Etiology: Pulmonary hamartoma, originally thought to represent a congenital lesion, is now considered a true benign mesenchymal neoplasm. It contains predominantly cartilage, fat, and fibrous tissue. Occasionally, pulmonary hamartoma may also have smooth muscle, bone, and entrapped respiratory epithelium, which grow slowly.² Pulmonary hamartoma is rare in children (the peak incidence is in the fourth to sixth decades); however, it is the most common primary benign pulmonary neoplasm accounting for 7% to 14% of all solitary pulmonary nodules in children.³ Ninety percent of pulmonary hamartomas are parenchymal in location. They usually present as incidental findings, although a large pulmonary hamartoma could cause respiratory distress.

Imaging: The typical radiographic appearance of pulmonary hamartoma is a smooth or slightly lobulated, solitary pulmonary nodule or mass, usually located in the peripheral portion of the lungs. Characteristic punctuate or popcorn-like calcifications may be seen in approximately 10%. On computed tomography (CT), it is typically a well-circumscribed pulmonary nodule that is less than 2.5 cm in diameter. Pulmonary hamartoma often contains fat or calcification, which, in a solitary pulmonary nodule, is considered diagnostic (Fig. 55-1).⁴

Treatment and Follow-up: Pediatric patients with pulmonary hamartoma require no further treatment unless it grows rapidly or the patient becomes symptomatic because of recurrent pneumonia or atelectasis caused by the mass effect from the tumor.⁵ In such situations, surgical resection is usually curative.

Etiology: Pulmonary chondroma is a benign tumor composed of a well-differentiated benign cartilage with lack of bronchial epithelium.⁶ Pulmonary chondroma tends to occur before 30 years of age (82%), mainly in young women (85%). Affected persons are usually asymptomatic. Pulmonary chondroma is associated with the Carney triad.⁷ This syndrome commonly affects three organs: (1) stomach (gastrointestinal stromal tumor, 75%) (Fig. 55-2, B), (2) lung (pulmonary chondroma, 15%), and (3) paraganglionic system (paraganglioma, 10%). However, tumors arising from the adrenal gland (adrenal adenoma or pheochromocytoma, 20%) and the esophagus (leiomyoma, 10%) have also been reported in association with the Carney triad. The majority of patients present with two of three neoplasms. Seventy-five percent of patients with the Carney triad have pulmonary chondroma(s).

Imaging: Pulmonary chondroma may be single (40%), multiple unilateral (25%), or bilateral (15%) without predilection for specific lobe or side of lung.⁷ Chest radiography usually shows well-demarcated, often multiple, lung masses with central or popcorn-like calcification (Fig. 55-2, A). When calcified (45%), the appearance of chondroma is indistinguishable from that of pulmonary hamartoma on imaging studies.

Treatment and Follow-up: Although surgical resection is sometimes performed, pulmonary chondroma may be left in situ because it is benign and usually indolent. Periodic screening of patients is currently recommended for metachronous development of paragangliomas or gastrointestinal stromal tumors.

Etiology: Recurrent respiratory papillomatosis (RRP) is characterized by mucosal papillomas, which are ingrowths of squamous cell–lined fibrovascular core in the lumen of central airways. It is the most common neoplasm that occurs in the larynx of children. RRP is caused by the human papilloma virus (HPV) types 6 and 11, which is typically acquired during vaginal birth. The primary lesions commonly affect the larynx but may spread to the lung parenchyma (1.8%) especially if surgical or laser therapy had been provided earlier.⁸ The ultimate prognosis is poor when pulmonary involvement occurs. Malignant transformation into squamous cell carcinoma may occur.⁹

Imaging: On chest radiography, RRP typically presents as bilateral, multiple nodular and cystic lesions of varying size containing air or debris. Postobstructive atelectasis, bronchiectasis, or secondary infection presenting as consolidation may be also seen.¹⁰ On CT, usually, scattered nodules are seen in the lungs (Fig. 55-3), and these nodules may enlarge, become air-filled cysts, or form large cavities with thin or thick walls.¹¹ CT virtual bronchoscopy may be useful to evaluate mural nodules within the central airways.

Treatment and Follow-up: The typical management of RRP in the central airway is by endoscopic surgery with cryotherapy, laser, or microdebrider treatment.¹² Intravenous cidofovir has been used recently for treating pulmonary involvement of RRP but with inconsistent results.¹³

Etiology: Lymphatic malformation, previously referred to as lymphangioma, is characterized by a benign proliferation of nonfunctional lymphatic tissue that may involve nearly every organ of the body. Only 1% of lymphatic malformations remain confined to the chest. Primary pulmonary lymphatic malformation is even less common.¹⁴ Affected persons are often asymptomatic. However, some may present with compressive symptoms such as cough, dyspnea, stridor, or even pneumothorax. Younger patients tend to have lesions that affect the lung.¹⁵

Imaging: On chest radiography, lymphatic malformation typically presents as a masslike opacity. The most common CT finding is a smooth, well-marginated, nonenhancing, cystic mass. In neonates and infants, this may simulate congenital pulmonary airway malformation (CPAM) or diaphragmatic hernia. Older children may have a solid, low-attenuation, masslike lesion that may mimic pneumonia or tumors (e-Fig. 55-4).

Treatment and Follow-up: Early surgical removal of lymphatic malformation is currently recommended to prevent local growth and the resultant compression of vital structures.¹⁶

Etiology: Plasma cell granuloma is the most common tumorlike abnormality in the lungs of children. It arises in the lung parenchyma but may also involve the mediastinum or pleura. Due to the complexity and variable histologic characteristics, it is known by several different terms, including inflammatory or postinflammatory pseudotumor, fibroxanthoma, myofibroblastic tumor, fibrous histiocytoma, xanthogranuloma, or histiocytoma.17,18 Recently, it has been termed inflammatory myofibroblastic tumor (IMT) because myofibroblasts, fibroblasts, and histiocytes are the main constituents of this tumor (Fig. 55-5, B).¹⁹ A substantial proportion of tumors have ALK1 gene mutations.²⁰ The World Health Organization (WHO) currently recognizes IMT as a low-grade mesenchymal malignancy. The majority of children with IMT are older than 5 years, although it has been reported in younger children and even infants. Approximately 60% of affected children are symptomatic, typically presenting with fever, cough, chest pain, dyspnea, wheezing, or hemoptysis.

Imaging: Radiographically, IMTs may be seen as solitary (95%) or multiple (5%). IMTs are usually sharply circumscribed, lobulated mass(es) of varying sizes, typically located in the peripheral portion of the lungs. IMT may occasionally be endobronchial. On CT, it usually presents as a soft tissue mass with either homogeneous or heterogeneous attenuation (see Fig. 55-5, A). Although IMT does not enhance substantially, a thick enhancing rim has been reported. Less commonly, it may present with both solid and cystic components. IMT may also have an infiltrative pattern simulating an aggressive malignancy.²¹ If the mediastinum is involved or the mass contains calcifications (15% to 25%), IMT may mimic a germ cell tumor, neuroblastoma, or metastatic osteosarcoma in pediatric patients.

Treatment and Follow-up: Complete surgical resection is the treatment for IMT typically leading to excellent results. Irradiation, chemotherapy, and antiinflammatory medications have been proposed as adjuvant therapies but have not been successful in most patients.

Etiology: Mucosa-associated lymphoid tissue (MALT, or pseudolymphoma) is rare in children. Affected persons generally are not severely ill but may have nonspecific respiratory symptoms. Lymphoma has been reported to develop in some cases of MALT. It may be quite difficult to clearly differentiate pseudolymphoma from a true lymphoproliferative condition, even by using modern immunofluorescence techniques. Experts currently disagree about whether MALT should be considered a premalignant or a postinflammatory condition. Bronchus-associated lymphoid tissue (BALT) is a subcategory of the more widely distributed MALT. BALT is a lymphoid aggregate located in the submucosal area of bronchioles, which may become hyperplastic because of chronic antigen stimuli.²² It has been suggested that BALT is related to a hypersensitivity response to unidentified antigens. BALT has two forms: (1) lymphoid interstitial pneumonia and (2) follicular bronchitis or bronchiolitis. Lymphoid interstitial pneumonia type BALT is commonly seen in pediatric patients with acquired immunodeficiency syndrome (AIDS) or other immune compromise. Follicular bronchitis or bronchiolitis type of BALT typically occurs in children with chronic infection, connective tissue disorders, or immunodeficiency disorders and as a hypersensitivity reaction.

Imaging: On chest radiography, MALT typically presents as discrete, often multiple lesions, usually with air bronchograms ranging from 2 to 5 cm in diameter. A pleural effusion is commonly seen. A diffuse reticulonodular opacity, often associated with hyperinflation, is the common radiographic finding of BALT (e-Fig. 55-6, A). On CT, the usual imaging appearance of BALT consists of small centrilobular nodules (foci of lymphoid proliferation) and a ground-glass opacity predominantly involving the lower lobes (see e-Fig. 55-6, B). In patients with advanced BALT, bronchiectasis and peribronchovascular consolidation caused by recurrent infection and chronic airway obstruction may present.

Treatment and Follow-up: Aggressive management (e.g., complete surgical excision, radiotherapy, chemotherapy, or a combination of all of these) is the current treatment of choice for MALT. Because of the wide extent of disease often associated with BALT, surgical excision may be considered only for a minority of patients. Chemotherapy is the treatment of choice for the majority of patients with BALT.

Etiology: Lymphocytic interstitial pneumonitis (LIP) is characterized by diffuse proliferation of polyclonal lymphocytes and plasma cells in the pulmonary parenchymal interstitium, which expands to the alveolar septa. It is considered an AIDS-defining illness in children younger than 13 years old who are infected with HIV because LIP is rarely idiopathic.

Imaging: On chest radiography, LIP typically presents with reticular or reticulonodular opacities predominantly in the bilateral lower lung zones.²³ On high-resolution CT, diffuse centrilobular and subpleural nodules (representing local proliferation of lymphoid germinal centers), areas of ground-glass opacity, and bronchovascular and interstitial thickening in both lungs are often seen (Fig. 55-7). Thin-walled cysts and bronchiectasis may be also present.²⁴

Treatment and Follow-up: Steroid and other immunosuppressive agents are used for treating LIP with variable results. Prognosis of children with LIP depends on the associated underlying disease. Progressive honeycomb fibrosis or infectious complications may lead to increased mortality. Low grade B-cell lymphoma may develop in rare cases.²⁵

Etiology: Lymphomatoid granulomatosis, also known as pseudolymphoma, angiocentric lymphoma, or angiocentric immunoproliferative lesion, is characterized pathologically by an angiocentric and angiodestructive lymphocytic infiltration. It is considered an aggressive multisystem disease with a poor prognosis. The lung is often the primary site of involvement. This disease is associated with Epstein-Barr virus (EBV) infection in immunocompromised individuals. Progression of lymphomatoid granulomatosis to lymphoma occurs in 12% to 47% of patients, with the mortality rate over 50%.²⁶

Imaging: On chest radiography, bilateral, poorly defined, nodular and confluent lesions with a basilar predominance are usually seen (e-Fig. 55-8). Characteristic CT findings of lymphomatoid granulomatosis include peribronchovascular distribution of nodules (which reflects the tendency of lymphomononuclear cells to infiltrate the subintimal region of medium-sized arteries and veins), small thin-walled cysts, and conglomerate small nodules.^24,27 Lesions may cavitate, mimicking Wegener granulomatosis.

Treatment and Follow-up: Lymphomatoid granulomatosis may be resistant to ordinary chemotherapy. Retuximab, combined with other conventional chemotherapy, has been used with promising results.²⁸

Etiology: Posttransplantation lymphoproliferative disorder (PTLD) is a consequence of chronic immunosuppression following solid organ transplantation or, less often, bone marrow transplantation.29–32 It is believed to be induced by exposure to EBV. The lesions consist of uncontrolled proliferation of B lymphocytes ranging from benign lymphoid hyperplasia to invasive malignant lymphoma. The incidence of PTLD (1% to 18%) varies with the type of organ transplanted. It occurs most frequently in lung or heart-lung transplantation patients, likely because of the higher levels of immunosuppression required for these organ transplantations.^29,33–35 It is also more common in pediatric patients than in adult transplantation patients, possibly because of the lack of prior exposure to EBV. Improved surveillance, earlier diagnosis, and close monitoring of immunosuppression have led to a decreased incidence of PTLD in recent years, as well as a more favorable outcome. The most common sites for PTLD are the tonsils, cervical nodes, gastrointestinal tract, and the chest.^36,37 Intrathoracic PTLD tends to present earlier compared with extrathoracic PTLD. PTLD tends to occur within the allograft organ itself, as well as in adjacent anatomic regions.³⁸ Heart transplantation is the sole exception to this predilection.³⁹ Clinical symptoms of PTLD are often vague and include lethargy, fever, and weight loss. Biopsy is typically required to confirm the diagnosis.

Imaging: The imaging appearance of PTLD is not specific and overlaps with that of many opportunistic infections. On chest radiography, the most common finding in PTLD is the presence of multiple well-defined pulmonary nodules with or without mediastinal adenopathy (Fig. 55-9).³⁹ These are best visualized on CT. Large pulmonary nodules and mediastinal adenopathy tend to show central low attenuation, likely representing necrosis. Other less frequent patterns of thoracic involvement include air space consolidation, pleural or chest wall masses, pleural or pericardial effusions, and thymic enlargement.^40–42 For a more confident diagnosis, it is helpful to search for extrathoracic PTLD such as thickening of bowel loops, enlarged abdominal lymph nodes, cervical adenopathy, or enlarged oropharyngeal lymphatic tissues.^39,43 Fludeoxyglucose positron emission tomography or CT may also increase sensitivity and specificity for the diagnosis.⁴⁴

Treatment and Follow-up: Reduction in immunosuppressive therapy remains a primary component of treatment for EBV-positive PTLD, which may lead to resolution of disease in the majority of cases.⁴⁵ Chemotherapy is used when reduced immunosuppression fails to control disease progression. Newer treatments of PTLD include B-lymphocyte–depleting antibodies, adoptive T-cell immunotherapy using allogeneic, or autologous EBV-specific cytotoxic T-lymphocytes.⁴⁶ EBV vaccination is advocated to be effective prophylaxis against PTLD.

Etiology: The term bronchial adenoma, which implies a benign disease process, was recently recategorized as either carcinoid or salivary gland tumors by the WHO.⁴⁷ Historically, bronchial adenomas encompassed bronchial carcinoid tumor, mucoepidermoid tumor, and adenoid cystic carcinoma. Carcinoid tumor accounts for approximately 80% of previously classified pediatric bronchial adenomas, which are low-grade neuroendocrine carcinoma arising in lobar bronchi (75%), main stem bronchi (10%), or the lung parenchyma (15%).^48–50 Mucoepidermoid carcinoma (e-Fig. 55-10) and adenoid cystic carcinoma (cylindromas) (Fig. 55-11) arise from the salivary-type mucous cells of the submucosa along the tracheobronchial tree. Adenoid cystic carcinoma is extremely rare in children.⁵¹ Patients with carcinoid tumor and mucoepidermoid carcinoma frequently present with wheezing, cough, hemoptysis, or pneumonia.^48,52,53 Association with the carcinoid syndrome in children with carcinoid tumor is exceedingly rare. The differential diagnosis of these rare tumors includes foreign body aspiration, granulomatous infection, and asthma with mucus plugging.

Imaging: The radiographic presentation depends on the size and location of tumor within the airway or lungs. A centrally located tumor is typically seen as an intraluminal soft tissue attenuation mass with associated distal atelectasis or obstructive pneumonitis. A peripherally located tumor is commonly seen as a sharply marginated, oval, or lobulated intraluminal or exophytic mass.54–58 Associated stippled calcification is seen in up to 30% of carcinoid tumors. CT is particularly helpful for detecting and defining extrabronchial portion of the tumor and associated adenopathy.

Treatment and Follow-up: The current treatment of choice is surgical resection. Chemotherapy and radiotherapy are reserved for tumors with incomplete surgical resection. Overall survival rate for carcinoid and mucoepidermoid carcinoma is approximately 90%, whereas adenoid cystic carcinoma has a poorer survival rate of 55% because of higher likelihood of distant metastases.⁵⁹

Etiology: Traditionally, the term bronchogenic carcinoma has been used to include both small cell and non–small cell lung cancers (including squamous cell carcinoma, large cell carcinoma, and adenocarcinoma). These tumors are very rare in childhood. In the most recent WHO classification guideline, the term bronchogenic carcinoma is not used and each tumor type is listed individually.⁴⁷ Among these tumors, adenocarcinoma is the most common in children.⁵¹ Most children with adenocarcinoma present with advanced disease, which results in high mortality. Small cell carcinoma, squamous cell carcinoma, and large cell carcinoma are very rare in children.^60,61

Imaging: On chest radiography, these tumors often present as a solitary pulmonary nodule or central mass, often associated with postobstructive atelectasis or consolidation (e-Fig. 55-12). On CT, the attenuation and enhancement of masses vary substantially among different types of tumors. Concomitant mediastinal or hilar adenopathy as well as malignant pleural effusion may also present. Aggressive tumors may also invade adjacent mediastinal or osseous structures.

Treatment and Follow-up: Surgical resection often combined with subsequent chemotherapy and radiotherapy is the current management of choice. Unfortunately, bronchogenic carcinoma of childhood has been known for its unusually rapid disease course with early metastases.

Etiology: Pleuropulmonary blastoma (PPB) is an embryonal tumor of the lung, and it only occurs in young children. Over 90% of affected patients are below 6 years old at diagnosis. It recapitulates the morphogenesis of the fetal lung and may be regarded as a dysontogenetic analog to Wilms tumor, neuroblastoma, and hepatoblastoma. PPB contains primitive mesenchyma and varying degrees of more mature cartilage, skeletal and smooth muscle, and fibrous tissue. PPB is associated with hereditary tumor predisposition syndrome. Of the affected children, 25% to 30% have family members at risk of other dysplastic and neoplastic conditions.⁶² The three PPB types are (1) type I (purely cystic with primitive mesenchymal cells beneath an intact epithelium), (2) type II (cystic and solid, mesenchymal cells overgrow the septa), and (3) type III (purely solid, complex sarcomatous neoplasm). Type I lesions occur earlier at a median age of 9 months and have a more favorable prognosis, with 85% to 90% overall survival rate.⁶³ Type II and III lesions occur at a median age of 36 and 42 months, with an overall survival of 60% and 45%, respectively.⁶⁴ It has been suggested that PPB is probably the same malignant tumor that has been reported in previous studies as mesenchymal sarcoma, malignant mesenchymoma, embryonal sarcoma, primary pulmonary rhabdomyosarcoma, embryonal sarcoma, primary pulmonary rhabdomyosarcoma arising in congenital lung cysts, or pulmonary blastoma in children.^65,66 Current data support the assertion that congenital lung cysts do not degenerate to become PPB but that cystic type I PPB may progress to more aggressive type II or type III PPB.^67–71 PPB may metastasize to the central nervous system, bone, and liver.

Imaging: Imaging appearances of PPB depend on the type. PPBs present as solid, cystic, or mixed lesions. On chest radiography, the tumor may appear as a nodule or small mass that rapidly grows or as a large mass occupying the hemithorax. A large PPB may often result in mass effect on mediastinal structures. On CT, type 1 PPB is typically a cystic lesion often associated with multiple septations (Fig. 55-13), whereas type 3 PPB is a heterogeneously enhancing solid mass. Type 2 PPB has a combination of both cystic and solid components (Fig. 55-14). Type 1 PPB is often indistinguishable from CPAM on the basis of radiologic evaluation.⁷² Approximately, 25% of patients with PPB have other embryonal tumors, most commonly renal cystic nephroma.^73,74 Other tumors less commonly seen in patients with PPB include medulloblastoma, thyroid dysplasia, germ cell neoplasms, and ovarian teratoma.⁷⁵

Treatment and Follow-up: The current treatment of choice for PPB is lobectomy or pneumonectomy.⁷⁶ Chemotherapy and local radiotherapy are adjuvant therapies if residual disease is present. Many congenital cystic lung lesions are removed surgically because of the risk of recurrent infection and the possibility of underlying neoplasm. Lesions that are not removed should be monitored closely. If the cystic lesion develops a solid component or if a family history of pediatric neoplasm exists, surgical resection is recommended.

Etiology: Pulmonary epithelioid hemnagioendothelioma (PEH) is a rare tumor arising from endothelium with borderline malignant potential. PEH was first described by Dail and Liebow in 1975 as an intravascular bronchoalveolar tumor that may affect bone, soft tissue, liver, and lung. Later studies revealed that intravascular bronchoalveolar tumor and PEH are different manifestations of the same disease.77,78 Although most of the affected patients are adult women, it may also occur in children.⁷⁹ The majority of patients are asymptomatic, and lesions are typically detected incidentally.⁸⁰

Imaging: On chest radiography, PEH typically presents as bilateral multiple pulmonary nodules ranging from 5 mm to 2 cm in diameter (e-Fig. 55-15, A). Some patients may present with a solitary lesion. Concomitant hilar adenopathy and pleural effusion are seen in less than 10% of cases.⁸¹ On CT, multiple well-defined or ill-defined perivascular nodules located near medium-sized vessels and bronchi are usually seen (see e-Fig. 55-15, B). Some pulmonary nodules may show calcification.^82,83

Treatment and Follow-up: Surgical resection is preferred in patients with solitary or a limited number of pulmonary lesions localized within the one lobe. Chemotherapy, radiotherapy, and interferon are other treatment choices that are associated with variable results.⁸⁴ Close follow-up with no active therapy is usually used for asymptomatic patients with multiple lesions.⁸⁰ Recently, vascular endothelium growth factor was proposed as a potential treatment for PEH.

Etiology: Pulmonary metastatic disease most often occurs hematogenously via the pulmonary arterial system. However, it may also occur via lymphatics, airways, or direct invasion. Pediatric tumors that have a propensity to metastasize to the lung are listed in the order of frequency by anatomic system in Table 55-5.

Imaging: On imaging studies, most metastatic lesions are seen as round and sharply marginated and of homogeneous soft tissue attenuation. They tend to be located subpleurally in the outer two thirds of the lung. Metastatic lesions often appear to be directly contiguous with a pulmonary artery branch, reflecting their hematogenous origin. A greater number of metastatic lesions are located at the lung bases rather than in the upper lobes, likely because of gravity-dependent increased basilar blood flow. Lymphangitic tumors usually present as reticular or reticulonodular opacities on chest radiography. Thickening of interlobular or interlobar septa and bronchovascular bundles are often seen on CT of children with lymphangitic tumor spread.

CT is sensitive but not specific in detecting pulmonary metastasis. No specific CT features (e.g., location, attenuation, size, margin characteristics) can reliably distinguish benign lesions from malignant pulmonary lesions. However, in general, solitary pulmonary lesion larger than 5 mm in diameter with sharp margins, especially when multiple, are usually malignant.⁸⁵ Pulmonary nodules that decrease in size during antineoplastic therapy are usually assumed to be malignant, whereas those that decrease in size without therapy or remain stable during 12 months of follow-up are likely benign.

Although the imaging appearances of the majority of metastastic pulmonary nodules are nonspecific, some primary tumors may have a characteristic appearance of pulmonary metastasis. Metastatic osteosarcoma may ossify (Fig. 55-16), cavitate, or present with acute pneumothorax. Lymphangitic spread is most commonly seen in children with rhabdomyosarcoma, neuroblastoma, and lymphoma.

Treatment and Follow-up: Pulmonary metastases have been reported in 10% to 20% of patients with osteogenic sarcoma at initial diagnosis. Approximately 40% to 55% of patients with nonmetastatic osteosarcoma develop lung metastases in the later stages of the disease.86–90 Number, distribution, and timing but not the size of lung metastases are of prognostic value for survival.^91,92 The best treatment for this group of patients is a combination of metastatectomy and adjuvant chemotherapy.^93,94

The lung is the most common site of metastatic disease in children with Wilms tumor. Traditionally, treatment strategy for metastatic Wilms tumor has been based on lung lesions detectable with chest radiography. Currently, controversy exists over the optimal way for managing small pulmonary lesions that are detected only with CT and are not apparent on chest radiography because of the potential lung toxicity associated with aggressive therapy.⁹⁵ Previous studies^96,97 suggested that majority of these pulmonary lesions represent metastases and patients with these lesions probably require more potent chemotherapy than those children without metastatic disease.⁹⁸

Etiology: Approximately 20% to 60% of patients with leukemia have histologic evidence of lung involvement at autopsy; but fewer than 5% of these patients present with lung abnormality suggesting leukemic infiltrates on chest radiography.⁹⁹ Pulmonary involvement of leukemia is most often seen in patients with acute monocytic and myelogenous leukemia.¹⁰⁰

Imaging: On chest radiography, leukemic infiltrates usually show a diffuse reticular pattern of opacities (Fig. 55-17). Pulmonary nodules and focal homogeneous opacities are also reported in patients with leukemic involvement of lungs. On CT, interstitial thickening in peribronchial distribution, small pulmonary nodules in centrilobular or peribronchovascular distribution, and focal areas of consolidation are common imaging findings.^101,102

Treatment and Follow-up: Lung biopsy is required for a definitive diagnosis of lung involvement from leukemia. Once the diagnosis is established, chemotherapy is currently the treatment of choice in pediatric patients with pulmonary leukemic involvement.¹⁰³

Etiology: The lung is not commonly involved in lymphoma; involvement is 12% with Hodgkin disease (HD) and 10% with non-Hodgkin lymphoma (NHL) in pediatric patients. Lung involvement is almost always seen at initial presentation rather than at disease relapse.¹⁰⁴ In both HD and NHL, the underlying mechanisms of lung involvement from lymphoma are hematogenous spread, lymphangitic dissemination, and, less frequently, direct invasion.

Imaging: Lung involvement of lymphoma in pediatric patients typically presents as one of three patterns: (1) presence of single or multiple pulmonary nodules with irregular borders and sometimes central cavitation, which is the most common radiographic pattern (Figs. 55-18 and 55-19); (2) reticular interstitial opacities, which result from venous or lymphatic obstruction caused by hilar or mediastinal adenoapthy, or from interstitial tumor deposition; and (3) lobar or segmental consolidation, which may mimic an infectious process.^105–108 Occasionally, multiple tiny pulmonary nodules in a miliary pattern in children with HD may simulate miliary tuberculosis.^109,110 Pleural effusion is found in less than 5% of children with lymphoma.

Although the imaging appearance of lung involvement in children with HD and NHL is similar on imaging studies, lung involvement is usually concomitantly present with mediastinal or hilar lymphadenopathy in children with HD, whereas lung involvement may occur without associated lymphadenopathy in NHL.105,111

Treatment and Follow-up: Chemotherapy is the current treatment of choice. Although infection is more common in pediatric lymphoma patients, especially those undergoing treatment, development of new pulmonary lesions with a poor response to antibiotics may represent lymphoma lesions and therefore should promptly be biopsied for a definitive diagnosis. Pulmonary lesions from lymphoma usually decrease in size, disappear, or leave a parenchymal scar after chemotherapy treatment.¹¹²