F-18 fluorodeoxyglucose positron emission tomography “super scan” in a patient of metastatic primitive neuroectodermal tumor of the kidney
A twelve-year old male presented with multiple joint pains, periorbital and sternal swellings of one-month duration. Contrast-enhanced computed tomography (CT) scan of the abdomen revealed poorly enhancing, hypodense bilateral renal masses ranging from 4 cm to 5 cm in size along with multiple hepatic and pancreatic space occupying lesions. A 4.3-cm exophytic mass was noted in the lower pole of right kidney []. CT-guided biopsy from this mass revealed feature of renal primitive neuroectodermal tumor (PNET)/Ewing's sarcoma [].\nThereafter, patient underwent a “true” whole body PET scan including bilateral limbs and skull region as per the standard institution protocol for pre-treatment staging of the disease. The images revealed extensive hypermetabolic areas in CT described renal (SUVmax: 6.9), hepatic (SUVmax: 7.2), and pancreatic lesions (SUVmax: 5.4). In addition, intense and non-uniform uptake was seen in marrows of axial and appendicular skeletal system with distinct focus in palpable sternal swelling (SUVmax: 4.5). A medium-sized focus was also seen in left posterior chest wall with extension into basal pleura of left lung. Interestingly, low background tracer concentration was observed along with very low F-18 FDG uptake in the brain (SUVmax of 3.3 in occipital region and 2.9 in rest of the brain), skeletal muscles of limb, mediastinum, and bowel. Due to its resemblance with super scan of skeletal scintigraphy, these scan findings can be termed to represent “PET super scan” [].\nPatient was subjected to six cycles of Euro-Ewing 99 protocol including Vincristine, Ifosfamide, Doxorubicin, and Etoposide chemotherapeutic regimen as per the institution protocol.[] Repeat PET scans were done after three and six cycles, latter being done after 4 months of the initial scan []. The images revealed marked treatment response with disappearance of “super scan”-like pattern, reduction in number, size, and metabolic activity of the lesions that were shown in the earlier scan. SUVmax of the occipital region of the brain increased from the previous value of 3.3 to 9.9. For rest of the brain, the SUVmax increased from 2.9 to 8.6 []. The comparison of femoral marrow activity in the pre- and post-treatment scans showed hypermetabolic areas of stimulation in post-treatment scan, which is clearly missing from the previously diseased marrow and GCSF-induced stimulated marrow being seen in previously uninvolved marrow. We have termed this pattern as “marrow flip flop” and it appears that areas showing marrow flip flop are the ones that demonstrate treatment response [].