Serial 18 F-FDG PET/CT Revealing Mixed Histiocytosis in a Pediatric Patient

Area of Science:

• Pediatric oncology
• Nuclear medicine
• Histopathology

Background:

• Langerhans cell histiocytosis (LCH) and juvenile xanthogranuloma (JXG) are rare pediatric histiocytic disorders.
• Distinguishing between LCH and JXG can be challenging, especially in cases with overlapping clinical and imaging features.

Observation:

• A 6-month-old boy presented with calvarial lytic lesions and soft tissue swelling.
• 18F-FDG PET/CT revealed hypermetabolic lesions in the skull and femur.
• Initial biopsy confirmed LCH, but subsequent biopsy of a different lesion showed JXG.

Findings:

• Serial 18F-FDG PET/CT imaging demonstrated a mixed metabolic response to chemotherapy.
• Discordant metabolic activity in the femoral lesion indicated a different underlying pathology.
• Histopathological analysis confirmed a rare co-occurrence of LCH and JXG in a single patient.

Implications:

• Serial 18F-FDG PET/CT is valuable for monitoring treatment response and detecting discordant disease progression in pediatric histiocytosis.
• This case highlights the importance of integrating imaging, pathology, and clinical findings for accurate diagnosis and management.
• Understanding mixed histiocytosis is crucial for optimizing therapeutic strategies in pediatric patients.