Defectos de la pared toraxica by Eric Maldonado

Residents’ Section • Pat tern of the Month Baez et al. Chest Wall Lesions in Children

Residents’ Section Pattern of the Month

Residents

inRadiology Juan C. Baez1 Edward Y. Lee2 Ricardo Restrepo 3 Ronald L. Eisenberg 4 Baez JC, Lee EY, Restrepo R, Eisenberg RL

Chest Wall Lesions in Children

esions can arise from all components of the chest wall. Although there is overlap with processes in the adult population, many of the chest wall lesions are unique to the pediatric population (Table 1). Radiography after physical examination is generally the initial imaging modality in assessing chest wall lesions in children. This is often followed by ultrasound, which is especially valuable because it provides the radiologist the real time ability to examine the patient, palpate the area of concern, and scan the site of interest directly. CT or MRI may subsequently be required for confirmation and further characterization of a chest wall lesion. By combining the clinical history, physical examination, and imaging findings, the radiologist can localize a lesion and arrive at a differential diagnosis. In some cases, it is possible to make a specific diagnosis, thus sparing the child further workup or unnecessary treatment.

Congenital or Developmental Abnormalities Prominent Costal Cartilage

Keywords: chest wall, pediatrics DOI:10.2214/AJR.12.8883 Received February 29, 2012; accepted after revision May 22, 2012. 1 Department of Radiology, Brigham and Women’s Hospital and Harvard Medical School, Boston, MA. 2 Department of Radiology, Boston Children’s Hospital and Harvard Medical School, Boston, MA. 3 Department of Radiology, Miami Children’s Hospital, Miami, FL. 4 Departmet of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, 300 Brookline Ave, Boston, MA 02215. Address correspondence to R. L. Eisenberg (rleisenb@bidmc.harvard.edu).

WEB This is a Web exclusive article. AJR 2013; 200:W402–W419 0361–803X/13/2005–W402 © American Roentgen Ray Society

W402

Normal variations in chest wall anatomy, such as prominent costal cartilage, are a common source of concern if not correctly identified. These pseudolesions, which often come to medical attention when palpated by either a parent or examining physician, are typically painless and nontender. Based on the anatomic CT criteria used by Donnelly et al., costal cartilage is prominent when its anteroposterior diameter is ≥ 3 mm larger than the contralateral cartilage at the same level. Prominent costal cartilage and related anatomic variations (such as prominent convexity of the anterior rib and sternal tilt) are identified in up to 33% of the general population. Without underlying malignancy or immunodeficiency, the diagnosis of prominent costal cartilage is usually made clinically without the need for imaging. In the few asymptomatic cases that proceed to imaging, radiography with placement of a BB marker at the palpable site or a focused ultrasound evaluation can often exclude the possibility of underlying pathology. Further imaging evaluation with either CT or MRI, although rarely needed, can also directly visualize the underlying prominent but normal cartilage (Fig. 1).

Pectus Excavatum Pectus excavatum, a variant in chest wall development, refers to depression of the sternum relative to the rest of the anterior chest. The sternum often tilts rightward and the ribs protrude more than expected. In many cases, the clinical significance of this deformity is purely cosmetic. Severe cases, however, can result in pain, dyspnea, and restrictive lung disease. The incidence of pectus excavatum in the general population is between 1:400 and 1:1000. The leftward mediastinal shift of pectus deformity creates a pseudoinfiltrate to the right of the cardiac silhouette related to greater visibility of the hilar vessels (Fig. 2A). The sternal depression can be directly visualized on the lateral radiograph (Fig. 2B). In an effort to quantify the severity of the pectus deformity, the Haller index is calculated by dividing the maximal transverse diameter of the chest by the anteroposterior diameter of the chest from the vertebral body to the sternum (Fig. 3). A value < 2.56 is considered normal, whereas a measurement > 3.25 often leads to surgical correction. Mild pectus deformities with a Haller index between 2.56 and 3.25 typically do not require surgical correction; however, there is currently no established guideline for managing pediatric patients with mild pectus deformity. Although the Haller index was initially derived using routine CT, low-dose CT with a limited slice number (e.g., 5–7 axial images), radi-

AJR:200, May 2013

Chest Wall Lesions in Children TABLE 1: Chest Wall Lesions in Children Congenital or developmental abnormalities

Prominent costal cartilage Pectus excavatum Pectus carinatum Neoplasm Benign soft tissue tumors Infantile hemangioma Infantile fibrous hamartoma Inflammatory myofibroblastic tumor of the lung (inflammatory pseudotumor) Benign osseous tumors Osteoid osteoma Osteochondroma Fibrous dysplasia Mesenchymal hamartoma Malignant soft-tissue tumors Rhabdomyosarcoma Malignant peripheral nerve sheath tumors Pleuropulmonary blastoma Malignant osseous tumors Ewing sarcoma family of tumors Osteosarcoma Metastatic disease (most common) Neuroblastoma Rhabdomyosarcoma Lymphoma or leukemia Infection Bacterial infection Fungal infection Chronic recurrent multifocal osteomyelitis Trauma Accidental trauma Nonaccidental trauma (child abuse)

ography, and MRI using a single sequence in the axial plane are currently available alternative imaging techniques to either decrease or eliminate the ionizing radiation associated with CT. A recent study showed that 3D volume-rendered CT can help guide management and alter surgical planning in patients with pectus excavatum. CT also shows the typical rightward tilt of the sternum and often identifies a soft-tissue nodule at the inferior sternum. This soft-tissue nodule is thought to represent an island of cartilaginous tissue. Pediatric patients with severe pectus excavatum typically undergo surgical correction. Most commonly, a convex metal bar can be placed behind the sternum to fix the deformity (Nuss procedure) (Fig. 4). The metallic bar may become either infected or dislocated, requiring follow-up radiographic evaluation. The Ravitch procedure involves resecting the deformed cartilages and a wedge osteotomy of the upper sternal cortex, at times with the use of materials to fix the lower sternum. An additional method involves resecting portions of the costal cartilage and resuturing the stumps to the sternum.

Pectus Carinatum In contradistinction to the inward displacement of the sternum in pectus excavatum, pectus carinatum (or pigeon breast) is defined as anterior protrusion of the sternum. This condition occurs AJR:200, May 2013 W403

Baez et al.

less frequently than pectus excavatum, with an incidence of 1:1500 live births. A male predominance (4:1) has been reported, with nearly one third of cases associated with scoliosis and a smaller percentage with congenital heart disease. As with pectus excavatum, there is a genetic component in pectus carinatum and an association of this anatomic variant with numerous conditions such as Marfan disease, Noonan syndrome, prune belly, Morquio syndrome, osteogenesis imperfecta, mitral valve prolapse, and homocystinuria. In addition to the cosmetic deformity, pectus carinatum can manifest clinically as shortness of breath and exercise intolerance. Two variants of the condition have been described. Fig. 1—Prominent costal cartilage in 13-year-old Most commonly, there is protrusion of the boy with focal painless bump in lower anterior chest wall for 3 months. Unenhanced axial CT image of middle and lower sternum in cases of chonchest shows focal protrusion at costosternal junction drogladiolar deformity. A less common varidue to prominent costal cartilage (curved arrow) ant is chondromanubrial deformity, in which and parachondral nodule (straight arrow), likely the manubrium and upper sternum protrude representing cartilage rest. anteriorly. Distinguishing between the two variants helps guide surgical management. The imaging characteristics of pectus carinatum are essentially the inverse of pectus excavatum, with an increased anteroposterior diameter of the chest and anterior protrusion of the sternum (Fig. 5). The same imaging modalities (radiography, CT, and MRI) are used and a calculated Haller index grades severity (< 1.98 is indicative of pectus carinatum). The management of pectus carinatum is surgical correction of the anatomic deformity, most commonly resection of a portion of the distal sternum and uniting the remnant sternum with the xiphoid process in anatomic orientation.

Neoplasm Benign Soft-Tissue Tumors Infantile hemangioma—Infantile hemangiomas are the most common vascular tumor of infancy, affecting 2–3% of the general population with a female predominance. Though most of these high-flow tumors originate in the face and neck, up to 25% arise in the chest. The diagnosis of chest wall infantile hemangiomas is often strongly suggested by the clinical history and

Fig. 2—Pectus excavatum in 15-year-old boy with depression of anterior chest wall. A, Frontal chest radiograph shows characteristic pseudoinfiltrate (arrow) in right middle lobe. B, Lateral chest radiograph shows substantial depression of chest wall with narrowing of anteroposterior diameter (arrow) of chest cavity. Previously noted right middle lobe pseudoinfiltrate is not seen on lateral chest radiograph.

W404

AJR:200, May 2013

Chest Wall Lesions in Children Fig. 3â&#x20AC;&#x201D;Haller index. Unenhanced axial CT image of chest shows sample calculation of Haller index. Dividing maximal transverse diameter of chest by anteroposterior diameter between sternum and vertebral body yields Haller index of 5.2, diagnostic of pectus excavatum.

physical examination. These chest wall lesions are not typically seen at birth, but they grow rapidly during the first few months of life until they appear as palpable, subcutaneous, and bluish-red masses. Despite their initial rapid growth, these lesions usually enter a slow involutional phase and almost completely resolve by age 10 years. Although the diagnosis of an infantile hemangioma is often made clinically, imaging may be performed to define the extent of the tumor or detect a lesion that cannot be diagnosed by physical examination. If sufficiently large, a hemangioma appears as a soft-tissue opacity that distorts the expected contours on radiographs. However, the findings are nonspecific and the tumor may not be evident. The lesion is typically heterogeneous on ultrasound and often hyperechoic to the echogenicity of the adjacent muscle. The mass becomes more heterogeneous as the tumor begins to involute. The hallmark appearance is a hypervascular mass that shows multiple small vessels with low-resistance arterial waveforms and one or more draining veins (Fig. 6). CT findings of an infantile hemangioma consist of a well-demarcated mass that is isodense to surrounding soft tissue and markedly enhances after contrast administration. On MRI, an infantile hemangioma of the chest wall may show well-defined or ill-defined borders with multiple flow voids consistent with high-flow vessels. The mass is T2 hyperintense, has intermediate signal intensity on T1-weighted images, and enhances avidly after contrast administration. As the child ages and the infantile hemangioma begins to involute, the mass becomes more heterogeneous and hyperintense on T1-weighted images because of internal areas of necrosis and fatty change. Because infantile hemangiomas spontaneously regress, there is usually no need for treatment. Large infantile hemangiomas, however, can become symptomatic due to either local

Fig. 4â&#x20AC;&#x201D;Pectus excavatum repair in 15-year-old boy after surgical repair of pectus excavatum (same patient as in Figure 2). A, Frontal chest radiograph shows two horizontally oriented metallic bars at level of mid chest. B, Lateral chest radiograph shows that metallic bars are positioned under sternum and lifting it, improving anteroposterior diameter of chest.

AJR:200, May 2013 W405

Baez et al.

mass effect on vital structures, such as the airway, or altered vascular dynamics requiring intervention. Medical therapy is the initial treatment, with propranolol as the preferred agent. Embolization and surgery are options when symptoms persist. Low-flow vascular malformations, particularly lymphatic malformation, which is associated with Turner and Down syndrome, may arise from the neck or mediastinal regions and extend into the chest wall in pediatric patients. Kaposiform hemangioendotheliomas are distinct vascular neoplasms that can mimic infantile hemangiomas. These tumors are more aggressive than infantile hemangiomas, show malignant potenFig. 5â&#x20AC;&#x201D;Pectus carinatum in 16-year-old boy with tial, and are associated with the Kasabachbulging chest wall. Lateral chest radiograph shows Merritt phenomenon in more than 50% of substantial increase in anteroposterior diameter cases, wherein the patient develops coagu(straight arrow) of chest and anterior bowing of lopathy due to profound thrombocytopenia. sternum (curved arrow). Ill-defined margins and other subtle findings of local invasion can help differentiate kaposiform hemangioendotheliomas from the nonmalignant infantile hemangiomas. Infantile fibrous hamartomaâ&#x20AC;&#x201D;Infantile fibrous hamartomas are rare lesions, derived from the subcutis and dermis, which tend to develop within the first year of life and have a male predilection. They present clinically as painless nodules that may grow and typically arise in the shoulder girdle region. If the masses enlarge sufficiently, an intrathoracic component can impair normal respiratory function. These benign lesions have no potential for either local invasion or distant metastasis. On radiographs, an infantile fibrous hamartoma of the chest wall appears as a nonspecific extrapleural soft-tissue lesion that displaces local structures and can erode adjacent ribs and

W406

Fig. 6â&#x20AC;&#x201D;Infantile hemangioma in 2-monthold boy with raised reddish discoloration in anterior chest wall that started to grow at 1 month of age. A, Gray-scale ultrasound image of chest at level of nipple shows slightly heterogeneous but predominantly echogenic mass (asterisk) in subcutaneous tissues of nipple region overlying ribs (arrow). B, Color Doppler ultrasound image shows that mass is hypervascular.

AJR:200, May 2013

Chest Wall Lesions in Children cause deformity. Because this mesenchymal mass is composed of a mixture of mature bone, cartilage, and fibroblasts, calcification within the lesion is common. Because it contains several different cell types, the mass is heterogeneous but well defined on ultrasound. CT better delineates the anatomy as well as involvement of the adjacent ribs. An infantile fibrous hamartoma can develop a secondary aneurysmal bone cyst, which may bleed and produce fluid-fluid levels on imaging studies. MRI can show the different components of the lesion, with fat showing T1 hyperintensity whereas the fibrous components appear hypointense on both T1- and T2-weighted images. The treatment of an infantile fibrous hamartoma is surgical, with an excellent prognosis because there is no risk of metastasis and a low rate of recurrence.

Benign Osseous Tumors

Fig. 7—Osteoid osteoma in 13-year-old boy with painful scoliosis. Unenhanced axial bone window CT image of chest shows lucent nidus (arrows) in posterior aspect of left rib with central mineralization, surrounding sclerosis, and focal rib expansion.

Osteoid osteoma—Osteoid osteomas are small benign tumors that generally arise in long bones. Although less common in the thorax, osteoid osteomas can arise from the ribs, sternum, and vertebral column. They occur most frequently between ages of 7 and 25 years and are more common in males. Osteoid osteomas typically present with nocturnal pain that improves with nonsteroidal antiinflammatory drugs (NSAIDs). The characteristic radiographic appearance of an osteoid osteoma is a radiolucent center (nidus) surrounded by reactive sclerosis. CT is superior to MRI for defining the nidus and is the preferred imaging modality to confirm a suspected lesion. The center of the nidus often contains mineralization (Fig. 7). A recently reported radiologic finding to improve the diagnostic accuracy is the “CT vessel sign” in which a feeding vessel is seen either close to or entering the nidus. MRI can sometimes depict both the nidus and surrounding sclerosis, but its only advantage is showing adjacent edema. The nidus strongly enhances with gadolinium, but MRI still proves inferior to CT for showing it. Although it is usually not necessary to make the diagnosis of an osteoid osteoma, a 99mTc methylene diphosphonate (MDP) bone scan shows a characteristic double density sign, in which intense tracer uptake in the nidus is superimposed on a larger area of increased uptake.

Fig. 8—Osteochondroma in 14-year-old boy with hard and painless lump in lower aspect of right chest wall. A, Oblique rib radiograph shows small pedunculated osteochondroma arising from ninth right rib (arrow). B, Three-dimensional surface-rendered reconstruction of bony thorax confirms osteochondroma (arrow).

AJR:200, May 2013 W407

Baez et al.

Osteoid osteomas are self-limited, so that once diagnosed they are typically managed medically with NSAIDs. If the patient remains symptomatic, pain can be alleviated by a minimally invasive method, such as CT-guided excision, radiofrequency ablation, or cryoablation. Osteochondroma—Osteochondromas are common benign developmental lesions that form when fragments of epiphyseal growth plate cartilage herniate through the periosteal bone cuff. These tumors typically arise from the surface of the underlying bone, start developing before puberty, and continue to grow until the bone has reached maturation. In the ribs, they most frequently occur at the costochondral junction. Solitary lesions have a male predisposition. Costal osteochondromas tend to grow inward and are associated with reduced range of movement, pain, and cosmetic abnormality. An osteochondroma can fracture or cause compression of adjacent neurovascular structures. Additional complications associated with osteochondromas of the chest wall include pseudoaneurysm formation, hemothorax, pneumothorax, pericardial effusion, and overlying bursitis. On radiographs, an osteochondroma presents as an osseous protuberance in continuity with the surface of the originating bone (Fig. 8A). The lesion is characterized as either sessile or pedunculated on the basis of its attachment to the bone. CT is superior to radiography for showing the characteristic continuity of the cortex and medullary cavity with the osteochondroma (Fig. 8B). The cartilage cap (if calcified) can sometimes be seen on CT, but this structure is better visualized on MRI because of its characteristically T2-hyperintense appearance. Characterization of the cartilage cap has diagnostic importance because cap thickening may indicate malignant transformation. In adults, pain, swelling, and enlargement are signs of chondrosarcomatous progression; however, these signs are not specific in the pediatric population. Additional imaging signs of malignant transformation of an osteochondroma include bone erosion and irregular calcification. Malignant transformation to chondrosarcoma occurs more frequently (5–25%) in multiple hereditary exostoses, compared with a rate of < 1% in a solitary exostosis. In the pediatric population, the rate of chondrosarcomatous transformation is considered significantly lower, although at least eight cases have been reported in skeletally immature patients. The reported cases are too few for determining a specific incidence rate, but pediatric patients with multiple hereditary exostoses require close clinical follow-up and routine surveillance with skeletal surveys. Fibrous dysplasia—Fibrous dysplasia is a benign bone lesion in which the normal cancellous bone is replaced by immature fibroosseous tissue that undergoes calcification. Fibrous dysplasia is typically asymptomatic and found incidentally, although pain and pathologic fracture can be the presenting symptoms. Fibrous dysplasia can both expand and deform the bone, causing cosmetic deformity and mass effect on local structures. Traditionally, fibrous dysplasia has been classified into monostotic and polyostotic depending on the number of lesions. Monostotic fibrous dysplasia is usually an incidental finding, whereas polyostotic disease is associated with other syndromes. Mazabraud syndrome describes a rare nonhereditary disorder in which a patient with polyostotic fibrous dysplasia develops an intramuscular myxoma. McCune-Albright syndrome is defined by the clinical triad of fibrous dysplasia, café-au-lait pigmentation, and endocrine abnormality (such as precocious puberty). This syndrome predominantly affects females and is associated with a low rate (0.4–4.0%) of malignant transformation. Within the chest wall, fibrous dysplasia most commonly arises from the lateral or posterior arc of the ribs. The characteristic radiographic appearance of fibrous dysplasia is a focal well-defined expansile intramedullary lesion with a ground-glass matrix (Fig. 9). At times, the matrix may be lucent or sclerotic. Fibrous dysplasia rarely presents as a cystic lesion with fluid-fluid levels. Although the radiographic appearance is often diagnostic, chest wall lesions may be difficult to visualize so that cross-sectional imaging is required. CT can detect amorphous calcifications within the lesion that are not readily seen on radiography. On MRI, fibrous dysplasia typically is isointense to skeletal muscle on T1-weighted images and heterogeneously hyperintense on T2-weighted sequences and shows heterogeneous enhancement. A hypointense rim seen on both T1- and T2-weighted sequences corresponds with the sclerotic rim often present on radiographs. Most cases of fibrous dysplasia, particularly in the pediatric population, are asymptomatic and require no treatment. Follow-up imaging is recommended to ensure stability. In symptomatic disease, medical therapy with bisphosphonates has shown clinical efficacy. Surgical resection may be performed in patients with persistent pain or those with concerning features. Bone

W408

AJR:200, May 2013

Chest Wall Lesions in Children grafting can reinforce the underlying bone and reduce the risk of pathologic fracture. Mesenchymal hamartoma—Mesenchymal hamartomas of the chest wall are expansile intraosseous overgrowths of normal skeletal elements, including bone and hyaline cartilage, which typically involve the ribs. An exceedingly rare condition (≈100 reported cases), they usually present between birth and early infancy as hard immobile subcutaneous masses. Because mesenchymal hamartomas are not true neoplasms, there is no risk of local invasion or metastasis. Multifocal and bilateral mesenchymal hamartomas have been described. On radiography and CT, mesenchymal hamartoma of the chest wall presents as an ex- Fig. 9—Fibrous dysplasia in 17-year-old boy pansile chest mass that involves one or more with polyostotic fibrous dysplasia. Frontal chest radiograph shows near universal osseous ribs (Fig. 10A). Speckled popcornlike calcifi- involvement with expansion of ribs and clavicles as cations and secondary aneurysmal bone cyst well as underlying ground-glass matrix. Vertebrae formation have been reported. The presence of and proximal left humerus are also involved. hemorrhagic fluid-fluid levels within secondary aneurysmal bone cysts is a helpful identifying feature that has been observed in more than half of patients with this lesion. MRI features of mesenchymal hamartoma depend on their internal contents (Fig. 10B). The aneurysmal bone cyst components are hyperintense on fluid-sensitive sequences and have varying amounts of internal hemorrhage. Low T1 signal corresponds to regions of calcification. Using these imaging characteristics, it is sometimes possible to make the diagnosis of mesenchymal hamartoma prenatally with fetal MRI. Mesenchymal hamartomas are self-limited lesions that typically stop growing within the first year of life. Therefore, conservative treatment is recommended in asymptomatic patients, especially because the masses can spontaneously regress. For those patients with cardiorespiratory compromise or cosmetic deformity, surgical management is definitive, although radiofrequency thermoablation has also been advocated as a minimally invasive alternative. Inflammatory myofibroblastic tumor of the lung (inflammatory pseudotumor)—Inflammatory myofibroblastic tumors occur both within the lung and in extrapulmonary locations, typically in young pediatric patients. They are the most common primary lung masses in the pediatric

Fig. 10—Mesenchymal hamartoma in 3-day-old boy with palpable left lower chest wall mass. A, Coronal contrast-enhanced CT image of chest shows large well defined extrapleural mass (arrow) with central coarse calcifications in direct continuity with adjacent ribs in left hemithorax. B, Axial contrast-enhanced T1-weighted MR image of chest at same level as A shows heterogeneous and intense enhancement in anterior aspect of mass (arrow).

AJR:200, May 2013 W409

Baez et al.

population, often presenting in the second decade of life. Autoimmune and infectious causes have been proposed as inciting these lesions. Although the mass is not malignant, it can act locally aggressive and involve adjacent organs. Histopathologic analysis shows proliferating spindle cells and mononuclear inflammatory cells. The clinical presentation depends on the location of the mass. Cough, hemoptysis, chest pain, and dyspnea are common symptoms. Radiography typically shows a solid peripherally located pulmonary nodule. In rare instances, the entity can be multifocal or even bilateral. The nodule can invade mediastinal, hilar, pleural, and chest wall structures. On ultrasound, this lesion can be of heterogeneFig. 11â&#x20AC;&#x201D;Inflammatory myofibroblastic tumor of ous echotexture with either ill-defined or cirlung (inflammatory pseudotumor). Axial contrastcumscribed borders. Increased vascularity is enhanced CT of chest obtained for evaluation of noted with the use of Doppler ultrasound. CT fever and chest pain in 6-year-old girl shows large shows a heterogeneously enhancing mass of heterogeneously enhancing mass in left chest involving lung that extends to mediastinum (straight variable attenuation (Fig. 11). Calcification arrow) and left chest wall (curved arrow). has been described with variable morphologies, including amorphous, mixed, fine, and dystrophic. CT proves helpful to elucidate the full extent of the lesion. On 18F-FDG PET imaging, the lesion is metabolically active. Surgical excision is the preferred treatment of this lesion, with a good prognosis if completely resected. In those patients who have a surgical contraindication, radiation and corticosteroids have been used. Cases of sarcomatous degeneration, relapse, and distal metastases have been reported with this entity and surveillance is recommended after resection of the mass.

Fig. 12â&#x20AC;&#x201D;Rhabdomyosarcoma in 6-year-old girl with nontraumatic palpable lump in left paraspinal region for 6 weeks. A, Axial contrast-enhanced CT image of chest shows round mass (asterisk) in left paraspinal region, which is isodense to muscle and without adjacent bone destruction or abnormal calcifications. B, Sagittal STIR MR image shows elongated, hyperintense, and well-defined mass (asterisk) extending between intercostal spaces (arrow) but without associated adjacent bone destruction.

W410

AJR:200, May 2013

Chest Wall Lesions in Children

Fig. 13—Malignant peripheral nerve sheath tumor in 20-year-old woman with known neurofibromatosis type 1. Coronal contrast-enhanced CT image shows two large and heterogeneously enhancing masses (asterisks) on pleural surface of right chest wall along course of intercostal nerves.

Fig. 14—Pleuoropulmonary blastoma (type III). Axial contrast-enhanced CT of chest obtained for evaluation of respiratory distress in 3-year-old boy shows large solid hypodense mass (arrows) arises from pleura of right lung.

Malignant Soft-Tissue Tumors Rhabdomyosarcoma—Rhabdomyosarcomas are high-grade mesenchymal tumors of skeletal muscle origin. Although most commonly seen in the head and neck or abdomen, chest wall involvement can occur. These tumors are typically rapidly growing and painful, often secondary to nerve compression. More than 20% of these aggressive tumors invade adjacent bone, but unlike Ewing sarcoma tumors, bone involvement is less frequent and occurs later during the course of the disease. There are three histologic subtypes of rhabdomyosarcoma: embryonal, alveolar, and pleomorphic. The alveolar subtype, which is associated with the worst clinical prognosis, frequently occurs in the chest wall. The embryonal subtype, which is unique to the pediatric population, also can involve the lower chest wall and mediastinum. Regardless of subtype, the single most important prognostic factor in the patient with chest wall rhabdomyosarcoma is whether there is evidence of metastatic disease at the time of diagnosis. Because it is a soft-tissue tumor, rhabdomyosarcoma is not well evaluated on radiography. Advanced cases may show mass effect on adjacent structures and bone erosions. Ultrasound shows a well-defined mass that is heterogeneous, but predominantly hypoechoic. Doppler ultrasound may show increased internal vascularity within the tumor. CT can show the anatomic extent of the lesion as well as pulmonary metastases and bony metastases with intrathoracic extension (Fig. 12A). MRI findings include intermediate signal on T1-weighted sequences, T2 isointensity to hyperintensity, and intense contrast enhancement (Fig. 12B). Staging of rhabdomyosarcoma by imaging is best performed with FDG PET, which is superior to the exclusive anatomic imaging obtained with CT or MRI alone. The use of whole-body MRI has also been advocated as a useful adjunct to follow these patients after therapy. The current standard of care for the patient with rhabdomyosarcoma is surgical resection with neoadjuvant chemotherapy. Radiotherapy is often added in cases with positive margins at surgery. Malignant peripheral nerve sheath tumor—Malignant peripheral nerve sheath tumors (MPNSTs) most commonly occur in the head and neck but also can develop in the chest wall. These tumors originate within the nerve sheath and can occur either sporadically or develop within plexiform neurofibromas in patients with neurofibromatosis type 1 (NF1). There is a strong male predominance (4:1) in those with NF1 but no gender predilection in the sporadic type. Patients clinically present with a slow-growing masses that can cause pain (which suggests malignant transformation). Ultrasound can show the general shape and size of MPNST, but the tumor is better evaluated with CT or MRI. CT shows a large heterogeneous mass that tracks along the expected course of a peripheral nerve (Fig. 13). The tumor often erodes and destroys the adjacent bone. Because of varying degrees of necrosis, hemorrhage, and cellularity, the tumor may appear heterogeneous on MRI. Nevertheless, MPNST typically is iso- to hyperintense to muscle on

AJR:200, May 2013 W411

Baez et al.

T1-weighted sequences, high signal intensity on T2-weighted sequences, and heterogeneously enhancing. Two characteristic appearances that help define the neural origin of the tumor are the “split fat sign” (representing a rim of fat surrounding the neurovascular bundle) and the target sign (central T2 hypointensity and a T2 hyperintense peripheral rim). Absence of these signs suggests malignant degeneration. Edema within the surrounding structures on T2-weighted imaging also suggests the malignant nature of an MPNST, though a plexiform neurofibroma can have a similar appearance. Additional MRI features that favor MPNST over its benign counterparts include large size (> 5 cm), ill-defined margins, and rapid interval growth. Wide surgical resection, which may be combined with adjuvant chemotherapy or radiation, remains the standard care for pediatric patients with MPNST. Pleuropulmonary blastoma—Pleuropulmonary blastomas are tumors composed of mesenchymal and epithelial cells that resemble fetal lung. The diagnosis is distinct from pulmonary blastoma, which typically arises in adults. A familial component of pleuropulmonary blastomas has been described in up to 25% of cases. Associations with other tumors, including medulloblastoma, Wilm tumor, leukemias, and gonadal tumors, are reported. A pleuropulmonary blastoma is subclassified into three types. Type III is most aggressive, represents a solid enhancing mass arising either from the pleura or lung, and may involve the chest wall. Types I (purely cystic) and II (cystic and solid) behave less aggressively than the type III counterpart and rarely involve the chest wall. Type I pleuropulmonary blastomas have the best prognosis but can recur in the form of the more aggressive types II and III masses. These tumors usually present in young children below the age of 6 years. Patients with pleuropulmonary blastomas often present with symptoms of respiratory infection, including cough, fever, and pain. Inclusion of this entity in a radiologic differential diagnosis can help the pathologist arrive at the proper diagnosis because the microscopic appearance is similar to that of an embryonal rhabdomyosarcoma. Similar to other chest wall lesions, a pleuropulmonary blastoma is initially detected on chest radiography as a pleural- or parenchymal-based opacity, often in the presence of a pleural effusion. The mass is usually right sided, large, and causes contralateral mediastinal shift. Ultrasound shows a mass that is often heterogeneous, with cystic and necrotic areas (types II and III pleuropulmonary blastoma). CT findings include a heterogeneous, low-density mass that enhances to variable degrees secondary to internal foci of necrosis (Fig. 14). This tumor has a tendency to metastasize to the central nervous and skeletal systems. Therefore, MRI of the entire neuroaxis, radiographic skeletal surveys, and 99mTc MDP bone scans are recommended for patients with types II and III pleuropulmonary blastoma. Surgical excision provides the mainstay of therapy along with the use of adjuvant chemotherapy. Up 50% of patients will have recurrence within 2 years. A type I morphology predicts a better prognosis.

Malignant Osseous Tumors Ewing sarcoma family of tumors—The Ewing sarcoma family of tumors is a group of highgrade small round cell tumors, including classic Ewing sarcoma, atypical Ewing sarcoma, peripheral primitive neuroectodermal tumor, and Askin tumor. These tumors originate from a common precursor cell with a shared chromosomal translocation. The distinction between these lesions is based on anatomic location and their cellular differentiation. The Ewing sarcoma family of tumors show a slight male predominance and white predilection, and most are diagnosed within the second decade of life. Presenting symptoms include rapidly growing chest wall masses, pain, neurologic symptoms, and fever. Imaging of the Ewing sarcoma family of tumors often begins with radiography, which typically shows an extrapleural mass with prominent bone destruction and aggressive characteristically lamellated periosteal reaction. Although ultrasound can identify the soft-tissue component of the tumor, it is poor for assessing bone involvement (Fig. 15A). CT is helpful for identifying internal calcifications not visible on radiographs, as well as the full extent of cortical involvement of the tumor (Figs. 15B and 16). MRI is superb for characterizing the soft-tissue abnormality, bone marrow involvement, and any spread into adjacent tissues and organs. The tumor is isointense to slightly hyperintense to muscle on T1-weighted images and hyperintense on T2-weighted sequences. Contrast enhancement of the tumor is heterogeneous because of areas of necrosis. FDG PET has high sensitivity, specificity, and accuracy for

W412

AJR:200, May 2013

Chest Wall Lesions in Children

Fig. 15—Primitive peripheral neuroectodermal tumor in 13-year-old boy with atraumatic painful and hard mass in lower anterior chest wall for 3 months. A, Ultrasound image of palpable chest wall area shows heterogeneous soft-tissue mass (asterisk) with extension into thoracic cavity (arrows). B, Axial contrast-enhanced CT image of chest shows full extent of mass (asterisk), which arises from costal cartilage and extends predominantly posteriorly. Note normal contralateral costal cartilage (arrow).

the staging and restaging of the Ewing sarcoma family of tumors. As with other sarcomas with a propensity for spread to the lungs, chest CT is the best modality for localizing early pulmonary metastases and should be part of the imaging protocol. Treatment of the Ewing sarcoma family of tumors requires surgery with neoadjuvant chemotherapy. Radiation therapy is also often used for local control in patients with metastatic disease. Osteosarcoma—Osteosarcomas are high-grade tumors of mesenchymal origin that can arise within the bone, soft tissue, or pleura. Although a majority of these tumors originate in the long bones, such as the femur and tibia, 1–2% can occur in the ribs, manubrium, sternum, and clavicle. The larger of two age peaks in osteosarcoma occurs in adolescence and young adulthood. Pain is the most frequent presenting symptom, sometimes with a palpable mass. On radiography, osteosarcoma of the chest wall typically presents as a destructive bone lesion with associated ossification. The sunburst pattern typically attributed to extremity osteosarcomas

Fig. 16—Ewing sarcoma in 6-year-old boy with painful and palpable mass in right hemithorax. Axial contrast-enhanced CT image shows aggressiveappearing large heterogeneous mass (asterisk) arising from right anterolateral chest wall. Lesion extends into right hemithorax and anterior mediastinum and partially encases superior vena cava (SVC). Dystrophic calcification (arrow) is present along anterior aspect of mass.

Fig. 17—Osteosarcoma in 17-year-old boy with left chest pain and palpable mass. Axial contrastenhanced CT image shows large heterogeneous mass (asterisk) arising from left anterolateral aspect of rib, with both large soft-tissue and osseous components. Coarse dystrophic calcification is surrounded by speckled calcification centered on left rib. Filling defect (arrow) is also noted in SVC.

AJR:200, May 2013 W413

Baez et al.

often is not evident in lesions of the chest wall. CT is superior to MRI for visualizing the extent of cortical bone involvement (Fig. 17). MRI is the best modality for characterizing the extent of marrow involvement and any associated soft-tissue component, which appears hyperintense to muscle on both T1- and T2-weighted sequences. Foci of low signal intensity on all MRI sequences correspond to internal calcification. Osteosarcomas show enhancement with gadolinium and, as with other sarcomas, show intense FDG uptake on PET/CT. The therapy for osteosarcoma in pediatric patients currently consists of surgical resection and chemotherapy. Fig. 18â&#x20AC;&#x201D;Neuroblastoma metastasis to ribs in 11-year-old boy. Axial contrast-enhanced CT image of chest shows heterogeneous right paraspinal mass centered on posterior right rib. Mass expands and extends into adjacent neural foramen (arrow), effacing thecal sac.

Metastatic Disease

Metastases constitute a small but important percentage of chest wall lesions in the pediatric population. Neuroblastoma can directly invade the chest wall from a primarily posterior mediastinal tumor, or it may present as destructive metastatic lytic lesions in the ribs or thoracic spine (Fig. 18). Other tumors that can metastasize to the chest wall include rhabdomyosarcoma originating outside of the chest wall and hematologic malignancies, such as lymphoma or leukemia (Fig. 19). Most patients have a preexisting cancer diagnosis, which should raise suspicion for metastasis whenever a focal chest wall lesion develops. The imaging appearance of metastatic disease involving the chest wall is often nonspecific, but it typically presents as lytic lesions with overlying cortical disruption and periostitis (Fig. 20). Therapy for metastatic chest wall lesions is typically palliative and can consist of surgery, radiation, and chemotherapy.

Infection Bacterial Infection Bacterial infection of the chest wall is a rare condition that typically involves the ribs or sternum. Osteomyelitis develops secondary to either hematogenous spread or direct extension from an adja-

Fig. 19â&#x20AC;&#x201D;Lymphoma in 12-year-old girl who presented with shortness of breath and abnormal chest radiography. A, Axial contrast-enhanced CT image shows round anterior mediastinal mass (asterisk) with pleural involvement (straight arrow) and ipsilateral pleural effusion. There is also enlargement of right anterior chest wall (curved arrow). B, Axial 18F-FDG PET image at corresponding level to A shows increased uptake in mediastinal mass (asterisk). Increased FDG uptake is also noted on right side of anterior chest wall (curved arrow) and along posterior pleura (straight arrow).

W414

AJR:200, May 2013

Chest Wall Lesions in Children cent infectious process, most typically due to Staphylococcus aureus. The clinical signs and symptoms of chest wall osteomyelitis include fever, pain, swelling, erythema, and leukocytosis. Recent studies have shown that C-reactive protein (CRP) is more sensitive and specific than erythrocyte sedimentation rate (ESR) for the diagnosis of osseous bacterial infection. The radiographic findings of osteomyelitis, which often occur only after 7–10 days, consist of rib destruction, periosteal reaction, and overlying soft-tissue swelling (Fig. 21A). The associated soft-tissue swelling and fluid collections are well visualized with ultrasound, which also can show cortical irregularity in superficial osteomyelitis. However, Fig. 20—15-year-old boy with stage III large B CT and MRI remain the preferred imaging cell lymphoma after two cycles of chemotherapy. modalities. Although CT is limited in accu- Axial contrast-enhanced CT image of chest shows rately detecting subtle bone marrow abnor- lytic lesion in posterolateral aspect of right rib with associated periosteal reaction. A soft-tissue malities, it is more sensitive than MRI for component (arrow) extends into right hemithorax. showing cortical destruction and periosteal reaction. MRI can detect osteomyelitis in its earliest stage by showing bone marrow edema on T2-weighted sequences and marrow hypointensity on T1-weighted images. The use of IV contrast agents for the diagnosis of pediatric osteomyelitis remains controversial (Fig. 21B). Gadolinium administration aids in visualizing an associated soft-tissue abnormality, such as abscess, but its necessity is questionable because the diagnosis of the primary bone abnormality can usually be made on unenhanced images. Treatment of bacterial osteomyelitis of the chest wall consists of IV antibiotics that include coverage of S. aureus. If there is a focal fluid collection or a more extensive or aggressive chest wall process, such as empyema necessitans or necrotizing fasciitis, drainage or surgical débridement may be necessary to clear the infection. Fig. 21—Sternal osteomyelitis in 13-year-old boy with cellulitis of midline chest after insect bite. A, Lateral radiograph of sternum shows substantial overlying soft-tissue edema (asterisk). Osseous structures appear preserved. B, Sagittal contrast-enhanced T1-weighted MR image with fat saturation obtained 2 days after A shows focal irregularity and increased contrast enhancement of third sternal ossification center (arrow) with associated enhancing soft-tissue edema (asterisks), indicating osteomyelitis and cellulitis.

AJR:200, May 2013 W415

Baez et al.

Fungal Infection

Fungal infection of the soft tissues and bones of the chest wall is usually confined to the immunocompromised patient population. Aspergillus species account for up to 80–90% of these fungal infections. The ribs usually become involved by direct extension from an underlying pulmonary process and, less frequently, are involved by hematogenous spread. The imaging characteristics of fungal infection of the chest wall are nonspecific. As with bacterial infection, radiography can show cortical disruption and periosteal reaction as late findings. The soft-tissue components of chest wall fungal infection are better visualized with ultrasound, CT, or MRI and show an appearFig. 22—Fungal osteomyelitis in 15-year-old boy with ance similar to that in bacterial disease (Fig. acute myeloid leukemia. Axial contrast-enhanced CT image of chest shows large fluid collection (asterisk) 22). The diagnosis of fungal chest wall infecsurrounding right-sided ribs with extension into right tion in pediatric patients is usually made in the hemithorax and associated consolidative opacity appropriate clinical context and confirmed by (arrow). Aspiration of collection confirmed infection with Aspergillus. either culture or histopathology. Therapeutic management for chest wall fungal infection depends on the organism involved. Guidelines are not well established because of the rarity of this process, particularly in the pediatric population. For aggressive infections, surgical resection of the involved chest wall followed by antifungal therapy may be necessary.

Chronic Recurrent Multifocal Osteomyelitis Chronic recurrent multifocal osteomyelitis (CRMO) is an idiopathic (possibly autoimmune) inflammatory process that has findings similar to osteomyelitis but without signs of bacterial infection. The condition is usually limited to adolescents, with most patients presenting between ages 9 and 14 years. The nonspecific symptoms include recurrent pain, tenderness, or swelling. Skin disorders, such as pustulosis palmoplantaris or acne, may also occur. There usually is elevation of CRP, ESR, and leukocyte counts. Although CRMO most commonly involves the clavicle, it also can affect the sternum, ribs, and other sites within the chest wall (Fig. 23). Radiographic findings of CRMO include lytic bone lesions with thin sclerotic rims, usually without periosteal elevation (except in the clavicle) or bony sequestra. Because abscess formation and soft-tissue edema are rare in CRMO, cross-sectional imaging studies are less useful than in pyogenic osteomyelitis. On MRI, there is T2 prolongation in the affected marrow, with low T1 signal intensity in the corresponding region and heterogeneous contrast enhancement. Whole-body MRI may prove helpful in both the diagnosis and follow-up of children with CRMO. The goal of treatment in CRMO is symptomatic relief with NSAIDs. Other therapies that have proven successful include corticosteroids, bisphosphonates, methotrexate, sulfasalazine, interferons, γ-globulins, and infliximab. CRMO is a self-limited process that usually resolves without significant sequelae in 7–25 years.

Trauma Accidental Trauma Trauma to the chest wall resulting in fracture of the ribs and sternum occurs less frequently in children than adults because of the relative elasticity of the pediatric chest wall. In addition to blunt trauma, other causes of rib fractures include metabolic bone diseases that predispose the patient to fracture, such as rickets or osteogenesis imperfecta. Initial evaluation usually begins with radiography, which can show healing fractures with callous and displaced acute fractures (Fig. 24). Nondisplaced acute fractures are often not apparent on radiography but are readily identifiable on chest CT. Although the routine use of CT for evaluating fractures is not recommended because of the substantial associated ionizing radiation, this modality is often performed in children with significant trauma to exclude

W416

AJR:200, May 2013

Chest Wall Lesions in Children Fig. 23â&#x20AC;&#x201D;Chronic recurrent multifocal osteomyelitis in 8-year-old girl with plantar pustulosis. A, Axial unenhanced bone window CT image of chest shows focal expansion of proximal aspect of right sixth rib (arrow) with cortical thickening at costovertebral junction. B, Bone scintigraphy with 99mTc methylene diphosphonate shows intense focal uptake in posteromedial aspect of right sixth rib (curved arrows) and in metaphyses of both ankle joints (straight arrows).

B underlying parenchymal or cardiovascular injury not visible on radiography (Fig. 25). MRI also is not recommended for routine evaluation of accidental trauma, but it can show bone marrow edema and a T1-hypointense line that corresponds with the fracture. Hematoma and other soft-tissue abnormalities are better visualized on MRI than with radiography or CT. Ultrasound can identify cortical irregularity in fracture and hematoma, but the technique requires operator expertise. Management of accidental trauma of the chest wall depends on the extent and severity of injury. In the absence of parenchymal injury, treatment is supportive with analgesics. In the rare case of pediatric flail chest, ventilator support may prove necessary.

Nonaccidental Trauma Differentiation between accidental and nonaccidental (i.e., child abuse) trauma relies on a combination of clinical history and imaging findings. In the absence of major trauma, fractures of the ribs are unusual in pediatric patients and suggest nonaccidental trauma. Posterior fractures are highly specific for inflicted injury as is the presence of multiple fractures at different temporal stages of healing. Aside from anatomic location and multiplicity of lesions, the actual appearance of nonaccidental trauma does not differ from that of accidental trauma (Fig. 26).

AJR:200, May 2013 W417

Baez et al.

Fig. 24—Sternal fracture in 5-year-old boy who fell off bicycle and hit handle bar. Lateral radiograph of chest shows nondisplaced fracture (arrow) of second sternal ossification center.

Fig. 25—Rib fracture in 29-month-old boy with polytrauma including left humerus and femur fractures after motor vehicle collision. Axial bone window CT image of chest shows minimally displaced acute fracture (arrow) of left-sided rib. Of note: posterior location of rib fracture is somewhat atypical for accidental trauma. Adjacent left lower lobe consolidative opacity with air bronchograms is consistent with lung contusion (asterisk).

Fig. 26—Nonaccidental trauma in 2-year-old girl with multiple bruises. A, Oblique rib radiograph shows three consecutive fractures (arrows) of lateral aspects of right fifth to seventh ribs. B, Right posterior oblique (left) and anterior (right) views of 99mTc bone scan show focal uptake by three consecutive lateral rib fractures (arrows).

W418

AJR:200, May 2013

Chest Wall Lesions in Children

Conclusion Chest wall lesions are a common finding in pediatric patients. They may be due to underlying congenital or developmental abnormalities, neoplasm, infection, or trauma. Imaging evaluation plays a critical role in detecting and characterizing the various chest wall lesions in children. Recognition of the characteristic imaging features of these lesions is important for guiding treatment and may obviate unnecessary invasive procedures, such as biopsy or surgery. Suggested Readings 1. Chai JW, Hong SH, Choi JY, et al. Radiologic diagnosis of osteoid osteoma: from simple to challenging findings. RadioGraphics 2010; 30:737–749 2. Chelli Bouaziz M, Jelassi H, Chaabane S, Ladeb MF, Ben Miled-Mrad K. Imaging of chest wall infections. Skeletal Radiol 2009; 38:1127–1135 3. Demir HA, Varan A, Yalcin B, et al. Malignant peripheral nerve sheath tumors in childhood: 13 cases from a single center. J Pediatr Hematol Oncol 2012; 34:204–207 4. Donnelly LF, Frush DP, Foss JN, O’Hara SM, Bisset GS 3rd. Anterior chest wall: frequency of anatomic variations in children. Radiology 1999; 212:837–840 5. Foran P, Colleran G, Madewell J, O’Sullivan PJ. Imaging of thoracic sarcomas of the chest wall, pleura, and lung. Semin Ultrasound CT MR 2011; 32:365–376 6. Jaramillo D. Infection: musculoskeletal. Pediatr Radiol 2011; 41(suppl 1):S127–S134 7. Maheshwari AV, Cheng EY. Ewing sarcoma family of tumors. J Am Acad Orthop Surg 2010; 18:94–107 8. Moore MA, Wallace EC, Westra SJ. The imaging of paediatric thoracic trauma. Pediatr Radiol 2009; 39:485–496

9. Murphey MD, Choi JJ, Kransdorf MJ, Flemming DJ, Gannon FH. Imaging of osteochondroma: variants and complications with radiologic-pathologic correlation. RadioGraphics 2000; 20:1407–1434 10. Nam SJ, Kim S, Lim BJ, et al. Imaging of primary chest wall tumors with radiologic-pathologic correlation. RadioGraphics 2011; 31:749–770 11. Restrepo R, Palani R, Cervantes LF, Duarte AM, Amjad I, Allman NR. Hemangiomas revisited: the useful, the unusual and the new. Part 1. Overview and clinical and imaging characteristics. Pediatr Radiol 2011; 41:895–904 12. Restrepo R, Lee EY. Updates on imaging of chest wall lesions in pediatric patients. Semin Roentgenol 2012; 47:79–89 13. Tateishi U, Gladish GW, Kusumoto M, et al. Chest wall tumors: radiologic findings and pathologic correlation. Part 1. Benign tumors. RadioGraphics 2003; 23:1477–1490 14. Tateishi U, Gladish GW, Kusumoto M, et al. Chest wall tumors: radiologic findings and pathologic correlation. Part 2. Malignant tumors. RadioGraphics 2003; 23:1491–1508 15. Van Rijn RR, Wilde JC, Bras J, Oldenberger F, McHugh KM, Merks JH. Imaging findings in noncraniofacial childhood rhabdomyosarcoma. Pediatr Radiol 2008; 38:617–634

AJR:200, May 2013 W419