CASE 3

By: Dr. Mervat M. Aboualkheir; Dr. Muhammad Salman; Dr. Shankar Raja and Dr. Tuli Mahmoud Madhehebu

HISTORY: A 13-year-old girl who is a known case of localized osteosarcoma of right distal femur, status post surgical resection and expandable MUTARS prosthesis implant, done on May 07, 2014. Status post chemotherapy, Regimen A, completed on November 05, 2014. She was doing well and followed up by PET-CT. 

What are the findings in following PET-CT images?

What are the possible causes of abnormal uptake on PET-CT?

FINDINGS:

Follow-up FDG PET-CT Scan (Jan 19, 2015), post resection and prosthetic implant, showed no FDG avid local recurrence or residual disease in right femur. No distant metastasis. Note: focal uptake in left hand is at the site of injection.

2nd follow up FDG PET-CT Scan (Mar 20, 2017) showed mild Increased FDG avidity (SUV max 3.2) in the left femoral proximal- mid shaft with periosteal thickening on corresponding CT (not shown here separately).

DIAGNOSIS:

In given clinical context, asymmetric FGD avidity mainly in cortex of left femur shaft is more in favor of metachronous tumor.

DIFFERNTIAL DIAGNOSIS:

Metastatic osteosarcoma.

PEARLS AND DISCUSSION:

Metabolic evaluation with FDG-PET in pediatric patients in known sarcomas, provides additional information after conventional imaging (MRI/CT) for example whole body metastatic search, aggressiveness of tumor and prognostication (1). PET-CT has been demonstrated to accurately predict response to neoadjuvant chemotherapy in osteogenic sarcoma; furthermore, metabolic burden on PET-CT strongly correlates with pathologic response (2). Metabolic profiles on PET-CT also demonstrates earlier response to therapy as compared to morphologic correlates on CT/MRI. Allowing tailored therapies specific to patients (3).

PET CT has been found useful to confirm viable tumor and metachronous metastases vs benign etiology.

Focal discrete solitary lesion with more cortical involvement favors metachronous tumor rather metastases.

FURTHER READING:

1. Positron emission tomography for staging of pediatric sarcoma patients: results of a prospective multicenter trial. Völker T1, Denecke T, Steffen I, et al. J Clin Oncol. 2007 Dec 1;25(34):5435-41.

2. Prediction of chemotherapy response by PET-CT in osteosarcoma: correlation with histologic necrosis. Bajpai J1, Kumar R, Sreenivas V, Sharma MC, et al. J Pediatr Hematol Oncol. 2011 Oct;33(7):e271-8.

3. Prediction of tumour necrosis fractions using metabolic and volumetric 18F-FDG PET/CT indices, after one course and at the completion of neoadjuvant chemotherapy, in children and young adults with osteosarcoma. Im HJ1, Kim TS, Park SY, et al. Eur J Nucl Med Mol Imaging. 2012 Jan;39(1):39-49.