Retroperitoneal Mass

Alexander J. Towbin, MD

DIFFERENTIAL DIAGNOSIS

Common

Lymphoma
Neuroblastoma

Less Common

Abscess
Lymphatic Malformation
Metastases
Retroperitoneal Hematoma
Duodenal Hematoma

Rare but Important

Neurofibromatosis Type 1
Extraadrenal Pheochromocytoma
Lipoblastoma
Retroperitoneal Fibrosis

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Most retroperitoneal masses are malignant
- Lymphoma and neuroblastoma most common
US is useful screening modality

Helpful Clues for Common Diagnoses

Lymphoma
- 3rd most common pediatric malignancy after leukemia and CNS tumors
- 10-15% of all childhood cancers
- Incidence increases with age
- Non-Hodgkin lymphoma is more common than Hodgkin lymphoma in children younger than 10 years old
- More common in males
- Burkitt and diffuse large B-cell lymphoma most common types to affect retroperitoneum
Neuroblastoma
- Most common solid extracranial malignancy
  - 6-10% of all childhood cancers
  - 15% of pediatric cancer deaths
- 4th most common pediatric malignancy (leukemia, CNS tumors, and lymphoma)
- 2nd most common abdominal neoplasm (Wilms tumor)
- > 90% of patients diagnosed before age 5
  - Median age at diagnosis is 22 months
  - Peak incidence in 1st year of life (30%)
- Can arise anywhere along sympathetic chain
- ˜ 70% originate in retroperitoneum
  - 35% in adrenal medulla
  - 30-35% in extraadrenal paraspinal ganglia
- Mediastinum is 3rd most common location (20%)
- Patients < 1 year old have better prognosis
- Abdominal mass is most common presentation
  - Can present with bruising around eyes
  - Paraneoplastic syndromes in ˜ 2%
- 50% have metastases at diagnosis
  - Most common to liver, bone, and bone marrow
  - Hepatic metastases can be diffuse or nodular
- Calcifications are present in ˜ 85%
- I-123 MIBG uptake in 90-95% of patients
- MR is useful to see intraspinal involvement
- Prognosis varies depending on stage
  - Staged by International Neuroblastoma Staging System

Helpful Clues for Less Common Diagnoses

Abscess
- Can be due to ruptured appendix, surgery, Crohn disease, and osteomyelitis
- Most infections are polymicrobial
- Can cross boundaries
- Consider tuberculosis if vertebral osteomyelitis extends to retroperitoneal soft tissues
Lymphatic Malformation
- a.k.a. mesenteric cyst
- Congenital benign tumor
- Can be found at all anatomic locations
  - Most common in head and neck
  - ˜ 20% in abdomen
  - ˜ 5% in retroperitoneum
- Can cross anatomic compartments
- Large, thin-walled, multiseptated cystic mass
- Rare calcifications in wall
Metastases
- Testicular metastases are most common
  - Spreads to retroperitoneal lymph nodes
Retroperitoneal Hematoma
- Can be seen after trauma or in hypocoagulable state
- Appearance depends on time between hemorrhage and imaging
Duodenal Hematoma
- Unusual finding in setting of trauma
  - Accounts for < 5% of intraabdominal injuries
- Due to forces that compress duodenum between spine and fixed object
  - Seatbelt, handlebars, and abuse are most common causes
  - Iatrogenic trauma from instrumentation can also occur
- Associated with pancreatic injuries

Helpful Clues for Rare Diagnoses

Neurofibromatosis Type 1
- Autosomal dominant disorder
- Classical clinical findings include café-au-lait spots, axillary freckling, and dermal and plexiform neurofibromas
- Plexiform neurofibromas can occur in abdomen
  - Most common in abdominal wall and retroperitoneum
- Retroperitoneal neurofibromas can cause mass effect on spinal cord, bowel obstruction, and ureteric obstruction
- Plexiform neurofibromas have targetoid appearance on MR
  - Loss of targetoid appearance should raise concern for degeneration into malignant peripheral nerve sheath tumor
Extraadrenal Pheochromocytoma
- a.k.a. paraganglioma
- ˜ 30% of all pediatric pheochromocytomas are extraadrenal
- 85% of extraadrenal pheochromocytomas are retroperitoneal
  - Organ of Zuckerkandl is most common site of origin
- Most common in 2nd-3rd decade
- Associated with von Hippel Lindau, MEN type 2, and neurofibromatosis type 1
- 20-50% are malignant
  - Most commonly metastasize to bone, liver, and lungs
- Often presents with hypertension
  - Cause of hypertension in ˜ 1% of children
- Appear hyperintense on T2WIs
- I-123 MIBG both sensitive and specific for detection
- No proven risk of hypertensive crisis with iodinated contrast
Lipoblastoma
- Most common in children under age 3
- Most commonly occurs in trunk and extremities
Retroperitoneal Fibrosis
- Rare disorder in children
- In children, 50% are related to systemic process or autoimmune disorder
- Insidious onset with nonspecific signs and symptoms
- Appears as misty mesentery on CT early in disease process