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Current Imaging Assessment of Congenital Abdominal Masses in Pediatric Patients
Current Imaging Assessment of Congenital Abdominal Masses in Pediatric Patients Gabriella L. Crane, MD, and Marta Hernanz-Schulman, MD, FAAP, FACR
Introduction Although a wide variety of abdominal masses can present in pediatric patients, the focus of this review is on congenital abdominal masses, i.e. those that are present at birth, and therefore diagnosed in utero or in the neonatal period. These masses, although relatively rare, must be evaluated effectively to expedite diagnosis and treatment. In this article, considerations for optimal use of various currently available imaging modalities, principal imaging techniques, and imaging characteristics of the commonly encountered congenital abdominal masses are reviewed.
Imaging Techniques The evaluation of congenital abdominal masses relies primarily on ultrasound (US), which can provide high-resolution imaging assessment without sedation or radiation exposure in infants. However, there is a place for other imaging modalities, such as plain radiography, computed tomography (CT), magnetic resonance imaging (MRI), and nuclear medicine in the evaluation of congenital abdominal masses in pediatric patients, with findings which often are complementary to US. For each imaging modality, the currently recommended imaging protocols will be discussed briefly in the following sections.
Plain Radiography The first-line imaging modality for an infant or child who presents with clinical signs and symptoms suspicious for an abdominal mass is often a plain radiograph of the abdomen. This examination should include more than one view, often supine and left lateral decubitus, particularly when the child presents with acute symptoms, to exclude bowel obstruction or perforation as the cause for an acute abdomen. Abdominal
Department of Diagnostic Imaging, Monroe Carell Jr. Children’s Hospital at Vanderbilt, Nashville, TN. Address reprint requests to Gabriella L. Crane, MD, Assistant Professor, Radiology and Pediatrics, Department of Diagnostic Imaging, Monroe Carell Jr. Children’s Hospital at Vanderbilt, 2200 Children’s Way, Suite 1416, Nashville, TN 37232-9700. E-mail: [email protected]
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radiographs can also provide clues to the location and organ of origin of a mass based on its mass effect upon adjacent air-filled bowel loops. In addition, calcifications seen by plain radiography can offer clues to the diagnosis. Pseudomasses, such as a distended stomach or bladder, can also be identified.
Ultrasound US is an excellent imaging modality for the evaluation of the pediatric abdomen and can often provide all the information necessary in the diagnosis and surgical planning for a congenital abdominal mass. A radiologist experienced in US can often ascertain the origin of the mass, its internal architecture, and vascular supply, as well as regional metastases and vascular invasion. US is particularly beneficial in pediatric patients because the examination can be performed without sedation and without exposing the child to ionizing radiation. Depending on the lesion, US may be the optimal imaging examination and the only study necessary before definitive treatment. In contrast, US examinations are relatively nonstandardized and can be limited by intervening gas and bone. However, even in cases in which further imaging is necessary, US provides an excellent road map to guide and optimize subsequent imaging.
Computed Tomography If US is unable to fully evaluate a mass or if malignancy is suspected, CT is often a useful next step for further evaluation of congenital abdominal masses. CT is a standardized imaging modality in which the anatomy is always depicted sequentially and is unimpeded by intervening bowel gas or bone. However, it lacks the “real-time” capability of US and may remain limited in assessing the organ of origin for a very large mass. The CT protocol should be geared towards the suspected diagnosis, typically as guided by the clinical presentation and information obtained on preceding radiograph and US. Single-phase CT is usually sufficient for evaluation of congenital abdominal masses in most patients. However, in some cases, multiphase imaging may be indicated. For example, certain congenital abdominal masses characteristically contain calcifications, such as neuroblastoma. Therefore, the examination
Congenital abdominal masses in pediatric patients may begin with noncontrast CT imaging for the detection of calcifications that may be difficult to detect after the administration of contrast. This should be limited, however, to the mass or organ of interest to reduce overall radiation exposure, and typically the milliampere second (mAs) can be greatly reduced from that needed for the subsequent phase(s). If information regarding arterial and venous involvement is of clinical importance, particularly in a presurgical evaluation, arterial and/or venous phase scanning may be needed. Delayed images in renal excretory phase may be obtained when the collecting system/ureter needs to be visualized. Unfortunately, CT examinations expose these pediatric patients, who are much more sensitive to the potentially deleterious stochastic effects of radiation exposure, to ionizing radiation. Therefore, it is important that the study be undertaken only when diagnostic accuracy and management require it, and protocoled according to the As Low As Reasonably Achievable (ALARA) principle of diagnostic optimization. In infants and young children (ⱕ5 years), CT may require sedation to achieve diagnostic images, and these associated risks must also be carefully considered.1,2
Magnetic Resonance Imaging In recent years, MRI has become an increasingly valuable imaging modality in evaluating pediatric congenital abdominal masses, particularly with the advent of faster imaging sequences, greater strength magnets, and specialized pediatric coils. MRI can be used to delineate anatomic boundaries, assess perfusion patterns with dynamic contrast imaging, and newer techniques, such as diffusion-weighted imaging and MR spectroscopy, can provide functional and quantitative information as well.1,3 MRI is particularly useful in the evaluation of vascular malformations and in the characterization of hepatic and biliary masses. Some specific challenges when imaging the neonatal abdomen with MRI include the small size of the structures being evaluated, the inability of young patients to cooperate, and the inherently increased heart and respiratory rates of young patients.1 For example, the need for high-resolution images of small structures can be met by decreasing the field of view and increasing matrix size. However, this decreases signalto-noise and may require compensation, such as adding sequences which lengthens the overall scan time. When intravenous contrast is needed, gadolinium should be used carefully with attention to renal function, hepatic disease, previous surgery, or other proinflammatory conditions that increase the risk of nephrogenic systemic fibrosis. Nephrogenic systemic fibrosis in children is rare and, to our knowledge, not yet reported in the neonatal population.4 However, there may be potentially increased risk because of the normally lower glomerular filtration rate in the neonate, particularly in patients with abnormal kidneys and compromised renal function. Existing data, therefore, suggest that intravenous gadolinium be used carefully and only when necessary.3,5 Although a detailed discussion of MRI techniques is beyond the scope of this article, several general rules apply to
33 MRI of the pediatric abdomen.1 These include the use of fast isotropic 3D sequences that allow for multiplanar reconstructions; balanced steady-state free precession sequences for a quick preliminary imaging overview of the region of interest; heavily T2-weighted sequences, such as those used in magnetic resonance cholangiopancreatography (MRCP), which are useful in evaluating fluid-filled structures of the biliary and urinary tracts; and dynamic sequences and MR angiographic imaging using T1-weighted fast 3D gradient recalled echo or fast low-angle shot sequences, which are fast enough to not require breath-holding. The various methods currently available for minimizing respiratory artifact include controlled ventilation in anesthetized patients, respiratory triggering using external diaphragmatic bellows, and prospective gating using secondary images of diaphragmatic motion.1,3 Although neonates can often be imaged using “wrap-andfeed” technique with diagnostically sufficient results, older infants and young children need to be sedated to obtain diagnostic images, preferably by a dedicated pediatric sedation team.1,2,6 In addition, care should be taken that appropriate body temperature is maintained in all neonatal patients during MRI examination.
Nuclear Medicine Nuclear medicine is useful as a problem-solving imaging modality on a case-by-case basis. There is also a vital role for certain types of examinations, such as metaiodobenzylguanidine (MIBG) scans, in the surveillance of patients with specific tumors, such as neuroblastoma. The various examinations and their applications for evaluating congenital abdominal masses in pediatric patients will be discussed in the following sections.
Renal Masses Hydronephrosis Almost two-thirds of infantile abdominal masses arise from the kidneys, and most of these masses are benign.7 The most common abdominal “mass” found in this age group is hydronephrosis.8 It is often detected prenatally and can be caused by obstruction, vesicoureteral reflux, or both. The most common site of obstruction resulting in hydronephrosis is the ureteropelvic junction. Work-up for a child with hydronephrosis includes US to evaluate the degree of pelvocalyceal dilation and to assess whether there is ureteral dilatation or abnormalities of the contralateral kidney. The hydronephrotic kidney shows a dilated collecting system, with dilated calyces surrounding the centrally located hydronephrotic renal pelvis (Fig. 1). In evaluating hydronephrosis, it is important to assess the degree of thinning of the renal parenchyma and preservation of corticomedullary differentiation. Voiding cystourethrography is typically performed to exclude vesicoureteral reflux or extravesical abnormalities, whereas a nuclear medicine renogram with Lasix challenge is helpful in confirming obstruction as the cause of dilatation and in quantifying renal function.9 MR urography
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is currently assuming a role as an alternative imaging modality that can evaluate both renal anatomy and function.
Multicystic Dysplastic Kidney The differential diagnosis for hydronephrosis secondary to ureteropelvic junction obstruction is multicystic dysplastic kidney (MCDK). On US, MCDK typically appears as multiple noncommunicating cysts of various sizes with dysplastic and hyperechoic tissue separating the cystic components. There is usually no discernible normal renal tissue (Fig. 2). Often the largest cystic structure will not be located centrally, as is true with hydronephrosis. On renal scintigraphy, MCDK demonstrates no renal function.
Autosomal Recessive Polycystic Kidney Disease Pediatric patients with autosomal-recessive polycystic kidney disease (ARPKD) present with bilateral renal enlargement resembling bilateral masses on physical examination and on abdominal radiographs. Renal enlargement is secondary to hyperplasia of the collecting tubules, resulting in a spectrum of disease that can lead to presentation in utero or later in life. On US, the enlarged kidneys demonstrate overall increased echogenicity because of the multiplicity of interfaces presented by the collecting tubules. With current high-resolution US equipment, small macroscopic components can at times be identified (Fig. 3).
Congenital Mesoblastic Nephroma The most common renal neoplasm of infancy is congenital mesoblastic nephroma (CMN).7,10,11 CMN was first described as a leiomyomatous lesion with an excellent prognosis and benign course.12 However, the authors of numerous reports have since described 2 pathologic subtypes: the clas-
Figure 1 Hydronephrosis in a newborn, diagnosed prenatally. Sagittal US image of the right kidney demonstrates marked dilatation of the renal pelvis and calyces. Hypoechoic renal pyramids (arrow) denote preservation of corticomedullary differentiation, and should not be mistaken for dilated calyces or cysts.
Figure 2 Multicystic dysplastic kidney in a newborn. Sagittal US image of the right kidney demonstrates multiple noncommunicating cysts of varying size with intervening dysplastic, hyperechoic tissue, and no discernible normal renal parenchyma.
sic CMN and the more aggressive cellular variant, which can recur and even metastasize.13-15 Patients with CMN usually present in the first 3 months of life with an abdominal mass, less often with hematuria or a paraneoplastic syndrome, such as hypertension or hypercalcemia.11 Polyhydramnios has been reported in 71% of pregnancies with CMN on prenatal US.16 Those with the cellular type of CMN tend to present later in infancy and, therefore, with larger, more heteroge-
Figure 3 ARPKD in a newborn girl presenting with bilateral abdominal masses. Sagittal US image reveals a markedly enlarged kidney that extended from the diaphragm to the pelvis. The kidney is hyperechoic with scattered macroscopic cysts. The vertical line through the figure is the result of a fusion of 2 linear images, performed to include the entire kidney. The left kidney had an identical appearance.
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35 over CMN.19 Wilms tumor can also present with a paraneoplastic syndrome similar to CMN.11
Multilocular Cystic Nephroma Multilocular cystic nephroma (MLCN), or multilocular cystic renal tumor, can have a similar imaging appearance to a predominantly cystic CMN or cystic Wilms tumor. Although MLCN usually presents in older children, it can present as early as 3 months.19 Therefore, it should be included in the differential diagnosis of a renal mass in a neonate. MLCN
Figure 4 CMN in a 6-month-old girl with abdominal distention. Coronal reformatted image from a contrast-enhanced CT of the abdomen and pelvis demonstrates a large, heterogeneous, solid and cystic mass arising from the left kidney and filling most of the abdomen and pelvis, displacing bowel loops and compressing the stomach (short arrows). The mass encases the left renal artery (long arrow) and vein (not shown). Biopsy was consistent with a cellular CMN, or renal infantile fibrosarcoma.
neous tumors.17,18 This cellular variant has been shown histologically to represent the renal form of infantile fibrosarcoma.17 Imaging characteristics of CMN are largely determined by the pathologic subtype.18 The classic type of CMN is usually more uniformly solid. In contrast, the cellular type is usually heterogeneous, with complex hyperechoic regions and cystic components corresponding to hemorrhage and necrosis. It also has a tendency to encase and invade adjacent structures (Fig. 4). These features are well demonstrated on both US and CT.18 On MRI, CMNs tend to be of low signal intensity on T1-weighted images with focal regions of T1 shortening secondary to hemorrhage, while the solid portions are bright on fluid-sensitive sequences with variable enhancement.18 Calcifications are not characteristic of CMN.
Wilms Tumor Although much more common in toddlers and preschool-age children, Wilms tumor should be considered when evaluating a renal mass in infancy because it is indistinguishable from CMN by imaging. The cellular type CMN with hemorrhage and necrosis is particularly similar to Wilms tumor on imaging studies. Involvement of adjacent vessels and evidence of pulmonary metastases would favor Wilms tumor
Figure 5 Nephroblastomatosis in an 8-month-old boy with abdominal distention. (A) Sagittal US image shows reniform enlargement of the left kidney with numerous hypoechoic nodules replacing the renal cortex. (B) Coronal reformatted image from a contrast enhanced CT shows similar findings in both kidneys. The low-density nodules representing nephrogenic rests compress the normal renal tissue, represented by linear areas of parenchymal enhancement centrally (arrows).
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Renal Vein Thrombosis Renal vein thrombosis can present as an enlarged kidney secondary to venous congestion and hemorrhage, simulating a renal mass. This diagnosis should be considered in the clinical setting of hematuria, thrombocytopenia, and hypertension in a neonate, particularly if polycythemic or the infant of a diabetic mother. The affected kidney is enlarged and heterogeneous. There may be accompanying adrenal hemorrhage (Fig. 6). Doppler US is helpful in the evaluation of intrarenal clot extension into the ipsilateral renal vein or inferior vena cava, and in identifying draining collaterals.
Suprarenal Masses A congenital suprarenal mass usually arises from the adrenal gland, such as adrenal hemorrhage or congenital neuroblastoma. In addition, it can arise adjacent to the adrenal gland, such as subdiaphragmatic extralobar pulmonary sequestration (SEPS).
Adrenal Hemorrhage Figure 6 Renal vein thrombosis in a newborn girl with hematuria. US reveals an enlarged, heterogeneously hyperechoic left kidney with loss of normal corticomedullary differentiation. Flow in the renal vein could not be identified with Doppler imaging. An adrenal hemorrhage (arrow) is also present.
Adrenal hemorrhage is not a rare finding in a neonate, and it is occasionally detected prenatally.23 Adrenal hemorrhage is usually associated with specific risk factors, such as birth trauma, perinatal asphyxia, sepsis, and coagulopathy, some of which are shared with neonatal renal vein thrombosis. An acute adrenal hemorrhage typically appears as an iso- or hyperechoic mass (Fig. 7). In the subacute phase, the hemor-
typically presents as a multilocular cyst with numerous enhancing septations.
Other Renal Tumors Additional renal tumors to consider in this age group are rhabdoid tumor, clear cell sarcoma, and renal cell carcinoma, but these are even less common. Ossifying renal tumor of infancy is a rare, benign tumor which typically presents with hematuria. It is typically a smaller, calcified mass attached to the renal papilla, and because it mainly resides within the calyceal lumen, can sometimes be mistaken for a calculus.20
Nephroblastomatosis Nephroblastomatosis refers to persistent foci of metanephric blastema, resulting in either multifocal subcapsular nodules or, less frequently, diffuse involvement of both kidneys with nephrogenic rests. Nephroblastomatosis appears on CT and MRI as homogeneous solid masses of low attenuation or low signal intensity, respectively.21 In the diffuse form of nephroblastomatosis, reniform enlargement of the kidney(s) with a thick rind of nephrogenic rests peripherally and striated enhancement is usually seen.22 Although less sensitive, US may demonstrate nodules of low echogenicity in the multifocal form, or reniform enlargement of the kidneys in the diffuse form (Fig. 5). These nephrogenic rests have the potential to transform into Wilms tumors, more commonly in patients with an associated syndrome, such as Beckwith-Wiedemann.22
Figure 7 Adrenal hemorrhage in a 4-day-old boy with history of birth asphyxia. Sagittal US image demonstrates a heterogeneously enlarged right adrenal gland with hemorrhage (arrow). This was followed with serial ultrasound and completely resolved.
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37 Cushing syndrome. Imaging appearance alone cannot distinguish a congenital adrenocortical neoplasm from neuroblastoma.27,28 Therefore, a definitive diagnosis is based on histologic analysis.
Subdiaphragmatic Extralobar Pulmonary Sequestration
Figure 8 Congenital neuroblastoma in a 7-week-old boy presenting with skin nodules since birth that were thought to be decreasing in size. Because of suspicion for multiple infantile hemangiomas, the infant underwent US evaluation of the liver (not shown), which identified a heterogeneous liver and a left suprarenal mass. Contrast-enhanced CT, which followed, demonstrates a well-circumscribed, heterogeneous suprarenal mass (arrow). The liver is also heterogeneous (L), reflecting characteristic diffuse tumor infiltration. In conjunction with skin nodules and a negative bone scan for cortical metastases, a diagnosis of stage IV–S congenital neuroblastoma was made.
rhage liquefies, and the mass may become cystic and smaller over time. Ultimately, the hemorrhage resolves completely or is replaced by calcification.
Congenital Neuroblastoma Congenital neuroblastoma (CNB) is the most common neonatal malignancy. It usually arises from the adrenal gland, although it can arise from the sympathetic chain. CNB can present incidentally on prenatal US as a suprarenal cystic, solid, or mixed lesion, with or without calcifications. CT and MRI help to delineate the margins of the mass and to assess for possible intraspinal extension and metastatic disease (Fig. 8). Radiographs and bone scintigraphy can be performed to detect cortical bone metastases. Prenatally detected CNB is usually a localized stage I or stage IV–S disease, and postnatal monitoring with US is considered adequate imaging follow-up in these stages.24,25 Helpful factors in distinguishing CNB from an adrenal hemorrhage are prenatal detection, vascularity, evolution into a more complex mass, and importantly correlation with catecholamine levels.23
SEPS is usually found on the left and located adjacent to the ipsilateral adrenal gland. The most helpful distinguishing features between SEPS and neuroblastoma are location, sonographic appearance, and gestational age at presentation.29 SEPS is typically homogeneously hyperechoic with occasional small cystic areas (Fig. 9). Unlike other suprarenal masses, SEPS conforms to the retroperitoneal space in which it lies,30 sometimes shaped as a dumbbell.24 It is usually diagnosed in the second trimester. Spontaneous involution may render accurate diagnosis moot, as such has been reported in both SEPS and congenital neuroblastoma.30-32
Hepatobiliary Masses Vascular Tumors of the Liver There are several types of vascular neoplasms that can arise in the liver, and differentiating them has been difficult because of confusing terminology. The classification system proposed in 1982 by Mulliken and Glowacki33 serves as the foundation of the current classification system used by the International Society for the Study of Vascular Anomalies. When this classification system is used, vascular tumors of the liver can be differentiated primarily based on clinical presentation and imaging features. Infantile Hemangioma Infantile hemangiomas are the most common benign tumors of children, occurring in approximately 10%-12% of infants.34,35 These tumors are most often found in the skin but can occur anywhere in the body, particularly the liver. Absent or small at
Adrenocortical Neoplasms Adrenocortical neoplasms—adenoma and carcinoma—are extremely rare but should be considered in the differential diagnosis of an adrenal mass in the fetus or neonate.26,27 These masses may be seen on prenatal US or present as a palpable postnatal mass. Affected patients can have associated hormonerelated symptoms, such as virilization, precocious puberty, or
Figure 9 SEPS identified in utero. Sagittal US image demonstrates the typical homogeneously hyperechoic appearance of this mass (M), which lies superior to the left kidney (LK) and adjacent to the left adrenal gland (arrows). (Courtesy of Judy Estroff, MD, from Children’s Hospital Boston.)
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birth, infantile hemangiomas undergo a rapid proliferative phase in the first few months of life which usually levels off by 9 or 10 months, followed by a slow involuting phase, which can take up to 10 years.35 Hepatic infantile hemangiomas are typically multiple but can be solitary or diffuse. They are usually associated with multiple cutaneous hemangiomas, a feature that helps to differentiate this lesion from other vascular tumors or malformations.36 Sonographically, infantile hemangiomas are typically well-circumscribed and homogeneous, either hyperechoic or hypoechoic to normal liver (Fig. 10), although large lesions may be heterogeneous. In the proper clinical setting and with the typical sonographic appearance, no further imaging is necessary as these lesions have a benign natural history and eventually involute. CT or MRI may be required for patients experiencing rare complications from large lesions, such as ulceration and hemorrhage. These imaging modalities will reveal well-circumscribed, lobulated masses with feeding and draining vessels at the center or periphery of the lesion.35 Flow voids may be demonstrated by MRI, and enhancement is usually homogeneous.35 If the clinical course or imaging features are atypical, biopsy may be required for definitive diagnosis, as infantile hemangioma cells test strongly positive for the glucose transporter protein isoform 1 (GLUT-1) immunohistochemical marker.37 Congenital Hemangioma Congenital hemangioma of the liver is another subtype of vascular tumor, distinguished from infantile hemangioma by a different presentation and clinical course, as well as a lack of GLUT-1 positivity.37 Congenital hemangiomas grow during fetal development and are mature at birth.37,38 Therefore, prenatal detection favors the diagnosis of congenital hemangioma over infantile hemangioma. Furthermore, congenital hemangiomas are usually solitary. They are more likely to be large and heterogeneous, with complex vascular anatomy that may include systemic collaterals and components of arteriovenous shunts or malformations (Fig. 11). Large congenital hemangiomas may present with high-output cardiac failure. Congenital hemangiomas are divided into 2 types, the rapidly involuting congenital hemangioma (RICH) and the noninvoluting congenital hemangioma (NICH). It is their behavior that differentiates the two, not the imaging findings. The RICH type will undergo involution, which begins soon after birth and is complete by 1 to 2 years of life.39 The NICH type will not regress, and may even grow with the patient.39 Imaging in both cases reveals a high-flow lesion that is typically heterogeneous on US and may contain calcifications.38 Although US is very effective in characterizing these lesions and in following them to confirm involution, CT or MRI with intravenous contrast may be needed to evaluate the extent of the mass at diagnosis. Kaposiform Hemangioendothelioma Hemangioendothelioma is a term that causes confusion and is therefore best reserved for specific lesions, such as the kaposiform hemangioendothelioma (KH), a rare vascular tumor that is locally aggressive and often associated with con-
Figure 10 Multiple infantile hemangiomas in a 5-day-old girl with abdominal distention. (A) Sagittal US image through the liver reveals multiple well-circumscribed, hypoechoic nodules. (B) Color Doppler confirms that these are vascular lesions. The abdominal distention was attributable to intraperitoneal hemorrhage, thought to be secondary to a ruptured subcapsular hemangioma. Serial follow-up ultrasounds documented complete resolution by 2 years of age. (Color version of figure is available online.)
sumptive coagulopathy.35,40 Although imaging features are not specific for KH and may be similar to congenital hemangiomas, these tumors do not involute over time and have malignant potential. Therefore, if KH is suspected clinically, biopsy should be considered.40
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Hepatic Mesenchymal Hamartoma Hepatic mesenchymal hamartoma is characterized by a hamartomatous overgrowth of mesenchymal tissues which are normally present in the liver. Therefore, it can consist of cysts, bile ducts, hepatocytes, mesenchyme, and branches of the portal vein. These are benign tumors that most often present as an abdominal mass. Although surgical resection is curative, complications can arise because of mass effect from rapid expansion and nonimmune hydrops in utero.41,42 Most tumors are cystic, but they can be solid or mixed. Although the vast majority are intrahepatic, pedunculated lesions have also been reported, mimicking extrahepatic lesions.43 US will demonstrate multiple cysts with thin septa and sometimes nodules of solid tissue. Similarly, CT and MRI will reveal a multicystic mass with or without septations or solid nodules (Fig. 12).
Hepatoblastoma Hepatoblastoma is the most common primary malignant liver tumor in infants and young children. Although most of the tumors are sporadic, there is a well-documented association with genetic disorders, such as Beckwith-Wiedemann and Aicardi syndromes.44,45 On US, hepatoblastoma usually appears as a solitary solid mass which can be heterogeneous with areas of decreased echogenicity corresponding to areas of hemorrhage or necrosis. CT and MRI can further characterize the lesion, its vascularity, vascular invasion, and calcifications (Fig. 13). The utility of serum alpha 1-fetoprotein (AFP) levels in differentiating hepatoblastoma from other tumors is well described. Because serum AFP levels are normally high at birth in term and premature infants, this tool needs to be applied cautiously by experienced pediatric oncologists.46 Other rare solid tumors should be considered in the differential diagnosis of a solid liver mass, such as embryonal sarcoma or biliary rhabdomyosarcoma.
Choledochal Cyst
Figure 11 Congenital hemangioma of the liver in a newborn male with prenatal diagnosis of a liver mass. (A) Postnatal US reveals a large, heterogeneous mass (arrowheads), which occupies most of the right hepatic lobe and contains multiple punctate calcifications (long arrows). (B) Duplex Doppler demonstrates a dominant feeding artery, as well as a large draining vein (not shown). The mass demonstrated spontaneous involution on follow-up ultrasounds, consistent with a rapidly involuting congenital hemangioma, or RICH. (Color version of figure is available online.)
Choledochal cyst refers to congenital cystic dilatation of the biliary tree and is an important diagnostic consideration when a right upper quadrant cystic mass is encountered on imaging studies. Although this lesion can be detected incidentally, when symptomatic its presentation may be as a triad of mass effect, jaundice, and acholic stools. Choledochal cysts are subdivided into several types,47 with fusiform dilatation of the common bile duct representing the most common form. US is the initial examination of choice, demonstrating the relationship of the cystic mass to the biliary tree. CT does not play a major role in the diagnosis, but MRCP can be useful in detailing the preoperative anatomy (Fig. 14). Scintigraphy can confirm communication with the biliary tree.
Pancreatic Masses Congenital Pancreatic Cyst Congenital pancreatic cysts are rare lesions that may be detected incidentally. In symptomatic patients, they can pres-
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Pancreaticoblastoma Pancreaticoblastoma, or pancreatoblastoma, is a rare tumor that arises from primitive acinar cells of the pancreas which are identifiable in the fetus at 7 weeks of gestation. Although pancreaticoblastomas may arise in the fetus, these tumors rarely present in the neonatal period, at which time they typically appear cystic and may mimic a congenital pancreatic cyst.51,52 Pancreaticoblastoma more commonly presents beyond the neonatal period, after a long period of slow growth, and because of mass effect upon adjacent abdominal structures.53 At presentation, US, CT and MRI will usually reveal a large and heterogeneous mass, with areas of central necrosis (Fig. 15), features which are indistinguishable from pancreatic adenocarcinoma.54
Figure 12 Hepatic mesenchymal hamartoma in a 15-month-old girl with progressive abdominal distention. (A) Transverse US image through the liver (L) reveals a large cyst (arrow) surrounded by hyperechoic solid tissue (star) and smaller cysts (not shown). (B) Coronal reformatted image from a contrast-enhanced CT clearly demonstrates that the mass arises from the liver and contains both large and small cysts, as well as solid tissue. Surgical biopsy of this hepatic mass confirmed the diagnosis of hepatic mesenchymal hamartoma. (Courtesy of Gerald Behr, MD, from Columbia University.)
ent prenatally with polyhydramnios or postnatally with abdominal distention, vomiting and jaundice.48,49 The cysts are typically unilocular, solitary, and most often located in the pancreatic body or tail.48,50 CT or MRI may be used as adjuncts to delineate preoperative anatomy.
Figure 13 Hepatoblastoma in a 10-month-old girl with an abdominal mass. (A) Transverse US image reveals a large, heterogeneous mass (M) arising from the liver (L). (B) Axial image from a contrastenhanced CT further demonstrates the heterogeneity of the mass (M) and its relationship to normal liver (L) and hepatic vessels for surgical planning. The infant’s serum AFP was greater than 7000, and biopsy of this mass confirmed the diagnosis of hepatoblastoma.
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Splenic Masses Congenital Splenic Cyst Primary neoplasms of the spleen are exceedingly rare in the neonatal period. Congenital splenic cysts are also rare lesions. They may be true, primary cysts with an epitheliumlined wall or pseudocysts with a fibrous capsule. Although typically small and incidental, these cysts may become symptomatic because of post-traumatic rupture, infection, or hemorrhage, thus warranting follow-up.55 Spontaneous postnatal regression has been reported (Fig. 16).55,56
Masses Related to the Gastrointestinal Tract and Mesentery Gastrointestinal Tract Duplications Gastrointestinal (GI) duplications can occur anywhere from the mouth to the anus. They are named for the portion of the GI tract where they are located, most commonly ileal. GI
Figure 15 Pancreaticoblastoma in a child. Axial contrast-enhanced CT shows a large, heterogeneously enhancing mass (M) arising from the body and tail of the pancreas. (Courtesy of Marilyn Siegel, MD, from St. Louis, MO, reprinted with permission.54)
duplications are typically spherical cysts, rarely tubular, and are composed of smooth muscle with an inner epithelial lining of mucosa from any portion of the GI tract. However, they do not typically communicate with the adjacent bowel lumen.41 Although GI duplications may be discovered incidentally, they can also lead to symptoms by acting as a lead point for intussusception or segmental volvulus, or by developing ulcerations which can present with GI bleeding if there is communication with the lumen of the alimentary canal. Isolated GI duplications have been rarely reported.57 Radiographs may suggest the presence of a large soft-tissue mass in patients with GI duplications. US shows typical features of a cyst that is closely associated with the adjacent stomach or bowel wall. The cyst fluid may be clear and anechoic, or hemorrhagic with a fluid-debris level. The cyst
Figure 14 Choledochal cyst in an 8-week-old boy with jaundice. US (not shown) revealed a large cyst in the porta hepatis with dilatation of left portal branches. MRCP performed for surgical planning reveals marked fusiform dilatation of the entire extrahepatic bile duct (long arrow) with saccular dilatation of intrahepatic bile ducts in the left hepatic lobe (short arrows). This is consistent with a type IV-A choledochal cyst using the Todani classification system.47
Figure 16 Congenital splenic cyst with fluid-fluid level in a 13-dayold boy, discovered incidentally during a renal ultrasound performed for unrelated reasons. The lesion resolved on follow-up examination.
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G.L. Crane and M. Hernanz-Schulman omentum or bowel mesentery. These omental and mesenteric LMs must be differentiated from GI duplication cysts. Abdominal LMs can be detected incidentally or present as an abdominal mass in the newborn, rarely reported to cause obstruction.62
Figure 17 Gastrointestinal duplication in a child presenting with pancreatitis. US reveals a cystic mass in the retroperitoneum, abutting the third portion of the duodenum. This image demonstrates the characteristic “gut signature” or “muscular rim” sign of a GI duplication, with a hyperechoic inner mucosal lining (straight arrow) and a hypoechoic outer muscular wall (curved arrow).
wall may exhibit bowel signature or the “muscular rim” sign, with an inner hyperechoic mucosal lining and an outer hypoechoic muscular wall (Fig. 17).58,59 Although other lesions can mimic the bowel signature of a GI duplication cyst,60 it is still considered a reliable sign and no further preoperative imaging may be necessary. If performed, CT and MRI will show similar findings of a cyst intimately associated with adjacent bowel, with clear or complex internal fluid content.
Meconium Pseudocyst Meconium peritonitis is a sterile chemical peritonitis resulting from in utero intestinal perforation and spillage of meconium into the peritoneum. It is usually suspected when a fetus or newborn is found to have intraperitoneal or scrotal calcifications, especially when associated with ascites or polyhydramnios. Meconium pseudocysts result when intraperitoneal adhesions form to contain the meconium. On radiographs, a meconium pseudocyst may appear as a rim-calcified mass displacing bowel loops, whereas on US it typically appears as a circumscribed cyst with heterogeneous internal echotexture and sometimes a calcified wall (Fig. 18). Noncystic dense masses with calcium deposits can also form in an attempt to seal off the perforation.61
Abdominal Lymphatic Malformation Lymphatic malformations (LMs) most often occur in the neck and axilla but can also arise in the abdomen. These benign lesions are congenital developmental anomalies of the lymphatic system. Abdominal LMs can be located in the retroperitoneum or within the peritoneal cavity, arising from the
Figure 18 Meconium pseudocyst in a newborn with abdominal distention. (A) Abdominal radiograph reveals a large calcified mass in the right abdomen (arrows). (B) Transverse US image of the right upper quadrant demonstrates a circumscribed complex cyst with hyperechoic wall abutting the liver (L). The calcified wall of the pseudocyst causes mild posterior acoustic shadowing (arrows).
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References
Figure 19 Abdominal lymphatic malformation in a 2-month-old girl. (A) US image of the left lower quadrant reveals a large multilocular cystic mass with internal echoes. (B) MRI also demonstrates fluidfluid levels, which suggests intralesional hemorrhage. (Courtesy of Ryan Arnold, MD, at Children’s Hospital Boston.)
Abdominal radiographs may demonstrate features of an abdominal mass in patients with abdominal LMs. US typically shows a circumscribed thin-walled cystic mass, often with internal septa, typically lacking the bowel signature of the GI duplication cyst. The serous fluid is anechoic, but there may be scattered internal echoes or fluid-fluid levels secondary to intralesional hemorrhage. Although the diagnosis can be made by US, CT and MRI may be needed to define the extent of the lesion preoperatively (Fig. 19). Complete surgical excision, which sometimes requires bowel resection, is curative.63
Conclusions The category of congenital abdominal masses includes a wide variety of lesions ranging from cystic to solid, benign to malignant, asymptomatic to life-threatening. Familiarity with these entities and their imaging characteristics in pediatric patients is important for optimal diagnosis and expedited treatment.
1. Riccabona M: Potential of MR-imaging in the paediatric abdomen. Eur J Radiol 68:235-244, 2008 2. Malviya S, Voepel-Lewis T, Eldevik OP, et al: Sedation and general anaesthesia in children undergoing MRI and CT: Adverse events and outcomes. Br J Anaesth 84:743-748, 2000 3. Olsen OE: Practical body MRI—A paediatric perspective. Eur J Radiol 68:299-308, 2008 4. Weinreb JC: Improving gadolinium-based contrast safety. Imaging http://Biz.com, 2008, Vol 3, No 2. Available at: http://www.lhai.org/ nsf2.pdf. Accessed July 26, 2011 5. Mendichovszky IA, Marks SD, Simcock CM, et al: Gadolinium and nephrogenic systemic fibrosis: Time to tighten practice. Pediatr Radiol 38:489-496, 2008 6. Keengwe N, Hegde S, Dearlove O, et al: Structured sedation programme for magnetic resonance imaging examination in children. J Anesth 54:1069-1072, 1999 7. Pinto E, Guignard JP: Renal masses in the neonate. Biol Neonate 68: 175-184, 1995 8. Brown T, Mandell J, Lebowitz RL: Neonatal hydronephrosis in the era of sonography. AJR Am J Roentgenol 148:958-963, 1987 9. Babcock DS, Patriquin HB: The pediatric kidney and adrenal glands, in Rumack CM, Wilson SR, Charboneau JW (eds): Diagnostic Ultrasound (ed 3). St. Louis, Mosby, 2005, pp 1905-1940 10. Marsden HB, Lawler W: Primary renal tumours in the first year of life. A population based review. Virchows Arch A Pathol Anat Histopathol 399:1-9, 1983 11. Glick RD, Hicks MJ, Nuchtern JG, et al: Renal tumors in infants less than 6 months of age. J Pediatr Surg 39:522-525, 2004 12. Bolande RP, Brough AJ, Izant RJ Jr: Congenital mesoblastic nephroma of infancy. A report of eight cases and the relationship to Wilms’ tumor. Pediatrics 40:272-278, 1967 13. Joshi VV, Kay S, Milsten R, et al: Congenital mesoblastic nephroma of infancy: Report of a case with unusual clinical behavior. Am J Clin Pathol 60:811-816, 1973 14. Chan HS, Cheng MY, Mancer K, et al: Congenital mesoblastic nephroma: A clinicoradiologic study of 17 cases representing the pathologic spectrum of the disease. J Pediatr 111:64-70, 1987 15. Loeb DM, Hill DA, Dome JS: Complete response of recurrent cellular congenital mesoblastic nephroma to chemotherapy. J Pediatr Hematol/ Oncol 24:478-481, 2002 16. Haddad B, Haziza J, Touboul C, et al: The congenital mesoblastic nephroma: A case report of prenatal diagnosis. Fetal Diagn Ther 11:6166, 1996 17. Bayindir P, Guillerman RP, Hicks MJ, et al: Cellular mesoblastic nephroma (infantile renal fibrosarcoma): Institutional review of the clinical, diagnostic imaging, and pathologic features of a distinctive neoplasm of infancy. Pediatr Radiol 39:1066-1074, 2009 18. Chaudry G, Perez-Atayde AR, Ngan BY, et al: Imaging of congenital mesoblastic nephroma with pathological correlation. Pediatr Radiol 39:1080-1086, 2009 19. Lowe LH, Isuani BH, Heller RM, et al: Pediatric renal masses: Wilms tumor and beyond. RadioGraphics 20:1585-1603, 2000 20. Sotelo-Avila C, Beckwith JB, Johnson JE: Ossifying renal tumor of infancy: A clinicopathologic study of nine cases. Pediatr Pathol Lab Med 15:745-762, 1995 21. Rohrschneider WK, Weirich A, Rieden K, et al: US, CT and MR imaging characteristics of nephroblastomatosis. Pediatr Radiol 28:435-443, 1998 22. Lonergan GJ, Martínez-León MI, Agrons GA, et al: Nephrogenic rests, nephroblastomatosis, and associated lesions of the kidney. Radiographics 18:947-968, 1998 23. Eo H, Kim JH, Jang KM, et al: Comparison of clinico-radiological features between congenital cystic neuroblastoma and neonatal adrenal hemorrhagic pseudocyst. Korean J Radiol 12:52-58, 2011 24. Moon SB, Shin HB, Seo JM, et al: Clinical features and surgical outcome of a suprarenal mass detected before birth. Pediatr Surg Int 26:241246, 2010
44 25. Forman HP, Leonidas JC, Berdon WE, et al: Congenital neuroblastoma: Evaluation with multimodality imaging. Radiology 175:365-368, 1990 26. Satge D, Philippe E, Ruppe M, et al: Neonatal carcinoma. Review of the literature apropos of a case. Bull Cancer 75:373-384, 1988 27. Sarwar ZU, Ward VL, Mooney DP, et al: Congenital adrenocortical adenoma: Case report and review of literature. Pediatr Radiol 34:991994, 2004 28. Daneman A, Chan HS, Martin J: Adrenal carcinoma and adenoma in children: A review of 17 patients. Pediatr Radiol 13:11-18, 1983 29. Curtis MR, Mooney DP, Vaccaro TJ, et al: Prenatal ultrasound characterization of the suprarenal mass: Distinction between neuroblastoma and subdiaphragmatic extralobar pulmonary sequestration. J Ultrasound Med 16:75-83, 1997 30. Hernanz-Schulman M, Johnson JE, Holcomb GW III, et al: Retroperitoneal pulmonary sequestration: Imaging findings, histopathologic correlation, and relationship to cystic adenomatoid malformation. AJR Am J Roentgenol 168:1277-1281, 1997 31. Chowdhury M, Samuel M, Ramsay A, et al: Spontaneous postnatal involution of intraabdominal pulmonary sequestration. J Pediatr Surg 39:1273-1275, 2004 32. Haas D, Ablin AR, Miller C, et al: Complete pathologic maturation and regression of stage IVS neuroblastoma without treatment. Cancer 62: 818-825, 1988 33. Mulliken JB, Glowacki J: Hemangiomas and vascular malformations in infants and children: A classification based on endothelial characteristics. Plast Reconstr Surg 69:412-422, 1982 34. Bruckner AL, Frieden IJ: Hemangiomas of infancy. J Am Acad Dermatol 48:477-496, 2003 35. Burrows PE, Laor T, Paltiel H, et al: Diagnostic imaging in the evaluation of vascular birthmarks. Dermatol Clin 16:455-488, 1998 36. Boon LM, Burrows PE, Paltiel HJ, et al: Hepatic vascular anomalies in infancy: A twenty-seven-year experience. J Pediatr 129:346-354, 1996 37. Moore CW, Lowe LH: Hepatic tumors and tumor-like conditions, in Slovis TL (ed): Caffey’s Pediatric Diagnostic Imaging. Philadelphia, PA, Mosby Elsevier, 2008, pp 1929-1948 38. Fadell MF, Jones BV, Adams DM: Prenatal diagnosis and postnatal follow-up of rapidly involuting congenital hemangioma (RICH). Pediatr Radiol 41:1057-1060, 2011 39. Mulliken JB, Enjolras O: Congenital hemangiomas and infantile hemangioma: Missing links. J Am Acad Dermatol 50:875-882, 2004 40. Fernández Y, Bernabeu-Wittel M, García-Morillo JS: Kaposiform hemangioendothelioma. Eur J Intern Med 20:106-113, 2009 41. Chandler JC, Gauderer MW: The neonate with an abdominal mass. Pediatr Clin North Am 51:979-997, 2004 42. Isaacs H Jr: Fetal and neonatal hepatic tumors. J Pediatr Surg 42:17971803, 2007 43. Cornette J, Festen S, van den Hoonaard TL, et al: Mesenchymal hamartoma of the liver: A benign tumor with deceptive prognosis in the perinatal period. Case report and review of the literature. Fetal Diagn Ther 25:196-202, 2009
G.L. Crane and M. Hernanz-Schulman 44. Hamada Y, Takada K, Fukunaga S, et al: Hepatoblastoma associated with Beckwith–Wiedemann syndrome and hemihypertrophy. Pediatr Surg Int 19:112-114, 2003 45. Tanaka T, Takakura H, Takashima S, et al: A rare case of Aicardi syndrome with severe brain malformation and hepatoblastoma. Brain Dev 7:507-512, 1985 46. Blohm ME, Vesterling-Hörner D, Calaminus G, et al: Alpha 1-fetoprotein (AFP) reference values in infants up to 2 years of age. Pediatr Hematol Oncol 15:135-142, 1998 47. Todani T, Watanabe Y, Narusue M, et al: Congenital bile duct cysts: Classification, operative procedures, and review of thirty-seven cases including cancer arising from choledochal cyst. Am J Surg 134:263269, 1977 48. Chung JH, Lim GY, Song YT: Congenital true pancreatic cyst detected prenatally in neonate: A case report. J Pediatr Surg 42:E27-E29, 2007 49. Pilot LM, Gooselaw JG, Isaacson PG: Obstruction of the common bile duct in the newborn by a pancreatic cyst. J Lancet 84:204-205, 1964 50. Auringer ST, Ulmer JL, Sumner TE, et al: Congenital cyst of the pancreas. J Pediatr Surg 28:1570-1571, 1993 51. Klimstra DS, Adair CF, Hefess CS, et al: Papillary cystic tumor of the pancreas. An analysis of cellular differentiation by electron microscopy and immunohistochemistry. Am J Surg Pathol 11:855-865, 1987 52. Drut R, Jones MC: Congenital pancreatoblastoma in Beckwith-Wiedemann syndrome: An emerging association. Pediatr Pathol 8:331-339, 1988 53. Montemarano H, Lonergan GJ, Bulas DI, et al: Pancreatoblastoma: Imaging findings in 10 patients and review of the literature. Radiology 214:476-482, 2000 54. Kaste SC: The pancreas, in Slovis TL (ed): Caffey’s Pediatric Diagnostic Imaging. Philadelphia, PA, Mosby Elsevier, 2008, pp 1983-2004 55. Chen IL, Ching-Chung T, San-Nan Y, et al: Spontaneous regression of congenital splenic cyst in a neonate. Clin Pediatr 46:73-75, 2007 56. Garel C, Hassan M: Foetal and neonatal splenic cyst-like lesions. US follow-up of seven cases. Pediatr Radiol 25:360-362, 1995 57. Okamoto T, Takamizawa S, Yokoi A, et al: Completely isolated alimentary tract duplication in a neonate. Pediatr Surg Int 24:1145-1147, 2008 58. Kangarloo H, Sample WF, Hansen G, et al: Ultrasonic evaluation of abdominal gastrointestinal tract duplication in children. Radiology 131:191-194, 1979 59. Segal SR, Sherman NH, Rosenberg HK, et al: Ultrasonographic features of gastrointestinal duplications. J Ultrasound Med 13:863-870, 1994 60. Cheng G, Soboleski D, Daneman A, et al: Sonographic pitfalls in the diagnosis of enteric duplication cysts. AJR Am J Roentgenol 184:521525, 2005 61. Konje JC, de Chazal R, MacFadyen U, et al: Antenatal diagnosis and management of meconium peritonitis: A case report and review of the literature. Ultrasound Obstet Gynecol 6:66-69, 1995 62. Kosir MA, Sonnino RE, Gauderer MW: Pediatric abdominal lymphangiomas: A plea for early recognition. J Pediatr Surg 26:1309-1313, 1991 63. Luo CC, Huang CS, Chao HC, et al: Intra-abdominal cystic lymphangiomas in infancy and childhood. Chang Gung Med J 27:509-514, 2004
Introduction Although a wide variety of abdominal masses can present in pediatric patients, the focus of this review is on congenital abdominal masses, i.e. those that are present at birth, and therefore diagnosed in utero or in the neonatal period. These masses, although relatively rare, must be evaluated effectively to expedite diagnosis and treatment. In this article, considerations for optimal use of various currently available imaging modalities, principal imaging techniques, and imaging characteristics of the commonly encountered congenital abdominal masses are reviewed.
Imaging Techniques The evaluation of congenital abdominal masses relies primarily on ultrasound (US), which can provide high-resolution imaging assessment without sedation or radiation exposure in infants. However, there is a place for other imaging modalities, such as plain radiography, computed tomography (CT), magnetic resonance imaging (MRI), and nuclear medicine in the evaluation of congenital abdominal masses in pediatric patients, with findings which often are complementary to US. For each imaging modality, the currently recommended imaging protocols will be discussed briefly in the following sections.
Plain Radiography The first-line imaging modality for an infant or child who presents with clinical signs and symptoms suspicious for an abdominal mass is often a plain radiograph of the abdomen. This examination should include more than one view, often supine and left lateral decubitus, particularly when the child presents with acute symptoms, to exclude bowel obstruction or perforation as the cause for an acute abdomen. Abdominal
Department of Diagnostic Imaging, Monroe Carell Jr. Children’s Hospital at Vanderbilt, Nashville, TN. Address reprint requests to Gabriella L. Crane, MD, Assistant Professor, Radiology and Pediatrics, Department of Diagnostic Imaging, Monroe Carell Jr. Children’s Hospital at Vanderbilt, 2200 Children’s Way, Suite 1416, Nashville, TN 37232-9700. E-mail: [email protected]
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radiographs can also provide clues to the location and organ of origin of a mass based on its mass effect upon adjacent air-filled bowel loops. In addition, calcifications seen by plain radiography can offer clues to the diagnosis. Pseudomasses, such as a distended stomach or bladder, can also be identified.
Ultrasound US is an excellent imaging modality for the evaluation of the pediatric abdomen and can often provide all the information necessary in the diagnosis and surgical planning for a congenital abdominal mass. A radiologist experienced in US can often ascertain the origin of the mass, its internal architecture, and vascular supply, as well as regional metastases and vascular invasion. US is particularly beneficial in pediatric patients because the examination can be performed without sedation and without exposing the child to ionizing radiation. Depending on the lesion, US may be the optimal imaging examination and the only study necessary before definitive treatment. In contrast, US examinations are relatively nonstandardized and can be limited by intervening gas and bone. However, even in cases in which further imaging is necessary, US provides an excellent road map to guide and optimize subsequent imaging.
Computed Tomography If US is unable to fully evaluate a mass or if malignancy is suspected, CT is often a useful next step for further evaluation of congenital abdominal masses. CT is a standardized imaging modality in which the anatomy is always depicted sequentially and is unimpeded by intervening bowel gas or bone. However, it lacks the “real-time” capability of US and may remain limited in assessing the organ of origin for a very large mass. The CT protocol should be geared towards the suspected diagnosis, typically as guided by the clinical presentation and information obtained on preceding radiograph and US. Single-phase CT is usually sufficient for evaluation of congenital abdominal masses in most patients. However, in some cases, multiphase imaging may be indicated. For example, certain congenital abdominal masses characteristically contain calcifications, such as neuroblastoma. Therefore, the examination
Congenital abdominal masses in pediatric patients may begin with noncontrast CT imaging for the detection of calcifications that may be difficult to detect after the administration of contrast. This should be limited, however, to the mass or organ of interest to reduce overall radiation exposure, and typically the milliampere second (mAs) can be greatly reduced from that needed for the subsequent phase(s). If information regarding arterial and venous involvement is of clinical importance, particularly in a presurgical evaluation, arterial and/or venous phase scanning may be needed. Delayed images in renal excretory phase may be obtained when the collecting system/ureter needs to be visualized. Unfortunately, CT examinations expose these pediatric patients, who are much more sensitive to the potentially deleterious stochastic effects of radiation exposure, to ionizing radiation. Therefore, it is important that the study be undertaken only when diagnostic accuracy and management require it, and protocoled according to the As Low As Reasonably Achievable (ALARA) principle of diagnostic optimization. In infants and young children (ⱕ5 years), CT may require sedation to achieve diagnostic images, and these associated risks must also be carefully considered.1,2
Magnetic Resonance Imaging In recent years, MRI has become an increasingly valuable imaging modality in evaluating pediatric congenital abdominal masses, particularly with the advent of faster imaging sequences, greater strength magnets, and specialized pediatric coils. MRI can be used to delineate anatomic boundaries, assess perfusion patterns with dynamic contrast imaging, and newer techniques, such as diffusion-weighted imaging and MR spectroscopy, can provide functional and quantitative information as well.1,3 MRI is particularly useful in the evaluation of vascular malformations and in the characterization of hepatic and biliary masses. Some specific challenges when imaging the neonatal abdomen with MRI include the small size of the structures being evaluated, the inability of young patients to cooperate, and the inherently increased heart and respiratory rates of young patients.1 For example, the need for high-resolution images of small structures can be met by decreasing the field of view and increasing matrix size. However, this decreases signalto-noise and may require compensation, such as adding sequences which lengthens the overall scan time. When intravenous contrast is needed, gadolinium should be used carefully with attention to renal function, hepatic disease, previous surgery, or other proinflammatory conditions that increase the risk of nephrogenic systemic fibrosis. Nephrogenic systemic fibrosis in children is rare and, to our knowledge, not yet reported in the neonatal population.4 However, there may be potentially increased risk because of the normally lower glomerular filtration rate in the neonate, particularly in patients with abnormal kidneys and compromised renal function. Existing data, therefore, suggest that intravenous gadolinium be used carefully and only when necessary.3,5 Although a detailed discussion of MRI techniques is beyond the scope of this article, several general rules apply to
33 MRI of the pediatric abdomen.1 These include the use of fast isotropic 3D sequences that allow for multiplanar reconstructions; balanced steady-state free precession sequences for a quick preliminary imaging overview of the region of interest; heavily T2-weighted sequences, such as those used in magnetic resonance cholangiopancreatography (MRCP), which are useful in evaluating fluid-filled structures of the biliary and urinary tracts; and dynamic sequences and MR angiographic imaging using T1-weighted fast 3D gradient recalled echo or fast low-angle shot sequences, which are fast enough to not require breath-holding. The various methods currently available for minimizing respiratory artifact include controlled ventilation in anesthetized patients, respiratory triggering using external diaphragmatic bellows, and prospective gating using secondary images of diaphragmatic motion.1,3 Although neonates can often be imaged using “wrap-andfeed” technique with diagnostically sufficient results, older infants and young children need to be sedated to obtain diagnostic images, preferably by a dedicated pediatric sedation team.1,2,6 In addition, care should be taken that appropriate body temperature is maintained in all neonatal patients during MRI examination.
Nuclear Medicine Nuclear medicine is useful as a problem-solving imaging modality on a case-by-case basis. There is also a vital role for certain types of examinations, such as metaiodobenzylguanidine (MIBG) scans, in the surveillance of patients with specific tumors, such as neuroblastoma. The various examinations and their applications for evaluating congenital abdominal masses in pediatric patients will be discussed in the following sections.
Renal Masses Hydronephrosis Almost two-thirds of infantile abdominal masses arise from the kidneys, and most of these masses are benign.7 The most common abdominal “mass” found in this age group is hydronephrosis.8 It is often detected prenatally and can be caused by obstruction, vesicoureteral reflux, or both. The most common site of obstruction resulting in hydronephrosis is the ureteropelvic junction. Work-up for a child with hydronephrosis includes US to evaluate the degree of pelvocalyceal dilation and to assess whether there is ureteral dilatation or abnormalities of the contralateral kidney. The hydronephrotic kidney shows a dilated collecting system, with dilated calyces surrounding the centrally located hydronephrotic renal pelvis (Fig. 1). In evaluating hydronephrosis, it is important to assess the degree of thinning of the renal parenchyma and preservation of corticomedullary differentiation. Voiding cystourethrography is typically performed to exclude vesicoureteral reflux or extravesical abnormalities, whereas a nuclear medicine renogram with Lasix challenge is helpful in confirming obstruction as the cause of dilatation and in quantifying renal function.9 MR urography
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is currently assuming a role as an alternative imaging modality that can evaluate both renal anatomy and function.
Multicystic Dysplastic Kidney The differential diagnosis for hydronephrosis secondary to ureteropelvic junction obstruction is multicystic dysplastic kidney (MCDK). On US, MCDK typically appears as multiple noncommunicating cysts of various sizes with dysplastic and hyperechoic tissue separating the cystic components. There is usually no discernible normal renal tissue (Fig. 2). Often the largest cystic structure will not be located centrally, as is true with hydronephrosis. On renal scintigraphy, MCDK demonstrates no renal function.
Autosomal Recessive Polycystic Kidney Disease Pediatric patients with autosomal-recessive polycystic kidney disease (ARPKD) present with bilateral renal enlargement resembling bilateral masses on physical examination and on abdominal radiographs. Renal enlargement is secondary to hyperplasia of the collecting tubules, resulting in a spectrum of disease that can lead to presentation in utero or later in life. On US, the enlarged kidneys demonstrate overall increased echogenicity because of the multiplicity of interfaces presented by the collecting tubules. With current high-resolution US equipment, small macroscopic components can at times be identified (Fig. 3).
Congenital Mesoblastic Nephroma The most common renal neoplasm of infancy is congenital mesoblastic nephroma (CMN).7,10,11 CMN was first described as a leiomyomatous lesion with an excellent prognosis and benign course.12 However, the authors of numerous reports have since described 2 pathologic subtypes: the clas-
Figure 1 Hydronephrosis in a newborn, diagnosed prenatally. Sagittal US image of the right kidney demonstrates marked dilatation of the renal pelvis and calyces. Hypoechoic renal pyramids (arrow) denote preservation of corticomedullary differentiation, and should not be mistaken for dilated calyces or cysts.
Figure 2 Multicystic dysplastic kidney in a newborn. Sagittal US image of the right kidney demonstrates multiple noncommunicating cysts of varying size with intervening dysplastic, hyperechoic tissue, and no discernible normal renal parenchyma.
sic CMN and the more aggressive cellular variant, which can recur and even metastasize.13-15 Patients with CMN usually present in the first 3 months of life with an abdominal mass, less often with hematuria or a paraneoplastic syndrome, such as hypertension or hypercalcemia.11 Polyhydramnios has been reported in 71% of pregnancies with CMN on prenatal US.16 Those with the cellular type of CMN tend to present later in infancy and, therefore, with larger, more heteroge-
Figure 3 ARPKD in a newborn girl presenting with bilateral abdominal masses. Sagittal US image reveals a markedly enlarged kidney that extended from the diaphragm to the pelvis. The kidney is hyperechoic with scattered macroscopic cysts. The vertical line through the figure is the result of a fusion of 2 linear images, performed to include the entire kidney. The left kidney had an identical appearance.
Congenital abdominal masses in pediatric patients
35 over CMN.19 Wilms tumor can also present with a paraneoplastic syndrome similar to CMN.11
Multilocular Cystic Nephroma Multilocular cystic nephroma (MLCN), or multilocular cystic renal tumor, can have a similar imaging appearance to a predominantly cystic CMN or cystic Wilms tumor. Although MLCN usually presents in older children, it can present as early as 3 months.19 Therefore, it should be included in the differential diagnosis of a renal mass in a neonate. MLCN
Figure 4 CMN in a 6-month-old girl with abdominal distention. Coronal reformatted image from a contrast-enhanced CT of the abdomen and pelvis demonstrates a large, heterogeneous, solid and cystic mass arising from the left kidney and filling most of the abdomen and pelvis, displacing bowel loops and compressing the stomach (short arrows). The mass encases the left renal artery (long arrow) and vein (not shown). Biopsy was consistent with a cellular CMN, or renal infantile fibrosarcoma.
neous tumors.17,18 This cellular variant has been shown histologically to represent the renal form of infantile fibrosarcoma.17 Imaging characteristics of CMN are largely determined by the pathologic subtype.18 The classic type of CMN is usually more uniformly solid. In contrast, the cellular type is usually heterogeneous, with complex hyperechoic regions and cystic components corresponding to hemorrhage and necrosis. It also has a tendency to encase and invade adjacent structures (Fig. 4). These features are well demonstrated on both US and CT.18 On MRI, CMNs tend to be of low signal intensity on T1-weighted images with focal regions of T1 shortening secondary to hemorrhage, while the solid portions are bright on fluid-sensitive sequences with variable enhancement.18 Calcifications are not characteristic of CMN.
Wilms Tumor Although much more common in toddlers and preschool-age children, Wilms tumor should be considered when evaluating a renal mass in infancy because it is indistinguishable from CMN by imaging. The cellular type CMN with hemorrhage and necrosis is particularly similar to Wilms tumor on imaging studies. Involvement of adjacent vessels and evidence of pulmonary metastases would favor Wilms tumor
Figure 5 Nephroblastomatosis in an 8-month-old boy with abdominal distention. (A) Sagittal US image shows reniform enlargement of the left kidney with numerous hypoechoic nodules replacing the renal cortex. (B) Coronal reformatted image from a contrast enhanced CT shows similar findings in both kidneys. The low-density nodules representing nephrogenic rests compress the normal renal tissue, represented by linear areas of parenchymal enhancement centrally (arrows).
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Renal Vein Thrombosis Renal vein thrombosis can present as an enlarged kidney secondary to venous congestion and hemorrhage, simulating a renal mass. This diagnosis should be considered in the clinical setting of hematuria, thrombocytopenia, and hypertension in a neonate, particularly if polycythemic or the infant of a diabetic mother. The affected kidney is enlarged and heterogeneous. There may be accompanying adrenal hemorrhage (Fig. 6). Doppler US is helpful in the evaluation of intrarenal clot extension into the ipsilateral renal vein or inferior vena cava, and in identifying draining collaterals.
Suprarenal Masses A congenital suprarenal mass usually arises from the adrenal gland, such as adrenal hemorrhage or congenital neuroblastoma. In addition, it can arise adjacent to the adrenal gland, such as subdiaphragmatic extralobar pulmonary sequestration (SEPS).
Adrenal Hemorrhage Figure 6 Renal vein thrombosis in a newborn girl with hematuria. US reveals an enlarged, heterogeneously hyperechoic left kidney with loss of normal corticomedullary differentiation. Flow in the renal vein could not be identified with Doppler imaging. An adrenal hemorrhage (arrow) is also present.
Adrenal hemorrhage is not a rare finding in a neonate, and it is occasionally detected prenatally.23 Adrenal hemorrhage is usually associated with specific risk factors, such as birth trauma, perinatal asphyxia, sepsis, and coagulopathy, some of which are shared with neonatal renal vein thrombosis. An acute adrenal hemorrhage typically appears as an iso- or hyperechoic mass (Fig. 7). In the subacute phase, the hemor-
typically presents as a multilocular cyst with numerous enhancing septations.
Other Renal Tumors Additional renal tumors to consider in this age group are rhabdoid tumor, clear cell sarcoma, and renal cell carcinoma, but these are even less common. Ossifying renal tumor of infancy is a rare, benign tumor which typically presents with hematuria. It is typically a smaller, calcified mass attached to the renal papilla, and because it mainly resides within the calyceal lumen, can sometimes be mistaken for a calculus.20
Nephroblastomatosis Nephroblastomatosis refers to persistent foci of metanephric blastema, resulting in either multifocal subcapsular nodules or, less frequently, diffuse involvement of both kidneys with nephrogenic rests. Nephroblastomatosis appears on CT and MRI as homogeneous solid masses of low attenuation or low signal intensity, respectively.21 In the diffuse form of nephroblastomatosis, reniform enlargement of the kidney(s) with a thick rind of nephrogenic rests peripherally and striated enhancement is usually seen.22 Although less sensitive, US may demonstrate nodules of low echogenicity in the multifocal form, or reniform enlargement of the kidneys in the diffuse form (Fig. 5). These nephrogenic rests have the potential to transform into Wilms tumors, more commonly in patients with an associated syndrome, such as Beckwith-Wiedemann.22
Figure 7 Adrenal hemorrhage in a 4-day-old boy with history of birth asphyxia. Sagittal US image demonstrates a heterogeneously enlarged right adrenal gland with hemorrhage (arrow). This was followed with serial ultrasound and completely resolved.
Congenital abdominal masses in pediatric patients
37 Cushing syndrome. Imaging appearance alone cannot distinguish a congenital adrenocortical neoplasm from neuroblastoma.27,28 Therefore, a definitive diagnosis is based on histologic analysis.
Subdiaphragmatic Extralobar Pulmonary Sequestration
Figure 8 Congenital neuroblastoma in a 7-week-old boy presenting with skin nodules since birth that were thought to be decreasing in size. Because of suspicion for multiple infantile hemangiomas, the infant underwent US evaluation of the liver (not shown), which identified a heterogeneous liver and a left suprarenal mass. Contrast-enhanced CT, which followed, demonstrates a well-circumscribed, heterogeneous suprarenal mass (arrow). The liver is also heterogeneous (L), reflecting characteristic diffuse tumor infiltration. In conjunction with skin nodules and a negative bone scan for cortical metastases, a diagnosis of stage IV–S congenital neuroblastoma was made.
rhage liquefies, and the mass may become cystic and smaller over time. Ultimately, the hemorrhage resolves completely or is replaced by calcification.
Congenital Neuroblastoma Congenital neuroblastoma (CNB) is the most common neonatal malignancy. It usually arises from the adrenal gland, although it can arise from the sympathetic chain. CNB can present incidentally on prenatal US as a suprarenal cystic, solid, or mixed lesion, with or without calcifications. CT and MRI help to delineate the margins of the mass and to assess for possible intraspinal extension and metastatic disease (Fig. 8). Radiographs and bone scintigraphy can be performed to detect cortical bone metastases. Prenatally detected CNB is usually a localized stage I or stage IV–S disease, and postnatal monitoring with US is considered adequate imaging follow-up in these stages.24,25 Helpful factors in distinguishing CNB from an adrenal hemorrhage are prenatal detection, vascularity, evolution into a more complex mass, and importantly correlation with catecholamine levels.23
SEPS is usually found on the left and located adjacent to the ipsilateral adrenal gland. The most helpful distinguishing features between SEPS and neuroblastoma are location, sonographic appearance, and gestational age at presentation.29 SEPS is typically homogeneously hyperechoic with occasional small cystic areas (Fig. 9). Unlike other suprarenal masses, SEPS conforms to the retroperitoneal space in which it lies,30 sometimes shaped as a dumbbell.24 It is usually diagnosed in the second trimester. Spontaneous involution may render accurate diagnosis moot, as such has been reported in both SEPS and congenital neuroblastoma.30-32
Hepatobiliary Masses Vascular Tumors of the Liver There are several types of vascular neoplasms that can arise in the liver, and differentiating them has been difficult because of confusing terminology. The classification system proposed in 1982 by Mulliken and Glowacki33 serves as the foundation of the current classification system used by the International Society for the Study of Vascular Anomalies. When this classification system is used, vascular tumors of the liver can be differentiated primarily based on clinical presentation and imaging features. Infantile Hemangioma Infantile hemangiomas are the most common benign tumors of children, occurring in approximately 10%-12% of infants.34,35 These tumors are most often found in the skin but can occur anywhere in the body, particularly the liver. Absent or small at
Adrenocortical Neoplasms Adrenocortical neoplasms—adenoma and carcinoma—are extremely rare but should be considered in the differential diagnosis of an adrenal mass in the fetus or neonate.26,27 These masses may be seen on prenatal US or present as a palpable postnatal mass. Affected patients can have associated hormonerelated symptoms, such as virilization, precocious puberty, or
Figure 9 SEPS identified in utero. Sagittal US image demonstrates the typical homogeneously hyperechoic appearance of this mass (M), which lies superior to the left kidney (LK) and adjacent to the left adrenal gland (arrows). (Courtesy of Judy Estroff, MD, from Children’s Hospital Boston.)
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birth, infantile hemangiomas undergo a rapid proliferative phase in the first few months of life which usually levels off by 9 or 10 months, followed by a slow involuting phase, which can take up to 10 years.35 Hepatic infantile hemangiomas are typically multiple but can be solitary or diffuse. They are usually associated with multiple cutaneous hemangiomas, a feature that helps to differentiate this lesion from other vascular tumors or malformations.36 Sonographically, infantile hemangiomas are typically well-circumscribed and homogeneous, either hyperechoic or hypoechoic to normal liver (Fig. 10), although large lesions may be heterogeneous. In the proper clinical setting and with the typical sonographic appearance, no further imaging is necessary as these lesions have a benign natural history and eventually involute. CT or MRI may be required for patients experiencing rare complications from large lesions, such as ulceration and hemorrhage. These imaging modalities will reveal well-circumscribed, lobulated masses with feeding and draining vessels at the center or periphery of the lesion.35 Flow voids may be demonstrated by MRI, and enhancement is usually homogeneous.35 If the clinical course or imaging features are atypical, biopsy may be required for definitive diagnosis, as infantile hemangioma cells test strongly positive for the glucose transporter protein isoform 1 (GLUT-1) immunohistochemical marker.37 Congenital Hemangioma Congenital hemangioma of the liver is another subtype of vascular tumor, distinguished from infantile hemangioma by a different presentation and clinical course, as well as a lack of GLUT-1 positivity.37 Congenital hemangiomas grow during fetal development and are mature at birth.37,38 Therefore, prenatal detection favors the diagnosis of congenital hemangioma over infantile hemangioma. Furthermore, congenital hemangiomas are usually solitary. They are more likely to be large and heterogeneous, with complex vascular anatomy that may include systemic collaterals and components of arteriovenous shunts or malformations (Fig. 11). Large congenital hemangiomas may present with high-output cardiac failure. Congenital hemangiomas are divided into 2 types, the rapidly involuting congenital hemangioma (RICH) and the noninvoluting congenital hemangioma (NICH). It is their behavior that differentiates the two, not the imaging findings. The RICH type will undergo involution, which begins soon after birth and is complete by 1 to 2 years of life.39 The NICH type will not regress, and may even grow with the patient.39 Imaging in both cases reveals a high-flow lesion that is typically heterogeneous on US and may contain calcifications.38 Although US is very effective in characterizing these lesions and in following them to confirm involution, CT or MRI with intravenous contrast may be needed to evaluate the extent of the mass at diagnosis. Kaposiform Hemangioendothelioma Hemangioendothelioma is a term that causes confusion and is therefore best reserved for specific lesions, such as the kaposiform hemangioendothelioma (KH), a rare vascular tumor that is locally aggressive and often associated with con-
Figure 10 Multiple infantile hemangiomas in a 5-day-old girl with abdominal distention. (A) Sagittal US image through the liver reveals multiple well-circumscribed, hypoechoic nodules. (B) Color Doppler confirms that these are vascular lesions. The abdominal distention was attributable to intraperitoneal hemorrhage, thought to be secondary to a ruptured subcapsular hemangioma. Serial follow-up ultrasounds documented complete resolution by 2 years of age. (Color version of figure is available online.)
sumptive coagulopathy.35,40 Although imaging features are not specific for KH and may be similar to congenital hemangiomas, these tumors do not involute over time and have malignant potential. Therefore, if KH is suspected clinically, biopsy should be considered.40
Congenital abdominal masses in pediatric patients
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Hepatic Mesenchymal Hamartoma Hepatic mesenchymal hamartoma is characterized by a hamartomatous overgrowth of mesenchymal tissues which are normally present in the liver. Therefore, it can consist of cysts, bile ducts, hepatocytes, mesenchyme, and branches of the portal vein. These are benign tumors that most often present as an abdominal mass. Although surgical resection is curative, complications can arise because of mass effect from rapid expansion and nonimmune hydrops in utero.41,42 Most tumors are cystic, but they can be solid or mixed. Although the vast majority are intrahepatic, pedunculated lesions have also been reported, mimicking extrahepatic lesions.43 US will demonstrate multiple cysts with thin septa and sometimes nodules of solid tissue. Similarly, CT and MRI will reveal a multicystic mass with or without septations or solid nodules (Fig. 12).
Hepatoblastoma Hepatoblastoma is the most common primary malignant liver tumor in infants and young children. Although most of the tumors are sporadic, there is a well-documented association with genetic disorders, such as Beckwith-Wiedemann and Aicardi syndromes.44,45 On US, hepatoblastoma usually appears as a solitary solid mass which can be heterogeneous with areas of decreased echogenicity corresponding to areas of hemorrhage or necrosis. CT and MRI can further characterize the lesion, its vascularity, vascular invasion, and calcifications (Fig. 13). The utility of serum alpha 1-fetoprotein (AFP) levels in differentiating hepatoblastoma from other tumors is well described. Because serum AFP levels are normally high at birth in term and premature infants, this tool needs to be applied cautiously by experienced pediatric oncologists.46 Other rare solid tumors should be considered in the differential diagnosis of a solid liver mass, such as embryonal sarcoma or biliary rhabdomyosarcoma.
Choledochal Cyst
Figure 11 Congenital hemangioma of the liver in a newborn male with prenatal diagnosis of a liver mass. (A) Postnatal US reveals a large, heterogeneous mass (arrowheads), which occupies most of the right hepatic lobe and contains multiple punctate calcifications (long arrows). (B) Duplex Doppler demonstrates a dominant feeding artery, as well as a large draining vein (not shown). The mass demonstrated spontaneous involution on follow-up ultrasounds, consistent with a rapidly involuting congenital hemangioma, or RICH. (Color version of figure is available online.)
Choledochal cyst refers to congenital cystic dilatation of the biliary tree and is an important diagnostic consideration when a right upper quadrant cystic mass is encountered on imaging studies. Although this lesion can be detected incidentally, when symptomatic its presentation may be as a triad of mass effect, jaundice, and acholic stools. Choledochal cysts are subdivided into several types,47 with fusiform dilatation of the common bile duct representing the most common form. US is the initial examination of choice, demonstrating the relationship of the cystic mass to the biliary tree. CT does not play a major role in the diagnosis, but MRCP can be useful in detailing the preoperative anatomy (Fig. 14). Scintigraphy can confirm communication with the biliary tree.
Pancreatic Masses Congenital Pancreatic Cyst Congenital pancreatic cysts are rare lesions that may be detected incidentally. In symptomatic patients, they can pres-
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Pancreaticoblastoma Pancreaticoblastoma, or pancreatoblastoma, is a rare tumor that arises from primitive acinar cells of the pancreas which are identifiable in the fetus at 7 weeks of gestation. Although pancreaticoblastomas may arise in the fetus, these tumors rarely present in the neonatal period, at which time they typically appear cystic and may mimic a congenital pancreatic cyst.51,52 Pancreaticoblastoma more commonly presents beyond the neonatal period, after a long period of slow growth, and because of mass effect upon adjacent abdominal structures.53 At presentation, US, CT and MRI will usually reveal a large and heterogeneous mass, with areas of central necrosis (Fig. 15), features which are indistinguishable from pancreatic adenocarcinoma.54
Figure 12 Hepatic mesenchymal hamartoma in a 15-month-old girl with progressive abdominal distention. (A) Transverse US image through the liver (L) reveals a large cyst (arrow) surrounded by hyperechoic solid tissue (star) and smaller cysts (not shown). (B) Coronal reformatted image from a contrast-enhanced CT clearly demonstrates that the mass arises from the liver and contains both large and small cysts, as well as solid tissue. Surgical biopsy of this hepatic mass confirmed the diagnosis of hepatic mesenchymal hamartoma. (Courtesy of Gerald Behr, MD, from Columbia University.)
ent prenatally with polyhydramnios or postnatally with abdominal distention, vomiting and jaundice.48,49 The cysts are typically unilocular, solitary, and most often located in the pancreatic body or tail.48,50 CT or MRI may be used as adjuncts to delineate preoperative anatomy.
Figure 13 Hepatoblastoma in a 10-month-old girl with an abdominal mass. (A) Transverse US image reveals a large, heterogeneous mass (M) arising from the liver (L). (B) Axial image from a contrastenhanced CT further demonstrates the heterogeneity of the mass (M) and its relationship to normal liver (L) and hepatic vessels for surgical planning. The infant’s serum AFP was greater than 7000, and biopsy of this mass confirmed the diagnosis of hepatoblastoma.
Congenital abdominal masses in pediatric patients
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Splenic Masses Congenital Splenic Cyst Primary neoplasms of the spleen are exceedingly rare in the neonatal period. Congenital splenic cysts are also rare lesions. They may be true, primary cysts with an epitheliumlined wall or pseudocysts with a fibrous capsule. Although typically small and incidental, these cysts may become symptomatic because of post-traumatic rupture, infection, or hemorrhage, thus warranting follow-up.55 Spontaneous postnatal regression has been reported (Fig. 16).55,56
Masses Related to the Gastrointestinal Tract and Mesentery Gastrointestinal Tract Duplications Gastrointestinal (GI) duplications can occur anywhere from the mouth to the anus. They are named for the portion of the GI tract where they are located, most commonly ileal. GI
Figure 15 Pancreaticoblastoma in a child. Axial contrast-enhanced CT shows a large, heterogeneously enhancing mass (M) arising from the body and tail of the pancreas. (Courtesy of Marilyn Siegel, MD, from St. Louis, MO, reprinted with permission.54)
duplications are typically spherical cysts, rarely tubular, and are composed of smooth muscle with an inner epithelial lining of mucosa from any portion of the GI tract. However, they do not typically communicate with the adjacent bowel lumen.41 Although GI duplications may be discovered incidentally, they can also lead to symptoms by acting as a lead point for intussusception or segmental volvulus, or by developing ulcerations which can present with GI bleeding if there is communication with the lumen of the alimentary canal. Isolated GI duplications have been rarely reported.57 Radiographs may suggest the presence of a large soft-tissue mass in patients with GI duplications. US shows typical features of a cyst that is closely associated with the adjacent stomach or bowel wall. The cyst fluid may be clear and anechoic, or hemorrhagic with a fluid-debris level. The cyst
Figure 14 Choledochal cyst in an 8-week-old boy with jaundice. US (not shown) revealed a large cyst in the porta hepatis with dilatation of left portal branches. MRCP performed for surgical planning reveals marked fusiform dilatation of the entire extrahepatic bile duct (long arrow) with saccular dilatation of intrahepatic bile ducts in the left hepatic lobe (short arrows). This is consistent with a type IV-A choledochal cyst using the Todani classification system.47
Figure 16 Congenital splenic cyst with fluid-fluid level in a 13-dayold boy, discovered incidentally during a renal ultrasound performed for unrelated reasons. The lesion resolved on follow-up examination.
42
G.L. Crane and M. Hernanz-Schulman omentum or bowel mesentery. These omental and mesenteric LMs must be differentiated from GI duplication cysts. Abdominal LMs can be detected incidentally or present as an abdominal mass in the newborn, rarely reported to cause obstruction.62
Figure 17 Gastrointestinal duplication in a child presenting with pancreatitis. US reveals a cystic mass in the retroperitoneum, abutting the third portion of the duodenum. This image demonstrates the characteristic “gut signature” or “muscular rim” sign of a GI duplication, with a hyperechoic inner mucosal lining (straight arrow) and a hypoechoic outer muscular wall (curved arrow).
wall may exhibit bowel signature or the “muscular rim” sign, with an inner hyperechoic mucosal lining and an outer hypoechoic muscular wall (Fig. 17).58,59 Although other lesions can mimic the bowel signature of a GI duplication cyst,60 it is still considered a reliable sign and no further preoperative imaging may be necessary. If performed, CT and MRI will show similar findings of a cyst intimately associated with adjacent bowel, with clear or complex internal fluid content.
Meconium Pseudocyst Meconium peritonitis is a sterile chemical peritonitis resulting from in utero intestinal perforation and spillage of meconium into the peritoneum. It is usually suspected when a fetus or newborn is found to have intraperitoneal or scrotal calcifications, especially when associated with ascites or polyhydramnios. Meconium pseudocysts result when intraperitoneal adhesions form to contain the meconium. On radiographs, a meconium pseudocyst may appear as a rim-calcified mass displacing bowel loops, whereas on US it typically appears as a circumscribed cyst with heterogeneous internal echotexture and sometimes a calcified wall (Fig. 18). Noncystic dense masses with calcium deposits can also form in an attempt to seal off the perforation.61
Abdominal Lymphatic Malformation Lymphatic malformations (LMs) most often occur in the neck and axilla but can also arise in the abdomen. These benign lesions are congenital developmental anomalies of the lymphatic system. Abdominal LMs can be located in the retroperitoneum or within the peritoneal cavity, arising from the
Figure 18 Meconium pseudocyst in a newborn with abdominal distention. (A) Abdominal radiograph reveals a large calcified mass in the right abdomen (arrows). (B) Transverse US image of the right upper quadrant demonstrates a circumscribed complex cyst with hyperechoic wall abutting the liver (L). The calcified wall of the pseudocyst causes mild posterior acoustic shadowing (arrows).
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References
Figure 19 Abdominal lymphatic malformation in a 2-month-old girl. (A) US image of the left lower quadrant reveals a large multilocular cystic mass with internal echoes. (B) MRI also demonstrates fluidfluid levels, which suggests intralesional hemorrhage. (Courtesy of Ryan Arnold, MD, at Children’s Hospital Boston.)
Abdominal radiographs may demonstrate features of an abdominal mass in patients with abdominal LMs. US typically shows a circumscribed thin-walled cystic mass, often with internal septa, typically lacking the bowel signature of the GI duplication cyst. The serous fluid is anechoic, but there may be scattered internal echoes or fluid-fluid levels secondary to intralesional hemorrhage. Although the diagnosis can be made by US, CT and MRI may be needed to define the extent of the lesion preoperatively (Fig. 19). Complete surgical excision, which sometimes requires bowel resection, is curative.63
Conclusions The category of congenital abdominal masses includes a wide variety of lesions ranging from cystic to solid, benign to malignant, asymptomatic to life-threatening. Familiarity with these entities and their imaging characteristics in pediatric patients is important for optimal diagnosis and expedited treatment.
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