Lung masses in children comprise a spectrum of neoplastic, developmental, and acquired lesions (Table 5-1). Most pulmonary masses in children are developmental or inflammatory. Blastomycosis can cause a large, solid lung mass that has imaging features similar to those of a neoplasm. Congenital bronchopulmonary malformations are important considerations in young children with a lung mass. Metastatic disease is the most common malignant lung lesion in children. The most common primary lung neoplasms are carcinoid, plasma cell granuloma, and pleuropulmonary blastoma. Children with immunodeficiency are at elevated risk for Epstein-Barr virus-related smooth muscle tumors, lymphoma, and lymphoproliferative disorders.^1–3

Plasma Cell Granuloma

Plasma cell granuloma is a benign parenchymal lung mass that may not be a true neoplasm. This lesion appears to develop as part of a reactive process following a pulmonary insult such as infection. However, some investigators consider it to be a low-grade fibrous histiocytoma. Plasma cell granuloma is also termed postinflammatory pseudotumor, inflammatory pseudotumor, and inflammatory myofibroblastic tumor. Other names that have been applied to this lesion in the medical literature include fibrous histiocytoma, fibroxanthoma, xanthogranuloma, and sclerosing hemangioma.

The varied terminology applied to plasma cell granulomas reflects the variability in the histological characteristics of these lesions. There is a mixture of fibroblasts, histiocytes, lymphocytes, and plasma cells. Those lesions with a predominance of plasma cells are most compatible with a chronic inflammatory reaction to an underlying unidentified agent or an exuberant reparative process in response to a pulmonary infection. This pattern has led to the terms plasma cell granuloma and postinflammatory pseudotumor. Some lesions, however, have a paucity of inflammatory cells, and the histological characteristics suggest a true neoplasm, such as benign “fibrous histiocytoma.”^4,5

Plasma cell granuloma is the most common primary tumor of the lung in children. This lesion can occur in pediatric and adult patients of any age. Approximately one-third are identified in children; most pediatric patients with this lesion are older than 5 years of age. Plasma cell granulomas are often clinically silent; many are detected serendipitously on chest radiographs obtained for another medical indication. Potential clinical manifestations of the lesion include dyspnea, chest pain, hemoptysis, nonproductive cough, fever, and wheezing. Hypertrophic pulmonary osteoarthropathy can occur in associated with this lesion.⁶

Plasma cell granuloma of the lung has a varied radiographic appearance. A solitary sharply circumscribed peripheral lung mass (often in a lower lobe) is probably the most common finding (Figure 5-1). Plasma cell granuloma can range from a small subcentimeter nodule to a very large lesion occupying nearly the entirety of the hemithorax. Most, however, are approximately 3 to 4 cm in diameter at the time of presentation. Larger lesions may have lobulated borders (Figure 5-2). Necrosis and cavitation are rare. Contrast-enhanced CT may demonstrate a thick peripheral rim of prominent enhancement because of an inflammatory pseudocapsule (Figure 5-3). The remainder of the mass usually undergoes little contrast enhancement. Calcifications are present in many plasma cell granulomas in children. Optimal detection of calcification is with CT. The pattern of calcification varies from an amorphous mixed pattern to dense collections, usually scattered at various locations in the mass. These characteristics are usually distinct from the central target density pattern of calcification in granulomas and the popcorn pattern of calcification in hamartomas.^7–10

Plasma cell granuloma occasionally presents as a small noncalcified endobronchial mass; this can mimic the appearance of an endobronchial adenoma. Another atypical presentation is that of a locally aggressive lesion, sometimes termed invasive inflammatory pseudotumor. This is usually a large mass that encases bronchi and central pulmonary vessels. It may invade the chest wall, mediastinum, or diaphragm. Rarely, there is angioinvasion.

In addition to granuloma and hamartoma as described above, the differential diagnosis for children with a suspected plasma cell granuloma of the lung includes a primary lung tumor such as pleuropulmonary blastoma, a chest wall tumor, and a neoplasm of mediastinal origin such as germ cell tumor or neuroblastoma.

Pulmonary Hamartoma

Pulmonary hamartoma is a rare benign lung tumor that is most often identified in adults. This lesion does occasionally occur in children as young as infants, and has been detected in utero. A hamartoma is composed of otherwise normal tissue that is arranged in an abnormal configuration or that is foreign to the site of the tumor. Pulmonary hamartomas are often predominantly composed of cartilage and fat, sometimes with epithelium and muscle tissue as well. A fibrous capsule forms the peripheral margin. Endobronchial hamartomas tend to contain more fat than those located within the parenchyma; the endobronchial variant of this tumor is rare in children. Congenital cystic adenomatoid malformation, pulmonary hemangioma, and pulmonary chondroma all have features that make them part of the broad spectrum of hamartomatous lesions; however, these lesions are distinct from the “classic” pulmonary hamartoma described here.

Potential symptoms of pulmonary hamartoma include chronic cough, hemoptysis, and recurrent pneumonia. Endobronchial hamartomas are often inflamed, and there may be symptoms related to airway obstruction and infections. Imaging studies of pulmonary hamartoma show a round or oval sharply defined mass, with smooth margins (Figure 5-4). Most often, the lesion is an isolated pulmonary nodule less than 4 cm in diameter, but the size at the time of presentation can range from tiny to very large. CT is helpful for determining the character of the tissue in the lesion. Focal collections of fat or regions of fat alternating with foci of calcification are common; the presence of fat is an important consideration in limiting the differential diagnosis (Table 5-2). When substantial calcification is present, it may have a “popcorn” pattern, although this is a more common feature in adults than in children.¹¹

Pulmonary Mesenchymal Cystic Hamartoma

Pulmonary mesenchymal cystic hamartoma is an uncommon primary lung lesion that is quite similar to congenital cystic adenomatoid malformation. This lesion contains low cuboidal or columnar nonciliated epithelium, as does cystic adenomatoid malformation. However, the stroma of cystic adenomatoid malformation is composed of mature elements, whereas mesenchymal cystic hamartoma contains primitive mesenchymal cells. Malignant transformation to a primitive sarcoma can occur.^12–14

Mesenchymal cystic hamartoma can present at any age. Symptoms may be produced by mass effect. Spontaneous pneumothorax or hemoptysis can occur. This lesion is occasionally multiple or bilateral. Imaging studies show a multiloculated, air-filled, cystic lung mass that is indistinguishable from a congenital cystic adenomatoid malformation.

Papilloma

Papillomas are benign neoplasms of the tracheal or laryngeal epithelium that result from an upper airway infection with human papillomavirus type 6 or 11. These are the most frequent masses of the airway in older children. Papillomas tend to spread inferiorly from the larynx by direct extension, and may reach the major bronchi. Spread into the lungs occurs in less than 1% of cases. Endoscopy and surgical procedures of the airway in patients with laryngotracheal papillomas can result in distal airway embolization and implantation. Recurrent respiratory papillomatosis (juvenile laryngotracheal papillomatosis) refers to the recurrent growth of papillomas within the epithelium of the respiratory tract.

Imaging studies of airway papillomas show predominantly endoluminal lesions, with minimal submucosal infiltration. The radiographic appearance of pulmonary involvement is the presence of either solid (multiple nodules) or cystic parenchymal lung lesions; the central cavities in these lesions may contain debris or air (Figure 5-5). The pulmonary lesions are sometimes located peripherally in the lungs, remote from the major bronchi.¹⁵

Leiomyoma

Leiomyoma is a very rare, benign lung tumor in children. Children with acquired immune deficiency syndrome are at increased risk for development of this lesion; leiomyoma may be multifocal in these patients, with GI as well as pulmonary sites. Most leiomyomas develop in the lung parenchyma, and less than one-third present as endobronchial lesions. There are rare reported cases of respiratory distress in newborns as a result of a large pulmonary leiomyoma. An endobronchial leiomyoma has clinical and diagnostic imaging features identical to those of bronchial adenoma. Those that develop in the lung parenchyma are less apt to result in symptoms.^16–19