DUSTIN R. HAFERBECKER
HISTORY OF PRESENT ILLNESS
A 5-week-old boy presented to the emergency department with a one-day history of fever and “wheezing.” His visit to the hospital was prompted by a rectal temperature of 38.6°C. His respiratory difficulty seemed worse with feeding. There had been no emesis, diarrhea, rhinorrhea, cough, or cyanosis. He had been drinking approximately 4 ounces of a cow milk-based formula every 3 hours. His only ill contact was his mother who had cough and rhinorrhea for one week.
The boy was born by spontaneous vaginal delivery at 39 weeks gestation. His birth weight was 3900 g. The pregnancy, labor, and delivery were uncomplicated. Prenatal ultrasound revealed polyhydramnios but was otherwise normal. The mother’s prenatal laboratory studies included a negative group B Streptococcus screen. Testing for antibodies to human immunodeficiency virus had not been performed. The infant had not previously been hospitalized.
T 38.5°C; HR 180 bpm; RR 70/min; BP 62/40 mmHg; SpO2 96% in room air
Length 25th percentile; Weight 50th percentile
The infant was ill appearing with moderate respiratory distress. His anterior fontanelle was open and flat. There was no conjunctival injection or discharge. There was intermittent grunting and nasal flaring. Moderate intercostal and subcostal retractions were present. Breath sounds were diminished throughout the left chest. The right lung was clear to auscultation. There was no wheezing. The heart sounds were normal. The liver was palpable 1 cm below the right costal margin. The spleen was not palpable. The moro reflex, grasp, tone, and reflexes were normal. There were no rashes or petechiae.
Arterial blood gas revealed the following: pH, 7.40; PaCO2, 40 mmHg; PaO2, 214 mmHg; and bicarbonate, 26 mEq/L. Complete blood count demonstrated 37 900 white blood cells/mm3 (3% band forms; 67% segmented neutrophils; and 30% lymphocytes). The platelet count was 520 000/mm3 and hemoglobin was 9.4 g/dL. Serum electrolytes, blood urea nitrogen, and creatinine were normal. There were no white blood cells, protein, or nitrites on urinalysis. A blood culture was obtained. Lumbar puncture was not performed because of the patient’s respiratory distress. Chest radiograph demonstrated left lower lobe consolidation with an associated pleural effusion causing rightward shift of the mediastinal structures (Figure 1-4).
FIGURE 1-4. Chest radiograph.
COURSE OF ILLNESS
The patient was diagnosed with bacterial pneumonia and treated with vancomycin and cefotaxime. The blood culture was subsequently negative. CT scan of the chest, performed to better delineate the pulmonary findings, suggested an alternate diagnosis (Figure 1-5).
FIGURE 1-5. Chest CT scan.
DISCUSSION CASE 1-3
In this 5-week-old boy with respiratory distress and lobar consolidation, the most likely diagnosis is bacterial pneumonia with pleural empyema. Etiologic organisms in this age group include group B Streptococcus, Streptococcus pneumoniae, Listeria monocytogenes, and Gram-negative enteric bacilli. The radiographic appearance of the lung suggests a congenital lung malformation, such as pulmonary sequestration, bronchogenic cyst, and congenital cystic adenomatoid malformation. Infantile lobar emphysema is unlikely because the lung, despite causing mediastinal shift, does not appear to be overinflated. Other congenital considerations include enterogenic cysts and congenital diaphragmatic hernia. Acquired causes include mediastinal neoplasms, such as neuroblastoma and chronic pulmonary infection distal to an aspirated foreign body or an area of bronchiectasis. Chronic pulmonary infection may result in neovascularization of the infected tissue by ingrowth of systemic arteries. Such acquired systemic vascularization typically consists of several small arteries rather than one or two large arteries that typically supply a pulmonary sequestration. It may be impossible to make the distinction between true pulmonary sequestration and the so-called pseudosequestration secondary to chronic infection preoperatively.
CT of the chest (Figure 1-5) revealed a large (6 cm × 5 cm × 8 cm) heterogeneously enhancing mass with disorganized vasculature in the posterior aspect of the left hemithorax. These findings were most consistent with an extralobar pulmonary sequestration.
INCIDENCE AND ANATOMY
The term pulmonary sequestration refers to a congenital malformation consisting of abnormally developed pulmonary parenchyma that is separate from the normal lung. The tissue is nonfunctioning, does not communicate with the tracheobronchial tree, and derives its blood supply from the aorta. There may be a single large anomalous artery but occasionally multiple small anomalous arteries from above or below the diaphragm supply the sequestered lobe. The venous drainage may be pulmonary or systemic (inferior vena cava, azygous vein, or portal vein). Drainage into systemic veins produces a left to right shunt. In this case, the vessels appeared to drain into the azygous and hemiazygous veins.
The overall incidence of pulmonary sequestration is not well defined, but sequestrations have been found in 1% to 2% of all resected pulmonary specimens. Pulmonary sequestration occurs when an accessory lung bud originates during embryonic development. If the bud originates early, the sequestration is considered intralobar because the normal and sequestered lung shares a common pleural covering. If the bud originates later, the sequestration is considered extralobar because the sequestered lung has its own pleura. About 75% of reported cases of pulmonary sequestration are intralobar; 1% have both an intra- and extralobar component.
Associated malformations occur in 60% of extralobar sequestrations and 10% of intralobar sequestrations. The most common associated malformations include duplications of the colon or terminal ileum, esophageal cysts or communications, vertebral or rib anomalies, diaphragmatic hernia, and congenital heart disease (Table 1-4). Pulmonary sequestration is left-sided in 90% of cases and bilateral in fewer than 0.5% of cases. Approximately two-thirds of all cases involve the left lower lobe.
TABLE 1-4. Anomalies associated with pulmonary sequestration.*
*Anomalies are more common with extralobar (60% of patients) than with intralobar (10% of patients) pulmonary sequestration.
Most children with extralobar pulmonary sequestration present during the first year of life. They may be discovered during the neonatal period while undergoing evaluation for other congenital anomalies. In such cases, the associated congenital anomalies usually dominate the clinical picture. A few children with extralobar sequestration present with respiratory distress when the sequestered lobe impairs ventilation by impinging on the surrounding lung. Cases not diagnosed in the neonatal period may be detected incidentally on chest radiographs obtained during a respiratory illness. Infection of an extralobar sequestration is uncommon.
Intralobar pulmonary sequestration is rarely detected during infancy; two-thirds of cases present after 10 years of age. Common symptoms include productive cough, hemoptysis, recurrent pneumonia, fever, and chest pain. A few patients with large supplying arteries have worsening exercise tolerance or congestive heart failure because of a large systemic arterial-to-pulmonary venous shunt through the sequestration. Infection of the sequestration, usually because of a fistula between the sequestration and the respiratory or digestive tracts, occurs more commonly with intralobar as compared to extralobar sequestrations.
Physical examination reveals dullness to percussion and decreased breath sounds in the area of the sequestration. Digital clubbing and cyanosis may be present, depending on the presence and severity of shunting. Skeletal abnormalities such as pectus excavatum, thoracic asymmetry, and rib anomalies are noted in some patients. Rarely, an intrathoracic bruit is heard in the region of the sequestration.
Prenatal ultrasound. Pulmonary sequestration may be diagnosed during routine obstetric screening or during investigation of polyhydramnios, which is reported in many cases.
Chest radiograph. It is difficult to distinguish between intra- and extralobar sequestrations by chest radiograph alone. Both are typically found in the postero-medial aspect of the lower lobe and calcifications are occasionally present. Intralobar sequestrations more often appear cyst-like. Air-fluid levels indicate a pulmonary communication. Extralobar sequestrations appear as a solid mass.
Chest CT. CT enables differentiation of pulmonary sequestration from other lung abnormalities.
Magnetic resonance angiography (MRA) and computed tomography angiography (CTA). Both MRA and CTA have been shown to provide excellent anatomic details and are helpful in preparation for surgical resection.
Angiography. Angiography of the thoracic and abdominal aorta demonstrates both the systemic arterial blood supply and the venous drainage. This technique, however, is largely being replaced by less invasive methods as discussed above.
Nuclear scintigraphy. After intravenous injection, peak radioisotope activity occurs earlier in lung tissue with normal pulmonary blood supply than in the sequestration with systemic blood supply. Nuclear scintigraphy has been proposed as an alternative to traditional angiography.
Other studies. Magnetic resonance angiography is a less invasive study that may eventually replace traditional angiography in the evaluation of pulmonary sequestration. An upper gastrointestinal barium study should be considered to exclude the possibility of a communication with the gastrointestinal tract.
Symptomatic intralobar and extralobar sequestrations require immediate resection. Asymptomatic sequestrations also require removal because of the risk of subsequent serious infection. Extralobar sequestrations because of their separate pleural covering can often be removed without disrupting the normal lung. Intralobar sequestrations require lobectomy for removal because of the inability to separate the sequestration from the normal lung. In cases of acute infection, preoperative antibiotic coverage should be directed against common respiratory pathogens, Staphylococcus aureus, and anaerobes. Vancomycin or clindamycin in combination with third-generation cephalosporins (e.g., ceftriaxone, cefotaxime) provides appropriate empiric coverage. The resected tissue should be sent for aerobic and anaerobic bacterial cultures, mycobacterial cultures, and fungal cultures, as well as microscopic examination.
Intraoperative mortality is highest in those with associated congenital anomalies. Intraoperative complications are usually due to severance of a systemic artery. Postoperative complications include emphysema, hemothorax, and bronchopleural fistulae; the incidence of each is approximately 1%. The long-term prognosis in those without other debilitating congenital anomalies is excellent.
In this case, MR angiography was performed and the extralobar sequestration was removed without complications on the following day. Cultures of the resected sequestration were sterile. The patient recovered uneventfully.
1. Yu H, Li HM, Liu SY, et al. Diagnosis of arterial sequestration using multidetector CT angiography. Eur J Radiol. 2010;76:274-278.
2. Carter R. Pulmonary sequestration. Ann Thorac Surg. 1969;7:68-88.
3. Collin PP, Desjardins JG. Pulmonary sequestration. J Pediatr Surg. 1987;22:750-753.
4. Kravitz RM. Congenital malformation of the lung. Pediatr Clin North Am. 1994;41:453-472.
5. Lierl M. Congenital abnormalities. In: Hilman BC, ed. Pediatric Respiratory Disease: Diagnosis and Treatment. Philadelphia: W.B. Saunders; 1993:457-498.
6. Oliphant L, McFadden RG, Carr TJ, et al. Magnetic resonance imaging to diagnose intralobar pulmonary sequestration. Chest. 1987;91:500-502.
7. Savic B, Birtel FJ, Tholen W, et al. Lung sequestration: report of seven cases and review of 540 published cases. Thorax. 1979;34:96-101.
8. Stocker JT, Kagan-Hallet K. Extralobar pulmonary sequestration: analysis of 15 cases. Am J Clin Pathol. 1979;72:917-925.