PEDIATRIC ABDOMINAL MASSES 1 Abdominal masses are common

PEDIATRIC ABDOMINAL MASSES

1 -Abdominal masses are common in infants and children, 2 - and imaging plays an important role in their diagnosis and management. 3 -Plain radiographs provide clues to the location of the mass and the presence of calcifications. 4 -US is generally the most valuable procedure for the initial evaluation. 5 -US differentiates cystic from solid masses, indicates the organ of origin, and commonly suggests the diagnosis. 6 - CT or MR may be needed when the mass is large, poorly defined, or obscured by bowel gas.

1 -Pseudomasses may be caused on abdominal radiographs by a fluid-filled stomach, urinary bladder, or a loop of intestine. 2 -Structures outside the abdomen, such as large skin lesions, umbilical hernias, and meningomyelocele, can also mimic an abdominal mass. 3 -The most common abdominal masses in infants and children are enlarged kidneys caused by hydronephrosis or cystic renal disease.

Renal and Adrenal Masses Large Kidneys 1 -Unilateral enlargement of a kidney results from hydronephrosis, multicystic dysplastic kidney, renal vein thrombosis, or renal tumors. 2 -Bilateral renal enlargement can be seen with hydronephrosis, polycystic kidney disease, storage diseases, and glomerulonephropathies, including nephrotic syndrome. 3 - Bilateral renal enlargement caused by neoplasms is less common, although leukemia or lymphoma may infiltrate the renal parenchyma bilaterally

Nephroblastomatosis 1 -Small islands of primitive metanephric blastema, which are thought to be a precursor of Wilms tumor, commonly exist in the kidneys of the normal newborn infant. 2 - These primitive cells usually spontaneously regress by 4 months of age. 3 - A diffuse and proliferative form of persistent renal blastoma is referred to as nephroblastomatosis. The abnormal tissue can form as multiple discrete nodules within the renal parenchyma or may completely replace the renal cortex. Nephroblastomatosis appears on CT or IV pyelogram as bilateral lobulated and enlarged kidneys with marked compression, stretching, and distortion of the pelvicaliceal structures

� FIGURE 52. 55. Nephroblastomatosis. A. The kidneys are massively enlarged, with lobulated thickening of the parenchyma and stretching and compression of the collecting structures. B. T 1 WI in another patient shows multiple peripheral Wilms tumors (arrows) in a child with nephroblastomatosis.

On US, the kidneys are enlarged, lobular, and echogenic, or enlarged with diffuse hypoechoic thickening of the cortex. In such cases, Wilms tumor should be suspected. Nephrogenic rests are more likely to appear cortical, tend to be homogeneous, and are of low echogenicity on US, low attenuation on CT, and low signal intensity on T 1 WIs. Small, focal nephrogenic rests smaller than 1 cm are difficult to visualize by US and are better evaluated with contrastenhanced CT or T 1 WI

Wilms tumor is the most common renal neoplasm of childhood (81). It arises from the primitive metanephric epithelium and demonstrates varied histologies, which are classified into favorable and unfavorable groups. The prognosis is dependent on tumor histology and resectability, with survival above 90% for tumors with favorable histology. Wilms tumor presents as a nontender, rapidly growing, unilateral abdominal mass in a young child. The mean age of presentation is 3 years. Bilateral tumors are found in 10% of patients—more commonly in children with associated congenital anomalies or nephroblastomatosis

On US, Wilms tumor characteristically is a well-defined, predominantly solid mass arising from the kidney Hypoechoic or anechoic areas within the tumor represent necrosis. Hydronephrosis is commonly present. Wilms tumor has a propensity to extend into the renal vein, inferior vena cava, and RA; all of these structures must be evaluated preoperatively CT is used to evaluate large tumors and the lungs, which are a common site of metastasis. Either CT or MR can be used to exclude small masses in the contralateral kidney, which can be difficult to identify with US. Calcification is uncommon in Wilms tumor.

FIGURE 52. 56. Wilms Tumor. A. The large, heterogeneous, left-sided tumor (T) shows a well-defined, enhancing rim (arrows). Note that the left renal parenchyma is stretched along the margin of the mass (claw sign), indicating an intrarenal mass. B. Tumor extension into the inferior vena cava (arrow) in another patient is seen with US. C. CT scan in a different child shows a large, partially cystic Wilms tumor (T) on the left and identifies a smaller Wilms tumor mass in the contralateral kidney (arrows).

Renal cell carcinoma is very rare in young children but sometimes occurs in older children and adolescents. Like Wilms tumor, renal cell carcinoma usually presents as an asymptomatic abdominal mass, although hematuria is sometimes present. Hypertension is less common with renal cell carcinoma than with Wilms tumor. The imaging characteristics of renal cell carcinoma are indistinguishable from those of Wilms tumor.

Other malignant tumors are rare in children. Clear -cell sarcoma and rhabdoid tumor of the kidney are highly aggressive neoplasms that were once considered variants of Wilms tumor. They are distinguished by a very poor prognosis and different metastatic patterns. The primary tumors have an imaging appearance identical to that of Wilms tumor, but bone metastases are common in clear-cell sarcoma, and rhabdoid tumor is associated with brain metastases and second intracranial primaries. Metastatic disease to the kidneys is uncommon. The kidneys may be infiltrated by leukemia or lymphoma, causing diffuse enlargement or multiple masses

� FIGURE 52. 57. Renal Lymphoma. Multiple nodular tumor masses (arrows) are visible within the enlarged kidney on US.

Mesoblastic nephroma is the most common renal tumor of the neonate. Like Wilms tumor, mesoblastic nephroma arises from the metanephric blastema, and these tumors are indistinguishable on US. Although mesoblastic nephroma is usually considered benign, metastasis occasionally occurs (82, 83).

Adrenal Hemorrhage Adrenal masses characteristically cause downward and outward displacement of the kidney. In the newborn, the most common cause of adrenal enlargement is adrenal hemorrhage. Predisposing factors include large babies, obstetric trauma, neonatal sepsis, and hypoxia. The infants may present with an abdominal mass, jaundice, hypotension, or anemia, but small hemorrhages may go unnoticed. Hemorrhage occurs more frequently on the right and is occasionally bilateral. Older children develop adrenal hemorrhage as a result of accidental trauma, child abuse, meningococcemia, or anticoagulant therapy

US is an ideal modality for evaluating adrenal hemorrhage. The normal adrenal gland in the newborn is larger and more easily visualized than that of the adult. The gland appears as an inverted V–shaped structure with an echogenic central region and a peripheral hypoechoic zone.

FIGURE 52. 58. Normal Adrenal Gland. Note the characteristic “Y� shape (arrow) of the normal adrenal gland sitting astride the kidn

Hemorrhage enlarges the gland causes loss of the V shape. Initially, the hematoma resembles a solid, echogenic mass. As the hemorrhage resolves, it becomes increasingly hypoechoic, starting in the central region and progressing peripherally. The hematoma decreases in size within the first week and sometimes calcifies. The calcifications begin around the rim of the gland, but eventually a small, completely calcified gland remains. Adrenal insufficiency rarely develops. Adrenal hemorrhage may be complicated by compression of the kidney, renal vein thrombosis, or infection.

FIGURE 52. 59. Adrenal Hemorrhage. A. In the early stages, hemorrhage into the adrenal gland presents as an echogenic suprarenal mass (arrows). B. A resolving adrenal hemorrhage in a different infant appears cystic centrally on US (arrows).

Neuroblastoma belongs to a group of neural crest origin tumors that range from the benign ganglioneuroma to the highly malignant neuroblastoma. Neuroblastoma arises from the adrenal gland or from sympathetic ganglia in the retroperitoneum, posterior mediastinum, neck, or pelvis. It is a neoplasm of early childhood, presenting in children younger than 5 years of age. Most children present with advanced disease and large abdominal masses. Symptoms are often related to bone metastases or intraspinal extension. In contrast to Wilms tumor, neuroblastoma is a poorly marginated mass that frequently extends across the midline and into the chest. The kidney may be invaded, causing the tumor to be mistaken for an intrarenal mass (Fig. 52. 60 A

FIGURE 52. 60. Neuroblastoma. A. Note the large, ill-defined, heterogeneous left abdominal mass (arrows). The mass crosses the midline and secondarily invades the left kidney. B. Radiograph shows a large soft tissue mass that displaces the right kidney inferiorly. Irregular, amorphous calcifications are seen within the mass (arrow). C. MR in a different patient shows a large mass (M) displacing the left kidney (K). A second tumor mass is identified adjacent to the spine in the right upper hemithorax (arrow). D. Axial T 1 WI in another patient clearly shows tumor extension into the spinal canal (arrows).

Most neuroblastomas appear echogenic and heterogeneous. In some cases, a characteristic echogenic nodule can be identified within the larger part of the tumor mass. CT and MR can be used to better define the extent of involvement of large tumors and to detect metastatic deposits. Neuroblastoma metastasizes to the liver, lymph nodes, and bone marrow. MR demonstrates intraspinal extension , bone marrow infiltration, and encasement of blood vessels without using IV contrast. Skeletal metastases are shown with technetium bone scintigraphy. Iodine-131 -meta-iodobenzylguanidine is a tracer that resembles norepinephrine and is metabolized by neuroblastoma, pheochromocytoma, and other catecholamine-producing tumors. Octreotide is a ligand for G-protein receptor cell membranes. These two tracers have improved detection of primary tumor and metastases in some cases

Diffuse adrenal enlargement occurs with adrenocortical hyperplasia, which causes adrenogenital syndrome. The enlarged adrenals may have an undulating configuration, described as cerebriform. Marked, reversible adrenal enlargement is seen in infants treated with adrenocorticotropic hormone for infantile spasm Wolman disease is a rare lipidosis that results in enlarged, densely calcified adrenal glands. Plain films are usually diagnostic. Wolman disease is usually fatal at an early age

� FIGURE 52. 61. Congenital Adrenal Hyperplasia. Note the undulating configuration of the enlarged adrenal gland

Hepatobiliary Masses A variety of cystic and solid masses may arise from the liver and biliary tract in children Most conditions can be differentiated with US. Acute hydrops of the gallbladder is a poorly understood condition probably caused by transient obstruction of the cystic duct. It has been associated with the mucocutaneous lymph node syndrome (Kawasaki disease); however, in many cases the cause is unknown. US shows a markedly enlarged, tender gallbladder with a thin wall. Acute acalculous cholecystitis causes similar gallbladder enlargement, but the gallbladder distension is less pronounced and gallbladder wall thickening is present. Transient distension of the gallbladder sometimes occurs in the neonate, particularly in premature infants. Prolonged total parenteral nutrition and sepsis have been implicated as possible etiologic factors

Appendiceal abscess Genitourinary Ovarian cyst Abdominoscrotal hydrocele Hydrometrocolpos Urachal cyst Teratoma/dermoid cyst Miscellaneous CSF pseudocyst

Choledochal cysts are congenital malformations of the intrahepatic or extrahepatic bile ducts. Multiple factors probably lead to the development of choledochal cysts, but the majority of cysts are associated with an anomalous junction of the common bile duct and pancreatic duct (abnormal pancreatobiliary junction [APBJ]). The APBJ allows pancreatic enzymes to reflux into the common bile duct, which may lead to inflammation and weakening of the bile duct wall. Jaundice, pain, and a right upper quadrant mass comprise the classic triad of findings seen with a choledochal cyst. Young infants more commonly present with fluctuating jaundice, pain, and fever

The most common type of choledochal cyst (type 1) is a localized, fusiform or saccular dilation of the common bile duct below the cystic duct. Choledochal cysts are usually diagnosed by US, appearing as a cystic mass in the porta hepatis, separate from the gallbladder and associated with dilated intrahepatic ducts Hepatobiliary scintigraphy confirms that the cyst communicates with the biliary tract, aiding in differentiation from other cystic abdominal masses MR cholangiopancreatography may provide more detailed information about bile duct anatomy and anatomic relationships to adjacent structures

� FIGURE 52. 62. Choledochal Cyst. A. US shows a large, multilobulated anechoic cyst (C) that is adjacent to, but separate from, the gallbladder (arrows). B. Cholangiography confirms the presence of a large intrahepatic choledochal cyst (arrows) involving the right hepatic duct. GB, gallbladder. C. CT scan of a different child shows a well-defined cyst in the porta hepatis

Hepatic cysts are less common in infants and children than in adults. Solitary congenital cysts of the liver are usually encountered as an incidental finding at US or CT. The cyst walls are thin and the fluid is anechoic on US. Some cysts are very large and pedunculated, and their hepatic origin may be difficult to ascertain. Multiple hepatic cysts occur in patients with autosomal dominant polycystic disease. Acquired hepatic cysts may be solitary or multiple and are most commonly of infectious origin (Fig. 52. 63). Resolving hematoma of the liver may also appear as a well-defined cystic lesion

� FIGURE 52. 63. Candida Abscess of the Liver. Two irregular cystic collections with peripheral echogenicity are liver abscesses in this newborn infant with Candida sepsis

Hemangioendothelioma is the most common benign liver tumor encountered in infancy. This vascular lesion may be solitary or multiple and is associated with cutaneous hemangiomas in 40% of cases. Hemangioendothelioma may be complicated by highoutput cardiac failure, hemorrhage, jaundice, hemolytic anemia, or thrombocytopenia because of sequestration of platelets within the tumor. The typical sonographic appearance is a solid or complex mass associated with large feeding and draining vessels, seen best with color Doppler US The mass is well circumscribed and low in attenuation on CT and shows predominantly peripheral contrast enhancement. High signal intensity is seen on T 2 WIs, with multiple flow voids throughout the lesion representing vessels. The tumor may be treated with steroids, but arterial embolization or surgery may be needed in more symptomatic cases.

FIGURE 52. 64. (Color Plates) Vascular Neoplasms of the Liver. A. This solitary hemangioendothelioma appears echogenic on US, with multiple hypoechoic vascular channels. B. Color flow Doppler shows the large feeding and draining vessels of the hemangioendothelioma. C. Multiple sonolucent liver masses (arrows) represent hemangioendotheliomas. D. Arteriography demonstrates the marked vascularity (arrows) of a hemangioendothelioma.

Mesenchymal hamartoma is an uncommon benign tumor seen most often in infants and young children. Hamartomas are usually solitary and predominantly cystic, with multiple thin septations and intervening nodules of solid tissue apparent on US. CT shows multiple areas of low attenuation within the tumor mass. Hepatic adenomas are rare in childhood but have been reported in association with Fanconi anemia, glycogen-storage disease type 1, Hurler disease, and severe combined immunodeficiency.

Focal nodular hyperplasia presents as a masslike lesion that most likely represents a hyperplastic response to a congenital arteriovenous malformation. Scintigraphy using sulfur colloid demonstrates normal to increased tracer uptake in many cases, differentiating it from adenomas that do not concentrate the tracer. On CT, the lesions show early phase enhancement but become isoattenuating with the liver on delayed images. An enhancing central scar may be seen.

Metastatic Disease Neuroblastoma is the most common childhood tumor to metastasize to the liver, followed by lymphoma, leukemia, and Wilms tumor. Metastatic lesions are usually multiple, and their imaging appearance is generally nonspecific

Hepatoblastoma is a tumor of early childhood, presenting before 3 years of age. The tumor is more common in children with Beckwith-Wiedemann syndrome and familial adenomatous polyposis

FIGURE 52. 65. Hepatoblastoma. A CT scan demonstrates a large inhomogeneous tumor within the right lobe of the liver (arrows).

Hepatocellular carcinoma is more commonly seen in older children and adolescents. Sonographically, these tumors appear as single or multiple hyperechoic lesions, sometimes containing hypoechoic or anechoic areas because of hemorrhage or necrosis. Invasion of the hepatic or portal veins may be identified. On CT, the tumors appear as low-attenuation lesions with variable contrast enhancement. MR is comparable with CT for the initial diagnosis of these tumors; however, MR is more sensitive in the detection of postoperative tumor recurrence. MR angiography with three-dimensional reconstruction helps to evaluate tumor blood supply for surgical planning. Complete resection is required for survival, and orthotopic liver transplantation has been successful in some advanced cases of hepatoblastoma that would otherwise be unresectable. PET-CT promises to be a more sensitive modality for identifying tumor metastases and local recurrence (

Other less common primary malignant tumors in children include undifferentiated (embryonal) sarcoma and embryonal rhabdomyosarcoma of the biliary ducts. The latter tumor typically occurs in children between 2 and 5 years of age. When the tumor originates in a major bile duct, the patient presents with jaundice. Those tumors that originate within the intrahepatic ducts cannot be differentiated from other primary malignancies of the liver

Splenic Lesions Splenomegaly is a relatively common cause of a left upper quadrant mass in children. Splenic enlargement is most often secondary to a systemic illness. Common causes include hematologic diseases, infections, portal hypertension, and infiltrative diseases (mucopolysaccharidoses, reticuloendothelioses, leukemia, and lymphoma). P. 1320 The imaging characteristics are usually nonspecific and insufficient for diagnosing the cause of splenomegaly.

In the newborn and young infant, splenomegaly most often occurs because of bacterial sepsis and infection. Hepatomegaly is generally also present. In older children, infections such as infectious mononucleosis, typhoid fever, and catscratch fever are more common. Multiple small, poorly defined hypoechoic lesions can be seen with US in granulomatous splenic infection such as Bartonella (catscratch fever), tuberculosis, or fungal infection. Splenic abscess is uncommon in children and is most often associated with an impaired immune system

FIGURE 52. 66. Catscratch Disease. US demonstrates the multiple hypoechoic nodules in the spleen (arrows) that are characteristic of this infection

Cystic masses of the spleen are uncommon and include congenital epidermoid cysts, posttraumatic pseudocysts, and echinococcal cysts. Cystic lymphangiomatosis is a benign lymphatic malformation with a characteristic multiloculated cystic appearance. The lesion may contain calcification and enhances on CT

Splenic Neoplasms Primary neoplasms of the spleen (hemangioma, hamartoma, angiosarcoma) are rare. Lymphoma and leukemia commonly involve the spleen. However, splenic involvement with lymphoma does not necessarily result in splenic enlargement. Conversely, children with leukemia or lymphoma may have an enlarged spleen without neoplastic involvement. Hemophagocytic lymphohistiocytosis (HLH) is a rare disease that consists of overactive histocytes and macrophages that phagocytize the normal cellular structures of the blood. This condition is not truly malignant and is probably caused by an inappropriate immune reaction. HLH usually occurs in infants under 1 year of age and is characterized by hepatosplenomegaly, ascites , gallbladder wall thickening, lymphadenopathy, and pleural effusion.

Splenic Infarction In children, infarction of the spleen occurs most often as a complication of sickle cell anemia, leukemia, Gaucher disease, or cardiac valvular disease. Acute splenic infarction results in decreased echogenicity on US and diminished or mottled enhancement on CT. Rarely, a poorly fixed (“wandering�) spleen may undergo torsion, leading to infarction