Acta Radiológica Portuguesa, Vol.XVIII, nº 70, pág. 61-70, Abr.-Jun., 2006 Pediatric Retroperitoneal Masses Radiologic-Pathologic Correlation Marilyn J. Siegel Mallinckrodt Institute of Radiology, Washington University School of Medicine, ST. Louis Distinguished Scientist, Armed Forces Institute of Pathology Objectives Discuss roles for sonography, CT and MRI in imaging retroperitoneal masses Describe imaging features of common masses in neonates and older children Describe pitfalls in diagnosis : US Findings Well-defined margins Solid, intrarenal mass Tumor matrix Evenly echogenic: 50% Heterogeneous : 50% IVC thrombus (5-10%) : Clinical Features Mean age: 30-36 mos (range, 6 mos-4 yr) Symptoms Mass: 90% Pain, fever, hematuria: 30% Hypertension: 75% - 90% Aniridia, hemihypertrophy Budd-Chiari syndrome Long axis Transverse Wilms Tumor: Pathology Well marginated Replaces whole kidney Hemorrhage & necrosis (90%) Pseudocapsule Calcification & fat <10% ARP 61
Caval thrombus Calcified Wilms Tumor (< 5%) Sensitivity (%) Accuracy (%) US 100 25 CT 100 > 95% US performed to confirm presence of a mass and its location CT to determine tumor extent Contrast enhanced CT: low density, intrarenal mass rim of compressed parenchyma Central necrosis 75% Calcifications rare Role of CT To confirm presence of tumor and assess tumor extent Diagnostic questions: Tumor thrombus (5-10%) Contralateral tumor (5-10%) Hepatic or lung metastases Wilms Tumor Wilms Tumor: Venous Extension 5-10% of cases Often clinically silent May extend into heart (30%) Tumor thrombus in heart or hepatic segment of IVC alters surgical approach Exophytic mass, pseudocapsule 62 ARP
Tumor Thrombus Magnetic Resonance Imaging Dark on T1-weighted images Bright on fat-suppressed images Contrast enhances Tumor thrombus seen as a luminal defect Bilateral : MRI 5-10% of patients at diagnosis (synchronous disease) Younger mean age: 27 mos Almost 100% incidence of nephroblastomatosis : Bilateral Tumors Distant Metastases Lung mets in 10% at diagnosis Plain radiographs have FN rate of 7-29% when CT positive CT is study of choice for distant staging (Babyn, Hematol Oncol Clin NA 1995; 9:217 Wilms Tumor ARP 63
Monitoring High-risk Patients Hemihypertrophy: Aniridia: US recommended as screening study q 4-6 months during risk period (5 to 6 years) Nephroblastomatosis: Imaging Two patterns Focal cortical nodules or masses Diffuse peripheral tumor rind US: isoechoic to normal tissue CT: Low attenuation lesions Soft Tissue Masses Diffuse Nephroblastomatosis < 5 years of age Nephroblastomatosis Rhabdoid tumor Clear cell sarcoma Mesoblastic nephroma > 5 years of age Renal cell cancer Lymphoma Nephroblastomatosis Diffuse Nephroblastomatosis Defined as the presence of diffuse or multifocal nephrogenic rests i.e., primitive blastema Important because it is a precursor to Wilms tumor Clue is peripheral tissue rind Nephrogenic Rests: Pathology 2 types by location Perilobar Peripheral cortex or columns of Bertin Intralobar Deep cortex Greater risk of Wilms tumor Nephroblastomatosis 64 ARP
Focal Nephroblastomatosis Rhabdoid Tumor Clue: perinephric fluid Focal Nephroblastomatosis Rhabdoid Tumor with PNET Left Kidney Rhabdoid Tumor 2.5% of tumors Malignant rhabdoid tumor lethal neoplasm mets widespread at diagnosis brain and lung Imaging Solid renal mass with or without perinephric fluid Clear Cell Sarcoma (Bone metastasizing renal tumor of childhood) 4% of pediatric renal neoplasms Peak incidence 2nd year of life Aggressive tumor Mets to bone (40-75%), lung, nodes Survival rates 60%-70% Rhabdoid Tumor Clear Cell Sarcoma: Pathology Large tumor Infiltrating margins Cystic changes Irregular margins Infiltrates kidney ARP 65
Clear Cell Sarcoma: Imaging Mesoblastic Nephroma: Imaging Heterogeneous intrarenal mass Cystic changes (70%) Indistinct margins Bone metastases Solid mass Cystic changes rare Well circumscribed Clear Cell Sarcoma Mesoblastic Nephroma Clue: bone/marrow lesions Mesoblastic Nephroma 5% of all renal tumors Diagnosis in neonatal period mean age, 2 months Benign & cured by nephrectomy Metastases & recurrence very rare Tumors of Older Children Renal Cell Cancer < 2% of all renal cell neoplasms Mean age, 9 years Clinical findings flank pain, hematuria, mass Metastases 30%: lung, nodes, bone, liver Mesoblastic Nephroma: Path Renal Cell Cancer: Pathology Unencapsulated Well-marginated Hemorrhage & necrosis uncommon Non-specific mass with hemorrhage & necrosis 66 ARP
Renal Cell Cancer: Imaging Solid renal mass Average diameter, 4 cm Cystic Masses Solitary Lesions Multilocular cystic nephroma Simple cysts (rare) Multiple lesions polycystic disease tuberous sclerosis turner s syndrome Von Hippel-Lindau disease Renal Cell Cancer 10-year-old boy Multilocular Cystic Nephroma Multiple cysts separated by fibrous stroma Boys under 4 years Symptoms abdominal mass hematuria Clue: small lesion, older pt age Lymphoma Multilocular Cystic Renal Tumor (CN) 2nd decade of life Occurs late in course of disease CT patterns: multiple nodules 80% direct invasion 10% diffuse infiltration 5% Solitary nodule 5% Renal Lymphoma Multilocular Cystic Renal Tumor ARP 67
Multiple Cysts Mean size 6-8 cm Hemorrhage and necrosis common Path-deep red to gray-white to tan appearance Tuberous Sclerosis ARPKD Fatty Tumors: Angiomyolipoma Associated with tuberous sclerosis Multiple, bilateral small renal masses No dominant mass Clue: Contains fat Small blue cell tumors with occasional cluster of cells arranged in rosettes : US Irregular, poorly-defined margins Heterogeneous 90% Evenly echogenic 10% Mixed pattern reflects high cellularity, dystrophic calcification and necrosis Median age: 22 months Infants > 6 months : palpable abdominal mass bone pain, hepatomegaly paraplegia opsoclonus, ataxia, diarrhea Infants < 6 mos: skin nodules hepatomegaly : US Typical appearance infants & children Predominantly solid mass 68 ARP
: MRI CT diagnosis: irregular extrarenal mass density less than adjacent tissues no definable capsule midline extension calcifications 85% Variations in Appearance Neonatal 25% of cases Predominantly cystic lesions Local Disease Diagnostic Questions Midline extension (> 30%) Vascular encasement (>30%) Liver metastases (5-10%) Intraspinal extension (15%) 75% of cases-midline extension : MRI Midline Disease Vascular encasement T1-weighted images: low signal intensity (black) Fat-suppressed images: high signal intensity (bright) Contrast enhances T2 ARP 69
Spinal Invasion Adrenocortical Tumors Adrenal carcinoma most common Hormonally active producing virilization, less often Cushing syndrome > 4 cm, often contain necrosis and sometimes calcifications Adenomas & hyperplasia rare Hepatic Metastases (5-10%) Adrenocortical Cancer T2 9 yo girl with virilization Bone Metastases: Sensitivity Imaging Studies Bone scintigraphy: 90% Metaiodobenzylguanidine (MIBG) I-123 MIBG: 95% Total body MRI: > 95% FDG PET: 100% X-ray: 35-70% Pheochromocytoma 10 yo boy with hypertension Differential Diagnosis Adrenal cortical tumors Pheochromocytoma Retroperitoneal teratoma 70 ARP