Mediastinal Masses in Children: Radiologic-Pathologic Correlation.

Most pediatric masses in the chest are located in the mediastinum. These masses are often initially detected incidentally on chest radiographs in asymptomatic children, although some patients may present with respiratory symptoms. At chest radiography, the mediastinum has been anatomically divided into anterior, middle, and posterior compartments. However, with the International Thymic Malignancy Interest Group classification scheme, which is based on cross-sectional imaging findings, the mediastinum is divided into prevascular, visceral, and paravertebral compartments. In the prevascular compartment, tumors of thymic origin, lymphomas, germ cell tumors, and vascular tumors are encountered. In the visceral compartment, lymphadenopathy and masses related to the foregut are seen. In the paravertebral compartment, neurogenic tumors are most common. Using the anatomic location in combination with knowledge of the imaging and pathologic features of pediatric mediastinal masses aids in accurate diagnosis of these masses to guide treatment and management decisions. An invited commentary by Lee and Winant is available online. ©RSNA, 2021.

Primary Lung Tumors in Children: Radiologic-Pathologic Correlation From the Radiologic Pathology Archives.

Primary lung tumors in children are rare, with a narrow range of diagnostic considerations. However, the overlapping imaging appearances of these tumors necessitate attention to key discriminating imaging and pathologic features. In the neonate and infant, the important considerations include pleuropulmonary blastoma (PPB), infantile fibrosarcoma, and fetal lung interstitial tumor. Among these tumors, imaging findings such as air-filled cysts in type 1 PPB and homogeneously low attenuation of fetal lung interstitial tumors are relatively specific. Key pathologic and genetic discriminators among this group of tumors include the DICER1 germline mutation found in PPB and the t(12,15)(p13;q25) translocation and ETV6-NTRK3 fusion gene seen in infantile fibrosarcoma. Primary lung tumors in older children include inflammatory myofibroblastic tumors (IMTs), carcinoid salivary gland-type tumors of the lung, recurrent respiratory papillomatosis, and other rare entities. IMT, a spindle-cell proliferation with inflammatory elements, is the most common lung tumor in children. Anaplastic lymphoma kinase, a receptor-type protein tyrosine kinase, is present in 50% of these tumors, and this finding may support an imaging diagnosis of IMT. Carcinoid tumors account for a substantial portion of childhood lung tumors, and their characteristic avid enhancement on images corresponds to the compressed fibrovascular stroma histologically. Furthermore, novel imaging agents used with somatostatin receptor analogs have an emerging role in the evaluation of carcinoid tumors. Although less common than mucoepidermoid carcinoma, adenoid cystic carcinoma tends to recur given the perineural spread seen histologically. Integrating radiologic and pathologic knowledge is critical to accurate diagnosis, treatment planning, and surveillance of primary lung tumors in children.

Renal Tumors of Childhood: Radiologic-Pathologic Correlation Part 2. The 2nd Decade: From the Radiologic Pathology Archives.

Malignant renal tumors account for 7% of childhood cancers, and Wilms tumors are by far the most common-but not in older children and adolescents. Among individuals in the latter half of their 2nd decade of life, renal cell carcinoma (RCC) is more common than Wilms tumor. The histopathologic spectrum of RCCs in children differs from that in adults. The most common subtype of RCC in children and adolescents is Xp11.2 translocation RCC, which is distinguished by hyperattenuation at nonenhanced computed tomography, a defined capsule, and associated retroperitoneal lymphadenopathy. Papillary RCC is the second most common histologic subtype. It enhances less intensely compared with the adjacent renal parenchyma and has a propensity for calcification. Clear cell RCC is seen in patients with von Hippel-Lindau disease and is distinguished by its relatively hypervascular nature. Medullary carcinoma affects adolescents with the sickle cell trait and is characterized by an infiltrative growth pattern and extensive metastasis at presentation. Angiomyolipoma is seen in children with tuberous sclerosis complex and is often multifocal and hypervascular, with macroscopic fat. Metanephric tumors are central, circumscribed, and typically calcified. Lymphoma usually manifests as multifocal masses, but it may involve a solitary mass or infiltrative pattern. Extensive adenopathy and involvement of the gastrointestinal tract or other organs also may be seen. Primitive neuroectodermal tumor is an aggressive neoplasm that is typically quite large at diagnosis. Knowledge of the clinical, biologic, and histopathologic features of renal tumors in older children and adolescents and their effects on the imaging appearance can help the radiologist offer a useful preoperative differential diagnosis.

Imaging of the Pediatric Urinary System.

Recent advances in pediatric urinary tract imaging include development of alternative imaging methods without use of ionizing radiation; evolving understanding of the relationship of urinary tract infection, vesicoureteral reflux, and renal scarring, including the important role of dysfunctional voiding; development of a consensus nomenclature and risk-based classification for fetal and antenatal urinary tract dilation; advances in the understanding of sporadic and inherited renal cystic disease; and a proposed modification of the Bosniak criteria for distinguishing complex renal cysts from cystic renal tumors in children.

Pediatric Extranodal Lymphoma.

Lymphoma is the third most common pediatric neoplasm. Non-Hodgkin lymphoma (NHL) accounts for nearly half of cases and commonly involves extranodal sites. Compared with adults, this histologic spectrum of pediatric NHL is very narrow and consists of aggressive tumors. Patients typically present with widespread disease. Generally, NHL occurring in children includes Burkitt lymphoma, lymphoblastic lymphoma, diffuse large B-cell lymphoma, and anaplastic large cell lymphoma. Staging and assessment of therapeutic response are usually based on FDG-PET/CT. Due to the increased susceptibility of young patients to the effects of ionizing radiation, alternative methods of imaging are being explored.

Renal Tumors of Childhood: Radiologic-Pathologic Correlation Part 1. The 1st Decade: From the Radiologic Pathology Archives.

Wilms tumor is the second most common pediatric solid tumor and by far the most common renal tumor of infants and young children. As most tumors are large at presentation and are treated with nephrectomy, the role of imaging is primarily in preoperative planning and evaluation for metastatic disease. However, with treatment protocols increasingly involving use of preoperative (neoadjuvant) chemotherapy (the standard in Europe) and consideration of nephron-sparing surgery, the role of imaging is evolving to include providing initial disease staging information and a presumptive diagnosis to guide therapy. Differential diagnostic considerations include lesions that are clinically benign and others that require more intensive therapy than is used to treat Wilms tumor. In part 1 of this article, the unique histologic spectrum of renal neoplasms of infants and young children is reviewed with emphasis on radiologic-pathologic correlation. Part 2 will focus on renal tumors of older children and adolescents.

Solid tumors of the peritoneum, omentum, and mesentery in children: radiologic-pathologic correlation: from the radiologic pathology archives.

Intraperitoneal solid tumors are far less common in children than in adults, and the histologic spectrum of neoplasms of the peritoneum and its specialized folds in young patients differs from that in older patients. Localized masses may be caused by inflammatory myofibroblastic tumor, Castleman disease, mesenteric fibromatosis, or other mesenchymal masses. Inflammatory myofibroblastic tumor is a mesenchymal tumor of borderline biologic potential that appears as a solitary circumscribed mass, possibly with central calcification. Castleman disease is an idiopathic lymphoproliferative disorder that appears as a circumscribed, intensely enhancing mass in the mesentery. Mesenteric fibromatosis, or intra-abdominal desmoid tumor, is a benign tumor of mesenchymal origin associated with familial adenomatous polyposis. Mesenteric fibromatosis appears as a mildly enhancing, circumscribed solitary mass without metastases. Diffuse peritoneal disease may be due to desmoplastic small round cell tumor (DSRCT), non-Hodgkin lymphoma, or rhabdomyosarcoma. DSRCT is a rare member of the small round blue cell tumor family that causes diffuse peritoneal masses without a visible primary tumor. A dominant mass is typically found in the retrovesical space. Burkitt lymphoma is a pediatric tumor that manifests with extensive disease because of its short doubling time. The bowel and adjacent mesentery are commonly involved. Rhabdomyosarcoma may arise as a primary tumor of the omentum or may spread from a primary tumor in the bladder, prostate, or scrotum. Knowledge of this spectrum of disease allows the radiologist to provide an appropriate differential diagnosis and suggest proper patient management.

From the radiologic pathology archives imaging of osteonecrosis: radiologic-pathologic correlation.

Osteonecrosis is common and represents loss of blood supply to a region of bone. Common sites affected include the femoral head, humeral head, knee, femoral/tibial metadiaphysis, scaphoid, lunate, and talus. Symptomatic femoral head osteonecrosis accounts for 10,000-20,000 new cases annually in the United States. In contradistinction, metadiaphyseal osteonecrosis is often occult and asymptomatic. There are numerous causes of osteonecrosis most commonly related to trauma, corticosteroids, and idiopathic. Imaging of osteonecrosis is frequently diagnostic with a serpentine rim of sclerosis on radiographs, photopenia in early disease at bone scintigraphy, and maintained yellow marrow at MR imaging with a serpentine rim of high signal intensity (double-line sign) on images obtained with long repetition time sequences. These radiologic features correspond to the underlying pathology of osseous response to wall off the osteonecrotic process and attempts at repair with vascularized granulation tissue at the reactive interface. The long-term clinical importance of epiphyseal osteonecrosis is almost exclusively based on the likelihood of overlying articular collapse. MR imaging is generally considered the most sensitive and specific imaging modality both for early diagnosis and identifying features that increase the possibility of this complication. Treatment subsequent to articular collapse and development of secondary osteoarthritis typically requires reconstructive surgery. Malignant transformation of osteonecrosis is rare and almost exclusively associated with metadiaphyseal lesions. Imaging features of this dire sequela include aggressive bone destruction about the lesion margin, cortical involvement, and an associated soft-tissue mass. Recognizing the appearance of osteonecrosis, which reflects the underlying pathology, improves radiologic assessment and is important to guide optimal patient management.

From the radiologic pathology archives: pediatric polycystic kidney disease and other ciliopathies: radiologic-pathologic correlation.

Genetic defects of cilia cause a wide range of diseases, collectively known as ciliopathies. Primary, or nonmotile, cilia function as sensory organelles involved in the regulation of cell growth, differentiation, and homeostasis. Cilia are present in nearly every cell in the body and mutations of genes encoding ciliary proteins affect multiple organs, including the kidneys, liver, pancreas, retina, central nervous system (CNS), and skeletal system. Genetic mutations causing ciliary dysfunction result in a large number of heterogeneous phenotypes that can manifest with a variety of overlapping abnormalities in multiple organ systems. Renal manifestations of ciliopathies are the most common abnormalities and include collecting duct dilatation and cyst formation in autosomal recessive polycystic kidney disease (ARPKD), cyst formation anywhere in the nephron in autosomal dominant polycystic kidney disease (ADPKD), and tubulointerstitial fibrosis in nephronophthisis, as well as in several CNS and skeletal malformation syndromes. Hepatic disease is another common manifestation of ciliopathies, ranging from duct dilatation and cyst formation in ARPKD and ADPKD to periportal fibrosis in ARPKD and several malformation syndromes. The unifying molecular pathogenesis of this emerging class of disorders explains the overlap of abnormalities in disparate organ systems and links diseases of widely varied clinical features. It is important for radiologists to be able to recognize the multisystem manifestations of these syndromes, as imaging plays an important role in diagnosis and follow-up of affected patients.

MR findings in the arthropathy of relapsing polychondritis.

We report a case of relapsing polychondritis involving three synovial joints in a child. Initial presentation was at 5 years of age with periorbital edema and chemosis of the conjunctiva with a definite diagnosis established at 9 years of age following an acute monoarticular arthropathy of the knee. The role of MRI in suggesting the diagnosis of relapsing polychondritis is emphasized by demonstrating a unique pattern of inflammation and enhancement that preferentially involves the perichondrium and chondroepiphysis.

From the radiologic pathology archives: precocious puberty: radiologic-pathologic correlation.

Precocious puberty represents a unique diagnostic problem in which imaging plays an important role. Development of secondary sex characteristics may result from inappropriate activation of the hypothalamic-pituitary axis with release of gonadotropin, or from gonadotropin-independent secretion of sex steroids by the adrenal glands or gonads. A variety of lesions can manifest with precocious puberty, including various central nervous system (CNS) lesions, adrenal lesions, and sex cord-stromal tumors of the testis or ovary. CNS lesions causing precocious puberty are much more common in boys than in girls and are well evaluated with brain magnetic resonance imaging. Neoplastic (hypothalamic-chiasmatic astrocytoma, suprasellar germinoma) and nonneoplastic (hypothalamic hamartoma, hydrocephalus, trauma, empty sella, infection, congenital midline anomalies) conditions may affect the function of the hypothalamic-pituitary axis. The adrenal cortex may produce sex hormones. Some adrenal cortical neoplasms (ACNs) in patients under 5 years of age are related to a mutation of the tumor suppressor gene p53 and represent a disease that is distinct from ACNs in older children and adults. Adrenal cortical hyperplasia secondary to an enzymatic defect in steroid biosynthesis causes virilization and salt wasting, which usually manifest in the neonatal period; however, milder forms of the disease may manifest in childhood. Female precocious puberty may be caused by an autonomously functioning ovarian cyst or a juvenile granulosa cell tumor of the ovary. Male precocious puberty may be caused by a sex steroid-producing Leydig or Sertoli cell tumor of the testis. Ultrasonography is the primary modality for evaluating the sex organs and may also be used to evaluate for adrenal abnormalities.

From the archives of the AFIP: Pediatric liver masses: radiologic-pathologic correlation. Part 2. Malignant tumors.

Malignant primary hepatic tumors in children include lesions unique to the pediatric age group and others that are more common in adults. Important considerations when evaluating a child with a liver tumor are the age of the patient, laboratory findings, and specific imaging features. The most common primary malignant hepatic tumor in the pediatric population, hepatoblastoma occurs almost exclusively in patients younger than 5 years with no history of liver disease. Hepatoblastoma is associated with elevated serum α-fetoprotein (AFP) level and appears predominantly solid. Hepatocellular carcinoma (HCC) is the most common malignant liver tumor in older children, often with a history of liver disease. HCC is associated with elevated serum AFP level and also appears as a solid mass. Fibrolamellar carcinoma occurs in adolescents without elevated AFP level and contains a T2-hypointense fibrous scar that usually does not enhance. Undifferentiated (embryonal) sarcoma occurs in young children, contains cystic and mucoid components, and mimics a cyst at magnetic resonance imaging and computed tomography but appears solid at ultrasonography. Epithelioid hemangioendothelioma is a multifocal vascular tumor in older children with a distinctive imaging appearance of confluent peripheral nodules with adjacent capsular retraction. Angiosarcoma rarely occurs in young children and frequently shows evidence of hemorrhage. Embryonal rhabdomyosarcoma of the biliary tree is unique to children, usually under 5 years of age, and frequently demonstrates an intraductal growth pattern. Knowledge of the pathologic features of these tumors and their imaging appearances can help radiologists offer an appropriate differential diagnosis and management plan.

From the archives of the AFIP: Pediatric liver masses: radiologic-pathologic correlation part 1. Benign tumors.

Benign hepatic tumors in children include lesions that are unique to the pediatric age group and others that are more common in adults. Infantile hemangioendothelioma, or infantile hepatic hemangioma, is a benign vascular tumor that may cause serious clinical complications. It is composed of vascular channels lined by endothelial cells. At imaging, large feeding arteries and draining veins and early, intense, peripheral nodular enhancement with centripetal filling on delayed images are characteristic features. Mesenchymal hamartoma of the liver occurs in young children and is characterized pathologically by mesenchymal proliferation with fluid-containing cysts of varying size and number. The mesenchymal component or cystic component may predominate; this predominance determines the imaging appearance of the tumor. Benign epithelial tumors that are common in adults may infrequently occur in childhood. These include focal nodular hyperplasia (FNH), hepatocellular adenoma, and nodular regenerative hyperplasia. All are composed of hyperplastic hepatocytes similar to surrounding liver parenchyma and may be difficult to discern at imaging. Preferential hepatic arterial phase enhancement helps distinguish FNH and hepatic adenoma from uninvolved liver. Hepatic adenoma often has intracellular fat and a propensity for intratumoral hemorrhage, neither of which are seen in FNH. Unlike adenoma, FNH often contains enough Kupffer cells to show uptake at sulfur colloid scintigraphy. Nodular regenerative hyperplasia is often associated with portal hypertension, which may be evident at imaging. Knowledge of how the pathologic features of these tumors affect their imaging appearances helps radiologists offer an appropriate differential diagnosis and management plan.

From the archives of the AFIP: breast masses in children and adolescents: radiologic-pathologic correlation.

The spectrum of breast lesions in children and adolescents varies markedly from that for adults, with the former lesions being overwhelmingly benign. A breast mass in a young boy or girl may arise from normal and abnormal breast development. Other causes of masses include infection, trauma, and cyst formation. After onset of puberty, most cases of breast enlargement arise from benign fibroadenoma in girls and gynecomastia in boys. These conditions have specific imaging appearances, although juvenile (often giant) fibroadenoma cannot be distinguished from phyllodes tumor, which can be benign or malignant. In children, both conditions usually appear as well-circumscribed, hypoechoic masses at sonography and show diffuse enhancement except for nonenhancing septations at magnetic resonance imaging. A diagnosis of juvenile papillomatosis (a benign lesion) portends later development of breast cancer, and patients with this condition should be closely monitored. Malignant lesions of the breast in children are rare. The most common malignant lesions are metastases and are usually associated with widespread disease. The most common primary breast malignancy is malignant phyllodes tumor. Primary breast carcinoma is exceedingly rare in the pediatric age group, but its imaging appearance in children is the same as seen in adults and is different from that of almost all benign lesions. In girls, diagnostic interventions may injure the developing breast and cause subsequent disfigurement. Given this risk and the low prevalence of malignant disease in this population, a prudent course should be followed in the diagnosis of breast lesions. Imaging findings are very helpful for selecting patients for further diagnostic procedures. Although malignancy is rare, lesions with suspicious imaging findings or progressive growth should be subjected to cytologic or histologic examination.

From the Archives of the AFIP. Pediatric orbit tumors and tumorlike lesions: osseous lesions of the orbit.

Many extraocular masses involving the pediatric orbit have an osseous origin. The most common is the dermoid inclusion cyst; these cystic lesions may contain lipid and are most often found near the zygomaticofrontal suture, adjacent to an indolent-appearing erosion of bone. Some primary bone lesions may involve the orbit, producing a lytic or dense lesion with enlargement of the bone; these lesions include fibrous dysplasia, juvenile ossifying fibroma, and osteosarcoma. Fibrous dysplasia tends to produce a mass of ground-glass appearance with longitudinal osseous expansion, whereas juvenile ossifying fibroma is likely to produce a mixed lytic and sclerotic lesion and focal osseous enlargement. Osteosarcoma causes marked bone destruction and variable osteoid production. Langerhans cell histiocytosis, an idiopathic reticuloendothelial proliferative disorder, tends to involve the bones of the skull, especially the lateral orbital roof; it produces lytic destruction of bone with a sclerotic rim and a large intraorbital soft-tissue mass. Granulocytic sarcoma is a solid tumor that may occur in children with myelogenous leukemia. These tumors tend to arise in the subperiosteum of the lateral orbital wall, although they usually do not disrupt the bone. Finally, the orbit is a common site for bone metastases from neuroblastoma, which cause aggressive periosteal reaction in the orbital roof or lateral wall. The last three conditions are often bilateral. At imaging evaluation, osseous lesions may appear similar to each other and to nonosseous masses of the orbit. Knowledge of the pathologic features of these tumors and how these features are reflected in their imaging appearances may help radiologists differentiate them.

Pediatric liver: focal masses.

Imaging is a standard part of the evaluation of pediatric liver disease. Advances in MR imaging have improved detection, characterization, and staging of hepatic lesions. This article addresses the MR imaging appearances of various focal hepatic lesions that can present in children. Techniques for performing hepatic MR imaging also are reviewed.

Wilms' tumor and other pediatric renal masses.

Wilms' tumor is the most common solid renal tumor in children. Imaging plays a crucial role in the evaluation of the primary tumor and regional and metastatic disease. This article reviews the biologic, clinical, and MR imaging features of this tumor and other renal tumors that can mimic Wilms' tumor.

From the archives of the AFIP: Pediatric orbit tumors and tumorlike lesions: nonosseous lesions of the extraocular orbit.

The histologic spectrum of nonosseous tumors and tumorlike lesions of the extraocular orbit in children differs from that in adults, and the appearance of these lesions at imaging reflects their pathologic features. Rhabdomyosarcoma is the most common extraocular orbital tumor in children. This neoplasm usually manifests in young children, grows quite rapidly, and is fairly vascular. Vasculogenic lesions are common orbital lesions in newborns and young infants. The most prevalent of these are infantile hemangioma, a true neoplasm, and venous-lymphatic malformation, a developmental anomaly. Hemangioma is quite vascular, has a predictable course of proliferation followed by slow involution, and is distinguished on magnetic resonance images by the finding of flow voids within the mass and at its periphery. Venous-lymphatic malformation in the orbit is an anomaly of venous and lymphatic development that is characterized by unenhancing, cystic lymphatic and enhancing, solid venous components. Intralesional hemorrhage is common and frequently produces distinctive fluid-fluid levels within the cystic portions. Unlike hemangiomas, venous-lymphatic malformations grow with the patient and never involute spontaneously. Infantile fibromatosis is one of the fibromatoses and affects newborns and young infants. The tumor is nodular and composed of a zonal architecture, with frequent hemorrhage or necrosis in the central portion, characteristics that confer a target appearance at imaging. These lesions usually stop growing or spontaneously regress. All of these extraocular masses typically manifest with proptosis, and imaging differentiation is desirable because the treatments and prognoses vary greatly.