Pediatric Oncology Imaging

Pediatric Oncology Imaging - Tiny Tumors, Big Scans

• Key principles: ALARA (As Low As Reasonably Achievable), frequent need for sedation/anesthesia, distinct tumor types & imaging protocols vs. adults.

⭐ The ALARA principle is paramount in pediatric radiology due to increased radiosensitivity and longer life expectancy.

• Common Cancers & Initial Imaging:

Neuroblastoma Imaging - Belly Bad Guys

• Origin: Neural crest cells; adrenal medulla (>50%), sympathetic chain.
• Key Imaging:
  • US: Heterogeneous, ± calcifications.
  • CT: Calcifications (~85%), vascular encasement, defines Image-Defined Risk Factors (IDRFs).
  • MRI: Spinal canal/marrow involvement, IDRF assessment.
• MIBG Scintigraphy: High specificity; staging & follow-up. 📌 MIBG = Most Important Bad Guy scan!
• Staging: INRGSS based on IDRFs.
• DDx: Ganglioneuroma, adrenal hemorrhage, Wilms' tumor.

⭐ Calcification is seen in up to 85% of neuroblastomas on CT, often fine and punctate.

Wilms' Tumor Imaging - Kidney Capers

• Origin: Metanephric blastema; Peak age: 3-4 years.
• Imaging:
  • US: Initial, shows intrarenal mass.

    ⭐ The 'claw sign' on US/CT, where renal parenchyma is splayed around an intrarenal mass, is characteristic of Wilms' tumor.

  • CT: Staging (chest, abdomen, pelvis), contralateral kidney, vascular invasion (renal vein/IVC).
  • MRI: Problem-solving (e.g., IVC thrombus extent).
• Features: Well-defined, pseudocapsule; necrosis, hemorrhage common. Typically NO calcification (vs. Neuroblastoma).
• Assess: Contralateral kidney (synchronous tumor/nephroblastomatosis).
• Associations: WAGR, Denys-Drash, Beckwith-Wiedemann.

Bone & Soft Tissue Sarcomas - Skeletal Spooks

• Osteosarcoma:
  • Location: Metaphysis (esp. knee - distal femur/proximal tibia).
  • X-ray: Sunburst periostitis, Codman's triangle, cumulus cloud/osteoid matrix.
• Ewing's Sarcoma:
  • Location: Diaphysis/metadiaphysis, flat bones. 📌 Ewing's = Ends (diaphysis) & Everywhere (soft tissue).
  • X-ray: Onion-peel periostitis, permeative/moth-eaten destruction, saucerization.
• Rhabdomyosarcoma: Most common pediatric soft tissue sarcoma (head/neck, GU, extremities).

⭐ MRI is crucial for local staging of bone sarcomas, assessing intramedullary extent, soft tissue involvement, neurovascular proximity, and detecting skip lesions.

Lymphoma, Leukemia & Response - Cellular Chaos Control

• Leukemia:
  • Bone: Metaphyseal bands, lytic lesions, periosteal reaction.
  • CNS: Leptomeningeal enhancement, chloromas (myeloid sarcoma).
• Lymphoma (Hodgkin & NHL):
  • Nodal: Mediastinal (CXR, CT), abdominal, peripheral (US, CT).
  • Extranodal: Bone, GI, CNS (MRI).
• Imaging Modalities: CXR, US, CT (staging), MRI (CNS, MSK), PET-CT.
  • PET-CT: Staging (Lugano adapted), response (Deauville adapted: score 1-3 good).

  ⭐ FDG-PET/CT is the standard imaging modality for staging and response assessment in most pediatric lymphomas (e.g., Hodgkin lymphoma, DLBCL).

• Emergencies: Imaging for typhlitis, SVC obstruction.

High‑Yield Points - ⚡ Biggest Takeaways

• Neuroblastoma: Most common extracranial solid tumor; look for calcification & MIBG avidity.
• Wilms' tumor: Commonest renal tumor; shows claw sign, respects midline.
• Hepatoblastoma: Top pediatric liver cancer; ↑ AFP, use PRETEXT staging.
• Ewing's sarcoma: Bone tumor; onion-skin periostitis, t(11;22) translocation.
• Osteosarcoma: Bone tumor; sunburst pattern, metaphyseal location.
• Rhabdomyosarcoma: Most frequent soft tissue sarcoma; botryoid type in hollow organs.
• Leukemia/Lymphoma: Most common childhood malignancies; imaging shows mediastinal mass or bone marrow signs.