Pneumonia in children as it differs from adult pneumonia

Pneumonia

in Children

as it Differs

From Adult Pneumonia

John A. Kirkpatrick

T

HERE ARE DIFFERENCES in response to infection of the airways and pulmonary parenchyma in early life as compared to later life. These differences reflect in great measure anatomic factors, but immunologic factors are probably involved as well. Iii discussing pneumonia in the infant and young child, it is important to consider the context in which pneumonia may be encountered. In the neonate, it may be mistaken for hyaline membrane disease or fetal aspiration syndrome; later in infancy and childhood, the pneumonia may appear round and may therefore be confused with neuroblastoma. The natural history of pulmonary infection in early life may differ somewhat from the same disease encountered later. For example, staphylococcal pneumonia is a rapidly progressive process in the infant with the expected complications of empyema, pneumothorax, abscess formation, and pneumatocele. Furthermore, in this age group, infections of the upper airway are common and occasionally these infections are associated with pulmonary parenchymal alterations as well. Finally, there are conditions in which the initial insult to the lung is not infectious but chemical or mechanical, with subsequent infection, as in aspiration of a foreign body, ingested material, or hydrocarbon solution. At no time during life is it more important to relate history, signs, and symptoms to the radiographic findings than during infancy and early childhood. ANATOMIC

CONSIDERATIONS

The airways are developed by the 16th wk of intrauterine life. No further generations of airways arise after birth although the alveoli continue to proliferate and enlarge. The airways are small because the infant is small, but the peripheral generations of airways are probably

From the Department of Radiology, Harvard Medical School, Boston, Mass. Address reprint requests to John A. Kirkpatrick, Jr., M.D., Radiologist-in-Chief, The Children’s Hospital Medical Center, 300 Longwood Avenue, Boston, Mass. 021 IS. Q 1980 by Grune & Stratton, Inc. 0037-I

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smaller relative to the size of the central airways in the young child than in the adult. Thus, minor amounts of edema, mucus, or inflammatory debris may compromise or occlude bronchi or bronchioles, resulting in atelectasis or air trapping. The dynamics of respiration are much more apt to be disturbed in the infant and young child as a result of inflammatory disease than in the adult. The collateral pathways of ventilation are less well developed in infants. As a result, atelectasis distal to occlusion of bronchi or bronchioles is encountered more frequently in infants than in adults. It has been said that the airways of young infants contain more mucus glands than the airways of adults. Perhaps there are also differences in the chemical composition of mucus. Increased mucus production probably results in a greater potential for airway obstruction. The airways are soft and more collapsible in early life than later. Thus, forceful expiration, engorged vessels, edema, or exudate in the supporting structures of the lungs will result in compromise in caliber of the airways. In addition to these factors, during the first months of life, infection in the lungs is poorly localized and this may well be related to immunologic mechanisms5 As an example, overaeration of the lungs is to be expected in the first 12-18 mo of life as a result of a variety of infectious agents, viral or bacterial (Fig. 1). DIFFERENTIAL DIAGNOSIS OF PNEUMONIA RELATED TO AGE GROUP

In the neonate with respiratory distress who does not have a surgical lesion or cardiac anomaly, a number of abnormalities come first to mind. These include hyaline membrane disease and the fetal aspiration syndrome. In neither of these conditions is the initial radiographic examination pathognomonic. The newborn with hyaline membrane disease is apt to be premature and in respiratory distress at or soon after birth, and may radiographically demonstrate a fine pattern of density throughout the lungs that is confluent at the bases and is associated with an air bronchogram. These densities reflect atelectasis. Unfortunately, in the newborn period, infec-

Seminars in Roentgenology, Vol. XV, No. 1 (January),

1980

PNEUMONIA

Fig. age.

1. The

depressed. Patchy middle

IN CHILDREN

Viral

infection

lungs and

are the

atelectasis lobes, better

(bronchiolitis)

in a boy,

voluminous.

thorax

is

the increased

is evident in the seen in the lateral

5 mo

diaphragm in

AP

right upper film.

is

diameter. and

of

right

JOHN A. KIRKPATRICK

Fig. 2. Group B streptococcal pneumonia. The fine pattern of density throughout the lungs cannot be distinguished from the atelectasis of hyaline membrane disease in this 24-hr-old neonate.

tion with group B streptococcus may cause much the same symptomatology and roentgen appearance (Fig. 2).8 Only by thinking of this possibility will appropriate laboratory examinations be made to confirm the diagnosis. The presence of pleural effusion is not expected in hyaline membrane disease but is noted with some frequency in beta streptococcal infection. The patient with fetal aspiration syndrome is apt to be postmature and have respiratory distress. The roentgenogram usually reveals

Fig. 3. Fetal aspiration syndrome in a neonate, l-day-old. who was 2 wk postmature. The lungs show patchy areas of confluent density. The alterations are indistinguishable from pneumonia on this initial examination.

diffuse overaeration of the lungs with areas of linear and patchy confluent density throughout (Fig. 3).’ This roentgen appearance cannot be distinguished from that caused by a variety of infections acquired transplacentally. However, in the fetal aspiration syndrome the alterations are primarily related to the mechanical effects of aspirated squamous cells and meconium. As a result, over a period of hours the appearance of the lungs will change as the aspirated material is cleared from the airways and the areas of

PNEUMONIA

IN CHILDREN

Fig. 4. Round pneumonia. (A and Bl The rounded pleural-based area of consolidation posteriorly and medially in the right lung closely resembles a tumor. (C) Three days after initiation of appropriate antiobiotic therapy, there is partial resolution.

100

JOHN A. KIRKPATRICK

Fig. 6. Two patients with staphylococcal pneumonia. (A) This 18-mo-old infant has ampyama on the left. Less than 3 days earlier, the chest film showed segmental pneumonia in the left lower lobe with a small pleural effusion. (8) The initial pneumonia was on the right and was characterized bv. pleural fluid, abscesses. and then pneumothorax. Over a 7-day period, a . similar sequence occur&d on the left.

disturbed aeration become normal. Such rapid change cannot be expected in the patient with exudate in the alveoli and supporting structures of the lungs. A mass lesion in the posterior aspect of the thorax always raises the question of tumor, particularly neuroblastoma. In “round pneumonia,” often pneumococcal, staphylococcal, or klebsiellar, the alveolar exudate is pleural-based and rounded in configuration. It may at first be mistaken for neoplasm (Fig. 4). When a rounded shadow is associated with the clinical picture of pneumonia, it is important to observe the effects of treatment for pneumonia before additional studies are performed.4 NATURAL HISTORY OF STAPHYLOCOCCAL PNEUMONIA

Staphylococcal pneumonia in the infant and young child has a rapid, progressive course. The initial examination of the chest may reveal only diffuse overaeration of the lungs with a patchy confluent exudate in one or more portions of the lungs. This is followed within hours by the appearance of pleural reaction and exudate. Soon, the accumulation of exudate in the pleural cavity may be such as to fill one side of the thorax and displace the mediastinum to the opposite side. Bronchopleural fistula is common, so that pneumothorax or pyopneumothorax is to be expected. Pulmonary abscess may be encoun-

tered. As the pneumonia clears, one or more pneumatoceles may appear and persist for weeks (Fig. 5)’ UPPER AIRWAY

INFECTION

Infectious disease involving the upper airway may be associated with intrathoracic complications. The patient with viral croup may exhibit involvement of the bronchi, as well as disturbed aeration. In this instance, the obstruction of the upper airway results in underaeration of the lungs, often associated with diffuse interstitial exudate or patchy areas of bronchopneumonia. Epiglottitis caused by H influenzae type B is considered to be a disease predominantly of the upper airway.3 However, the organism may involve the lungs or the pleura (Fig. 6).6 The patient with infection and obstruction of the upper airway may present with signs and symptoms that suggest pneumonia, and roentgenograms of the chest may be the first examination. If there is underaeraction of the lungs or pulmonary edema, the possibility of upper airway obstruction should be considered. MECHANICAL OR CHEMICAL TO THE LUNGS

INSULTS

The patient who has suffered a mechanical or chemical insult to the lungs may present with signs and symptoms that suggest pneumonia or may later suffer from a secondary pneumonia.

PNEUMONIA

Fig. 6. pneumonia

IN CHILDREN

(A) Epiglottitis and empyema Type B.

101

(arrow) and (BI secondary to Ii

For example, the patient who aspirates a foreign body such as a peanut may develop a chemical pneumonia secondary to the vegetable foreign matter. Atelectasis may supervene, followed by signs and symptoms of pneumonia from secondary infection of the obstructed pulmonary tissue (Fig. 7). The patient who aspirates a chemical compound containing a hydrocarbon will initially develop parenchymal disease in the dependent portions of the lungs (Fig. 8). This may clear without complication or the involved area may become infected. A pneumatocele may appear as a consequence of the chemical injury

and simulate abscess formation. The patient who aspirates because of a central nervous system abnormality, as seen in the Riley-Day syndrome, or as a result of gastroesophageal reflux, will initially have changes secondary to mechanical and chemical factors, but again the involved areas may become infected. Of course, swallowed material may enter the airway via laryngotracheobronchial anomalies, such as laryngeal cleft or H-type fistula.’ CORRELATION

WITH

SIGNS

AND

SYMPTOMS

At no time during life is correlation of clinical information more important than in infancy.

JOHN A. KIRKPATRICK

Fig. 7. Infection from aspiration of a peanut 6 wk earlier in a I-yr-old boy whose early symptoms cleared. Recent onset of fever, cough, and rales on the right. There is atelectasis of the right lower lobe. Bronchoscopy revealed an obstructing peanut and infection distal to it.

Infection with group B streptococcus is often associated with maternal obstetric complications, such as premature rupture of the membranes, traumatic delivery, or maternal peripartum infection. Pulmonary infection with cytomegalovirus is associated with hepatosplenomegaly, chorioretinitis, microcephaly, and intracranial calcifications. Infection with rubella may be associated with involvement of other organ systems as well as the lungs, and there may be a history of maternal exposure to rubella during pregnancy. The overall evaluation of the neonate

and of the course of the pregnancy are important in pulmonary illness in early life. Another example of this correlation has to do with pulmonary infection with chlamydia trichomatis. This organism, having the characteristics of both a virus and a bacteria, may cause pulmonary infection in the first month of life. The radiographs are characterized by overaeration of the lungs and diffuse interstitial exudate. A diagnosis of pneumonia may be made from the chest radiograph but cannot be further characterized (Fig. 9). However, if it is known that the infant has been ill for a week or so; is suffering from conjunctivitis; is afebrile; and has an unusual cough similar to that associated with pertussis but without the whoop, then one may suggest the possibility of chlamydial infection and institute appropriate diagnostic procedures.’ Finally, it is important to look at more than the lungs in considering the possibility of pneumonia in an infant or a child. Other evidence of chronic or systemic disease must be sought. Is the thymus small? Are the bones osteopenic? Is there a decreased amount of fat about the thorax? Is aeration of the lungs disturbed, suggesting upper airway obstruction? Is there evidence of a mediastinal mass or compromise in the caliber of the trachea? Because of anatomic factors peculiar to the age group, one must recognize the fact that a variety of infectious and chemical agents may cause similar roentgen

Fig. 6. Hydrocarbon pneumonia. This infant, age 16 mo. drank 2 oz of turpentine while in the sitting position. The psrenchymal alteretions are in the dependent portion of the lungs.

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IN CHILOREN

103

Chlamydia trachomatis pneumonia in a 7-wk-old boy. Ovsraoration Fig. 9. diffuse patchy areas of confluence are present. The diagnosis was suspected Clearing was relatively slow but complete.

changes, the hallmark of which is disturbed aeration of the lungs in the first year or two of life. REFERENCES 1. Avery ME, Fletcher BD: The Lung and its Disorders in the Newborn Infant. Philadelphia, WB Saunders, 1974 2. Caffey J: Pediatric X-Ray Diagnosis, (ed 7). Chicago, Year Book Medical Publishers, 1978 3. Dunbar JS: Upper respiratory tract obstruction in infants and children. Am J Roentgen01 109:227-246, 1970

of the lungs, interstitial linear densities, and because of a peculiar cough and conjunctivitis.

4. Greenfield H, Gyepes MT: Oval-shaped consolidation simulating new growth of the lungs. Am J Roentgen01 91:125-131.1964 5. Griscom NT, Wohl MEB, Kirkpatrick JA Jr: Lower respiratory infections: How infants differ from adults. Radio1 Clin North Am 16:367-387, 1978 6. Jacobs NM, Harris VJ: Acute hemophilus pneumonia in childhood. Am J Dis Child 133:603-605, 1979 7. Vaughn VD III, McKay JR Jr, Behrman RE: Nelson Textbook of Pediatrics, (ed I I). Philadelphia, WB Saunders, 1979 8. Weller MH, Katzenstein AA: Radiological findings in group B streptococcal sepsis. Radiology 118:385-387, 1976