Abdominal Mass in a Child

Alexander J. Towbin, MD

DIFFERENTIAL DIAGNOSIS

Common

Hydronephrosis
Splenomegaly
Appendiceal Abscess
Wilms Tumor
Neuroblastoma

Less Common

Rhabdomyosarcoma
Ovarian Tumors
Multicystic Dysplastic Kidney
Hemangioendothelioma/Hemangioma
Hepatoblastoma
Mesoblastic Nephroma
Hepatocellular Carcinoma

Rare but Important

Renal Cell Carcinoma
Pancreatoblastoma

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

> 50% of abdominal masses are renal
- Hydronephrosis and multicystic dysplastic kidney are most common in neonates
- Hydronephrosis and Wilms tumor are most common in infants and children
Neuroblastoma and Wilms tumor account for majority of abdominal malignancies

Helpful Clues for Common Diagnoses

Hydronephrosis
- Most common abdominal mass
- Diagnosed in 1-5% of pregnancies
  - Up to 30% are bilateral
  - Resolves on postnatal US in ˜ 50%
  - 10% have UPJ obstruction
  - Vesicoureteral reflux in 10%
- Postnatal US should be 1st imaging test
- Hint: In males with bilateral hydronephrosis, consider posterior urethral valves
Splenomegaly
- Many causes of splenomegaly in children
  - Common causes include infection, right heart failure, and leukemia/lymphoma
- May appear as mass on radiograph with displacement of bowel and stomach
Appendiceal Abscess
- Seen after ruptured appendix
  - Occurs in ˜ 4% of cases
  - More common in children < 4 years
- Often have symptoms more than 3 days
Wilms Tumor
- Most common abdominal neoplasm
- 2nd most common pediatric solid tumor
- Occurs in children < 15 years of age with peak at 3 years
- May be bilateral
- Associated with WAGR, Denys-Drash syndrome, and Beckwith-Wiedemann
  - 2x more common with horseshoe kidney
- Appears as heterogeneous renal mass
  - Calcifications in 15-20%
  - Typically displaces vessels ± inferior vena cava invasion
Neuroblastoma
- Most common pediatric solid tumor
  - 6-10% of all childhood cancers
  - ˜ 15% of cancer-related deaths in children
  - ˜ 30% occur in 1st year of life with peak at 0-4 years
- 2nd most common abdominal tumor
  - ˜ 65% arise in abdomen
- Usually arise from adrenal medulla
  - Can arise anywhere along sympathetic chain
- Usually presents as asymptomatic abdominal mass
- Metastases present in 70% at diagnosis
  - Bone and bone marrow
  - Liver metastases can be focal or diffuse
- Urine catecholamines are elevated in 90%
- I-123 MIBG positive in 90%
- Calcifications present in ˜ 85% on CT
- Typically encases vessels

Helpful Clues for Less Common Diagnoses

Rhabdomyosarcoma
- Most common pediatric soft tissue sarcoma
  - Accounts for 5% of pediatric cancers
- GU origin common for abdominal tumors
  - Bladder is most common organ of origin
  - Usually presents before age 5
- Metastases to lung and marrow
Ovarian Tumors
- Teratomas are most common tumor
  - Majority are benign
- Malignant ovarian tumors account for 1% of pediatric cancers
  - 75-80% are germ cell tumors
- Can become very large and extend to abdomen
Multicystic Dysplastic Kidney
- More common in males
- Left kidney more commonly affected
- Natural history is involution of kidney
- Distinguished from hydronephrosis as cysts do not connect with renal pelvis
Hemangioendothelioma/Hemangioma
- a.k.a. infantile hepatic hemangioma
- Most common benign hepatic tumor
- 85% diagnosed in 1st 6 months
- Skin hemangiomas present in ˜ 50%
- Can present with high-output heart failure
Hepatoblastoma
- Most common pediatric liver malignancy
  - 1% of all pediatric malignancies
  - 79% of liver malignancies < 15 years
  - Most diagnosed under 18 months of age
- Associated with low birth weight, hemihypertrophy, Beckwith-Wiedemann, familial adenomatous polyposis, trisomy 18, and fetal alcohol syndrome
- 90% have increased serum AFP
- Most common in right lobe of liver
- Calcifications in 40-55%
- Distant metastases in 20% at diagnosis
  - Lung, brain, and bone
Mesoblastic Nephroma
- 3-10% of pediatric renal tumors
- Most common renal tumor in infants, 90% diagnosed in 1st year
- 2x more common in males
- Predominantly solid with variable cystic areas
Hepatocellular Carcinoma
- 2nd most common pediatric liver malignancy
  - Rare before age 5
- ˜ 75% are not associated with liver disease
  - Risks: Preexisting cirrhosis due to biliary atresia, Fanconi syndrome, viral hepatitis, hereditary tyrosinemia, or glycogen storage disease
  - Other risks: Androgen steroids, oral contraceptives, methotrexate
- Metastases common at diagnosis
  - Regional lymph nodes, lungs, bone
- Elevated AFP in 60-80%

Helpful Clues for Rare Diagnoses

Renal Cell Carcinoma
- Accounts for 2-5% of pediatric renal tumors
- Mean age 9-15 years
- Metastases in 20% at diagnosis
- Associated with von Hippel-Lindau disease
Pancreatoblastoma
- Most common pediatric pancreatic neoplasm
- Neoplasm of acinar cells
- Most common in 1st decade of life
- Associated with Beckwith-Wiedemann
- AFP elevated in up to 55%
- Usually large solitary pancreatic mass
  - Well defined with lobulated margins
  - ˜ 50% in pancreatic head