Abdominal Mass in Neonate

Eva Ilse Rubio, MD

DIFFERENTIAL DIAGNOSIS

Common

Urinary Tract Obstruction
- Ureteropelvic Junction Obstruction
- Ureteropelvic Duplications
Multicystic Dysplastic Kidney
Neuroblastoma, Congenital
Adrenal Hemorrhage
Gastrointestinal Duplication Cyst
Mesenteric Lymphatic Malformations
Mesoblastic Nephroma
Teratoma

Less Common

Ovarian Torsion
Hepatoblastoma
Meconium Pseudocyst
Hemangioendothelioma
Vascular Malformation
Pulmonary Sequestration

Rare but Important

Hydrocolpos/Hydrometrocolpos
Wilms Tumor (Congenital)

ESSENTIAL INFORMATION

Key Differential Diagnosis Issues

Male vs. female
Other clinical findings: Skin lesions, urinary output, meconium passage
Cystic, solid, or mixed cystic/solid
Presence or absence of calcifications

Helpful Clues for Common Diagnoses

Urinary Tract Obstruction
- Ureteropelvic junction obstruction: Larger cystic, anechoic renal pelvis surrounded by smaller cystic, anechoic calyces
  - Most common congenital obstruction of urinary tract
  - Hydronephrosis without hydroureter
  - Sometimes difficult to differentiate from multicystic dysplastic kidney (MCDK)
  - Abnormalities common in contralateral kidney: Reflux or ureteropelvic junction obstruction
- Duplication with obstructed upper pole appear as complex or simple cystic structure
  - Reflux common in lower pole ureter
  - Diagnosis is often bilateral but asymmetric in severity
Multicystic Dysplastic Kidney
- Most common appearance is noncommunicating cysts of varying sizes; usually spontaneously involute over time
- Variable appearance depending on stage
  - May be massive and bizarre
  - Large enough to cause respiratory distress in rare cases
  - May have residual intervening dysplastic renal parenchyma
  - ± identifiable ureter
  - Timing to complete involution varies from prenatal period to late teens
- Higher incidence of other genitourinary abnormalities
Neuroblastoma, Congenital
- Origin in sympathetic chain ganglia
  - Occurs anywhere from coccyx to skull base
  - Vast majority arise in adrenal gland
- Often heterogeneous, mixed cystic and solid
- Coarse calcifications are common
- Assess for vertebral involvement, spinal canal invasion, rib splaying
- Engulfs large vessels
  - Mass often elevates aorta from spine
Adrenal Hemorrhage
- May be large and difficult to differentiate from neuroblastoma
- No internal blood flow detected on US
- Involutes over time
- Usually circumscribed, heterogeneous, often with cystic components
Gastrointestinal Duplication Cyst
- Usually round structure
  - ± bowel “wall signature” of hypoechoic wall/mucosa layers
  - Hypoechoic or echogenic contents
  - Usually does not communicate with GI lumen
- Most common locations are terminal ileum and esophagus
  - Other GI locations are uncommon
Mesenteric Lymphatic Malformations
- Nonspecific hypoechoic/anechoic structure
  - May have irregular or lobulated borders
  - May have septations
Mesoblastic Nephroma
- Most common neonatal renal neoplasm
- Encapsulated calcifications rare
- Solid, may be heterogeneous
  - US: Whorled, heterogeneous, compared to uterine fibroid
  - CT: Solid, with mild enhancement
  - MR: Intermediate on T1, bright on T2
- Usually benign; however, beware small subset that may recur or metastasize

Helpful Clues for Less Common Diagnoses

Ovarian Torsion
- May be suspected if only 1 ovary can be identified
- Circumscribed, heterogeneous pelvic mass; may see peripheral follicles
- May be precipitated by dominant cyst or underlying mass, such as teratoma
- Pitfall: Demonstration of blood flow by US may confound diagnosis due to intermittent torsion or multiplicity of blood supply to ovaries
Meconium Pseudocyst
- Radiographically, large soft tissue density with mass effect
  - Lesional or peritoneal calcifications may have wispy or “eggshell” appearance
- Distal bowel obstruction pattern typical
Hemangioendothelioma
- Variable appearance; most commonly multiple focal, round, target-like lesions within liver
- May present as large solitary lesion
- Highly vascular lesion
  - Great vessels distal to lesion (aorta, superior mesenteric artery) may be attenuated
  - Look for signs of congestive heart failure
Vascular Malformation
- Highly variable appearance, depending on histology, presence of necrosis, stage of involution

Helpful Clues for Rare Diagnoses

Hydrocolpos/Hydrometrocolpos
- Often associated with other anomalies
  - Cloaca, urogenital sinus, renal agenesis, cystic kidneys, esophageal/duodenal atresia, anorectal malformation
- Occasionally seen in intersex conditions
Wilms Tumor (Congenital)
- Cannot be differentiated from mesoblastic nephroma by imaging
- Associated with other conditions
  - Beckwith-Wiedemann: Hypertrophy
  - WAGR: Wilms, aniridia, genitourinary anomalies, mental retardation
  - Drash: Pseudohermaphroditism, renal failure
- Tends to invade vessel lumen (renal vein, IVC) rather than surround/engulf vessels (as seen with neuroblastoma)
- Contralateral kidney risks: Bilateral Wilms, nephroblastomatosis
- Wilms tumor nearly always occurs after 1st year of life; congenital/neonatal presentation extremely uncommon

Image Gallery

Longitudinal ultrasound shows massive and somewhat disproportionate dilatation of the renal pelvis with concomitant dilation of the calyces. Severe UPJ may be difficult to distinguish from MCDK in some patients.