Staging and Restaging Pediatric Abdominal and Pelvic Tumors

Neuroblastoma

• Most common extracranial solid tumor in kids
• Calcifications = key clue (80–90% on CT)
• Crosses midline, encases vessels (NOT invades)
• Intraspinal extension → think neuroblastoma (Wilms NEVER does)
• Image-Defined Risk Factors= everything → ≥1 IDRF = L2 disease
• MIBG imaging mandatory (FDG PET only if MIBG-negative)
• Diffuse liver mets → easy to MISS on US/CT → MRI + DWI saves you
• Stage MS: <18 months + skin/liver/BM mets → better prognosis

Easy-to-forget pitfall

• Below L2 vertebral level, intraspinal extension is NOT an IDRF

Wilms Tumor

• Most common renal malignancy
• Claw sign = renal origin
• Calcifications are uncommon (~10%)
• Invades vessels (renal vein / IVC thrombus) — not encasement
• Never goes in spinal canal
• SIOP vs COG → surgery timing differs (Europe vs US)
• Biopsy upstages to stage III (SIOP!)

Response clue

• Size may stay same ↑ necrosis = good response
• ADC ↑ after chemo = good prognosis

Hepatoblastoma

• Usually <3 years, non-cirrhotic liver
• AFP ↑ in 80–90%
• Calcifications common (~50%)
• Hypovascular, no hepatobiliary contrast retention
• LI-RADS NOT recommended in kids

PRETEXT pearls

• Based on tumor-free liver sections, not tumor size
• Caudate lobe = report separately
• During chemo → POST-TEXT, after surgery → STOP using PRE/POST-TEXT

Lymphoma

• Hodgkin: adolescents, contiguous nodal spread
• Nodes abnormal if >2 cm long axis or FDG-avid
• Bulky disease → X suffix = worse prognosis
• Spleen ≠ solid organ → use S suffix, not stage IV
• NHL: more aggressive, extranodal, GI tract involvement
• Aneurysmal bowel dilatation = classic NHL clue

Response

• FDG PET + Deauville score rules follow-up

Germ Cell Tumors (GCTs)

• Midline, gonadal or extragonadal
• Seminoma: solid, homogeneous, no cysts/calcifications
• Nonseminoma: fat + necrosis + cysts + calcifications
• AFP ↑ (yolk sac), β-hCG ↑ (choriocarcinoma)

Classic trap

Growing teratoma syndrome

• Mass grows
• Tumor markers normalize
• FDG PET negative
• Needs surgery, NOT chemo

Rhabdomyosarcoma

• Most common pediatric soft-tissue sarcoma
• Botryoid subtype = “bunch of grapes”
• MRI preferred (local extent + nodes)
• Fusion-positive (PAX3/7-FOXO1) = worse prognosis
• RECIST 1.1 standard — volumetric optional
• Lungs + bone marrow = common mets → CT chest + FDG PET

Pitfalls

• Size stability ≠ no response → look at necrosis + ADC
• Liver metastases (neuroblastoma) often invisible on CT/US
• Wilms ≠ biopsy unless atypical (you may upstage!)
• Use SAME modality for follow-up every time