Cystic Abdominal Mass

Alexander J. Towbin, MD

DIFFERENTIAL DIAGNOSIS

Common

Hydronephrosis
Ovarian Cyst
Multicystic Dysplastic Kidney
Pancreatic Pseudocyst
Appendiceal Abscess
Duplication Cyst

Less Common

Splenic Cyst
Urachal Cyst
Hydrometrocolpos
Choledochal Cyst
Cystic Wilms Tumor

Rare but Important

Meconium Pseudocyst
Multilocular Cystic Nephroma
Mesenchymal Hamartoma
Caroli Disease

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Organ of origin can be difficult to identify for large cystic masses
- Most cystic masses have renal origin
Patient age and mass location can focus differential diagnosis

Helpful Clues for Common Diagnoses

Hydronephrosis
- Most common pediatric abdominal mass
- Diagnosed in 1-5% of pregnancies
  - Up to 30% are bilateral
  - Resolves on postnatal US in ˜ 50%
  - 10% have ureteropelvic junction (UPJ) obstruction
  - Vesicoureteral reflux in 10%
- Postnatal US should be 1st imaging test
- Hint: Consider posterior urethral valves in males with bilateral hydronephrosis
Ovarian Cyst
- Most common during infancy and adolescence
- Fetal cysts more common with maternal diabetes, toxemia, and Rh isoimmunization
- At birth, up to 98% of girls have small ovarian cysts
  - 20% of neonatal cysts > 9 mm
  - Neonatal cysts resolve spontaneously
  - Cysts resolve as maternal hormones subside
- In prepubertal girls, large cysts can cause precocious puberty
- In adolescents, ovarian cysts are very common
  - Usually due to dysfunctional ovulation
  - Cysts often spontaneously resolve
  - Large cysts take longer to resolve
Multicystic Dysplastic Kidney
- More common in males
- Left kidney more commonly affected
- Distinguished from hydronephrosis as cysts do not connect with renal pelvis
- Natural history is involution of kidney
Pancreatic Pseudocyst
- Most common cystic lesion of pediatric pancreas
  - Can occur after blunt abdominal trauma or pancreatitis
  - Usually has thin, well-defined wall
Appendiceal Abscess
- Seen after ruptured appendix
  - Occurs in ˜ 4% of appendicitis cases
  - More common in children < 4 years old
- Patients have symptoms more than 3 days
Duplication Cyst
- Can occur anywhere along GI tract
- Located adjacent to GI wall
  - Usually spherical or tubular in shape
- Lined with GI tract mucosa
  - Can have gastric mucosa in lining
  - Usually along mesenteric side
- Ileum is most common site
  - Esophagus, duodenum next most common
- Can create obstruction, bleeding, or intussusception

Helpful Clues for Less Common Diagnoses

Splenic Cyst
- Can be congenital or acquired
  - Acquired cysts are due to trauma or infection
  - Congenital cysts are more common in girls
- Has well-defined, thin walls
- Calcifications can be seen within cyst wall
Urachal Cyst
- Urachus remains patent between umbilicus and bladder
  - Can become infected
- US shows thick-walled cyst above bladder
- CT shows thick-walled cyst with surrounding inflammation
Hydrometrocolpos
- Fluid-filled vagina + uterus
- Can be caused by imperforate hymen, cervical stenosis, or atresia
- Associated with anorectal malformations
  - Can lead to obstructive uropathy in neonate
Choledochal Cyst
- Cystic or fusiform dilation of biliary tree
- Todani classification with 5 types
  - Type 1 (cystic dilation of extrahepatic bile duct) is most common
- Associated with ductal and vascular anomalies
  - Anomalous hepatic arteries, accessory ducts, and primary duct strictures
- US is best screening test
- HIDA scan can be used to prove connection to biliary system
Cystic Wilms Tumor
- Most common abdominal neoplasm
- Peak age is 3 years
- Usually heterogeneous solid mass
  - Occasionally cystic mass

Helpful Clues for Rare Diagnoses

Meconium Pseudocyst
- After meconium peritonitis
- Underlying condition may be meconium ileus, volvulus, or atresia
- Calcifications often present
- On US, cyst is thick walled and echogenic
Multilocular Cystic Nephroma
- a.k.a. multilocular cystic mass
- Septae are only solid component
- 2 age peaks with differing pathology
  - Boys ages 3 months to 4 years: Cystic, partially differentiated nephroblastoma
  - Adult women: Cystic nephroma
- Must be differentiated from cystic Wilms tumor
Mesenchymal Hamartoma
- 2nd most common benign hepatic tumor in children
  - 85% present before age 3 years
- Often presents as large RUQ mass
  - 75% in right lobe of liver
  - α-fetoprotein can be elevated
- Multiloculated cystic mass
  - Tiny cysts can appear solid
  - On US, septae of cysts can be mobile
  - Large portal vein branch may feed mass
  - Calcification is uncommon
- Reports of malignant degeneration to undifferentiated embryonal sarcoma
Caroli Disease
- a.k.a. type 5 choledochal cyst
  - May be associated with autosomal recessive polycystic kidney disease
- Congenital cystic dilation of intrahepatic bile ducts
- Presents with recurrent cholangitis or portal hypertension

Image Gallery

Longitudinal ultrasound shows marked hydronephrosis of the kidney

. Hydronephrosis is the most common abdominal mass in children and is most commonly caused by an obstruction of the ureteropelvic junction.

Anteroposterior retrograde pyelogram shows marked hydronephrosis with dilation of the renal calyces

. The ureter is dilated

proximal to a focal area of narrowing near the ureteropelvic junction

(Left) Transverse ultrasound in a 6-day-old girl shows an anechoic lesion

arising from the ovary. There is a thin claw of normal ovarian tissue

surrounding the cyst. Ovarian cysts are present in 98% of girls at birth due to maternal hormones. (Right) Axial CECT shows a large cystic mass

extending from the pelvis to the mid-abdomen. The mass had simple characteristics on CT and ultrasound (not shown). Giant ovarian cysts such as this are uncommon.

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