Catecholamines; VMA and HVA of serum and urine
CT or MRI
Although US is often the initial radiologic study of choice for abdominal mass, primary tumor site and possible nodes on are better evaluated on CT or MRI
CXR
Biopsy for definitive diagnosis
Although US is often the initial radiologic study of choice for abdominal mass, primary tumor site and possible nodes on are better evaluated on CT or MRI
Neuroblastoma 
Wilms' tumor
Hepatoblastoma
Giant cell tumor
Lymphoma
Pheochromocytoma
Other adrenal gland tumor
Vestibular schwannoma