (BOOP)
BOOP is a lung disease, which is pathologically characterized by the deposition of granulous tissue in respiratory bronchioli with dilatation of the alveoli and growth of pneumonia [13]. This process can lead to formation of scar tissue and obstruction of small peripheral airways. The vast majority of BOOP cases are idiopathic. Other reasons are: inhalation of toxic substances, infections (e.g mycoplasma), reactions to medicines, connective tissue diseases, implant rejection. Diffuse opacities of “ground-glass” appearance and bronchi dilatations are illustrated on chest radiographs and on H.R.C.T. (image 9), (image 12).
Recommended radiological examination: Thorax H.R.C.T.
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